Large-Volume Sample Sweeping with a High Theoretical Plate Number Using a Coupled-Capillary in Capillary Electrophoresis

Abstract

Experimental ApparatusThe violet-LED (light-emitting diode) light source (∼2 mW), CE set-up and data-acquisition system used were similar to that described previously, 10 and are abbreviated herein. A large-volume sample injection (> 5 µL) with an extremely high theoretical plate number (N > 10 7 ) was achieved when the sweeping-MEKC mode and a coupled-capillary (100 -50 µm i.d.) were simultaneously used in a capillary electrophoresis (CE) separation. A low-cost and compact violet-LED (∼2 mW) was used as the fluorescence excitation source. As a result, the theoretical plate numbers of the detected peaks (two model compounds: naphthalene-2,3-dicarboxaldehyde derivatized-dopamine and -norepinephrine) were 1.0 × 10 7 and 7.4 × 10 6 , respectively. The limits of detection (at S/N = 3) of these were determined to be 2.8 × 10 -10 M (92 ppt) and 2.3 × 10 -10 M (83 ppt), respectively.

Micellar electrokinetic chromatography: Methodological and instrumental advances focused on practical aspects

“…The contributions toward the use of LED‐induced fluorescence detection in MEKC in the period covered by this review are essentially those reported by Li et al 28, 30, 147. Thus, blue (476 nm) 28, violet (410 nm) 30 and UV (380 nm) 147 LEDs have been used for the determination of phenethylamine designer drugs with FITC, dopamine and norepinephrine with NDA, and tryptophan with phenylglyoxal, respectively. In all cases, on‐line sample concentration techniques were used to improve sensitivity.…”

“…As stated above, little work has been conducted to improve the phenomenon of sweeping; thus, the contributions have mainly been focused on the analytical use of this on‐line concentration technique. In most cases the protocol for sweeping neutral and anionic analytes uses anionic micelles like SDS and suppressed EOF in a low pH BGE provided by phosphoric acid or phosphate buffer (pH 2–3) 26–32. Under suppressed EOF conditions, other anionic surfactants, di(2‐ethylhexyl) sulfosuccinate and Brij‐S, and cationic ones, CTAB, octyltrimethylammonium bromide and tetradecyltrimethylammonium bromide, have also been used as alternatives for SDS, but with lower enhancement factors 33.…”

“…In general, up to 100‐fold improvement in concentration sensitivity can be achieved in the determination of different analytes, mainly in samples of pharmaceutical or clinical interest such as strychnine and brucine in Chinese medicinal preparations 26, 27, phenethylamine designer drugs 28 and ketamine and norketamine 29 in urine samples and carbamazepine in tablet and human serum 32. In some cases, LODs were also enhanced by combining on‐line sweeping with an off‐line concentration approach such as liquid‐phase microextraction 27 or by using a more sensitive detection technique such as LED‐LIF detection 28, 30. The sweeping protocol has also been applied under basic conditions (BGE with borate buffer at pH over 8.5–9.5), but only two approaches have been reported.…”