Separation of open-cage fullerenes using nonaqueous capillary electrophoresis

In this study, nonaqueous capillary electrophoresis (NACE) was used to separate three open-cage fullerenes. Trifluoroacetic acid (TFA) was used as the nonaqueous background electrolyte to change the analytes’ mobilities. The selectivity and separation efficiency were critically affected by the nature of the buffer system, the choice of organic solvent, and the concentrations of TFA and sodium acetate (NaOAc) in the background electrolyte. The optimized separation occurred using 200 mM TFA/20 mM NaOAc in MeOH/acetonitrile (10:90, v/v), providing highly efficient baseline separation of the open-cage fullerenes within 5 min. The migration time repeatability for the three analytes was less than 1% (relative standard deviation). Thus, NACE is a rapid, useful alternative to high-performance liquid chromatography for the separation of open-cage fullerenes.     

Rapid separation of basic drugs by nonaqueous capillary electrophoresis

Summary Nonaqueous capillary electrophoresis (NACE) has been used to achieve rapid separations of basic drugs. A high electric field was obtained by using short capillaries. Baseline separations of basic drugs, including amphetamines, tropane alkaloids and local anesthetics, were achieved in 1 min by selection of the appropriate organic solvent and electrolyte composition. Thus, high-throughput analyses can be performed. Peak efficiency up to 9154 theoretical plates s⁻¹ was achieved in a separation performed at 923V cm⁻¹. No discernible loss in resolution was observed when a conventional capillary (64.5cm) was replaced by a short (32.5 cm) capillary.     

Separation and determination of aconitine alkaloids in traditional Chinese herbs by nonaqueous capillary electrophoresis

An easy, rapid, and simple nonaqueous capillary electrophoresis (NACE) method was developed for the identification and determination of three aconitine alkaloids, hypaconitine (HN), aconitine (AN), and mesaconitine (MN) within 6 min. The most suitable running buffer was composed of 60 mM ammonium acetate, 0.5% acetic acid, and 15% acetonitrile (ACN) in methanol with a fused-silica capillary column (50 cm x 75 microm ID). In the concentration range 12.5-1000 mg/L the calibration curves reveal linear relationships between the peak area for each analyte and its concentration (correlation coefficients: 0.9997 for HN, 0.9999 for AN, and 0.9995 for MN). The relative standard deviations of the migration time and peak area of the three alkaloids were 0.13, 0.57, 0.33 and 2.87, 1.06, 3.49%, respectively. The method was successfully applied to determine the three alkaloids in two commonly used traditional Chinese herbal medicines, the recoveries of the three constituents ranging between 94.7-101.9% for HN, 98.3-102.3% for AN, and 98.1-104.6% for MN.     

Simultaneous separation of organomercury species by nonaqueous capillary electrophoresis using methanol containing acetic acid and imidazole

A simple and rapid nonaqueous capillary electrophoresis method for simultaneous separation of four kinds of mercury species, namely inorganic mercury, methylmercury, ethylmercury, and phenylmercury, is reported. The effective mobilities of organomercury in aqueous and nonaqueous electrolytes were compared. Imidazole was confirmed not only as a co-ion for the separation but also as an online complexing reagent for mercury species. The optimum conditions for separation were achieved by using methanol solvent containing 0.15 M acetic acid and 15 mM imidazole as electrolyte. The sensitive detection of mercury species was accomplished at 191 nm.     

Separation and determination of the anthraquinones in Xanthophytum attopvensis pierre by nonaqueous capillary electrophoresis

A nonaqueous capillary electrophoresis (NACE) method with direct on-column UV detection has been developed for the separation of the pharmaceutically important anthraquinones from the total grass of Xanthophytum attopvensis pierre extract. The separation of three main anthraquinones (1-hydroxy-2-methoxy-3-hydroxymethyl-9, 10-anthraquinone-1-O-β-d-glucoside (1), rubiadin- 1-methylether (2) and 1-methoxy-2-formyl-3-hydroxy-9, 10-anthraquinone (3)) was optimized with respect to concentration of sodium cholate (SC) and acetic acid, addition of acetonitrile (ACN), and applied voltage. Baseline separation was obtained for the three analytes within 5 min using a running buffer containing 50 mM sodium cholate (SC), 1.0% acetic acid and 40% ACN in methanol. The method of NACE for the separation and determination of bioactive ingredient in traditional Chinese medicines was discussed.     

