Capillary zone electrophoresis for the analysis of low molecular weight organic acids in environmental systems
Abstract: Capillary zone electrophoretic (CZE) methods were developed to identify and quantify low molecular weight (LMW) organic acids in environmental samples. Sensitivity and selectivity were optimised by adapting the background electrolyte to the characteristics of analytes, and by using different modes of detection and injection. Electrokinetic injection mode in combination with an isotachophoretic state increased the sensitivity remarkably for LMW organic acids using UV detection. Calcium ions were added to the background electrolyte, inducing an on-column complexation between acids and calcium ions, which gave good separation of the acids. Mass spectrometric detection (compared to UV detection) increased the sensitivity when using hydrodynamic injection mode during analysis, and selectivity was improved by mass identification. A CZE method for determination of the dissociation constants of LMW organic acids in the pKa range of 3.54.5 was also developed.The developed procedures were applied to different areas where LMW organic acids play an important environmental role:Low molecular weight organic acids were analysed in rainwater and soil water in the low ?g/l range, within ten minutes after sampling. Rapid analysis and high sensitivity are essential when studying samples with rapid turnover due to microbial activity and photodegradation. The use of CZE-ESI-MS proved to be a robust analytical tool for determining LMW organic acids in samples rich in interfering ions. Organic acids excreted by soil fungi as response to metal exposure was easily and rapidly quantified with CZE-ESI-MS compared to HPLC and CZE-UV analysis. Dissociation constants for isosaccharinic acid (ISA) and gluconic acid were determined by CZE to 3.87 and 3.64, respectively. The ability to make the determinations in the presence of impurities as well as not having to know the exact concentration of analyte were identified as the major benefits of CZE. Isosaccharinic acid was identified as the main degradation product from alkaline degradation of cellulose by CZE analysis. Long-term predictions on both cellulose degradation and ISA production were made based on three years of sampling data. A control sampling after seven years indicated that the degradation of cellulose and the production of ISA were lower than predicted.
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