Quantitative determination of the main aliphatic carboxylic acids in wood kraft black liquors by high-performance liquid chromatography-mass spectrometry

The versatile characterization of organic material and especially of the significant aliphatic hydroxy acids in black liquor is of great importance, for example, in monitoring the progress of the kraft pulping process. This paper describes a simple high-performance liquid chromatographic separation method with atmospheric-pressure chemical ionization mass spectrometry (HPLC-APCI-MS) which was developed for the rapid quantitative analysis of these acids, mainly formed as the alkaline degradation products of feedstock carbohydrates. The fraction of carbohydrate degradation products is mainly composed of hydroxy monocarboxylic and volatile acids (formic and acetic acids) along with lesser amounts of various dicarboxylic acids. This method was thoroughly tested and validated to determine the most abundant nonvolatile low-molecular-mass aliphatic mono- and dicarboxylic acids present in softwood (pine and spruce) and hardwood (birch and aspen) kraft black liquors. This straightforward technique provides, compared to the conventional gas chromatographic methods, some important advantages such as simple sample preparation and a faster analysis time, thus enabling almost real-time monitoring of these acids.