Simultaneous determination of p-hydroxybenzoic acid and parabens by capillary electrophoresis with improved sensitivity in nonaqueous media

New methods based on nonaqueous capillary electrophoresis (NACE) were developed as promising alternatives for the simultaneous separation and determination of p-hydroxybenzoic acid (PHBA) and a group of parabens (methyl, ethyl, propyl, butyl and benzyl p-hydroxybenzoates), with good resolution and excellent sensitivity. As an effective on-line preconcentration technique, large-volume sample stacking (LVSS) was successfully combined with NACE allowing significant sensitivity enhancement. Identification and quantification of the analytes were performed by diode array detection (DAD). The influence of different parameters, such as buffer apparent pH, concentration of electrolyte, temperature, applied voltage and sample volume, on the efficiency, resolution and sensitivity of the electrophoretic separation was studied. The analytical performance was evaluated, and both NACE-DAD and LVSS-NACE-DAD methods showed good linearity, precision and instrumental LODs at low ng/mL levels. These LODs were compared with those described in the literature, and it was found that NACE-DAD method was comparable to GC-MS, while LVSS-NACE-DAD procedure achieved sensitivity similar to LC-MS, LC-MS/MS and GC-MS/MS, even using conventional ultraviolet-visible absorption detection. To test their suitability, proposed methods were evaluated for the analysis of PHBA and parabens at low and sub-ng/mL levels in environmental water samples.     

Specific background electrolytes for nonaqueous capillary electrophoresis

The use of organic solvents or mixture of solvents in capillary electrophoresis is gaining wider attention. The electroosmotic flow mobility of eight organic solvents (acetonitrile, acetone, dimethylformamide, dimetylsulphoxide, propylene carbonate, methanol, ethanol, n-propanol) and of mixtures of several solvents (methanol-acetonitrile, methanol-propylene carbonate, acetonitrile-propylene carbonate) has been studied. The influence of 1,3-alkylimidazolium salts in different solvents on the separation of different analytes has been investigated. Some of these salts have shown usefulness for matrix-assisted laser desorption ionization matrices and off-line analysis of electrophoresis fractions. It also appears that nonaqueous capillary electrophoresis with 1,3-alkylimidazolium salts as background electrolytes is suitable for separation small inorganic ions.     

Enhanced detection of seven glucoconjugated and hydroxylated porphyrins and chlorins by nonaqueous capillary electrophoresis combined with stacking

The nonaqueous capillary electrophoresis mode which includes a preconcentration step based on a transient pseudo-isotachophoresis to the simultaneous separation of seven glucoconjugated and hydroxylated porphyrins and chlorins, exhibiting very close structures, is reported. A high methanol content, of the buffer solution, was necessary in order to prevent self-assembly of the compounds and to enhance their solubility during separation. With the addition of 66% (v/v) methanol and 1% (w/v) NaCl in the aqueous sample solution, large volumes could be injected (44% capillary volume) without a loss in resolution. Sensitivity of detection was therefore improved by a 100-fold factor with regard to the method employing normal injection (2% capillary volume). Optimum electrophoretic conditions, in terms of sensitivity and performance, were obtained by using 20 mM phosphoric acid buffer, pH 2.2 and 50% methanol. The method was validated and applied to qualitative analysis of glucoconjugates in serum samples.     

Peptide separations and dissociation constants in nonaqueous capillary electrophoresis: comparison of methanol and aqueous buffers

Nonaqueous capillary electrophoresis was evaluated for its potential to separate peptides in methanolic background electrolytes in comparison to aqueous-methanol (50% v/v) and water. Isomeric aspartyl dipeptides and Leu- and Met-enkephalin served as model compounds. pK(a) values were determined in the three solvent systems based on the apparent pH scale and in the case of methanol additionally based on the conventional pH scale. Changing from water to methanol led to an increase of the ionization constants describing the dissociation equilibria of the carboxyl group and the amino group, respectively. The pK(a) shift was more pronounced for the carboxylic acid function leading to a compression of the mobility-pH curve. As reported for aqueous buffers, efficient separations of the peptides were achieved in methanolic background electrolytes including the resolution of the diastereomers of the isomeric alpha- and beta-aspartyl dipeptides. In contrast to aqueous buffers, the separation of Leu- and Met-enkephalin could also be obtained in buffers in methanol at high pH.     

