Chemometric modeling of neurotransmitter amino acid separation in normal and reversed migration micellar electrokinetic chromatography

CE with sequential light-emitting diode-induced fluorescence and electro-chemiluminescence detections for the determination of amino acids and alkaloids

This paper describes the determination of alkaloids and amino acids (AAs) using CE in conjunction with sequential light-emitting diode-induced fluorescence (LEDIF) and electrochemiluminescence (ECL) detections. In the CE-LEDIF-ECL system, the ECL detector was located in the outlet of the capillary, while the LEDIF detector was positioned 12 cm from the outlet. Naphthalene-2,3-dicarboxaldehyde (NDA) was used to form fluorescent AA-NDA derivatives from AAs possessing primary amino groups, while Ru(bpy)(3) (2+) was used to obtain ECL signals for analytes having secondary and tertiary amino groups. In the presence of poly(ethylene oxide), we accomplished the CE-LEDIF-ECL separation of a mixture of 12 AA-NDA derivatives, anabasine, nicotine, and proline within 11 min. This low-cost CE-LEDIF-ECL system allows the analysis of these AA-NDA derivatives and alkaloids at concentrations in the ranges of 49 nM-0.2 microM and 0.66-4.7 microM, respectively. We applied our CE-LEDIF-ECL system to the analysis of a urine sample and also to tobacco extracts. We obtained good qualitative and quantitative results when using this method with these analytes: the RSDs were below 3.0 and 2.8%, respectively. This CE-LEDIF-ECL system provides the advantages of high efficiency, speed, and sensitivity for the analysis of analytes possessing amino groups.

Use of multivariate analysis for optimization of separation parameters and prediction of migration time, resolution, and resolutionper unit time in micellar electrokinetic chromatography

The optimization of separation parameters in chromatography for better separation and resolution of analytes continues to be a labor intensive procedure usually performed by a trial and error method. A multivariate analysis in the form of multilinear regression (MLR) is used to optimize separation parameters and predict the migration behavior, resolution, and resolution per unit time of achiral (4-chlorophenol, pentachlorophenol, clonazepam, and diazepam) and chiral (1,1'-binaphthyl 2,2'-dihydrogen phosphate (BNP), and 1,1'-bi-2-naphthol (BOH)) compounds in MEKC. Separations of achiral and chiral analytes were performed using an achiral (poly(sodium N-undecylenic sulfate)) molecular micelle and chiral (poly(sodium N-undecanoyl-L-leucylvalinate) or poly(sodium N-undecanoyl-L-isoleucylvalinate)) molecular micelle, respectively, at various operating temperatures, applied voltages, pH values, and molecular micelle concentrations in the BGE. The separation parameters were subsequently used as input variables for MLR models. The models were validated with independent samples. The root-mean-square percent relative error (RMS%RE) is used as a figure of merit for characterizing the performance of the migration time, resolution, and resolution per unit time models. The RMS%RE obtained for predicted migrated times, resolutions, and resolution per unit time of 4-chlorophenol, pentachlorophenol, clonazepam, diazepam, BNP, and BOH ranged between 8 and 19%. The same experimental procedure was used to optimize the separation parameters of six other chiral analytes of different compound class. The predicted migration times, resolutions, and resolution per unit time of the chiral as well as the achiral analytes compare favorably with the experimental migration times and resolutions, indicating versatility and wide applicability of the technique in MEKC.

Sequential uniform designs for fingerprints development of Ginkgo biloba extracts by capillary electrophoresis

A sequential procedure for the method of development of fingerprints based on a uniform design approach has been described in this paper. The sequential uniform design is used to reach the global optimum for a separation. The procedure is illustrated through developing the fingerprint of a Ginkgo biloba extract by capillary electrophoresis (CE) with diode array detection (DAD). The local overlap index (LOVI) is proposed as a criterion to evaluate the separation quality of two-dimensional hyphenated data in the optimization process. The successful application of the described techniques, including a sequential procedure, the CE-DAD hyphenated method and the LOVI criterion, shows their practicality in the fingerprint development of herbal medicines. However, some critical remarks on their use can also be made.

