A fast method for determining low-molecular-mass aliphatic carboxylic acids by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

A fast quantitative high‐performance liquid chromatographic separation method with atmospheric pressure chemical ionization mass spectrometric detection (HPLC‐APCI‐MS) was developed for the determination of low‐molecular‐mass aliphatic mono‐ and dicarboxylic acids typically present in different industrial process waters. A mixture of glycolic, lactic, α‐glucoisosaccharinic, oxalic, maleic, fumaric, succinic, malic, glutaric, methylsuccinic, and adipic acids was separated using an RP chromatographic system. Adipic acid was used as an internal standard to calculate correlation coefficients for the acids studied. The chromatographic analysis of these acids was primarily carried out by means of gradient elution with an aqueous formic acid solution (0.15%, pH 2.5) and methanol using a modified C18 stationary phase. Good acid separation could be obtained for all acids by optimizing the chromatographic conditions. The method provides a simple sample preparation and faster analysis time compared to the traditional gas chromatographic methods, thus enabling almost real‐time monitoring of these acids. Finally, the method developed was applied to the analysis of a complex mixture of aliphatic hydroxy carboxylic acids, which are formed as alkaline degradation products of carbohydrates during wood delignification and are present in the cooking spent liquor (black liquor).