Micelle to solvent stacking of two alkaloids in nonaqueous capillary electrophoresis

This paper for the first time describes the development of micelle to solvent stacking (MSS) to nonaqueous capillary electrophoresis (NACE). In this proposed MSS-NACE, sodium dodecyl sulfate (SDS) micelles transport, release, and focus analytes from the sample solution to the running buffer using methanol as their solvent. After the focusing step, the focused analytes were separated via NACE. The focusing mechanism and influencing factors were discussed using berberine (BBR) and jatrorrhizine (JTZ) as model compounds. And the optimum condition was obtained as following: 50 mM ammonium acetate, 6% (v/v) acetic acid and 10 mM SDS in redistilled water as sample matrix, 50 mM ammonium acetate and 6% (v/v) acetic acid in pure methanol as the running buffer, -20 kV focusing voltage with 30 min focusing time. Under these conditions, this method afforded limits of detection (S/N=3) of 0.002 μg/mL and 0.003 μg/mL for BBR and JTZ, respectively. In contrast to conventional NACE, the concentration sensitivity was improved 128-153-fold.     

Separation and determination of 2,4-D, dicamba and 2,4,5-T in tobacco by nonaqueous capillary electrophoresis

A practical method for residue analysis of 2,4-D, dicamba and 2,4,5-T in baked tobacco leaves has been developed using nonaqueous CE (NACE). The herbicide residues of 2,4-D, dicamba and 2,4,5-T in tobaccos were extracted by ultrasonication with ethyl acetate, followed by a cleanup procedure with gel permeation chromatography. The separation of 2,4-D, dicamba and 2,4,5-T by NACE was optimized based on orthogonal experiment design with four factors at three levels. The optimal NACE condition was established with the running buffer of 40.0 mmol/L ammonium acetate in 90% CH3CN (apparent pH 10.2), and the applied voltage of -25 kV over a capillary of 50 microm id x 46 cm (37.5 cm to the detector window), which gave a baseline separation of 2,4-D, dicamba and 2,4,5-T within 15 min. The LOD were ca. 0.4-0.6 microg/mL for the three herbicides, whereas the overall recovery ranged from 80.8 to 84.1%. The proposed method has been successfully applied to measure 300 real tobacco samples, and the residue profiles of the three herbicides in tobacco samples were obtained and evaluated.     

Novel nonaqueous capillary electrophoresis separation and determination of bioactive flavone derivatives in Chinese herbs

Nonaqueous CE (NACE) coupled to UV detection is described for the separation and determination of bioactive flavone derivatives in Chinese herbs extraction. After optimization of electrophoresis parameters, including the electrolyte nature and the organic solvent composition, a reliable separation of the analytes in an ACN/methanol (60:40, v/v) mixture containing 80 mM Tris and 10 mM sodium cholate was performed. The detection was performed at 254 nm. Method performances, including migration time and peak area reproducibility, linearity, sensitivity, and accuracy, were evaluated. The method was applied to determine bioactive flavone derivatives in seven Chinese herbs.     

Separation of living and dead polymers in synthetic polypeptide mixtures by nonaqueous capillary electrophoresis using differences in ionization states

The complexity in the mechanisms of polymerization of N-carboxyanhydrides requires the development of new analytical techniques able to separate mixtures of synthetic polypeptides. This work focuses on the separation of poly(N(epsilon)-trifluoroacetyl-L-lysine) (PTLL) mixtures by nonaqueous capillary electrophoresis (CE). The main goal of this work was to find electrophoretic conditions that permit the separation and the quantification of the dead polymer families that were previously identified in the samples. The influence of the pH of the electrolyte on the selectivity of the separation was carefully investigated. The mechanisms of separation of the PTTLs are discussed as a function of their ionization state. The separations obtained on a noncovalently coated capillary were compared with those obtained on a fused-silica capillary. Finally, using two different electrolytes, it is possible to quantify the three families of PTLLs, namely, the living PTLLs, the dead PTLLs with N-formyl end group and the dead PTLLs with a carboxylic end group. These results confirm the importance of CE for the separation of synthetic organic polymers in nonaqueous electrolytes.     

