MODUL KIMIA ANALISIS

DIKTAT MATA KULIAH K I M I A A N A L I S I S

Disusun oleh :

Drs. AdiwarnaJURUSAN TEKNIK KIMIA FAKULTAS TEKNIKUNIVERSITAS MUHAMMADIYAH JAKARTA

2008

1. Pengantar kimia Analisis Kimia analisis adalah suatu cabang ilmu kimia yang digunakan untuk analisa kimia berdasarkan besaran parameter kimia dan fisika dari suatu sampel secara kualitatif dan kuantitatif. 1.1. analisa kualitatif dan kuantitatif, a. Analisa kimia kualitatif adalah analisa kimia untuk mengetahui jenis atom, unsure, ion, molekul atau spesies yang terdapat dalam suatu larutan sampel. Analisa kualitatif bisa dilakukan dengan analisa aroma, warna, warna pembakaran, rasa, warna nyala, analisa kation, analisa anion, menggunakan pereaksi spesifik, atau dengan menggunakan alat analisa kimia kualitatif.- Analisa kation meliputi golongan I yakni Ag+, Hg2+2, Pb+2 ( golongan chlorida ), golongan IIA yakni Hg+2, Cu+2, Bi+3, Cd+2 (golongan H2S), golongan IIB yakni As+3, As+5, Sb+3, Sb+5, Sn+2, Sn+4 (golongan S=); golongan III yakni Fe+3, Cr+3, Al+3, Co+2, Ni+2, Mn+2, Zn+2 (golongan hidroksida), golongan IV yakni Ca+2, Ba+2, Sr+2 (golongan karbonat), Golongan V yakni Na+, K+, Mg+2, NH4+, H+, Li+ (golongan sisa)- Analisa anion meliputi golongan :

-- A1 CO3=, HCO3-, S=, S2O3=, SO3=, NO2-, OCl-, CN-, CNO- ( golongan asam encer),

-- A2 yakni F-, SiF6=, Cl-, Br-, I-, NO3-, ClO3-, ClO4-, MnO4-, CNS-, HCOO-, H3CCOO-, C2O4=, tartarat, citrate (golongan sulfat pekat). -- Golongan B1 yakni SO4=, S2O8=, PO4-3, PO3-3, AsO4-3, AsO3-3, CrO4=, Cr2O7=, SiO3=, SiF6=, Salisilat, Benzoat, H4C4O4= (golongan pengendapan), -- golongan B2 yakni MnO4-, MnO4=, CrO4=, Cr2O7= (golongan redoks)b. Analisa kimia kuantitatif adalah analisa kimia untuk mengetahui kadar atom, unsur, ion, molekul, spesies yang terdapat dalam suatu sampel. Analisa kuantitatif dinyatakan dalam satuan %, ppt, molaritas, normalitas, molalitas, ppm, ppb.1.2. Sampling

Sampling adalah cara pengambilan sampel untuk digunakan dalam analisa kimia. Pada dasarnya cara sampling dapat dibagi menjadi :

a. Gross sampling adalah pengambilan sampel secara kasar b. Random sampling adalah penganbilan sampel secara acak dari distribusi sampelc. Sistematik sampling adalah pengambilan sampel secara sitematik dari distribusi sampeld. Industrial sampling adalah pengambilan sampel sesuai dengan sampling port yang telah ditetapkan dalam suatu sistem industri kimia.3.2. kesalahan analisa

3.2.1. Kesalahan konstan

a. kesalahan operasional dan personal

b. kesalahan alat dan reagen

c. kesalahan metode

d. kesalahan additive dan proporsional

3.2.2. Kesalahan aksidental

3.2.3. Minimasi kesalahan

a. kalibrasi Perlakuan dengan blanko

c. Perlakuan larutan standar

d. menggunakan berbagai cara analisa

e. Perlakuan analisa parallel

f. Standard addisi

g. standard dalam

h. Aplikasi metode

i. Dilusi isotop

3.2.4. Statistik sampling

a. Ketepatan : nilai hasil ukur analisa mendekati nilai sebenarnya b. Ketelitian: selisih antara dua hasil ukur c. Nilai rata-rata (: Jumlah hasil ukur (xi)/ jumlah pengukuran (n)

ml

d. Deviasi relatif rata-rata :

e. Kesalahan - kesalahan absolut ( e )

- kesalahan random ( xi - - bias (e = (xi -

e. Distribusi Normal

f. Pembandingan hasil

h. Standar deviasi

--------------------------------------------------

s = (Xi Xr )2/ n - 1

VARIANSI = (Xi Xr )2/ n - 1i. Koefisien variansi

- uji tt = ( x - n )/suji t untuk pembandingan metode

t10 dari tabel = 2,23 untuk P = 0,05

- uji F

F = S2A /S2B

- uji O

j. Analisa parallel

ts/n = kesalahan absolut

L = ( 100 z ) %

L = rentang data1.3. tipe-tipe analisa kimia

Analisa kimia dapat digolongkan menjadi :

- Analisa pendahuluan adalah analisa secara awal dari suatu sampel.

- Analisa proximate dimana kadar masing unsur dalam sampel ditentukan berdasarkan senyawa-senyawa yang ada dalam sampel .- Analisa parsil adalah analisa menentukan konstituen tertentu dalam sampel.

- Analisa konstituen runut adalah analisa penentuan kontituen dengan kadar sangat kecil sekali.

- Analisa komplit adalah analisa masing-masing konstituen tergantung pada kadar nya dalam sampel

analisa kimia berdasarkan kadar sampel dapat dibagi menjadi :

- Analisa makro yakni penentuan konstituen dalam kadar lebih besar dari 0,1 gr.

- Analisa semi mikro yakni penetuan kadar konstituen berkisar antara 0,01 0,1 gr.

- Analisa mikro yakni penetuan konstituen dalam sampel kecil dari 0,001 gr, 1.4. Teknik analisa kimia

Beberapa teknik yang sering digunakan dalan analisa kimia kuantitatif adalah :

a. penentuan kadar yang cocok untuk suatu reaksi kimia baik dengan mengukur kadar reagen yang diperlukan untuk menyempurnakan reaksi atau pun berdasarkan kadar produk yang dihasilkan.b. menentukan alat analisa elektrik yang tepat. ( Amperometri, voltametri, konduktometri, potensiometri, coulombmetri ) c. Penentuan dengan menggunakan alat optik tertentu ( Spektrofotometer sinartampak-UV, spektrofotometer inframerah, spektrofotmeter resonansi magnit inti NMR, Spketrofotometer massa, spektrofotometer sinar X, spektrofotometer serapan atom, Spektrofotometer massa 2. Prinsip dasar kimia analisis

2.1. disosiasi elektrolitik, Beberapa reaksi analisa kualitatif dan kuantitatif berlangsung dalam larutan encer. Oleh karena itu Hal ini merupakan pengetahuan dasar dimana pada kondisi tersebut reaksi ini berlangsung. Konsep tersebut merupakan teori sederhana dari disosiasi elektrolitik.Ionisasi asam dan basa di dalam larutan. Suatu asam bisa didefinisikan sebagai suatu senyawa yang bila dilarutkan dalam air akan mengalami disosiasi dengan pembentukan ion hidrogen sebagai ion positif. Kenyataannya ion hydrogen tak terdapat dalam kedaan bebas dalam larutan encer, tetapi setiap ion hydrogen bergabung dengan satu molekul air membentuk ion hidroksonium. Ion hidroksonium adalah proton terhidrasi sebagai berikut :

a. Asam mono proton

HCl + H2O H3O+ + Cl-HNO3 + H2O H3O+ + NO3 -Ionisasi dapat menggambarkan seberapa besar kecengerungan ion hydrogen untuk bergabung dengan molekul air membentuk ion hidroksonium. Asam klorida dan asam nitrat diatas terurai dengan hampir sempurna di dalam larutan encer sesuai dengan persamaan reaksi di atas. Hal ini dapat dijelaskan dengan pengukuran titik beku dan metoda lainnnya.b. asam poliproton terionisasi dalam beberapa tahap. Pada asam sulfat satu ion hidrogennya dapat terdisosiasi hamper sempurna

H2SO4 + H2O

H3O+ + HSO4-

HSO4-+ H2O

H3O+ + SO4=

H3PO4 + H2O

H3O+ + H2PO4-

H2PO4- + H2O

H3O+ + HPO4=

HPO4= + H2O

H3O+ + PO4-3

c. Asam lemah

HOAct + H2O

H3O+ + ActO -

c. basa

NaOH + 2H2O

Na(H2O)2+ + OH-d. Basa poli hidroksi Ca(OH)2 + 4 H2O

Ca(H2O)4+2 + 2 OH-Al(OH)3 + 6H2O

Al(H2O)6+3 + 3OH-Kesetimbangan asam dan basaMenurut Bronsted-Lowry definisi asam dan basa adalah sebagai berikut :

Asam adalah spesis yang mendonorkan (H+).andbases are adalah spesis yang menerima proton

AirAir akan mengalami reaksi kesetimbangan berikut :

H2O H+ + OH-, Maka konstanta kesetibangan air :

[H+] [OH-]

Keq = ----------

[H2O]

Konsentrasi air dalam larutan air konstan dan ungkapan ini disederhanakan menjadi:Kw = (55,56 M) * Keq = [H +] [OH-]mana Kw disebut disosiasi konstan air dan sama 1.00x10-14 pada suhu kamar. Konsentrasi [H +] dan [OH-] karena sama 1.00x10-7 M.

