On-line concentration of peptides and proteins with the hyphenation of polymer monolithic immobilized metal affinity chromatography and capillary electrophoresisAn iminodiacetic acid (IDA)-type adsorbent is prepared at the one end of a capillary by covalently bonding IDA to the monolithic rods of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate). Cu(II) is later introduced to the support via the interaction with IDA. By this means, polymer monolithic immobilized metal affinity chromatography (IMAC) materials are prepared. With such a column, IMAC for on-line concentration and capillary electrophoresis (CE) for the subsequent analysis are hyphenated for the analysis of peptides and proteins. The reproducibility of such a column has been proved good with relative standard deviations (RSDs) of dead time of less than 5% for injection-to-injection and 12% for column-to-column (n = 3). Through application on the analysis of standard peptides and real protein samples, such a technique has shown promising in proteome study.
IntroductionCapillary electrophoresis (CE) has become a powerful separation tool and is widely used in the analysis of biomolecules, such as peptides, proteins, and polynucleotides, due to its high separation efficiency, high resolution, and fast speed [1][2][3]. However, the poor detection limit of CE caused by the short optical path length across the capillary and small injection volume is still a serious problem. Therefore, dedicated sample preparation schemes to enrich the target components before separation are usually necessary for real sample analysis. However, the commonly used procedures, such as solvent-solvent extraction and solid-phase extraction, are often laborious and time-consuming. In addition, a number of sensitive detectors, such as electrochemical detector, fluorescence detector, and mass spectrometry (MS), have also been successfully developed [4][5][6]. Nevertheless, they are sophisticated, expensive, selective, or difficult to automation compared with absorption detection.On-line concentration of sample is an alternative in CE to improve the concentration detection limits [7][8][9][10][11][12][13]. Up to now, two distinctly different methods for on-column sample enrichment have been developed, namely electrophoretic stacking [7][8][9][10][11][12][13] and chromatographic concentration [14,15]. The former one includes isotachophoresis [7], sample stacking [8,9], sweeping [10,11], and a dynamic pH junction [12,13], caused by the different electric fields applied on the sample zone and background electrolyte. In the latter one, in a capillary with stationary phase, the sample zone could be sharpened under the condition that the modified organic concentration in the mobile phase is higher than that in the sample buffer.Recently, immobilized metal affinity chromatography (IMAC) has shown great potential in the purification of proteins and peptides [16,17], and two types of IMAC columns have been applied to proteomics [18]. One is for the enrichment of phosphorylated...