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Calibration Techniques. 1. Calibration Curve Method 2. Standard Additions Method 3. Internal Standard Method. Calibration Curve Method. Most convenient when a large number of similar samples are to be analyzed. Most common technique. Facilitates calculation of Figures of Merit.

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Calibration techniques l.jpg

Calibration Techniques

1. Calibration Curve Method

2. Standard Additions Method

3. Internal Standard Method


Calibration curve method l.jpg

Calibration Curve Method

Most convenient when a large number of similar samples are to be analyzed.

Most common technique.

Facilitates calculation of Figures of Merit.


Calibration curve procedure l.jpg

Calibration Curve Procedure

Prepare a series of standard solutions (analyte solutions with known concentrations).

Plot [analyte] vs. Analytical Signal.

Use signal for unknown to find [analyte].


Example pb in blood by gfaas l.jpg

Example: Pb in Blood by GFAAS

Results of linear regression:

S = mC + b

m = 5.56 mAbs/ppb

b = 0.93 mAbs


Slide6 l.jpg

A sample containing an unknown amount of Pb gives a signal of 27.5 mAbs. Calculate the Pb concentration.

S = mC + b

C = (S - b) / m

C = (27.5 mAbs – 0.92 mAbs) / 5.56 mAbs / ppb

C = 4.78 ppb

(3 significant figures)


Slide7 l.jpg

Calculate the LOD for Pb of 27.5 mAbs. Calculate the Pb concentration.

20 blank measurements gives an average signal

0.92 mAbs

with a standard deviation of

σbl = 0.36 mAbs

LOD = 3 σbl/m = 3 x 0.36 mAbs / 5.56 mAbs/ppb

LOD = 0.2 ppb

(1 significant figure)


Slide8 l.jpg

Find the LDR for Pb of 27.5 mAbs. Calculate the Pb concentration.

Lower end = LOD = 0.2 ppb

(include this point on the calibration curve)

SLOD = 5.56 x 0.2 + 0.93 = 2.0 mAbs

(0.2 ppb , 2.0 mAbs)


Slide9 l.jpg

Find the LDR for Pb of 27.5 mAbs. Calculate the Pb concentration.

Upper end = collect points beyond the linear region and estimate the 95% point.

Suppose a standard containing 18.5 ppb gives rise to s signal of 98.52 mAbs

This is approximately 5% below the expected value of 103.71 mAbs

(18.50 ppb , 98.52 mAbs)


Slide10 l.jpg

Find the LDR for Pb of 27.5 mAbs. Calculate the Pb concentration.

LDR = 0.2 ppb to 18.50 ppb

or

LDR = log(18.5) – log(0.2) = 1.97

2.0 orders of magnitude

or

2.0 decades


Slide11 l.jpg

Find the Linearity of 27.5 mAbs. Calculate the Pb concentration.

Calculate the slope of the log-log plot


Slide12 l.jpg

Not Linear?? of 27.5 mAbs. Calculate the Pb concentration.


Slide13 l.jpg

Not Linear?? of 27.5 mAbs. Calculate the Pb concentration.


Slide14 l.jpg

Remember of 27.5 mAbs. Calculate the Pb concentration.

S = mC + b

log(S) = log (mC + b)

b must be ZERO!!

log(S) = log(m) + log(C)

The original curve did not pass through the origin. We must subtract the blank signal from each point.


Slide15 l.jpg

Corrected Data of 27.5 mAbs. Calculate the Pb concentration.


Slide16 l.jpg

Linear! of 27.5 mAbs. Calculate the Pb concentration.


Standard addition method l.jpg

Standard Addition Method of 27.5 mAbs. Calculate the Pb concentration.

Most convenient when a small number of samples are to be analyzed.

Useful when the analyte is present in a complicated matrix and no ideal blank is available.


Standard addition procedure l.jpg

Standard Addition Procedure of 27.5 mAbs. Calculate the Pb concentration.

Add one or more increments of a standard solution to sample aliquots of the same size. Each mixture is then diluted to the same volume.

Prepare a plot of Analytical Signal versus:

volume of standard solution added, or

concentration of analyte added.


Standard addition procedure19 l.jpg

Standard Addition Procedure of 27.5 mAbs. Calculate the Pb concentration.

The x-intercept of the standard addition plot corresponds to the amount of analyte that must have been present in the sample (after accounting for dilution).

The standard addition method assumes:

the curve is linear over the concentration range

the y-intercept of a calibration curve would be 0


Example fe in drinking water l.jpg

Example: Fe in Drinking Water of 27.5 mAbs. Calculate the Pb concentration.

The concentration of the Fe standard solution is 11.1 ppm

All solutions are diluted to a final volume of 50 mL


Slide21 l.jpg

-6.08 mL of 27.5 mAbs. Calculate the Pb concentration.


Slide22 l.jpg

[Fe] = ? of 27.5 mAbs. Calculate the Pb concentration.

x-intercept = -6.08 mL

Therefore, 10 mL of sample diluted to 50 mL would give a signal equivalent to 6.08 mL of standard diluted to 50 mL.

Vsam x [Fe]sam = Vstd x [Fe]std

10.0 mL x [Fe] = 6.08 mL x 11.1 ppm

[Fe] = 6.75 ppm


Internal standard method l.jpg

Internal Standard Method of 27.5 mAbs. Calculate the Pb concentration.

Most convenient when variations in analytical sample size, position, or matrix limit the precision of a technique.

May correct for certain types of noise.


Internal standard procedure l.jpg

Internal Standard Procedure of 27.5 mAbs. Calculate the Pb concentration.

Prepare a set of standard solutions for analyte (A) as with the calibration curve method, but add a constant amount of a second species (B) to each solution.

Prepare a plot of SA/SB versus [A].


Notes l.jpg

Notes of 27.5 mAbs. Calculate the Pb concentration.

The resulting measurement will be independent of sample size and position.

Species A & B must not produce signals that interfere with each other. Usually they are separated by wavelength or time.


Example pb by icp emission l.jpg

Example: Pb by ICP Emission of 27.5 mAbs. Calculate the Pb concentration.

Each Pb solution contains 100 ppm Cu.


Slide28 l.jpg

No Internal Standard Correction of 27.5 mAbs. Calculate the Pb concentration.


Slide29 l.jpg

Internal Standard Correction of 27.5 mAbs. Calculate the Pb concentration.


Results for an unknown sample after adding 100 ppm cu l.jpg

Results for an unknown sample after adding 100 ppm Cu of 27.5 mAbs. Calculate the Pb concentration.


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