Determination of C-4-C-14 carboxylic acids by capillary zone electrophoresis - Application to the identification of diamide degradation products and partitioning studies

Capillary zone electrophoresis (CZE) was investigated for the determination of linear saturated carboxylic acid homologues ranging from C-4 to C-14. S eparation conditions were optimised to overcome the problems of decreasing solubility and decreasing selectivity between successive homologues with in creasing chain length. Separations were performed at 20 degreesC, using a 2 0 kV separation voltage and a pH 8 electrolyte containing 30% methanol. A s uitable chromophore (4-aminobenzoate) was added to ensure indirect W detect ion of the analytes. Calibration curves and repeatability were established. Minimum detectable concentrations of 3.10(-6) mol l(-1) were achieved. Res olution between successive homologues was better than 2. The electrophoreti c mobility of each homologue (n=7-14) was assessed and a quasi-linear relat ionship between the mobility value and 1/n was observed. The quantitative a nalysis of a diamide degradation solution was performed and compared to pot entiometric results. The CZE method was also applied to the determination o f C-7-C-14 partitioning between an organic medium containing tributylphosph ate in n-dodecane and different basic solutions. Their behaviour was establ ished according to the chain length and the pH of the aqueous phase. For C- 10-C-14 compounds, results were validated by comparison with gas chromatogr aphic analysis of the organic phases. (C) 2001 Elsevier Science B.V. All ri ghts reserved.