asamAsam dalam air akan memisahkan, yang itu menyumbangkan proton itu. Kami menyebutnya asam yang terdisosiasi asam benar-benar kuat dan asam yang terdisosiasi asam hanya sebagian yang lemah.Kuat Asam Contoh:HNO3 (aq) + H2O NO3-(aq) + H3O + (aq)Keq = jumlah yang sangat besarDalam contoh ini, HNO3 adalah asam dan H2O bertindak sebagai basis.NO3-disebut basa konjugasi dari asam HNO3, dan H3O + adalah asam konjugasi dari basa H2O.basaBasis dalam air dapat menerima sebuah proton dari air untuk menghasilkan OH-. Basa kuat adalah garam hidroksida yang terdisosiasi sepenuhnya dalam air, jadi pernyataan ini berlebihan. Tapi basa lemah tidak harus mengandung hidroksida sendiri, tetapi mereka menghasilkan solusi dasar dengan bereaksi dengan air.Lemahnya dasar contoh: NH3 (aq) + H2O NH4 + (aq) + OH-(aq) K = 1.8x10-5Dalam contoh ini, NH3 adalah basa dan H2O bertindak sebagai asam. NH4 + adalah asam konjugasi dari dasar NH3, dan OH-adalah basa konjugat dari asam H2O.Sebuah senyawa yang dapat bertindak baik se2.2. hukum aksi massa aktivitas larutan, k1

A + B ==== C + D

k2

v1 = k1 [ A ] [ B ]

v2 = k2 [ C ] [ D ]

k1 [ A ] [ B ] = k2 [ C ] [ D ]

k1

[ C ] [ D ]

K = --------- = -------------------

K2

[ A ] [ B ]

Titrasi terbagi menjadi 4 bahagian :

Tirasi adalah penyetaraan antara titrat ( zat yang dititrasi) dan titran (zat pentitrasi) dengan rumus V1N1 = V2N21. titrasi asam basa ( kesetimbangan asam basa)

2. titrasi pengendapan ( kesetibangan hasil kali kelarutan)

3. titrasi redoks ( kesemtibangan redoks )

4. titrasi kompleksometri (kesetimbangan komleksometri)2.1. Titrasi asam-basaFrom Wikipedia, the free encyclopedia

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Titrasi setup. Buret biasanya akan dipegang oleh penjepit, tidak ditampilkan di sini. Merah muda ini kemungkinan besar disebabkan oleh penggunaan indikator fenolftalein.Titrasi asam-basa adalah penentuan konsentrasi asam atau basa dengan persis menetralkan asam / basa dengan asam atau basa konsentrasi diketahui. Hal ini memungkinkan untuk analisis kuantitatif dari konsentrasi asam diketahui atau larutan basa. Itu membuat penggunaan reaksi netralisasi yang terjadi antara asam dan basa dan pengetahuan tentang bagaimana asam dan basa akan bereaksi jika rumus mereka diketahui.Asam-Base titrasi juga dapat digunakan untuk mencari kemurnian persen bahan kimia. Methoda titrasiSebelum memulai suatu titrasi harus dipilih indikator yang cocok. Titik ekivalen pada suatu reaksi adalah titik dimana jumlah ekivalen dari reakstan yang bereaksi. Yang sangat realtif tergantung dengan asam dan basa yang digunakan. Ph pada titk equivalen dapat diperkirakan dengan menggunakan rumus berikut : Asam uat akan bereaksi dengan basa kuat membentuk pH netral. Asam kuat akan bereaksi dengan asam lemah membentuk pH larutan asam (pH7) .

Bila asam lemah bereaksi dengan basa lemah titik equivalen akan menjadi basa jika basanya lebih kuat dari asamnya. Jika asam dan basanya sama kuat akan terjadi titik equivalent pada pH netral. Akan tetapi jika asam lemah sering kali tak bisa dititrasi dengan basa lemah karena karena perubahan warna pada indikator sering kali sangant cepat oleh karena itu sulit sekali untuk diamati perubahan warna indikatornya.Titik pada saat perubahan warna indikator disebut titik akhir titrasi. Pemilihan indikator yang cocok harus dilakukan, sebaiknya agar perubahan warna indikator menunjukan titik ekivalen dari suatu titrasi.

Pertama buret harus dibasahi dengan larutan standard, pipet larutan yang tak diketahui, dan Erlenmeyer diisi dengan aquades. Kedua volume yang diketahui dari larutan yang tak diketahui konsentrasinya harus dipipet dan dimasukan kedalam erlenmeyer sambil ditambahkan beberapa tetes indikator. Buret harus selalu terisi larutan pentiter diatas skala buret agar mudah melakukan pembacaan skala volum pentiter yang terpakai.

Kemudian larutan pentiter dialirkan dari buret ke dalam labu erlenmeyer titrat. Dengan cara demikian bisa diketahui banyaknya pentiter terpakai untuk netralisasi. Larutan pentiter dialirkan melalui ujung buret sampai indikator dalam larutan titrat berubah warna untuk menadai titrasi telah berakhir.voluume larutan pentiter yang terpakai dicatat sebagai volume untuk perhitungan titrasi..

Tiga titrasi harus dilakukan, kali ini lebih akurat, dengan mempertimbangkan kira-kira di mana titik akhir akan terjadi. Pembacaan pada buret pada titik akhir harus dicatat, dan rata-rata untuk memberikan hasil akhir. Titik akhir tercapai ketika indikator hanya berubah warna secara permanen. Hal ini dapat dicapai dengan mencuci penurunan tergantung dari ujung buret ke dalam labu kanan pada akhir titrasi untuk mencapai penurunan yang lebih kecil dalam volume dari apa yang biasanya dapat dicapai dengan hanya solusi menetes dari buret.Asam-basa titrasi dilakukan dengan indikator fenolftalein, bila asam lemah - titrasi basa kuat, indikator biru bromthymol dalam asam kuat - reaksi basa kuat, dan indikator metil oranye untuk asam kuat - reaksi basa lemah. Jika dasar adalah dari skala, yaitu pH> 13,5, dan asam memiliki pH> 5,5, maka indikator kuning Alizarie dapat digunakan. Di sisi lain, jika asam adalah dari skala, yaitu pH 12) even in the presence of magnetic "dipole-dipole" interaction broadening (or simply, dipolar broadening) which is always much smaller than the quadrupolar interaction strength because it is a magnetic vs. an electric interaction effect.

Additional structural and chemical information may be obtained by performing double-quantum NMR experiments for quadrupolar nuclei such as 2H. Also, nuclear magnetic resonance is one of the techniques that has been used to design quantum automata, and also build elementary quantum computers.[6]

HYPERLINK "file:///D:\\Nuclear_magnetic_resonance.htm" \l "cite_note-Vandersypen-7" [7][edit] Continuous wave (CW) spectroscopyIn its first few decades, nuclear magnetic resonance spectrometers used a technique known as continuous-wave spectroscopy (CW spectroscopy). Although NMR spectra could be, and have been, obtained using a fixed magnetic field and sweeping the frequency of the electromagnetic radiation, this more typically involved using a fixed frequency source and varying the current (and hence magnetic field) in an electromagnet to observe the resonant absorption signals. This is the origin of the counterintuitive, but still common, "high field" and "low field" terminology for low frequency and high frequency regions respectively of the NMR spectrum.

CW spectroscopy is inefficient in comparison with Fourier analysis techniques (see below) since it probes the NMR response at individual frequencies in succession. Since the NMR signal is intrinsically weak, the observed spectrum suffers from a poor signal-to-noise ratio. This can be mitigated by signal averaging i.e. adding the spectra from repeated measurements. While the NMR signal is constant between scans and so adds linearly, the random noise adds more slowly - proportional to the square-root of the number of spectra (see random walk). Hence the overall signal-to-noise ratio increases as the square-root of the number of spectra measured.

[edit] Fourier transform spectroscopyMost applications of NMR involve full NMR spectra, that is, the intensity of the NMR signal as a function of frequency. Early attempts to acquire the NMR spectrum more efficiently than simple CW methods involved illuminating the target simultaneously with more than one frequency. A revolution in NMR occurred when short pulses of radio-frequency radiation began to be used -- centered at the middle of the NMR spectrum. In simple terms, a short square pulse of a given "carrier" frequency "contains" a range of frequencies centered about the carrier frequency, with the range of excitation (bandwidth) being inversely proportional to the pulse duration. The Fourier transform of an approximately square wave contains contributions from all the frequencies in the neighborhood of the principal frequency. The restricted range of the NMR frequencies made it relatively easy to use short (millisecond to microsecond) radio frequency pulses to excite the entire NMR spectrum.[citation needed]Applying such a pulse to a set of nuclear spins simultaneously excites all the single-quantum NMR transitions. In terms of the net magnetization vector, this corresponds to tilting the magnetization vector away from its equilibrium position (aligned along the external magnetic field). The out-of-equilibrium magnetization vector precesses about the external magnetic field vector at the NMR frequency of the spins. This oscillating magnetization vector induces a current in a nearby pickup coil, creating an electrical signal oscillating at the NMR frequency. This signal is known as the free induction decay (FID), and it contains the vector sum of the NMR responses from all the excited spins. In order to obtain the frequency-domain NMR spectrum (NMR absorption intensity vs. NMR frequency) this time-domain signal (intensity vs. time) must be Fourier transformed. Fortunately the development of Fourier Transform NMR coincided with the development of digital computers and the digital Fast Fourier Transform. Fourier methods can be applied to many types of spectroscopy. (See the full article on Fourier transform spectroscopy.)

