Non-aqueous electrolytes for isotachophoresis of weak bases and its application to the comprehensive preconcentration of the 20 proteinogenic amino acids in column-coupling ITP/CE--MS

KLER, PABLO A.; SYDES, DANIEL; HUHN, CAROLIN

ANALYTICAL AND BIOANALYTICAL CHEMISTRY

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2014 vol. 406 p. 7163 - 7174

1618-2642

Isotachophoresis (ITP) has long been used alone but also as a preconcentration technique for capillary elec- trophoresis (CE). Unfortunately, up to now, its application is restricted to relatively strong acids and bases as either the degree of (de)protonation is too low or the water disso- ciation is too high, evoking zone electrophoresis. With the comprehensive ITP analysis of all 20 proteinogenic amino acids as model analytes, we, here, show that non?aqueous ITP using dimethylsulfoxide as a solvent solves this ITP shortcoming. Dimethylsulfoxide changes the pH regime of analytes and electrolytes but, more importantly, strongly reduces the proton mobility by prohibiting hydrogen bonds and thus, the so-called Zundel?Eigen?Zundel elec- trical conduction mechanism of flipping hydrogen bonds. The effects are demonstrated in an electrolyte system with taurine or H+ as terminator, and imidazole as leader together with strong acids such as oxalic and even triflu- oroacetic acid as counterions, both impossible to use in aqueous solution. Mass spectrometric as well as capac- itively coupled contactless conductivity detection (C4D) are used to follow the ITP processes. To demonstrate the preconcentration capabilities of ITP in a two-dimensional set-up, we, here, also demonstrate that our non-aqueous ITP method can be combined with capillary electrophoresis? mass spectrometry in a column-coupling system using a hybrid approach of capillaries coupled to a microfluidic interface. For this, C4 D was optimized for on-chip detection with the electrodes aligned on top of a thin glass lid of the microfluidic chip.