A hydrodynamic injection approach for capillary electrophoresis using rotor-stator valves.

Sample injection is a critical step in a capillary electrophoresis (CE) analysis. Electrokinetic injection is the simplest approach and it is often selected for implementation in portable CE instruments. However, in order to minimize the effect of sample matrix upon the results of a CE analysis, hydrodynamic injection is preferred. Although portable CE instruments with hydrodynamic injection have been reported, injection has always been performed at the grounded end of the capillary. This simplifies fluidic handling but limits coupling with electrochemical detectors and electrospray ionization mass spectrometry (ESI-MS). We demonstrated previously that injection at the high voltage (HV) end of the capillary could be performed using a HV-compatible rotary injection valve (fixed-volume injection). However, the mismatch between the bore sizes of the channels on the rotor stator valve and the separation capillary caused peak tailing and undesired mixing, impairing analytical performance. In this work we present a HV-compatible hydrodynamic injection approach that overcomes the issues associated with the fixed-volume injection approach reported previously. The performance of the CE instrument was demonstrated by analyzing a mixture of 13 amino acids by CE coupled to laser-induced-fluorescence (CE-LIF), which showed relative standard deviations (RSD) for peak area and migration time below 5% and 1%, respectively for triplicate analysis. Additionally, replicate measurements of a mixture of amino acids, peptides, nucleobases, and nucleosides by CE coupled to electrospray ionization mass spectrometry (CE-ESI-MS) were performed to evaluate peak tailing and results were similar to those obtained with a commercial CE-ESI-MS setup. This article is protected by copyright. All rights reserved.