Richard R. Ernst was one of the pioneers of pulse NMR, and he won a Nobel Prize in chemistry in 1991 for his work on Fourier Transform NMR and his development of multi-dimensional NMR (see below).

[edit] Multi-dimensional NMR SpectroscopyThe use of pulses of different shapes, frequencies and durations in specifically designed patterns or pulse sequences allows the spectroscopist to extract many different types of information about the molecule. Multi-dimensional nuclear magnetic resonance spectroscopy is a kind of FT NMR in which there are at least two pulses and, as the experiment is repeated, the pulse sequence is systematically varied. In multidimensional nuclear magnetic resonance there will be a sequence of pulses and, at least, one variable time period. In three dimensions, two time sequences will be varied. In four dimensions, three will be varied.

There are many such experiments. In one, these time intervals allow (amongst other things) magnetization transfer between nuclei and, therefore, the detection of the kinds of nuclear-nuclear interactions that allowed for the magnetization transfer. Interactions that can be detected are usually classified into two kinds. There are through-bond interactions and through-space interactions, the latter usually being a consequence of the nuclear Overhauser effect. Experiments of the nuclear Overhauser variety may be employed to establish distances between atoms, as for example by 2D-FT NMR of molecules in solution.

Although the fundamental concept of 2D-FT NMR was proposed by Jean Jeener from the Free University of Brussels at an International Conference, this idea was largely developed by Richard Ernst who won the 1991 Nobel prize in Chemistry for his work in FT NMR, including multi-dimensional FT NMR, and especially 2D-FT NMR of small molecules.[8] Multi-dimensional FT NMR experiments were then further developed into powerful methodologies for studying biomolecules in solution, in particular for the determination of the structure of biopolymers such as proteins or even small nucleic acids.[9]In 2002 Kurt Wthrich shared the Nobel Prize in Chemistry (with John Bennett Fenn and Koichi Tanaka) for his work with protein FT NMR in solution.

[edit] Solid-state NMR spectroscopyMain article: Solid-state nuclear magnetic resonanceThis technique complements X-ray crystallography in that it is frequently applicable to molecules in a liquid or liquid crystal phase, whereas crystallography, as the name implies, is performed on molecules in a solid phase. Though nuclear magnetic resonance is used to study solids, extensive atomic-level molecular structural detail is especially challenging to obtain in the solid state. There is little signal averaging by thermal motion in the solid state, where most molecules can only undergo restricted vibrations and rotations at room temperature, each in a slightly different electronic environment, therefore exhibiting a different NMR absorption peak. Such a variation in the electronic environment of the resonating nuclei results in a blurring of the observed spectrawhich is often only a broad Gaussian band for non-quadrupolar spins in a solid- thus making the interpretation of such "dipolar" and "chemical shift anisotropy" (CSA) broadened spectra either very difficult or impossible.

Professor Raymond Andrew at Nottingham University in the UK pioneered the development of high-resolution solid-state nuclear magnetic resonance. He was the first to report the introduction of the MAS (magic angle sample spinning; MASS) technique that allowed him to achieve spectral resolution in solids sufficient to distinguish between chemical groups with either different chemical shifts or distinct Knight shifts. In MASS, the sample is spun at several kilohertz around an axis that makes the so-called magic angle m (which is ~54.74, where cos2m = 1/3) with respect to the direction of the static magnetic field B0; as a result of such magic angle sample spinning, the chemical shift anisotropy bands are averaged to their corresponding average (isotropic) chemical shift values. The above expression involving cos2m has its origin in a calculation that predicts the magnetic dipolar interaction effects to cancel out for the specific value of m called the magic angle. One notes that correct alignment of the sample rotation axis as close as possible to m is essential for cancelling out the dipolar interactions whose strength for angles sufficiently far from m is usually greater than ~10kHz for C-H bonds in solids, for example, and it is thus greater than their CSA values.

There are different angles for the sample spinning relative to the applied field for the averaging of quadrupole interactions and paramagnetic interactions, correspondingly ~30.6 and ~70.1

A concept developed by Sven Hartmann and Erwin Hahn was utilized in transferring magnetization from protons to less sensitive nuclei (popularly known as cross-polarization) by M.G. Gibby, Alex Pines and John S. Waugh. Then, Jake Schaefer and Ed Stejskal demonstrated also the powerful use of cross-polarization under MASS conditions which is now routinely employed to detect low-abundance and low-sensitivity nuclei.

[edit] SensitivityBecause the intensity of nuclear magnetic resonance signals and, hence, the sensitivity of the technique depends on the strength of the magnetic field the technique has also advanced over the decades with the development of more powerful magnets. Advances made in audio-visual technology have also improved the signal-generation and processing capabilities of newer instruments.

As noted above, the sensitivity of nuclear magnetic resonance signals is also dependent on the presence of a magnetically susceptible nuclide and, therefore, either on the natural abundance of such nuclides or on the ability of the experimentalist to artificially enrich the molecules, under study, with such nuclides. The most abundant naturally occurring isotopes of hydrogen and phosphorus (for example) are both magnetically susceptible and readily useful for nuclear magnetic resonance spectroscopy. In contrast, carbon and nitrogen have useful isotopes but which occur only in very low natural abundance.

Other limitations on sensitivity arise from the quantum-mechanical nature of the phenomenon. For quantum states separated by energy equivalent to radio frequencies, thermal energy from the environment causes the populations of the states to be close to equal. Since incoming radiation is equally likely to cause stimulated emission (a transition from the upper to the lower state) as absorption, the NMR effect depends on an excess of nuclei in the lower states. Several factors can reduce sensitivity, including

Increasing temperature, which evens out the population of states. Conversely, low temperature NMR can sometimes yield better results than room-temperature NMR, providing the sample remains liquid.

Saturation of the sample with energy applied at the resonant radiofrequency. This manifests in both CW and pulsed NMR; in the first case (CW) this happens by using too much continuous power that keeps the upper spin levels completely populated; in the second case (pulsed), each pulse (that is at least a 90 pulse) leaves the sample saturated, and four to five times the (longitudinal) relaxation time (5 T1) must pass before the next pulse or pulse sequence can be applied. For single pulse experiments, shorter RF pulses that tip the magnetization by less than 90 can be used, which loses some intensity of the signal, but allows for shorter recycle delays. The optimum there is called an Ernst angle, after the Nobel laureate. Especially in solid state NMR, or in samples with very few nuclei with spins > 0, (diamond with the natural 1% of Carbon-13 is especially troublesome here) the longitudinal relaxation times can be on the range of hours, while for proton-NMR they are more on the range of one second.

Non-magnetic effects, such as electric-quadrupole coupling of spin-1 and spin-32 nuclei with their local environment, which broaden and weaken absorption peaks. 14N, an abundant spin-1 nucleus, is difficult to study for this reason. High resolution NMR instead probes molecules using the rarer 15N isotope, which has spin-12.

[edit] IsotopesMany chemical elements can be used for NMR analysis.[10]Commonly used nuclei: 1H, the most commonly used spin nucleus in NMR investigation, has been studied using many forms of NMR. Hydrogen is highly abundant, especially in biological systems. It is the nucleus most sensitive to NMR signal (apart from 3H which is not commonly used due to its instability and radioactivity). Proton NMR produces narrow chemical shift with sharp signals. Fast acquisition of quantitative results (peak integrals in stoichiometric ratio) is possible due to short relaxation time. The 1H signal has been the sole diagnostic nucleus used for clinical magnetic resonance imaging.

2H, a spin 1 nucleus commonly utilized as signal-free medium in the form of deuterated solvents during proton NMR, to avoid signal interference from hydrogen-containing solvents in measurement of 1H solutes. Also used in determining the behavior of lipids in lipid membranes and other solids or liquid crystals as it is a relatively non-perturbing label which can selectively replace 1H. Alternatively, 2H can be detected in media specially labeled with 2H. Deuterium resonance is commonly used in high-resolution NMR spectroscopy to monitor drifts in the magnetic field strength (lock) and to improve the homogeneity of the external magnetic field.

3He, is very sensitive to NMR. There is a very low percentage in natural helium, and subsequently has to be purified from 4He. It is used mainly in studies of endohedral fullerenes, where its chemical inertness is beneficial to ascertaining the structure of the entrapping fullerene.

11B, more sensitive than 10B, yields sharper signals. Quartz tubes must be used as borosilicate glass interferes with measurement.

13C spin-1/2, is widely used, despite its relative paucity in naturally occurring carbon (approximately 1%). It is stable to nuclear decay. Since there is a low percentage in natural carbon, spectrum acquisition on samples which have not been experimentally enriched in 13C takes a long time. Frequently used for labeling of compounds in synthetic and metabolic studies. Has low sensitivity and wide chemical shift, yields sharp signals. Low percentage makes it useful by preventing spin-spin couplings and makes the spectrum appear less crowded. Slow relaxation means that spectra are not integrable unless long acquisition times are used.

14N, spin-1, medium sensitivity nucleus with wide chemical shift. Its large quadrupole moment interferes in acquisition of high resolution spectra, limiting usefulness to smaller molecules and functional groups with a high degree of symmetry such as the headgroups of lipids.

15N, spin-1/2, relatively commonly used. Can be used for labeling compounds. Nucleus very insensitive but yields sharp signals. Low percentage in natural nitrogen together with low sensitivity requires high concentrations or expensive isotope enrichment.

