Mercury concentraion of chicken feed in mg per gram?

Question

A commercial chicken feed contains 25% fish meal. The mercury concentration of the fish meal was determined using a 1 kg sample which was homogenised. Six subsamples of 1.500 g each were taken for analysis by strong acid/KMnO4/K2S2O8 digestion, each made up to 25.00 mL, and a 5.00 mL aliquot of each digest analysed by cold vapour AAS, yielding the following amounts of Hg in each 5.00 mL aliquot in micrograms: 0.51, 0.56, 0.62, 0.65, 0.68, 0.72 micro grams. Using the mean Hg concentration of the fish meal, calculate the Hg concentration of the chicken feed in micrograms per gram assuming the fishmeal to be the only source of Hg.

Answer 1

let's start here... from the analysis....

mean = (0.51, 0.56, 0.62, 0.65, 0.68, 0.72) µg / 6 = 0.62 µg

next.....

that was for a 5.00 ml aliquot.... which was 5.00 / 25.00 of the subsample so the amount of Hg in the subsample was....

0.62 µg x (25.00 / 5.00) = 3.12 µg per subsample

since each subsample contained 1500 g fishmeal, the concentration of Hg in the fish meal was 3.12 µg Hg / 1500 g fishmeal

next since

100 g feed = 25 g fish meal  { since feed is 25% fish meal }

the concentration in the feed is....

(3.12 µg Hg / 1500 g fishmeal) x (25 g feed / 100 g fishmeal) = 0.52 µg Hg / g fishmeal

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or if you prefer...

0.62 µg Hg = 1 aliquot fishmeal

5 aliquots = 1 subsample fishmeal

1 subsample ifishmeal = 1.500 g fishmeal

25 g fishmeal = 100 g feed

(0.62 µg Hg / 1 aliquot) x (5 aliquots / subsample) x (1 subsample / 1.500 g fishmeal) x (25 g fishmeal / 100 g feed) = 0.52 µg Hg / g fishmeal