Online coupling of microchip electrophoresis with ion mobility spectrometry for direct analysis of complex liquid samples

Abstract

This is the first report of coupling of microchip electrophoresis (MCE) with ion mobility spectrometry (IMS) for the analysis of liquid samples. Zone electrophoresis, employed on a microchip as a MCE technique, is suitable for coupling with IMS. Sample components separated electrophoretically in liquid phase were transferred from the microchip using auxiliary liquid. Direct liquid sampling interface was used for sample evaporation and introduction to IMS. In the IMS analyzer, the sample components were further separated in the gaseous phase. Online MCE-IMS coupling enabled acquisition of characteristic IMS response for the individual analytes. The proposed MCE-IMS technique was tested on a model mixture of a homologous series of carboxylic acids (formic acid, acetic acid, propionic acid, butyric acid, valeric acid and hexanoic acid) and subsequently applied to the analysis of wastewater sample obtained from a cattle farm. Total analysis time did not exceed six minutes regardless of the sample. Reproducibility of peak width in the MCE ranged from 0.56 to 1.95% RSD, while reproducibility of time of IMS response was in the range of 2.52–5.44% RSD for the studied carboxylic acids. RSD values of their reduced ion mobility were less than 0.56% for model and wastewater sample. Limits of detection ranged from 0.07 to 2.61 mg L−1. The results clearly show the great analytical potential of developed MCE-IMS coupling for the analysis of complex liquid samples.