A 5.00 mL sample of blood was treated with trichloroacetic acid to precipitate p

Question

A 5.00 mL sample of blood was treated with trichloroacetic acid to precipitate proteins. After centrifugation, the resulting solution was brought to pH of 3 and extracted with two 5.0 mL portions of methyl isobutyl ketone (MIBK) that also contained the organic Pb complexing agent APCD. The MIBK extract was analyzed, giving an absorbance of 0.310 at 283.3 nm.

5.0 mL aliquots of 2 standards containing 0.300 ppm and 0.500 ppm Pb were treated in the same way, yielding aborbances of 0.396 and 0.599. Plot this data and perform a linear regression on this line. A 1.00 cm cuvette cell was used.

What is the slope of this calibration line, and what is the epsilon value for this plot?

What is the ppm in the original blood sample?

Explanation / Answer

We can calculate the slope from the two points calibration by,
Slope of the standard plot = (A2 – A1)/(C2 – C1),
where A1 and A2 are the absorbances at different concentrations C2 and C1
Slope = (0.599 – 0.396)/(0.50 – 0.30) = 1.015
Therefore, we can calculate the intercept from the straight line equation:
y = mx + c , where ‘c’ is the intercept
0.599 = 1.015*0. 5 + c
c = 0.0092
Now, we can find the unknown concentration at which the absorbance is 0.310
0.31 = 1.015Cx + 0.0092
Cx = 0.296 ppm

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