UPSC Combined Geo-Scientist, Mains · 2019 · Mains Paper III
Q1(e). Observation zone in a flame
Question
Why is flame-photometric observation normally made in the interzonal region rather than the primary combustion zone or outer cone?
Answer in brief
The interzonal region usually gives a favourable population of free excited analyte atoms with less chemical and background interference.
Key points
- The primary combustion zone contains incompletely decomposed species and strong combustion-related emission.
- In the interzonal region, desolvation and atomisation have progressed and conditions favour useful atomic emission.
- In the outer oxidising cone, formation of refractory oxides can reduce the free-atom population.
- Optimise observation height for the actual element and flame composition; the best analytical zone is not identical for every analyte.
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.
CoversObservation zone in a flameFlame emission
All parts of Question 1
- 1(a) Activity-coefficient trends5 marks
- 1(b) Nanomolar concentration to ppb5 marks
- 1(c) Buffer capacity and dilution5 marks
- 1(d) Washing the flask walls5 marks
- 1(e) Observation zone in a flame5 marks
- 1(f) Proximate coal analysis5 marks
- 1(g) Volumetric manganese in steel5 marks
- 1(h) Gradient elution5 marks