Recent advances in enrichment techniques for trace analysis in capillary electrophoresis

Abstract

Recent advances in enrichment techniques for trace analysis in capillary electrophoresisCE is gaining great popularity as a well-established separation technique for many fields such as pharmaceutical research, clinical application, environmental monitoring, and food analysis, owing to its high resolving power, rapidity, and small amount of samples and reagents required. However, the sensitivity in CE analysis is still considered as being inferior to that in HPLC analysis. Diverse enrichment methods and techniques have been increasingly developed for overcoming this issue. In this review, we summarize the recent advances in enrichment techniques containing off-line preconcentration (sample preparation) and on-line concentration (sample stacking) to enhancing sensitivity in CE for trace analysis over the last 5 years. Some relatively new cleanup and preconcentration methods involving the use of dispersive liquid-liquid microextraction, supercritical fluid extraction, matrix solid-phase dispersion, etc., and the continued use and improvement of conventional SPE, have been comprehensively reviewed and proved effective preconcentration alternatives for liquid, semisolid, and solid samples. As for CE on-line stacking, we give an overview of field amplication, sweeping, pH regulation, and transient isotachophoresis, and the coupling of multiple modes. Moreover, some limitations and comparisons related to such methods/techniques are also discussed. Finally, the combined use of various enrichment techniques and some significant attempts are proposed to further promote analytical merits in CE.

Dual cloud point extraction coupled with hydrodynamic-electrokinetic two-step injection followed by micellar electrokinetic chromatography for simultaneous determination of trace phenolic estrogens in water samples

“…The limits of detection for all three PEEs, calculated as the analyte concentration for which the peak height was three times the background noise (signal-to-noise ratio of 3), were 7.9, 8.2, and 8.9 ng/mL, respectively (Table 1). This method has achieved the requirement for trace analysis [23]. Given that many of the EDCs identified have the potential to cause an estrogenic response at very low concentrations (parts per billion to parts per trillion levels), it is cause for concern that measurable concentrations of many of the chemicals mentioned herein have been found in wastewater, surface waters, sediments, groundwater, and even drinking water [37].…”

“…Fortunately, a number of strategies have been developed to improve the sensitivity of CE through online enrichment, which is collectively known as stacking, such as field amplified sample stacking, transient isotachophoresis, dynamic pH junction, and sweeping [22,23]. We adopted a simpler and more direct online strategy, namely, hydrodynamic-electrokinetic two-step injection, to increase the amounts of sample injected and thereby improve the CE sensitivity.…”

Recent advances in solid-phase sorbents for sample preparation prior to chromatographic analysis

“…MIPs have attracted great attention because they show promise as compound-selective or group-selective media. So, MIPs as SPE sorbents, have become a most important application area, which has been reviewed by Chen's group [5,18,59], by coupling with various chromatographic technologies, such as HPLC, GC and CE. MISPE has been applied using off-line, on-line and in-line modes.…”

“…The combination of molecular imprinting and these three extraction methods would therefore ideally provide powerful analytical tools with the characteristics of simplicity, flexibility, and selectivity. The principles of the three extraction methods have been described in detail [59], and here we do not describe them again. Table 2 summarizes some new applications of MIPs as SPSs in the three extraction methods.…”

A Miniaturized Transverse Flow Gating Interface for the On-line Coupling of Solid-phase Extraction with Capillary Electrophoresis

“…Additionally, as the SPE column is physically separated from the CE capillary in the on-line system, this allows for independent operation and optimization of the SPE and the CE. [2][3][4][5][6] On-line coupling of SPE with CE requires a specially designed interface. In addition to implementation of electric connection for CE, the interface should have the ability to exactly transfer nanoliters of fractions from SPE onto CE with minimized degradation of the efficiencies of SPE and CE.…”