Improving the detection limit in capillary isotachophoresis using asymmetric neutralisation reaction boundary

Abstract

An online method involving transient electrokinetic dosing and ITP with neutralization reaction boundary (NRB) and/or carrier ampholyte-free isoelectric focusing (CAF IEF) was developed for the preconcentration, preseparation, and analytical determination of glyphosate in aqueous samples containing low concentrations of the analyte of interest. Various parameters were investigated in the framework of an optimization study with the aim of achieving the maximum concentration limit of detection (cLOD) decrease in minimum time. The proposed method used CAF IEF and/or ITP with NRB. The sample was dosed to the column on the stationary reaction boundary (CAF IEF) and/or moving reaction boundary (ITP with NRB), whereat a sharp pH step exists. Here, charge reversal was due to the ampholytes, and/or acid accumulation occurred because of charge loss. Similarly, the accumulated sample was mobilized with TE and analyzed using classical ITP in the second analytical column. Glyphosate (GLY), the analyte of interest, was chosen as a model substance for ITP with NRB and preconcentration as well as focusing preconcentration and CAF IEF using the asymmetric purpose-built NRB. On one side of the asymmetric boundary was the zone of acidic pH; while the opposite side comprised a neutral/basic non-conductive zone of the ampholyte-in this case, GLY. Such an arrangement enables the use of a lower pH on the acidic side, which allows the focusing of strongly acidic ampholytes and the accumulation of weak acids. The electrolyte composition and the dosing time were optimized, and a 14-fold accumulation was achieved in 25 min compared to that by classical ITP and a 180-fold accumulation was achieved through CAF IEF and preconcentration with a glyphosate sample. Both methods are simple and can be conducted using all commercial ITP systems.

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications—Updated and completely revised edition

“…Also taking advantage of pH changes around the capillary inlet end in the sample vial (from 7.1 to <4, upon the application of +10 kV for 100 s), Hattori and Fukushi were able to charge analytes and control the behavior of l ‐histidine and creatinine during the EK injection [394] using a simple strategy called mobility boost. As a pH‐based variation of EK supercharging (EKS), Koukalová [395] used an asymmetric boundary, where one side featured lower pH (for the focusing of strongly acidic ampholytes and the accumulation of weak acids) and the opposite side comprised a neutral/basic nonconductive zone of the ampholyte. Under optimized conditions, authors achieved a 14‐fold accumulation (in 25 min) compared to that by classical ITP, reaching and LOD of 0.9 µM for glyphosate.…”