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Abstract
Carboxylic acids were determined spectrophotometrically by converting them into 2-nitrophenylhydrazides. The coupling reaction of carboxylic acids with 2-nitrophenylhydrazine was effected by a water-soluble carbociimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and proceeded efficiently in aqueous solution buffered at pH 4.5 with pyridine and hydrochloric acid. The yields of hydrazides from acetic and benzoic acids were nearly quantitative. The reaction mixture was then made strongly alkaline, and after heating to reduce the blank absorbance, the absorbance of the hydrazide was measured at around 540 nm. Calibration curves of various carboxylic acids were linear between 0.02 and 0.5 μmol through the origin.