17O, spin-5/2, low sensitivity and very low natural abundance (0.037%), wide chemical shifts range (up to 2000 ppm). Quadrupole moment causing a line broadening. Used in metabolic and biochemical studies in studies of chemical equilibria.

19F, spin-1/2, relatively commonly measured. Sensitive, yields sharp signals, has wide chemical shift.

31P, spin-1/2, 100% of natural phosphorus. Medium sensitivity, wide chemical shifts range, yields sharp lines. Spectra tend to have a moderate amount of noise. Used in biochemical studies and in coordination chemistry where phosphorus containing ligands are involved.

35Cl and 37Cl, broad signal. 35Cl significantly more sensitive, preferred over 37Cl despite its slightly broader signal. Organic chlorides yield very broad signals, its use is limited to inorganic and ionic chlorides and very small organic molecules.

43Ca, used in biochemistry to study calcium binding to DNA, proteins, etc. Moderately sensitive, very low natural abundance.

195Pt, used in studies of catalysts and complexes.

Other nuclei (usually used in the studies of their complexes and chemical binding, or to detect presence of the element):

6Li, 7Li

9Be

19F

21Ne

23Na

25Mg

27Al

29Si

31P

33S

39K, 40K, 41K

45Sc

47Ti, 49Ti

50V, 51V

53Cr

55Mn

57Fe

59Co

61Ni

63Cu, 65Cu

67Zn

69Ga, 71Ga

73Ge

75As

77Se

81Br

87Rb

87Sr

95Mo

109Ag

113Cd

119Sn

125Te

127I

133Cs

135Ba, 137Ba

139La

183W

199Hg

[edit] Applications[edit] Medicine

Medical MRI

See also: Magnetic resonance imagingThe application of nuclear magnetic resonance best known to the general public is magnetic resonance imaging for medical diagnosis and magnetic resonance microscopy in research settings, however, it is also widely used in chemical studies, notably in NMR spectroscopy such as proton NMR, carbon-13 NMR, deuterium NMR and phosphorus-31 NMR. Biochemical information can also be obtained from living tissue (e.g. human brain tumors) with the technique known as in vivo magnetic resonance spectroscopy or chemical shift NMR Microscopy.

These studies are possible because nuclei are surrounded by orbiting electrons, which are charged particles that generate small, local magnetic fields that add to or subtract from the external magnetic field, and so will partially shield the nuclei. The amount of shielding depends on the exact local environment. For example, a hydrogen bonded to an oxygen will be shielded differently than a hydrogen bonded to a carbon atom. In addition, two hydrogen nuclei can interact via a process known as spin-spin coupling, if they are on the same molecule, which will split the lines of the spectra in a recognizable way.

As one of the two major spectroscopic techniques used in metabolomics, NMR is used to generate metabolic fingerprints from biological fluids to obtain information about disease states or toxic insults.

[edit] ChemistryBy studying the peaks of nuclear magnetic resonance spectra, chemists can determine the structure of many compounds. It can be a very selective technique, distinguishing among many atoms within a molecule or collection of molecules of the same type but which differ only in terms of their local chemical environment. NMR spectroscopy is used to unambiguously identify known and novel compounds, and as such, is usually required by scientific journals for identity confirmation of synthesized new compounds. See the articles on carbon-13 NMR and proton NMR for detailed discussions.

By studying T2 information, a chemist can determine the identity of a compound by comparing the observed nuclear precession frequencies to known frequencies. Further structural data can be elucidated by observing spin-spin coupling, a process by which the precession frequency of a nucleus can be influenced by the magnetization transfer from nearby chemically bound nuclei. Spin-spin coupling is observed in NMR of hydrogen-1 (1H NMR), since its natural abundance is nearly 100%; isotope enrichment is required for most other elements.

Because the nuclear magnetic resonance timescale is rather slow, compared to other spectroscopic methods, changing the temperature of a T2*experiment can also give information about fast reactions, such as the Cope rearrangement or about structural dynamics, such as ring-flipping in cyclohexane. At low enough temperatures, a distinction can be made between the axial and equatorial hydrogens in cyclohexane.

An example of nuclear magnetic resonance being used in the determination of a structure is that of buckminsterfullerene (often called "buckyballs", composition C60). This now famous form of carbon has 60 carbon atoms forming a sphere. The carbon atoms are all in identical environments and so should see the same internal H field. Unfortunately, buckminsterfullerene contains no hydrogen and so 13C nuclear magnetic resonance has to be used. 13C spectra require longer acquisition times since carbon-13 is not the common isotope of carbon (unlike hydrogen, where 1H is the common isotope). However, in 1990 the spectrum was obtained by R. Taylor and co-workers at the University of Sussex and was found to contain a single peak, confirming the unusual structure of buckminsterfullerene.[11][edit] Non-destructive testingNuclear magnetic resonance is extremely useful for analyzing samples non-destructively. Radio waves and static magnetic fields easily penetrate many types of matter and anything that is not inherently ferromagnetic. For example, various expensive biological samples, such as nucleic acids, including RNA and DNA, or proteins, can be studied using nuclear magnetic resonance for weeks or months before using destructive biochemical experiments. This also makes nuclear magnetic resonance a good choice for analyzing dangerous samples.

[edit] Acquisition of dynamic informationIn addition to providing static information on molecules by determining their 3D structures in solution, one of the remarkable advantages of NMR over X-ray crystallography is that it can be used to obtain important dynamic information including the low-frequency collective motion in proteins and DNA, for example in the Ca2+-calmodulin system.[12] The low-frequency internal motion in biomacromolecules and its biological functions have been discussed by Chou.[13][edit] Data acquisition in the petroleum industryMain article: NMR in porous mediaAnother use for nuclear magnetic resonance is data acquisition in the petroleum industry for petroleum and natural gas exploration and recovery. A borehole is drilled into rock and sedimentary strata into which nuclear magnetic resonance logging equipment is lowered. Nuclear magnetic resonance analysis of these boreholes is used to measure rock porosity, estimate permeability from pore size distribution and identify pore fluids (water, oil and gas). These instruments are typically low field NMR spectrometers.

[edit] Flow probes for NMR spectroscopyRecently, real-time applications of NMR in liquid media have been developed using specifically designed flow probes (flow cell assemblies) which can replace standard tube probes. This has enabled techniques that can incorporate the use of high performance liquid chromatography (HPLC) or other continuous flow sample introduction devices.[14][edit] Process controlNMR has now entered the arena of real-time process control and process optimization in oil refineries and petrochemical plants. Two different types of NMR analysis are utilized to provide real time analysis of feeds and products in order to control and optimize unit operations. Time-domain NMR (TD-NMR) spectrometers operating at low field (220MHz for 1H) yield free induction decay data that can be used to determine absolute hydrogen content values, rheological information, and component composition. These spectrometers are used in mining, polymer production, cosmetics and food manufacturing as well as coal analysis. High resolution FT-NMR spectrometers operating in the 60MHz range with shielded permanent magnet systems yield high resolution 1H NMR spectra of refinery and petrochemical streams. The variation observed in these spectra with changing physical and chemical properties is modeled using chemometrics to yield predictions on unknown samples. The prediction results are provided to control systems via analogue or digital outputs from the spectrometer.

[edit] Earth's field NMRMain article: Earth's field NMRIn the Earth's magnetic field, NMR frequencies are in the audio frequency range, or the very low frequency and ultra low frequency bands of the radio frequency spectrum. Earth's field NMR (EFNMR) is typically stimulated by applying a relatively strong dc magnetic field pulse to the sample and, after the end of the pulse, analyzing the resulting low frequency alternating magnetic field that occurs in the Earth's magnetic field due to free induction decay (FID). These effects are exploited in some types of magnetometers, EFNMR spectrometers, and MRI imagers. Their inexpensive portable nature makes these instruments valuable for field use and for teaching the principles of NMR and MRI.

An important feature of EFNMR spectrometry compared with high-field NMR is that some aspects of molecular structure can be observed more clearly at low fields and low frequencies, whereas other aspects observable at high fields are not observable at low fields. This is because:

Electron-mediated heteronuclear J-couplings (spin-spin couplings) are field independent, producing clusters of two or more frequencies separated by several Hz, which are more easily observed in a fundamental resonance of about 2 kHz. "Indeed it appears that enhanced resolution is possible due to the long spin relaxation times and high field homogeneity which prevail in EFNMR."[15]

Chemical shifts of several ppm are clearly separated in high field NMR spectra, but have separations of only a few millihertz at proton EFNMR frequencies, so are usually lost in noise etc.

[edit] Quantum computingMain article: Nuclear magnetic resonance quantum computerNMR quantum computing uses the spin states of molecules as qubits. NMR differs from other implementations of quantum computers in that it uses an ensemble of systems, in this case molecules.

[edit] MagnetometersMain article: MagnetometerVarious magnetometers use NMR effects to measure magnetic fields, including proton precession magnetometers (PPM) (also known as proton magnetometers), and Overhauser magnetometers. See also Earth's field NMR.

[edit] Makers of NMR equipmentMajor NMR instrument makers include Oxford Instruments, Bruker, Spinlock SRL, General Electric, JEOL, Kimble Chase, Philips, Siemens AG, Varian, Inc. and Agilent Technologies, Inc..

[edit] See also Carbon-13 NMR

Chemical shift

Dynamic nuclear polarisation (DNP)

Earth's field NMR (EFNMR)

Free induction decay (FID)

In vivo magnetic resonance spectroscopy (MRS)

J-coupling

Larmor equation (Not to be confused with Larmor formula).

