Question

In which limit test, Thioglycolic acid is used:

• A. Limit test for arsenic
• B. Limit test for sulphate
• C. Limit test for iron
• D. Limit test for chloride

Answer 1

The Correct Option is C

Pharmacopoeial limit tests are usually built around a colour or turbidity reaction sensitive enough to detect trace impurity levels. For iron specifically, the official test uses thioglycolic acid in an ammoniacal solution, the reagent reduces ferric to ferrous iron and simultaneously forms a coloured iron-thioglycolate complex with a pink to purple tint, and the depth of colour produced in the sample is compared side by side with a standard solution containing a known trace amount of iron. Arsenic, sulphate and chloride each have their own distinct detection reagents (mercuric chloride paper, barium chloride, and silver nitrate respectively) that do not involve thioglycolic acid.

Therefore, the correct answer is Limit test for iron.