Measurement of carbonyl compounds as the 2,4-dinitrophenylhydrazonate anion. Reaction mechanism and an automated measurement system

Article abstract of DOI:10.1021/ac00085a007

The standard procedure for determining carbonyl compounds involves the addition of strong caustic alkali to 2,4-dinitrophenylhydrazones formed upon the reaction of carbonyl compounds with 2,4-dinitrophenylhydrazine (DNPH).¹ In strong base, the hydrazones form a dark red anion of quinonoid structure,² while the corresponding product from the unreacted DNPH decomposes rapidly, resulting in a low blank. The mechanism of this decomposition has never been clearly understood. In this work, we describe a photometric flow injection analyzer for the automated measurement of the carbonyl content of alcohol ethoxylate samples. A detailed study of the mechanism of the alkaline decomposition is reported. Parameters affecting the performance of the automated system were studied. The final system attained nearly equivalent responses of C₂-C₉ aliphatic carbonyl compounds (within ± 12%), a sample throughput of 20 h^-1, a limit of detection of 0.5 mg/L>C=O, and response linearity over 2 orders of magnitude. The method was applied to industrial samples, and the results compared well with those from the manual standard method. It should be applicable for the measurement of the carbonyl content in a variety of other organic matrices.