Larmor precession

Low field NMR

Magic angle spinning

Magnetometer

Magnetic resonance imaging (MRI)

NMR crystallography

NMR spectra database

NMR spectroscopy

NMR Microscopy

Nuclear magnetic resonance in porous media

Nuclear quadrupole resonance (NQR)

Protein dynamics

Protein NMR

Proton NMR

Rabi cycle

Relaxometry

Relaxation (NMR)

Sow-Hsin Chen, MIT

Spin echo

Solid-state NMR

Zero field NMR

[edit] Notes1. ^ I.I. Rabi, J.R. Zacharias, S. Millman, P. Kusch (1938). "A New Method of Measuring Nuclear Magnetic Moment". Physical Review 53 (4): 318327. Bibcode 1938PhRv...53..318R. doi:10.1103/PhysRev.53.318. PMID9981980.

2. ^ Biography of I. Rabi at Nobelprize.org

3. ^ Filler, Aaron (2009). "The History, Development and Impact of Computed Imaging in Neurological Diagnosis and Neurosurgery: CT, MRI, and DTI". Nature Precedings. doi:10.1038/npre.2009.3267.5.

4. ^ 1952 Nobel Prize for Physics at Nobelprize.org

5. ^ Principle of Shielding and Deshielding | NMRCentral.com

6. ^ Quantum automaton and quantum computation (see also references therein)

7. ^ Lieven M. K. Vandersypen; Steffen, Matthias; Breyta, Gregory; Yannoni, Costantino S.; Sherwood, Mark H.; Chuang, Isaac L. (2001). "Experimental realization of Shor's quantum factoring algorithm using nuclear magnetic resonance". Nature 414 (6866): 883887. arXiv:quant-ph/0112176. Bibcode 2001Natur.414..883V. doi:10.1038/414883a. PMID11780055.

8. ^ "Nuclear Magnetic Resonance Fourier Transform Spectroscopy" Ernst's Nobel lecture. (Includes mention of Jeener's suggestion.)

9. ^ I.C. Baianu. "Two-dimensional Fourier transforms". 2D-FT NMR and MRI. PlanetMath. http://planetmath.org/encyclopedia/TwoDimensionalFourierTransforms.html. Retrieved 2009-02-22.

10. ^ Multinuclear NMR

11. ^ R. Taylor, J.P. Hare, A.K. Abdul-Sada, H.W. Kroto (1990). "Isolation, separation and characterization of the fullerenes C60 and C70: the third form of carbon". Journal of the Chemical Society, Chemical Communications 20 (20): 14231425. doi:10.1039/c39900001423.

12. ^ Chou, J. J.; Li, S.; Klee, C. B.; Bax, A. (2001). "Solution structure of Ca2+-calmodulin reveals flexible hand-like properties of its domains". Nature Structural Biology 8 (11): 990997. doi:10.1038/nsb1101-990. PMID11685248.

13. ^ Kuo-Chen Chou (1988). "Low-frequency collective motion in biomacromolecules and its biological functions". Biophys Chem 30 (1): 348. doi:10.1016/0301-4622(88)85002-6. PMID3046672.

14. ^ R.L Haner and P.A, Keifer (2009). "Flow Probes for NMR Spectroscopy". Encyclopedia of Magnetic Resonance. doi:10.1002/9780470034590.emrstm1085. ISBN0470034599.

15. ^ Robinson J. N. et al. (2006). "Two-dimensional NMR spectroscopy in Earth's magnetic field". Journal of Magnetic Resonance 182 (2): 343347. Bibcode 2006JMagR.182..343R. doi:10.1016/j.jmr.2006.06.027. PMID16860581. http://www.sfu.ca/~simonw/phys431/references/nmr/robinson_nmr_imaging_JMR2006.pdf.

[edit] References Gary E. Martin, A. S. Zektzer (1988). Two-Dimensional NMR Methods for Establishing Molecular Connectivity. New York: Wiley-VCH. p.59. ISBN0-471-18707-0. http://books.google.com/books?id=9ysYrpe_NoEC&printsec=frontcover.

J.W. Akitt, B.E. Mann (2000). NMR and Chemistry. Cheltenham, UK: Stanley Thornes. pp.273, 287. ISBN0-7487-4344-8.

J.P. Hornak. "The Basics of NMR". http://www.cis.rit.edu/htbooks/nmr/. Retrieved 2009-02-23.

J. Keeler (2005). Understanding NMR Spectroscopy. John Wiley & Sons. ISBN0-470-01786-4.

Kurt Wthrich (1986). NMR of Proteins and Nucleic Acids. New York (NY), USA: Wiley-Interscience. ISBN0-471-11917-2.

J.M Tyszka, S.E Fraser, R.E Jacobs (2005). "Magnetic resonance microscopy: recent advances and applications". Current Opinion in Biotechnology 16 (1): 9399. doi:10.1016/j.copbio.2004.11.004. PMID15722021.

J.C. Edwards. "Principles of NMR". Process NMR Associates. http://www.process-nmr.com/pdfs/NMR%20Overview.pdf. Retrieved 2009-02-23.

R.L Haner, P.A. Keifer (2009). Encyclopedia of Magnetic Resonance. John Wiley. doi:10.1002/9780470034590.emrstm1085.

[edit] External links7.5. massa, Mass spectrometry

From Wikipedia, the free encyclopedia

Jump to: navigation, search

Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of charged particles.[1] It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and other chemical compounds. The MS principle consists of ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios.[1] In a typical MS procedure:

1. A sample is loaded onto the MS instrument and undergoes vaporization

2. The components of the sample are ionized by one of a variety of methods (e.g., by impacting them with an electron beam), which results in the formation of charged particles (ions)

3. The ions are separated according to their mass-to-charge ratio in an analyzer by electromagnetic fields

4. The ions are detected, usually by a quantitative method

5. The ion signal is processed into mass spectra

MS instruments consist of three modules:

An ion source, which can convert gas phase sample molecules into ions (or, in the case of electrospray ionization, move ions that exist in solution into the gas phase)

A mass analyzer, which sorts the ions by their masses by applying electromagnetic fields

A detector, which measures the value of an indicator quantity and thus provides data for calculating the abundances of each ion present

The technique has both qualitative and quantitative uses. These include identifying unknown compounds, determining the isotopic composition of elements in a molecule, and determining the structure of a compound by observing its fragmentation. Other uses include quantifying the amount of a compound in a sample or studying the fundamentals of gas phase ion chemistry (the chemistry of ions and neutrals in a vacuum). MS is now in very common use in analytical laboratories that study physical, chemical, or biological properties of a great variety of compounds.

Contents

[hide] 1 Etymology

2 History

3 Simplified example

4 Creating ions

4.1 Inductively coupled plasma

4.2 Other ionization techniques

5 Mass selection

5.1 Sector instruments

5.2 Time-of-flight

5.3 Quadrupole mass filter

5.4 Ion traps

5.4.1 Three-dimensional quadrupole ion trap

5.4.2 Linear quadrupole ion trap

5.4.3 Orbitrap

5.5 Fourier transform ion cyclotron resonance

6 Detectors

7 Tandem mass spectrometry

8 Common mass spectrometer configurations and techniques

9 Chromatographic techniques combined with mass spectrometry

9.1 Gas chromatography

9.2 Liquid chromatography

9.3 Ion mobility

10 Data and analysis

10.1 Data representations

10.2 Data analysis

11 Applications

11.1 Isotope ratio MS: isotope dating and tracking

11.2 Trace gas analysis

11.3 Atom probe

11.4 Pharmacokinetics

11.5 Protein characterization

11.6 Glycan analysis

11.7 Space exploration

11.8 Respired gas monitor

12 See also

13 References

14 Bibliography

15 External links

[edit] EtymologyThe word spectrograph had become part of the international scientific vocabulary by 1884.[2]

HYPERLINK "http://en.wikipedia.org/wiki/Mass_spectrometry" \l "cite_note-2" [3] The linguistic roots are a combination and removal of bound morphemes and free morphemes which relate to the terms spectr-um and phot-ograph-ic plate.[4] Early spectrometry devices that measured the mass-to-charge ratio of ions were called mass spectrographs which consisted of instruments that recorded a spectrum of mass values on a photographic plate.[5]

HYPERLINK "http://en.wikipedia.org/wiki/Mass_spectrometry" \l "cite_note-5" [6] A mass spectroscope is similar to a mass spectrograph except that the beam of ions is directed onto a phosphor screen.[7] A mass spectroscope configuration was used in early instruments when it was desired that the effects of adjustments be quickly observed. Once the instrument was properly adjusted, a photographic plate was inserted and exposed. The term mass spectroscope continued to be used even though the direct illumination of a phosphor screen was replaced by indirect measurements with an oscilloscope.[8] The use of the term mass spectroscopy is now discouraged due to the possibility of confusion with light spectroscopy.[1]

HYPERLINK "http://en.wikipedia.org/wiki/Mass_spectrometry" \l "cite_note-Price_1991-8" [9] Mass spectrometry is often abbreviated as mass-spec or simply as MS.[1][edit] HistoryFor more details on this topic, see History of mass spectrometry.

