Insights into the cITP process using on-line NMR spectroscopy.

Abstract

Recently, capillary isotachophoresis (cITP) has been coupled on-line with nuclear magnetic resonance (NMR) to enhance analysis of dilute charged analytes through sample concentration and separation. This study focuses on the unique detection capabilities of NMR to noninvasively examine the cITP process and obtain diagnostic information. With their enhanced mass sensitivity, microcoil NMR probes provide optimal detection for cITP/NMR. Whereas previous studies used deuterated buffers, a 1H NMR observable leading electrolyte, tetramethylammonium acetate, is employed here to better track cITP progression. Fortuitously, the 1H chemical shift of the acetate methyl resonance depends on pD. Hence, by using a calibration curve, the solution pD can be determined on-line during cITP. Similarly, intracapillary temperature can be measured in cITP/NMR by observing the HOD chemical shift. To obtain accurate chemical shift measurements, charge-neutral tert-butyl alcohol is added to all cITP electrolyte solutions as an internal reference. As an ancillary benefit, line width measurements of the ubiquitous tert-butyl alcohol enable NMR spectral resolution to be examined throughout the experiment. Capable of providing quantitative results, NMR simultaneously determines the concentrations of the leading ion, sample, and counterion over the course of the cITP experiment.