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A capillary electrochromatography method, using vancomycin chiral stationary phase packed capillary, was optimized for the simultaneous chiral separation of the antidepressant drug venlafaxine and its main active metabolite O-desmethylvenlafaxine. Simultaneous baseline enantiomeric separation of the two compounds was obtained using a mobile phase composed of 100 mM ammonium acetate buffer pH 6/water/acetonitrile (5:5:90, v/v). The electrokinetic injection for sample introduction provided a limit of quantitation for both the compounds of 0.05 microg/ml racemate concentration suitable for the analysis of venlafaxine and metabolite in biological samples. The acetonitrile mobile phase concentration was found to modulate the analytes elution times, the enantiomeric resolution and the efficiency of the separation. The column was tested for repeatability and linearity showing RSD values (%) in the range of 0.13-0.24, 2.47-3.66 and 1.35-2.50 for migration time, sample/internal standard peak area ratio and enantiomeric resolution, respectively and correlation coefficients higher than 0.9990. The method was applied to the analysis of clinical samples of patients under depression therapy showing a stereoselective metabolism for venlafaxine.

In this study capillary electrochromatography (CEC) was utilized for the separation of ten non-steroidal anti-inflammatory drugs (NSAIDs). Experiments were carried out in a commercially available CE instrument using a packed capillary with RP-18 silica particles where the stationary phase completely filled the capillary. The mobile phase consisted of a mixture of ammonium formate buffer pH 2.5 and acetonitrile. Selectivity and resolution were studied changing the pH and the concentration of the buffer, the acetonitrile content mobile phase and the capillary temperature. The optimum experimental conditions for CEC separation of the studied drug mixture were found using 50 mM ammonium formate pH 2.5-acetonitrile (40:60) at 25°C. The CEC capillary was coupled to an electrospray mass spectrometer for the characterization of the NSAIDs. A mobile phase composed by the same buffer but with a higher concentration of acetonitrile (90%) was used in order to speed up the separation of analytes. (C) 2000 Elsevier Science B.V.

Capillary electrochromatography (CEC) was used for the analysis of relevant compounds in cosmetic preparation. Hydroquinone (HQ) and some of its ethers (methyl-, dimethyl-, benzyl-, phenyl-, propyl-HQ derivatives) were analyzed by using an octadecylsilica (ODS) stationary phase packed in fused-silica capillary (100 ?m I.D.; 30 cm and 21.5 cm total and effective lengths, respectively). 20 mM Ammonium acetate pH 6-acetonitrile (50-70%) were the mobile phases used for the experiments. The acetonitrile (ACN) content strongly influenced the resolution of the studied compounds as well as the efficiency and the retention factor. Baseline resolution for the studied analytes was achieved at both the lowest and the highest percentage of ACN, the last one providing the shortest analysis time. Mobile phase containing 70% of ACN was therefore used for the analysis of an extract of skin-toning cream declared to contain HQ. Good repeatability of both retention times, peak areas and peak areas ratio (A(sample)/A(internal standard)) was found. The calibration graphs were linear in the concentration range studied (5-90 ?g/ml) with correlation coefficients between 0.9975 and 09991. The analysis of the cosmetic preparation revealed the presence of HQ (1.72%, w/w) and of two additional peaks (not identified). Copyright (C) 2000 Elsevier Science B.V.

Capillary high-performance liquid chromatography (capillary HPLC), pressure-assisted capillary electrochromatography (pCEC) and capillary electrochromatography (CEC) were performed in the same capillary packed with 5 ?m octadecylsilica (C18) as stationary phase. These three separation modes were compared from the viewpoint of peak efficiency and separation selectivity in order to critically evaluate the advantages which CEC may offer compared to capillary HPLC for the solution of practical biomedical problems. The separation of the non-steroidal anti-inflammatory drug etodolac (ET, 1) and its phase I metabolites, 6-hydroxy etodolac (6-OH-ET, 2), 7-hydroxy etodolac (7-OH-ET, 3) and 8-(1'-hydroxyethyl) etodolac (8-OH-ET, 4) was selected as an example. Baseline separation of all compounds was achieved in different modes and conditions. The effect of pure electrophoretic separation mechanism on the overall separation selectivity observed in CEC has been shown. A high electroosmotic flow (EOF) was observed in C18 packed capillary even at pH 2.5 in various buffers. Furthermore, these separations were coupled on-line with electrospray ionisation mass spectrometry (ESI-MS) and the parent drug and its metabolites were identified in urine. For the coupling of CEC with ESI-MS a laboratory-made electrophoretic device was used in order to overcome some technical disadvantages of commercial instrumentation. Copyright (C) 2000 Elsevier Science B.V.

The glycopeptide antibiotic MDL 63 246 (Hepta-Tyr), belonging to the teicoplanin family, has been adopted for the separation of several α-hydroxy acid enantiomers by capillary zone electrophoresis (CZE). A polyacrylamide coated capillary was employed for the electrophoretic runs in order to suppress/minimize both the electroosmotic flow (EOF) and the antibiotic adsorption. The experiments were carried out using a background electrolyte (BGE) (aqueous–organic buffer) in the pH range 4–6 that allowed the analytes to reach the detector, as negatively charged species, in a relatively short time while the antibiotic moved in the opposite direction (positively charged). The chiral selector, dissolved in the BGE at relatively low concentration, filled only part of the capillary (partial filling-counter current method) allowing the detection of analytes with good sensitivity and short analysis time (5–8 min). Experimental parameters influencing the enantioresolution such as antibiotic concentration, buffer pH, organic modifier type and concentration and capillary temperature were investigated. Hepta-Tyr antibiotic exhibited a high enantiorecognition capability towards mandelic acid and their hydroxy and chloro derivatives even at very low concentration (1 mg/ml) using a background electrolyte (BGE) at pH 4 containing 20% (v/v) of methanol. On the other hand 2- and 3-phenyllactic acids were baseline resolved in their enantiomers with the same BGE containing acetonitrile and 4 mg/ml of chiral selector.