Replica of an early mass spectrometer

In 1886, Eugen Goldstein observed rays in gas discharges under low pressure that traveled away from the anode and through channels in a perforated cathode, opposite to the direction of negatively charged cathode rays (which travel from cathode to anode). Goldstein called these positively charged anode rays "Kanalstrahlen"; the standard translation of this term into English is "canal rays". Wilhelm Wien found that strong electric or magnetic fields deflected the canal rays and, in 1899, constructed a device with parallel electric and magnetic fields that separated the positive rays according to their charge-to-mass ratio (Q/m). Wien found that the charge-to-mass ratio depended on the nature of the gas in the discharge tube. English scientist J.J. Thomson later improved on the work of Wien by reducing the pressure to create a mass spectrograph.

The first application of mass spectrometry to the analysis of amino acids and peptides was reported in 1958.[10] Carl-Ove Andersson highlighted the main fragment ions observed in the ionization of methyl esters.[11]Some of the modern techniques of mass spectrometry were devised by Arthur Jeffrey Dempster and F.W. Aston in 1918 and 1919 respectively. In 1989, half of the Nobel Prize in Physics was awarded to Hans Dehmelt and Wolfgang Paul for the development of the ion trap technique in the 1950s and 1960s. In 2002, the Nobel Prize in Chemistry was awarded to John Bennett Fenn for the development of electrospray ionization (ESI) and Koichi Tanaka for the development of soft laser desorption (SLD) and their application to the ionization of biological macromolecules, especially proteins.[12][edit] Simplified exampleSchematics of a simple mass spectrometer with sector type mass analyzer. This one is for the measurement of carbon dioxide isotope ratios (IRMS) as in the carbon-13 urea breath testThe following example describes the operation of a spectrometer mass analyzer, which is of the sector type. (Other analyzer types are treated below.) Consider a sample of sodium chloride (table salt). In the ion source, the sample is vaporized (turned into gas) and ionized (transformed into electrically charged particles) into sodium (Na+) and chloride (Cl-) ions. Sodium atoms and ions are monoisotopic, with a mass of about 23 amu. Chloride atoms and ions come in two isotopes with masses of approximately 35 amu (at a natural abundance of about 75 percent) and approximately 37 amu (at a natural abundance of about 25 percent). The analyzer part of the spectrometer contains electric and magnetic fields, which exert forces on ions traveling through these fields. The speed of a charged particle may be increased or decreased while passing through the electric field, and its direction may be altered by the magnetic field. The magnitude of the deflection of the moving ion's trajectory depends on its mass-to-charge ratio. Lighter ions get deflected by the magnetic force more than heavier ions (based on Newton's second law of motion, F = ma). The streams of sorted ions pass from the analyzer to the detector, which records the relative abundance of each ion type. This information is used to determine the chemical element composition of the original sample (i.e. that both sodium and chlorine are present in the sample) and the isotopic composition of its constituents (the ratio of 35Cl to 37Cl).

[edit] Creating ionsMain article: Ion sourceThe ion source is the part of the mass spectrometer that ionizes the material under analysis (the analyte). The ions are then transported by magnetic or electric fields to the mass analyzer.

Techniques for ionization have been key to determining what types of samples can be analyzed by mass spectrometry. Electron ionization and chemical ionization are used for gases and vapors. In chemical ionization sources, the analyte is ionized by chemical ion-molecule reactions during collisions in the source. Two techniques often used with liquid and solid biological samples include electrospray ionization (invented by John Fenn[13]) and matrix-assisted laser desorption/ionization (MALDI, initially developed as a similar technique "Soft Laser Desorption (SLD)" by K. Tanaka[14] for which a Nobel Prize was awarded and as MALDI by M. Karas and F. Hillenkamp[15]).

[edit] Inductively coupled plasmaInductively coupled plasma (ICP) sources are used primarily for cation analysis of a wide array of sample types. In this type of Ion Source Technology, a 'flame' of plasma that is electrically neutral overall, but that has had a substantial fraction of its atoms ionized by high temperature, is used to atomize introduced sample molecules and to further strip the outer electrons from those atoms. The plasma is usually generated from argon gas, since the first ionization energy of argon atoms is higher than the first of any other elements except He, O, F and Ne, but lower than the second ionization energy of all except the most electropositive metals. The heating is achieved by a radio-frequency current passed through a coil surrounding the plasma.

[edit] Other ionization techniquesOthers include glow discharge, field desorption (FD), fast atom bombardment (FAB), thermospray, desorption/ionization on silicon (DIOS), Direct Analysis in Real Time (DART), atmospheric pressure chemical ionization (APCI), secondary ion mass spectrometry (SIMS), spark ionization and thermal ionization (TIMS).[16] Ion attachment ionization is an ionization technique that allows for fragmentation free analysis.

[edit] Mass selectionMass analyzers separate the ions according to their mass-to-charge ratio. The following two laws govern the dynamics of charged particles in electric and magnetic fields in vacuum:

(Lorentz force law);

(Newton's second law of motion in non-relativistic case, i.e. valid only at ion velocity much lower than the speed of light).

Here F is the force applied to the ion, m is the mass of the ion, a is the acceleration, Q is the ion charge, E is the electric field, and v B is the vector cross product of the ion velocity and the magnetic field

Equating the above expressions for the force applied to the ion yields:

This differential equation is the classic equation of motion for charged particles. Together with the particle's initial conditions, it completely determines the particle's motion in space and time in terms of m/Q. Thus mass spectrometers could be thought of as "mass-to-charge spectrometers". When presenting data, it is common to use the (officially) dimensionless m/z, where z is the number of elementary charges (e) on the ion (z=Q/e). This quantity, although it is informally called the mass-to-charge ratio, more accurately speaking represents the ratio of the mass number and the charge number, z.

There are many types of mass analyzers, using either static or dynamic fields, and magnetic or electric fields, but all operate according to the above differential equation. Each analyzer type has its strengths and weaknesses. Many mass spectrometers use two or more mass analyzers for tandem mass spectrometry (MS/MS). In addition to the more common mass analyzers listed below, there are others designed for special situations.

There are several important analyser characteristics. The mass resolving power is the measure of the ability to distinguish two peaks of slightly different m/z. The mass accuracy is the ratio of the m/z measurement error to the true m/z. Mass accuracy is usually measured in ppm or milli mass units. The mass range is the range of m/z amenable to analysis by a given analyzer. The linear dynamic range is the range over which ion signal is linear with analyte concentration. Speed refers to the time frame of the experiment and ultimately is used to determine the number of spectra per unit time that can be generated.

[edit] Sector instrumentsFor more details on this topic, see sector instrument.

A sector field mass analyzer uses an electric and/or magnetic field to affect the path and/or velocity of the charged particles in some way. As shown above, sector instruments bend the trajectories of the ions as they pass through the mass analyzer, according to their mass-to-charge ratios, deflecting the more charged and faster-moving, lighter ions more. The analyzer can be used to select a narrow range of m/z or to scan through a range of m/z to catalog the ions present.[17][edit] Time-of-flightFor more details on this topic, see time-of-flight mass spectrometry.

The time-of-flight (TOF) analyzer uses an electric field to accelerate the ions through the same potential, and then measures the time they take to reach the detector. If the particles all have the same charge, the kinetic energies will be identical, and their velocities will depend only on their masses. Lighter ions will reach the detector first.[18][edit] Quadrupole mass filterFor more details on this topic, see Quadrupole mass analyzer.

Quadrupole mass analyzers use oscillating electrical fields to selectively stabilize or destabilize the paths of ions passing through a radio frequency (RF) quadrupole field created between 4 parallel rods. Only the ions in a certain range of mass/charge ratio are passed through the system at any time, but changes to the potentials on the rods allow a wide range of m/z values to be swept rapidly, either continuously or in a succession of discrete hops. A quadrupole mass analyzer acts as a mass-selective filter and is closely related to the quadrupole ion trap, particularly the linear quadrupole ion trap except that it is designed to pass the untrapped ions rather than collect the trapped ones, and is for that reason referred to as a transmission quadrupole. A common variation of the transmission quadrupole is the triple quadrupole mass spectrometer. The triple quad has three consecutive quadrupole stages, the first acting as a mass filter to transmit a particular incoming ion to the second quadrupole, a collision chamber, wherein that ion can be broken into fragments. The third quadrupole also acts as a mass filter, to transmit a particular fragment ion to the detector. If a quadrupole is made to rapidly and repetitively cycle through a range of mass filter settings, full spectra can be reported. Likewise, a triple quad can be made to perform various scan types characteristic of tandem mass spectrometry.

[edit] Ion traps[edit] Three-dimensional quadrupole ion trapFor more details on this topic, see quadrupole ion trap.

The quadrupole ion trap works on the same physical principles as the quadrupole mass analyzer, but the ions are trapped and sequentially ejected. Ions are trapped in a mainly quadrupole RF field, in a space defined by a ring electrode (usually connected to the main RF potential) between two endcap electrodes (typically connected to DC or auxiliary AC potentials). The sample is ionized either internally (e.g. with an electron or laser beam), or externally, in which case the ions are often introduced through an aperture in an endcap electrode.

There are many mass/charge separation and isolation methods but the most commonly used is the mass instability mode in which the RF potential is ramped so that the orbit of ions with a mass a > b are stable while ions with mass b become unstable and are ejected on the z-axis onto a detector. There are also non-destructive analysis methods.

Ions may also be ejected by the resonance excitation method, whereby a supplemental oscillatory excitation voltage is applied to the endcap electrodes, and the trapping voltage amplitude and/or excitation voltage frequency is varied to bring ions into a resonance condition in order of their mass/charge ratio.[19]

HYPERLINK "http://en.wikipedia.org/wiki/Mass_spectrometry" \l "cite_note-19" [20]The cylindrical ion trap mass spectrometer is a derivative of the quadrupole ion trap mass spectrometer.

