UPSC Combined Geo-Scientist, Mains · 2017 · Mains Paper III

Q1(h). ICP-MS dilution calculation

Question

0.1 g dolomite is digested and diluted to 25 mL. A 1 mL aliquot is diluted to 100 mL and gives Fe = 4 μg/L by ICP-MS. Find Fe in μg/g.

The ore contains 100 μg Fe per gram.

The final 100 mL contains 4(0.100)=0.400 μ g Fe. This came from 1 mL of stock.
The full 25 mL stock therefore contains 25(0.400)=10.0 μ g.
Divide by sample mass: 10.0/0.100=100 μg g⁻¹.
This assumes quantitative digestion and transfer, and that the reported instrumental concentration has not already been corrected for these dilution factors.

The full model answer

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