Chapter 116 of 2363 min read
Qualitative and quantitative analysis
Why this is asked: Kjeldahl's method for %N fails for nitro, azo and diazo compounds, and for nitrogen locked in a ring like pyridine — that nitrogen doesn't convert to ammonium sulphate the way amine nitrogen does, so the method silently underestimates. In Lassaigne's test, if both N and S are present but sodium is insufficient, NaSCN can form instead of separate NaCN and Na₂S — giving a false-negative Prussian-blue test for nitrogen.
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