[edit] Linear quadrupole ion trapA linear quadrupole ion trap is similar to a quadrupole ion trap, but it traps ions in a two dimensional quadrupole field, instead of a three-dimensional quadrupole field as in a 3D quadrupole ion trap. Thermo Fisher's LTQ ("linear trap quadrupole") is an example of the linear ion trap.[21]A toroidal ion trap can be visualized as a linear quadrupole curved around and connected at the ends or as a cross section of a 3D ion trap rotated on edge to form the toroid, donut shaped trap. The trap can store large volumes of ions by distributing them throughout the ring-like trap structure. This toroidal shaped trap is a configuration that allows the increased miniaturization of an ion trap mass analyzer. Additionally all ions are stored in the same trapping field and ejected together simplifying detection that can be complicated with array configurations due to variations in detector alignment and machining of the arrays.[22][edit] OrbitrapFor more details on this topic, see Orbitrap.

These are similar to Fourier transform ion cyclotron resonance mass spectrometers (see text below). Ions are electrostatically trapped in an orbit around a central, spindle shaped electrode. The electrode confines the ions so that they both orbit around the central electrode and oscillate back and forth along the central electrode's long axis. This oscillation generates an image current in the detector plates which is recorded by the instrument. The frequencies of these image currents depend on the mass to charge ratios of the ions. Mass spectra are obtained by Fourier transformation of the recorded image currents.

Orbitraps have a high mass accuracy, high sensitivity and a good dynamic range.[23][edit] Fourier transform ion cyclotron resonanceFor more details on this topic, see Fourier transform mass spectrometry.

Fourier transform mass spectrometry (FTMS), or more precisely Fourier transform ion cyclotron resonance MS, measures mass by detecting the image current produced by ions cyclotroning in the presence of a magnetic field. Instead of measuring the deflection of ions with a detector such as an electron multiplier, the ions are injected into a Penning trap (a static electric/magnetic ion trap) where they effectively form part of a circuit. Detectors at fixed positions in space measure the electrical signal of ions which pass near them over time, producing a periodic signal. Since the frequency of an ion's cycling is determined by its mass to charge ratio, this can be deconvoluted by performing a Fourier transform on the signal. FTMS has the advantage of high sensitivity (since each ion is "counted" more than once) and much higher resolution and thus precision.[24]

HYPERLINK "http://en.wikipedia.org/wiki/Mass_spectrometry" \l "cite_note-24" [25]Ion cyclotron resonance (ICR) is an older mass analysis technique similar to FTMS except that ions are detected with a traditional detector. Ions trapped in a Penning trap are excited by an RF electric field until they impact the wall of the trap, where the detector is located. Ions of different mass are resolved according to impact time.

[edit] Detectors

A continuous dynode particle multiplier detector.

The final element of the mass spectrometer is the detector. The detector records either the charge induced or the current produced when an ion passes by or hits a surface. In a scanning instrument, the signal produced in the detector during the course of the scan versus where the instrument is in the scan (at what m/Q) will produce a mass spectrum, a record of ions as a function of m/Q.

Typically, some type of electron multiplier is used, though other detectors including Faraday cups and ion-to-photon detectors are also used. Because the number of ions leaving the mass analyzer at a particular instant is typically quite small, considerable amplification is often necessary to get a signal. Microchannel plate detectors are commonly used in modern commercial instruments.[26] In FTMS and Orbitraps, the detector consists of a pair of metal surfaces within the mass analyzer/ion trap region which the ions only pass near as they oscillate. No DC current is produced, only a weak AC image current is produced in a circuit between the electrodes. Other inductive detectors have also been used.[27][edit] Tandem mass spectrometryMain article: Tandem mass spectrometryA tandem mass spectrometer is one capable of multiple rounds of mass spectrometry, usually separated by some form of molecule fragmentation. For example, one mass analyzer can isolate one peptide from many entering a mass spectrometer. A second mass analyzer then stabilizes the peptide ions while they collide with a gas, causing them to fragment by collision-induced dissociation (CID). A third mass analyzer then sorts the fragments produced from the peptides. Tandem MS can also be done in a single mass analyzer over time, as in a quadrupole ion trap. There are various methods for fragmenting molecules for tandem MS, including collision-induced dissociation (CID), electron capture dissociation (ECD), electron transfer dissociation (ETD), infrared multiphoton dissociation (IRMPD), blackbody infrared radiative dissociation (BIRD), electron-detachment dissociation (EDD) and surface-induced dissociation (SID). An important application using tandem mass spectrometry is in protein identification.[28]Tandem mass spectrometry enables a variety of experimental sequences. Many commercial mass spectrometers are designed to expedite the execution of such routine sequences as selected reaction monitoring (SRM) and precursor ion scanning. In SRM, the first analyzer allows only a single mass through and the second analyzer monitors for multiple user-defined fragment ions. SRM is most often used with scanning instruments where the second mass analysis event is duty cycle limited. These experiments are used to increase specificity of detection of known molecules, notably in pharmacokinetic studies. Precursor ion scanning refers to monitoring for a specific loss from the precursor ion. The first and second mass analyzers scan across the spectrum as partitioned by a user-defined m/z value. This experiment is used to detect specific motifs within unknown molecules.

Another type of tandem mass spectrometry used for radiocarbon dating is Accelerator Mass Spectrometry (AMS), which uses very high voltages, usually in the mega-volt range, to accelerate negative ions into a type of tandem mass spectrometer.

[edit] Common mass spectrometer configurations and techniquesWhen a specific configuration of source, analyzer, and detector becomes conventional in practice, often a compound acronym arises to designate it, and the compound acronym may be better known among nonspectrometrists than the component acronyms. The epitome of this is MALDI-TOF, which simply refers to combining a matrix-assisted laser desorption/ionization source with a time-of-flight mass analyzer. The MALDI-TOF moniker is more widely recognized by the non-mass spectrometrists than MALDI or TOF individually. Other examples include inductively coupled plasma-mass spectrometry (ICP-MS), accelerator mass spectrometry (AMS), Thermal ionization-mass spectrometry (TIMS) and spark source mass spectrometry (SSMS). Sometimes the use of the generic "MS" actually connotes a very specific mass analyzer and detection system, as is the case with AMS, which is always sector based.

Certain applications of mass spectrometry have developed monikers that although strictly speaking would seem to refer to a broad application, in practice have come instead to connote a specific or a limited number of instrument configurations. An example of this is isotope ratio mass spectrometry (IRMS), which refers in practice to the use of a limited number of sector based mass analyzers; this name is used to refer to both the application and the instrument used for the application.

[edit] Chromatographic techniques combined with mass spectrometryAn important enhancement to the mass resolving and mass determining capabilities of mass spectrometry is using it in tandem with chromatographic separation techniques.

[edit] Gas chromatography

A gas chromatograph (right) directly coupled to a mass spectrometer (left)

See also: Gas chromatography-mass spectrometryA common combination is gas chromatography-mass spectrometry (GC/MS or GC-MS). In this technique, a gas chromatograph is used to separate different compounds. This stream of separated compounds is fed online into the ion source, a metallic filament to which voltage is applied. This filament emits electrons which ionize the compounds. The ions can then further fragment, yielding predictable patterns. Intact ions and fragments pass into the mass spectrometer's analyzer and are eventually detected.[29][edit] Liquid chromatographySee also: Liquid chromatography-mass spectrometrySimilar to gas chromatography MS (GC/MS), liquid chromatography mass spectrometry (LC/MS or LC-MS) separates compounds chromatographically before they are introduced to the ion source and mass spectrometer. It differs from GC/MS in that the mobile phase is liquid, usually a mixture of water and organic solvents, instead of gas and the ions fragments cannot yield predictable patterns. Most commonly, an electrospray ionization source is used in LC/MS. There are also some newly developed ionization techniques like laser spray.

[edit] Ion mobilitySee also: Ion mobility spectrometry-mass spectrometryIon mobility spectrometry/mass spectrometry (IMS/MS or IMMS) is a technique where ions are first separated by drift time through some neutral gas under an applied electrical potential gradient before being introduced into a mass spectrometer.[30] Drift time is a measure of the radius relative to the charge of the ion. The duty cycle of IMS (the time over which the experiment takes place) is longer than most mass spectrometric techniques, such that the mass spectrometer can sample along the course of the IMS separation. This produces data about the IMS separation and the mass-to-charge ratio of the ions in a manner similar to LC/MS.[31]The duty cycle of IMS is short relative to liquid chromatography or gas chromatography separations and can thus be coupled to such techniques, producing triple modalities such as LC/IMS/MS.[32][edit] Data and analysis

Mass spectrum of a peptide showing the isotopic distribution

[edit] Data representationsSee also: Mass spectrometry data formatMass spectrometry produces various types of data. The most common data representation is the mass spectrum.

Certain types of mass spectrometry data are best represented as a mass chromatogram. Types of chromatograms include selected ion monitoring (SIM), total ion current (TIC), and selected reaction monitoring chromatogram (SRM), among many others.

Other types of mass spectrometry data are well represented as a three-dimensional contour map. In this form, the mass-to-charge, m/z is on the x-axis, intensity the y-axis, and an additional experimental parameter, such as time, is recorded on the z-axis.