An uncoated capillary with selected background electrolytes (BGEs) was used to study the migrating vacancies of UV-absorbing components of the buffer. Picric and salicylic acids were chosen as the UV-absorbing anionic species, to be used either as samples in normal capillary electrophoresis (CE) mode (direct CE) or as BGE components (reverse CE). To study the effect of BGE composition, 2-morpholinoethanesulfonic acid and monochloroacetate, with lower and higher mobilities, respectively, were selected as two different BGE co-ions of picrate and salicylate. In normal CE mode, anionic species provided tailing or fronting peaks (representing fronting or tailing migrating zones), depending on whether their effective mobilities were lower or higher than the mobility of the BGE co-ion, respectively. In reverse CE, the effect was the opposite. Picrate and salicylate vacancies were represented by fronting or tailing dips (migrating as tailing or fronting zones) when their mobilities were higher or lower than that of the BGE co-ion, respectively. The electroosmotic peak may be negative or positive, according to the original value of the Kohlrausch regulating function of the sample. Finally, the difference between migrating vacancies and indirect detection is demonstrated and explained, showing indirect detection of a mixture of potassium and sodium acetate detected simultaneously with a benzoic acid vacancy.

Enantiomers of several racemic basic compounds of pharmaceutical interest and three tryptophan derivatives were investigated by capillary electrophoresis employing a soluble β-cyclodextrin polymer and native β-cyclodextrin. The effects of the concentration of the polymer added to the background electrolyte and of the pH of the buffer on the effective mobility and resolution of the studied compounds were examined. The β-cyclodextrin polymer showed a higher stereoselectivity than the parent β-cyclodextrin. Enantionselectivity and resolution were influenced by the concentration of the β-cyclodextrin polymer and the background electrolyte. A pH study, carried out in the pH range 2.7–6, showed that an increase in pH caused a general decrease in both resolution and selectivity. The best results for the enantiomeric separation of the basic compounds studied were obtained at pH 2.7.

Preparative capillary zone electrophoresis of three synthetic peptides was performed either manually or automatically by simple manipulations of a commercial electropherograph that is equipped only with an autosampler without any built-in fraction collection capability. Manual fraction collection was achieved by replacing the outlet (cathode) beaker with a microcentrifuge tube, and automatic fraction collection was accomplished by converting the electropherograph's autosampler into a fraction collector. The latter was easily achieved mainly by the use of an extension wire, which completed the electrical circuit and facilitated fraction collection either at a specified time or within fixed time intervals.

The separation of hydroquinone and some of its ether derivatives was studied by micellar electrokinetic chromatography with sodium dodecyl sulphate as an anionic surfactant in the background electrolyte. The optimized method was used for the determination of hydroquinone in a sample of skin-toning cream. On-column detection at 254 nm with caffeine as an internal standard gave good quantitative results.

Endogenous enkephalin pentapeptides are measured with unambiguous molecular specificity in canine and human tissue and fluid extracts. Both field desorption and fast atom bombardment mass spectrometry have been used to produce a protonated molecular ion of the peptide high-performance liquid chromatography fraction. The protonated molecular ion is subjected to collision-activated dissociation processes and a linked-field scan (B/E) selects a unique amino acid sequence-determining ion for monitoring and measurement. Stable isotope-incorporated peptide internal standards are used for quantification. Endogenous enkephalins are measured in hypothalamus, cerebrospinal fluid, pituitary, caudate nucleus, and tooth pulp extracts. Part-per-billion levels of endogenous peptide are measured.

A combination of high-performance liquid chromatography and field desorption mass spectrometry is used to quantify endogenous amounts of leucine enkephalin in canine thalamus tissue. Reversed-phase high-performance liquid chromatography effects rapid high resolution of brain neuropeptides using a triethylamine formate buffer. An internal standard, 2Ala-leucine-enkephalin, is used. Field desorption mass spectra of neuropeptides generally display only protonated molecular ions. (M + H)+ ion currents of endogenous leucine enkephalin and internal standard were integrated by field desorption mass spectral-selected ion monitoring techniques. The ratio of the two integrated ion currents was used to calculate endogenous amount of leu-enkephalin in thalamus tissue extracts. Leucine enkephalin was determined in this structurally unambiguous fashion in canine thalamus tissue at 50 ng/g thalamus tissue, or the 50 part per billion level.

A high-performance liquid chromatographic system employing a chemically bonded alkyl phase and a tetraalkylammonium phosphate buffer has been evaluated for separation of synthetic mixtures of hypothalamic oligopeptides. Separation of two peptides in the mixture having very similar adjusted retention times has been achieved. Sensitivity down to 5 ng is attained. Peptides range in size from three to 31 amino acids. Field desorption mass spectra illustrate novel structural elucidation methods for individual peptides and signal a quantification method.