Low-temperature bath/coupled-capillary/sweeping-micellar electrokinetic capillary chromatography for the separation of naphthalene-2,3-dicarboxaldehyde-derivatized dopamine and norepinephrine

Abstract

The use of a low-temperature (0 degrees C) bath-assisted coupled capillary for the separation of naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized dopamine and norepinephrine using the sweeping-micellar electrokinetic capillary chromatography (MEKC) mode is described. In this technique, a capillary consisting of two portions with different inside diameters is used. Therefore, the field strength inside the capillary is different. Hence, the electrophoretic migration velocities of the analytes and the electro-osmotic flow (EOF) also are different. Furthermore, when a portion of the capillary (wide portion, used for sweeping) is immersed in a low-temperature bath, the viscosity of the buffer and the retention factor of the analytes inside are increased. Thus, not only are the interactions between the SDS micelles and the analytes increased, but the SDS-analytes also move more slowly. As a result, a more complete separation can be achieved, even when the sample injection volume is large, up to approximately 2 microL. In general, when the volume of an injected sample is larger, the effects of sweeping and separation would become insufficient, especially when the retention values (k) of the analytes are quite different. However, this limitation can be improved when the low-temperature bath/coupled capillary/sweeping-MEKC mode is used.

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

“…12. They followed this work by using a similar approach but with a section of the larger capillary cooled to 07C [164]. This improves analyte interaction with the micelles by increasing the phase ratio and also by altering the partition coefficient as well as through a change in viscosity.…”

MEKC: An update focusing on practical aspects

“…Although the method provided only a ten-fold enhancement of LODs with respect to standard sweeping mode (naphthalene-2,3-dicarboxaldehyde-labeled dopamine is used as a model compound), the number of plates was increased four times. One other approach reported by Shih and Lin [45,46] uses coupled capillaries, which can be made by directly connecting the different diameters of fused-silica capillaries via polyethylene tubing, to allow the use of larger volumes of sample injection. For the determination of dopamine and norepinephrine derivatized with naphthalene-2,3-dicarboxaldehyde, the BGE consisted of SDS at acidic pH (1.5) provided by phosphoric acid, and the procedure was similar to that of the single capillary, although the applied voltage and SDS concentration must be slightly changed.…”

Study of the naphthalene-2,3-dicarboxaldehyde pre-column derivatization of biogenic mono- and diamines in mixture and fluorescence−HPLC determination

“…Compared with the products formed by derivatization with OPA, the NDA/CN derivatives exhibit improved chemical stability, excitation maxima (420 and 440 nm) in the visible region, efficient chemiluminescence by the peroxyoxalate method and enhanced fluorescence quantum efficiency [41]. NDA has been used for the derivatization of amino acids and peptides [41][42][43][44][45], catecholamines [46][47][48][49], aliphatic amines [50], heterocyclic amines [51,52], aliphatic diamines [53], drugs [54][55][56] and lipids [57]. The main features of these methods are summarized in Electronic supplementary material (ESM) Table S1.…”