[edit] Data analysisBasicsMass spectrometry data analysis is a complicated subject that is very specific to the type of experiment producing the data. There are general subdivisions of data that are fundamental to understanding any data.

Many mass spectrometers work in either negative ion mode or positive ion mode. It is very important to know whether the observed ions are negatively or positively charged. This is often important in determining the neutral mass but it also indicates something about the nature of the molecules.

Different types of ion source result in different arrays of fragments produced from the original molecules. An electron ionization source produces many fragments and mostly single-charged (1-) radicals (odd number of electrons), whereas an electrospray source usually produces non-radical quasimolecular ions that are frequently multiply charged. Tandem mass spectrometry purposely produces fragment ions post-source and can drastically change the sort of data achieved by an experiment.

By understanding the origin of a sample, certain expectations can be assumed as to the component molecules of the sample and their fragmentations. A sample from a synthesis/manufacturing process will probably contain impurities chemically related to the target component. A relatively crudely prepared biological sample will probably contain a certain amount of salt, which may form adducts with the analyte molecules in certain analyses.

Results can also depend heavily on how the sample was prepared and how it was run/introduced. An important example is the issue of which matrix is used for MALDI spotting, since much of the energetics of the desorption/ionization event is controlled by the matrix rather than the laser power. Sometimes samples are spiked with sodium or another ion-carrying species to produce adducts rather than a protonated species.

The greatest source of trouble when non-mass spectrometrists try to conduct mass spectrometry on their own or collaborate with a mass spectrometrist is inadequate definition of the research goal of the experiment. Adequate definition of the experimental goal is a prerequisite for collecting the proper data and successfully interpreting it. Among the determinations that can be achieved with mass spectrometry are molecular mass, molecular structure, and sample purity. Each of these questions requires a different experimental procedure. Simply asking for a "mass spec" will most likely not answer the real question at hand.

Interpretation of mass spectraMain article: Mass spectrum analysisSince the precise structure or peptide sequence of a molecule is deciphered through the set of fragment masses, the interpretation of mass spectra requires combined use of various techniques. Usually the first strategy for identifying an unknown compound is to compare its experimental mass spectrum against a library of mass spectra. If the search comes up empty, then manual interpretation[33] or software assisted interpretation of mass spectra are performed. Computer simulation of ionization and fragmentation processes occurring in mass spectrometer is the primary tool for assigning structure or peptide sequence to a molecule. An a priori structural information is fragmented in silico and the resulting pattern is compared with observed spectrum. Such simulation is often supported by a fragmentation library[34] that contains published patterns of known decomposition reactions. Software taking advantage of this idea has been developed for both small molecules and proteins.

Another way of interpreting mass spectra involves spectra with accurate mass. A mass-to-charge ratio value (m/z) with only integer precision can represent an immense number of theoretically possible ion structures. More precise mass figures significantly reduce the number of candidate molecular formulas, albeit each can still represent large number of structurally diverse compounds. A computer algorithm called formula generator calculates all molecular formulas that theoretically fit a given mass with specified tolerance.

A recent technique for structure elucidation in mass spectrometry, called precursor ion fingerprinting identifies individual pieces of structural information by conducting a search of the tandem spectra of the molecule under investigation against a library of the product-ion spectra of structurally characterized precursor ions.

[edit] Applications[edit] Isotope ratio MS: isotope dating and tracking

Mass spectrometer to determine the 16O/18O and 12C/13C isotope ratio on biogenous carbonate

Main article: Isotope ratio mass spectrometryMass spectrometry is also used to determine the isotopic composition of elements within a sample. Differences in mass among isotopes of an element are very small, and the less abundant isotopes of an element are typically very rare, so a very sensitive instrument is required. These instruments, sometimes referred to as isotope ratio mass spectrometers (IR-MS), usually use a single magnet to bend a beam of ionized particles towards a series of Faraday cups which convert particle impacts to electric current. A fast on-line analysis of deuterium content of water can be done using Flowing afterglow mass spectrometry, FA-MS. Probably the most sensitive and accurate mass spectrometer for this purpose is the accelerator mass spectrometer (AMS). Isotope ratios are important markers of a variety of processes. Some isotope ratios are used to determine the age of materials for example as in carbon dating. Labeling with stable isotopes is also used for protein quantification. (see protein characterization below)

[edit] Trace gas analysisSeveral techniques use ions created in a dedicated ion source injected into a flow tube or a drift tube: selected ion flow tube (SIFT-MS), and proton transfer reaction (PTR-MS), are variants of chemical ionization dedicated for trace gas analysis of air, breath or liquid headspace using well defined reaction time allowing calculations of analyte concentrations from the known reaction kinetics without the need for internal standard or calibration.

[edit] Atom probeMain article: Atom probeAn atom probe is an instrument that combines time-of-flight mass spectrometry and field ion microscopy (FIM) to map the location of individual atoms.

[edit] PharmacokineticsMain article: PharmacokineticsPharmacokinetics is often studied using mass spectrometry because of the complex nature of the matrix (often blood or urine) and the need for high sensitivity to observe low dose and long time point data. The most common instrumentation used in this application is LC-MS with a triple quadrupole mass spectrometer. Tandem mass spectrometry is usually employed for added specificity. Standard curves and internal standards are used for quantitation of usually a single pharmaceutical in the samples. The samples represent different time points as a pharmaceutical is administered and then metabolized or cleared from the body. Blank or t=0 samples taken before administration are important in determining background and ensuring data integrity with such complex sample matrices. Much attention is paid to the linearity of the standard curve; however it is not uncommon to use curve fitting with more complex functions such as quadratics since the response of most mass spectrometers is less than linear across large concentration ranges.[35]

HYPERLINK "http://en.wikipedia.org/wiki/Mass_spectrometry" \l "cite_note-35" [36]

HYPERLINK "http://en.wikipedia.org/wiki/Mass_spectrometry" \l "cite_note-36" [37]There is currently considerable interest in the use of very high sensitivity mass spectrometry for microdosing studies, which are seen as a promising alternative to animal experimentation.

[edit] Protein characterizationMain article: Protein mass spectrometryMass spectrometry is an important emerging method for the characterization and sequencing of proteins. The two primary methods for ionization of whole proteins are electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). In keeping with the performance and mass range of available mass spectrometers, two approaches are used for characterizing proteins. In the first, intact proteins are ionized by either of the two techniques described above, and then introduced to a mass analyzer. This approach is referred to as "top-down" strategy of protein analysis. In the second, proteins are enzymatically digested into smaller peptides using proteases such as trypsin or pepsin, either in solution or in gel after electrophoretic separation. Other proteolytic agents are also used. The collection of peptide products are then introduced to the mass analyzer. When the characteristic pattern of peptides is used for the identification of the protein the method is called peptide mass fingerprinting (PMF), if the identification is performed using the sequence data determined in tandem MS analysis it is called de novo sequencing. These procedures of protein analysis are also referred to as the "bottom-up" approach.

[edit] Glycan analysisMass spectrometry (MS), with its low sample requirement and high sensitivity, has been predominantly used in glycobiology for characterization and elucidation of glycan structures.[38] Mass spectrometry provides a complementary method to HPLC for the analysis of glycans. Intact glycans may be detected directly as singly charged ions by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) or, following permethylation or peracetylation, by fast atom bombardment mass spectrometry (FAB-MS).[39] Electrospray ionization mass spectrometry (ESI-MS) also gives good signals for the smaller glycans.[40] Various free and commercial software are now available which interpret MS data and aid in Glycan structure characterization.

[edit] Space explorationAs a standard method for analysis, mass spectrometers have reached other planets and moons. Two were taken to Mars by the Viking program. In early 2005 the CassiniHuygens mission delivered a specialized GC-MS instrument aboard the Huygens probe through the atmosphere of Titan, the largest moon of the planet Saturn. This instrument analyzed atmospheric samples along its descent trajectory and was able to vaporize and analyze samples of Titan's frozen, hydrocarbon covered surface once the probe had landed. These measurements compare the abundance of isotope(s) of each particle comparatively to earth's natural abundance.[41] Also onboard the CassiniHuygens spacecraft is an ion and neutral mass spectrometer which has been taking measurements of Titan's atmospheric composition as well as the composition of Enceladus' plumes. A Thermal and Evolved Gas Analyzer mass spectrometer was carried by the Mars Phoenix Lander launched in 2007.[42]Mass spectrometers are also widely used in space missions to measure the composition of plasmas. For example, the Cassini spacecraft carries the Cassini Plasma Spectrometer (CAPS),[43] which measures the mass of ions in Saturn's magnetosphere.

[edit] Respired gas monitorMass spectrometers were used in hospitals for respiratory gas analysis beginning around 1975 through the end of the century. Some are probably still in use but none are currently being manufactured.[44]Found mostly in the operating room, they were a part of a complex system, in which respired gas samples from patients undergoing anesthesia were drawn into the instrument through a valve mechanism designed to sequentially connect up to 32 rooms to the mass spectrometer. A computer directed all operations of the system. The data collected from the mass spectrometer was delivered to the individual rooms for the anesthesiologist to use.

The uniqueness of this magnetic sector mass spectrometer may have been the fact that a plane of detectors, each purposely positioned to collect all of the ion species expected to be in the samples, allowed the instrument to simultaneously report all of the gases respired by the patient. Although the mass range was limited to slightly over 120 u, fragmentation of some of the heavier molecules negated the need for a higher detection limit.[45][edit] See also Mass spectrometry software

Calutron

Helium mass spectrometer

Mass spectrometry imaging

Reflectron

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