Angka Penting (Significant Figures)Limit Deteksi (Limit of Detection)/Limit kuantifikasi (Limit of Quantification)Sensitifitas (Sensitivity)

Significant Figures

Angka penting adalah semua angka yang diperoleh dari hasil pengukuran, yang terdiri dari angka eksak dan satu angka terakhir yang ditaksir (approximate). What is a significant figure?Bilangan penting diperoleh dari kegiatan mengukur, sedangkan bilangan eksak diperoleh dari kegiatan membilang.

What is a significant figure?There are 2 kinds of numbers:Exact: the amount of money in your account. Known with certainty.

What is a significant figure?

Approximate: weight, heightanything MEASURED. No measurement is perfect.

When to use Significant figures

If you measured the width of a paper with your ruler you might record 21.7cm.To a mathematician 21.70, or 21.700 is the same.

But, to a scientist 21.7 cm and 21.700 cm is NOT the same21.700 cm to a scientist means the measurement is accurate to within one thousandth of a cm.

But, to a scientist 21.7cm and 21.700 cm is NOT the sameIf you used an ordinary ruler, the smallest marking is the mm, so your measurement has to be recorded as 21.7cm.

How do I know how many Significant Figures?Rule: All digits are significant starting with the first non-zero digit on the left.

Exception to rule: In whole numbers that end in zero, the zeros at the end are not significant.How do I know how many Significant Figures?

How many significant figures?7400.50.000037 x 1057,000,000111111

How do I know how many Significant Figures?2nd Exception to rule: If zeros are sandwiched between non-zero digits, the zeros become significant.

How do I know how many Significant Figures?3rd Exception to rule: If zeros are at the end of a number that has a decimal, the zeros are significant.

How do I know how many Sig Figs?3rd Exception to rule: These zeros are showing how accurate the measurement or calculation are.

How many sig figs here?1.2210056.764.000.07927,083,000,000224334

How many sig figs here?340121002100.05.000.004128,000,050,000425336

What about calculations with sig figs?Rule: When adding or subtracting measured numbers, the answer can have no more places after the decimal than the LEAST of the measured numbers.

Add/Subtract examples2.45cm + 1.2cm = 3.65cm, Round off to = 3.7cm

7.432cm + 2cm = 9.432 round to 9cm

Multiplication and DivisionRule: When multiplying or dividing, the result can have no more significant figures than the least reliable measurement.

A couple of examples56.78 cm x 2.45cm = 139.111 cm2Round to 139cm2

75.8cm x 9.6cm = ?

(104.250 x 2.26) / 15.553 = ?

(0.002450 x 0.1478) / 0.120 =Hitung :4.0 x 10^4/ 1.15 x 10^4 =2.0 x 307 = 50 / 3.0069 =

Sensitivity

The sensitivity of a measuring instrument is its ability to detect quickly a small change in the value of a measurement.

A measuring instrument that has a scale with smaller divisions is more sensitive.Sensitivity

As an example, the length of a piece of wire is measured with rulers A and B which have scales graduated in intervals of 0.1 cm and 0.5 cm respectively, as shown in Figure below. Which of the rulers is more sensitive?Sensitivity

Results:Ruler A: Length = 4.8 cmRuler B: Length = 4.5 cmRuler A is more sensitive as it can measure to an accuracy of 0.1 cm compared to 0.5 cm for ruler B

Sensitivity

4In addition to the size of the divisions on the scale of the instrument, the design of the instrument has an effect on the sensitivity of the instrument. For example, a thermometer has a higher sensitivity if it can detect small temperature variations. A thermometer with a narrow capillary and a thin-walled bulb has a higher sensitivity.Sensitivity

The slope of the calibration curve at the concentration of interest is known as calibration sensitivity.S = mc + SblS = measured signal; c= analyte concentration; Sbl = blank signal; m = sensitivity (Slope of line)Analytical sensitivity () = m/ssm = slope of the calibration curvess = standard deviation of the measurement

Y = ax + b

LOD: The smallest amount or concentration of analyte that can be detected statistically

IUPAC:Limit of Detection (LOD)

LOD: the smallest concentrationor absolute amount of analyte that has a signal significantly larger than the signal arising from a reagent blankIUPAC:Limit of Detection (LOD)

Limit of Detection (LOD)LOD is the lowest amount of analyte in a sample which can be detected but not necessarily quantitated as an exact value.

Limit of Detection (LOD)

Calculation of LOD (1)The analytes signal at the detection limit, (SA)LOD(SA)LOD = Sreag + zsreagSreag : the signal for a reagent blanksreag : the known standard deviation for the reagent blanks signalz : factor accounting for the desired confidence level(typically, z is set to 3)

Calculation of LOD (1)LOD is calculated based on (SA)LOD divided with slope of calibration graph (a)y = ax + b(SA)LOD = a * LOD + b

(SA)LOQ = Sreag + 10sreagLimit of Quantification (LOQ)LOQ: The smallest concentration or absolute amount of analyte that can be reliably determined (American Chemical Society)y = ax + b(SA)LOQ = a * LOQ + b

Calculation of LOD (2)Signal to Noise Ratio (S/N) is a dimensionless measure of the relative strength of an analytical signal (S) to the average strength of the background instrumental noise (N)Signal to Noise Ratio (S/N) methodS/N = 3

Calculation of LOD (2)Signal to Noise Ratio (S/N) method

Calculation of LOD (2)Signal to Noise Ratio (S/N) methody = ax + b3N = a * LOD + b

Calculate LOD of Ga, Ge, and In

Ion Count (CPS)GaGeIn

blank 129.789.0818.67blank 230.539.5023.34blank 325.9110.7928.41blank 427.7310.1620.025blank 529.829.7823.49blank 629.1110.0931.93blank 725.3112.5223.80blank 828.6311.18824.72blank 926.2113.2217.21blank 1030.0412.5623.86Std 1 (1 ppb)250.8743.0760.56Std 2 (2 ppb )499.6877.36108.95Std 3 (3 ppb )773.46109.43151.83

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