maleic-acid and 2-6-lutidine

Electrophoretic focusing on inverse electromigration dispersion (EMD) gradient is a new analytical technique based on a unique separation principle where weak non-amphoteric ionogenic species are focused, separated and transported to the detector by an EMD profile of suitable properties. The present work extends the theoretical description of this method by introducing the concept of resolution and deriving the fundamental equation expressing resolution as function of basic system parameters. The results indicate that at constant current operation, resolution is proportional to the square root of time. For variable current regimes (e.g. constant voltage), the time variable is replaced by the product of electric current and passed electric charge. Computer simulations for a model pair of substances support the validity of the presented theory and confirm the theoretical conclusion that resolution can be increased by allowing longer electromigration of the gradient in terms of time or passed charge. The experimental example shown comprises an anionic electrolyte system based on maleic acid and 2,6-lutidine, combined with ESI-MS detection and operated in the reverse mode due to strong electroosmotic flow and ESI suction. The practical implementation of the proposed methodology is done by application of negative pressure at the inlet vial, resulting in very substantial resolution enhancement and baseline separation of otherwise unresolved substances. The performance and high sensitivity of the developed technique is demonstrated on the example of simultaneous analysis of four sulfonamides and three dichlorophenols in waters with limits of detection on the 1 nM level.

Topics: Chlorophenols; Drinking Water; Electrolytes; Electrophoresis, Capillary; Limit of Detection; Maleates; Pressure; Pyridines; Spectrometry, Mass, Electrospray Ionization; Sulfonamides

This article describes for the first time the combination of electrophoretic focusing on inverse electromigration dispersion (EMD) gradient, a new separation principle described in 2010, with electrospray-ionization (ESI) mass spectrometric detection. The separation of analytes along the electromigrating EMD profile proceeds so that each analyte is focused and concentrated within the profile at a particular position given by its pKa and ionic mobility. The proposed methodology combines this principle with the transport of the focused zones to the capillary end by superimposed electromigration, electroosmotic flow and ESI suction, and their detection by the MS detector. The designed electrolyte system based on maleic acid and 2,6-lutidine is suitable to create an inverse EMD gradient of required properties and its components are volatile enough to be compatible with the ESI interface. The characteristic properties of the proposed electrolyte system and of the formed inverse gradient are discussed in detail using calculated diagrams and computer simulations. It is shown that the system is surprisingly robust and allows sensitive analyses of trace amounts of weak acids in the pKa range between approx. 6 and 9. As a first practical application of electrophoretic focusing on inverse EMD gradient, the analysis of several sulfonamides in waters is reported. It demonstrates the potential of the developed methodology for fast and high-sensitivity analyses of ionic trace analytes, with reached LODs around 3 × 10(-9) M (0.8 ng mL(-1)) of sulfonamides in spiked drinking water without any sample pretreatment.

Topics: Computer Simulation; Drinking Water; Electrolytes; Electrophoresis, Capillary; Maleates; Pyridines; Rivers; Spectrometry, Mass, Electrospray Ionization; Sulfonamides; Water Pollutants, Chemical