Microemulsion electrokinetic chromatography with laser‐induced fluorescence detection: as tested with amino acid derivatives

Abstract

Over a decade ago, microemulsion electrokinetic chromatography was introduced as a novel mode of capillary electrophoresis. However, there has not been publication on the combination of microemulsion electrokinetic chromatography with laser-induced fluorescence detection. In this paper, a preliminary method using microemulsion eletrokinetic chromatography combined with laser-induced fluorescence detection and second derivative electrophoregram was established as a sensitive and selective assay for separation and determination of nine amino acids after derivatization with 4-chloro-7-nitrobenzo-2-oxa-1, 3-diazol. The derivatization and separation conditions were optimized. In the investigated concentration ranges correlation coefficients were better than 0.995. The relative standard deviation (n = 5) of the migration times and peak heights were 0.56-0.76 and 2.21-7.15%, respectively. The detection limits (S/N = 3) were at a neaomolar level (0.32-2.20 nM). The method was applied for the analysis of compound amino acid injection and a Chinese traditional herbal medicine. The recoveries were 95.9-107.9%.

Recent advances in microemulsion electrokinetic chromatography

“…Increasing the buffer concentration of the electrolyte has been shown to improve peak resolution [20,45]. Using a low concentration of borate buffer in the microemulsion gave a faster separation because of the faster EOF at low ionic strengths, but the precision of subsequent injections was lower due to electrolysis effects [28].…”

“…MEEKC methods have been used to perform quantitative determinations including UV filters in sunscreen lotions [41], preservatives in pharmaceutical and cosmetic products [10], catechins in green tea [27], pharmaceuticals [9,19,51,62] and biphenyl nitrile compounds [6]. Using MEEKC coupled with laserinduced fluorescence detection offers more sensitivity for quantitative methods of determining amino acid derivatives [45] and ephedrine and pseudoephedrine [63]. Table 1 shows some quantitative results obtained from various MEEKC methods.…”

Recent advances in the development and application of microemulsion EKC

“…Melin and Perret [73] compared the analysis of UV absorbing compounds in human urine by MEKC and MEEKC but found that MEEKC offered no advantages for routine analysis. The use of MEEKC for the analysis of amino acid derivatives resulted in poor reproducibility and long analysis time [54]. However, the use of a novel double coating of a combination of a removable covalent layer and an SDS layer on the capillary resulted in [54] faster and more reproducible Table 4 lists recent bioanalytical applications of MEEKC.…”

“…Increasing the buffer concentration in the aqueous phase of the microemulsion electrolyte has been shown to improve peak resolution [22,54]. High buffer concentrations suppress the EOF and generate high currents, which may limit the level of voltage that can be applied.…”

“…Recent methods to improve sensitivity and LODs have included sample stacking [68] to improve sensitivity up to 40-fold, and LIF detection (LIFD) [54,75], used for to achieve LODs of 5.3 and 3.9 ng/ml ephedrine and pseudoephedrine, respectively in Chinese herbal remedies [75].…”