Analysis of low molecular weight acids by monolithic immobilized pH gradient-based capillary isoelectric focusing coupled with mass spectrometry.

A novel method for the separation and detection of low molecular weight (LMW) acids was developed using monolithic immobilized pH gradient-based capillary isoelectric focusing coupled with mass spectrometry. Two main parameters, focusing conditions and delivery buffer conditions, which might affect separation efficiency, were optimized with the focusing time of 7 min at 350 V/cm and the delivery buffer of 50% (v/v) acetonitrile in 10 mmol/L ammonium formate (pH 3.0). Under these conditions, the linear correlation between the volume of delivery solvent and the pK(a) of the model components was observed. In addition, the separation mechanism of LMW acids was proposed as well. We suppose that this method may provide a useful tool for the characterization of LMW components (e.g. natural organic matter of different origins).