Sensitive analysis of poly-carboxylic acids in soil solution by capillary electrophoresis after excimer-forming fluorescence derivatization.

A sensitive method for the determination of citrate and malate in sub-microliter samples of soil solution is described. The organic acids were derivatized with a pyrene reagent (1-pyrenebutanoic acid hydrazide) and analysed by micellar electrokinetic chromatography separation. The citrate and malate derivatives were detected within 10 min by using a fluorescence detector with a broad excitation wavelength of 240-400 nm and an emission wavelength of 400 nm. The detection limits (noise x 3) were about 0.24 µM for citrate and 0.72 µM for malate. By using internal standardization, this method was applicable to the determination of citrate and malate in soil solution. Furthermore, application of siphon injection with a commercial micropipette enabled the injection of a sub-microliter sample into the analytical system with acceptable reproducibility. When combined with a microsampling method, the method presented here will be useful for the sensitive and selective analysis of citrate and malate in soil solution with high spatial resolution.