Preconcentration and frontal electroelution of amino acids for in-line solid-phase extraction–capillary electrophoresis

Abstract

A new frontal electroelution approach that can be used for the preconcentration of amino acids in in-line solid-phase extraction-capillary electrophoresis (SPE-CE) has been developed. A single capillary was employed featuring a short monolithic SPE column created inside the capillary via photo-initiated, free-radical polymerisation of 3-sulfopropyl methacrylate and butyl methacrylate monomers. A weak electrolyte of dilute H 2 SO 4 , pH 2.9, was found to promote adsorption of the amino acids onto the SPE column. Elution of the amino acids was achieved using a dual solvation/ion-exchange transient boundary mobilised via EOF by using a strong electrolyte containing 62.5 mM ethylenediamine, pH 2.9 with H 2 SO 4 and 40% (v/v) acetonitrile. Using these two electrolytes, tryptophan was adsorbed onto the SPE column in weak electrolyte and eluted via a frontal electroelution mechanism in the strong electrolyte. Injections up to 20 min, corresponding to over 14 column volumes (or 1400% of the capillary volume) of sample provided quantitative extraction of tryptophan from the weak electrolyte and were eluted without any loss in efficiency. This represents a practical increase of approximately 300-fold when compared to a typical hydrodynamic injection occupying 5% of the capillary volume.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips

“…In capillaries, there are a number of reports of using a monolith for in-line extraction. Baryla et al [260] used a methacrylic acid monolith for the extraction of propanol, and Schaller et al [261] and Breadmore [262] have used a sulphopropylmethacrylate monolith for the extraction of antidepressants and amino acids, respectively. In all the cases, an increase in sensitivity of several orders of magnitude was obtained.…”

Sensitivity enhancement for the analysis of naproxen in tap water by solid‐phase extraction coupled in‐line to capillary electrophoresis

“…On the other hand, in the in-line SPE-CE approach [5, 27 -34], an SPE microcartridge is inserted near the inlet of the separation capillary; the SPE column is an integrated part of the CE capillary and there is no need for modification of the commercial CE instrumentation. The off-line automatic and inline SPE-CE approaches have been reported for the anal-ysis of standard solutions [24,29,30,32,33] and biological samples [22,23,25,27,28], but only a few studies have been reported for the determination of analytes at trace levels in environmental samples [26,31,34], even that is a very promising field with a lot to explore.…”

On‐line coupling of SPE and CE‐MS for peptide analysis

“…Next to a more sensitive detector, the sensitivity may also be improved by concentration of the analytes prior to the CE separation by chromatographic methods in off-line [6,7], online [8][9][10][11] and in-line [12][13][14][15][16][17][18][19][20] fashions. Off-line preconcentration requires manual handling and is time consuming, while in-and on-line systems can minimize these disadvantages.…”