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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper III covers analytical and organic chemistry.

UPSC Combined Geo-Scientist, Mains · 2016 · Mains Paper III

Q1(i). AAS background correction

Question

Explain background absorption and the significance of background correction in AAS.

Answer in brief

Molecular absorption and scattering can add to atomic absorbance, causing a falsely high analyte result.

Key points

  • Matrix molecules, particulates and flame species may attenuate radiation at the analytical wavelength without representing analyte atoms.
  • Deuterium-lamp or Zeeman correction estimates this non-analyte contribution and subtracts it from total absorbance.
  • A reagent blank alone may not reproduce the sample-dependent background during atomisation; correction improves accuracy but does not remove every chemical interference.

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

Model answer to Q1(i), 2016 Mains Paper III: solution pages 3 and 4
Solution pages 3 and 4 of 22
Read the whole 2016 solution2016 question paper

CoversAAS background correctionAtomic spectroscopy

All parts of Question 1