MEKC-LIF of gamma-amino butyric acid in microdialysate: systematic optimization of the separation conditions by factorial analysis

Micellar electrokinetic chromatography allows the efficient separation of biogenic amines and amino acids in biological samples. Analytes of interest, sample composition, and sample matrix may vary between studies, which necessitates optimization of separations to meet the requirements and conditions of an experiment. Factorial analysis is an efficient tool to accomplish this type of optimization involving multiple interacting factors. The present study describes an optimization procedure for separation of the inhibitory neurotransmitter GABA utilizing capillary electrophoresis with laser induced fluorescence detection. Standards labeled with the flourogenic reagent 3-(2-furoyl)quinoline-2 carboxaldehyde were separated with varying concentrations of borate buffer, beta-cyclodextrin, sodium dodecyl sulfate and pH. The optimized separation method had a correlation coefficient between concentration of GABA and fluorescent signal of 0.98, and was linear in the desired concentration range of 25 nM-10 microM. Glutamic acid, aspartic acid and taurine were also quantified using this separation. When applied to microdialysate collected from the region of the suprachiasmatic nucleus, this separation was able to measure daily variations in GABA levels. The factorial design experiment has proven to be a useful tool, allowing adjustments in the separation of neurotransmitters based on individual requirements.

Rapid method for the determination of amino acids in serum by capillary electrophoresis

A rapid method for the determination of amino acids in serum is presented. The derivatization of amino acids with 2,4-dinitrofluorobenzene was performed in 0.5 M sodium borate (pH 9.5). The complete separation of derivatives of 16 amino acids and an internal standard (D-norleucine) was achieved within 8 min by capillary zone electrophoresis. The running buffer consisted of 30 mM sodium tetraborate (pH 9.8)-isopropanol-30% Brij 35 (825:150:25, v/v). The capillary used had an internal diameter of 75 microm and an effective length of 300 mm. A voltage of 28 kV was applied. Temperature was maintained at 15 degrees C. Detection was 360 nm. The assay was linear from 10 to 700 microM. The minimal detection limit was 2.5-7.9 microM. The recovery of amino acids added to serum samples was 86.3-107.4%. Within-run precision was 2.8-10.3%, and between-run precision was 3.5-11.6%. The concentrations of amino acids in serum of 32 patients with chronic renal failure were measured. Among them, the levels of serine, isoleucine and valine were significantly lower than those of healthy volunteers (P<0.01), but the concentrations of cystine, tryptophan and phenylane were significantly higher than those of healthy volunteers (P<0.01). The result showed that the method could be used for determining amino acids in clinical practice and scientific research.

Sweeping: concentration mechanism and applications to high-sensitivity analysis in capillary electrophoresis

Sweeping in capillary electrophoresis (CE) involves the interaction of a pseudostationary phase (PS) in the separation solution and a sample in the matrix that is free of the PS used. The PS includes not only the PSs employed in electrokinetic chromatography, but also complexation reagents such as borate. The sample matrix could have a lower, similar, or higher conductance than the separation solution. Thus, the basic condition for sweeping is a sample matrix free of the additive. The accumulation of analyte molecules during the interaction makes this interesting phenomenon very useful as an on-line preconcentration method for CE. Preconcentration occurs due to chromatographic partitioning, complexation, or any interaction between analytes and PS. Contact between analyte and PS is facilitated by the action of electrophoresis and is independent of electroosmosis. The analyte, PS, or both should have electrophoretic velocities when an electric field is applied. The extent of preconcentration is dictated by the strength of the interaction involved. From tens to several thousand-fold improvements in detector response for many neutral and charged analytes have been achieved with this technique, suggesting sweeping as a general approach to on-line preconcentration in CE. The mechanism and applications of the sweeping phenomenon under different experimental conditions are discussed in this review, with particular emphasis on a better understanding of the sweeping mechanism under reduced electric field (high conductivity) in the sample zone.