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Question

Please use full illustrations or explanations to display how you arrived at the answer:

A soil sample was analyzed for lead. A 1.765 gram sample was microwave digested with 30 mL of nitric acid. The resulting solution was quantitatively transferred to a 50 mL graduated tube and filled to the 50 mL mark. A 1 mL aliquot of the diluted digestate was then added to a separate 50 mL graduated tube and filled to the 50 mL mark. The sample was analyzed by GFAA and found to contain 15 ppb of lead. How many ug/g of lead are in this soil sample?

Explanation / Answer

Lead in the second graduated tube = 15 ppb = 15 g per 10^9 g

mass of graduated tube = 50 g (Assuming water density = 1 g/cc)

Lead in the 1 ml of sample = 15 * 50 / 10^9 = 750* 10^-9 g

So, Lead in the 50 ml of this sample (1st graduated tube) = 37500 * 10^-9 g = 37.5 ug

This was in 1.765 g smaple of soil.

So, Required answer = 21.25 ug/g

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