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Chapter 5

Q. 5.3

A second spectrophotometric method for the quantitative determination of Pb^{2+} levels in blood gives a linear normal calibration curve for which

S_{stand} = (0.296   ppb^{–1}) × C_S + 0.003

What is the Pb^{2+} level (in ppb) in a sample of blood if S_{samp} is 0.397?

Step-by-Step

Verified Solution

To determine the concentration of Pb^{2+} in the sample of blood, we replace S_{stand} in the calibration equation with S_{samp} and solve for C_A

C_A=\frac{S_{samp}-0.003}{0.296  ppb^{-1}} =\frac{0.397-0.003}{0.296   ppb^{-1}}=1.33  ppb

It is worth noting that the calibration equation in this problem includes an extra term that is not in equation 5.3.

k = \frac{S_{\text{stand}}}{C_s}        5.3

Ideally, we expect the calibration curve to give a signal of zero when C_S is zero. This is the purpose of using a reagent blank to correct the measured signal. The extra term of +0.003 in our calibration equation results from uncertainty in measuring the signal for the reagent blank and the standards.