How much systematic error ((both the absolute and the relative error) is introdu

Question

How much systematic error ((both the absolute and the relative error) is introduced by the determination of the lead content of human blood serum samples due to lead contamination in sodium acetate (CH_3COONa) that is utilized as background electrolyte in the assay with anodic stripping voltammetry. Assumption: the lead concentration in blood serum is: 300 ng/ml Protocol: 1 ml blood is mixed with 10 ml, 1 M sodium acetate solution. The sodium acetate (CH_3COONa) solution is prepared from the highest quality chemical (Merck suprapure). The label on the CH_3COONa salt claims a maximum of 0.05 ppm lead impurity.

Explanation / Answer

Given-

Lead concentration in blood is 300 ng/ml

0.01 ppm lead impurity

Convert ppm to ng/ml

1 ppm = 1000 ng/ml

0.05 ppm x 1000 = 50 ng/ml

1 ml blood is mixed with 10 ml, 1M CH3COONa

1 ml 1M CH3COONa contains 50 ng lead

10 ml 1M CH3COONa contains 10 x 50 ng = 500 ng lead

Absolute Error = Actual Value - Measured Value

Absolute Error = 500ng – 300ng = 200 ng

Relative error is expressed as fraction or is multiplied by 100 and expressed as a percent.

Relative Error = Absolute Error / Known Value

                  = 200ng /500 ng = 2/5 = 0.4

                  = 0.4 x 100 = 40%

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