Application of nonaqueous capillary electrophoresis for quantitative analysis of quinolizidine alkaloids in Chinese herbs

An easy, rapid method for simultaneous determination of tetrandrine (TET), fangchinoline (FAN), sinomenine (SIN) and tetrahydropalmatine (TEP) in Chinese herbs was developed by nonaqueous capillary electrophoresis without pretreatment for the first time. Optimum separation was achieved with a fused-silica capillary column ( i.d.) and a running buffer containing 50 mM ammonium acetate, 1.0% acetic acid and 20% acetonitrile in methanol medium. The applied voltage was 20.0 kV. The analytes were detected by UV at 214 nm. The effects of concentration of ammonium acetate, acetic acid and organic modifier on electrophoretic behavior of the analytes were studied. Regression equations revealed linear relationships (correlation coefficients: 0.9991-0.9999) between the peak area of each analyte and the concentration. The levels of analytes in Stephania tetrandra S. Moore, Rhizoma corydalis and Sinomenium acutum Rehd. et. Wils were easily determined with recoveries ranging from 96 to 107%.     

Ion-pair association and acid-base equilibria in nonaqueous capillary electrophoresis of weakly basic compounds

CE in nonaqueous media was used to study the migrating behavior of two weakly basic s-triazine pesticides and one of their metabolites. The target pesticides were selected to be representative for each of the two main groups: propazine and deethylatrazine for the chloro-s-triazines group and ametryn for the methylthio-s-triazines group. To elucidate the phenomena involved, systematic studies were carried out in the different organic media studied. Absolute mobilities were determined in 50% v/v methanol (MeOH)/ACN by extrapolation of the effective mobilities to zero ionic strength in the presence of different concentrations of perchloric acid. Conductivity measurements performed in MeOH and 50 and 20% v/v methanol/ACN permitted the evaluation of the associations of the components of the BGE. The effects of ionic strength on the actual mobilities of the compounds were determined in the presence of perchloric acid and SDS in different organic media. Two different ion-pair equilibria were considered: one due to the presence of perchlorate anions present in the BGE and second that from the added dodecyl sulfate anions. Bearing in mind that these weakly basic compounds can exhibit ion-pair and acid-base equilibria, the acid-base and ion-pair parasite reaction coefficients were determined. Finally, the effects of ionic strength, ion-pair interactions and acid-base properties on the effective electrophoretic mobilities of the analytes are discussed.     

Micro-porous membrane liquid-liquid extraction as an enrichment step prior to nonaqueous capillary electrophoresis determination of sulfonylurea herbicides

A method based on micro-porous membrane liquid-liquid extraction (MMLLE) enrichment and nonaqueous capillary electrophoresis (CE) separation, was established for the analysis of sulfonylurea herbicides in water samples. After MMLLE, the analyte trapped in the chloroform was treated mildly with nitrogen flow to dryness and then dissolved in 200 μl of 4 mM Tris methanol solution for CE analysis. Five sulfonylurea herbicides were separated by nonaqueous CE with Tris/acetate of methanol solution as the run buffer. MMLLE related parameters such as organic solvent used as acceptor, sample flow rate, sample pH, enrichment time, and salt effect were investigated with tribenuron methyl (TBM) as a model compound. Results showed that with a sample flow rate of 3.0 ml min⁻¹ and an enrichment time of 20 min, the proposed method has good linear relationship over the scope of 1-15 ng ml⁻¹ with related coefficient of R²=0.9911, and a detection limit of 0.4 ng ml⁻¹. This method was applied to determine TBM in realworld water samples with recoveries over the range of 89-97%.     

柱前衍生化-非水毛细管电泳法高效分离饮料中的脂肪醛

以9,10-菲醌作为柱前衍生试剂,采用非水毛细管电泳模式考察并优化了脂肪醛的分离条件。实验采用毛细管(总长58.5 cm,有效长度50 cm,内径50 μm),应用80 mmol/L NH4Ac、1.4 mol/L HAc缓冲体系,于20 ℃、5 kPa(50 mbar)下压力进样 8 s,在不加入其他添加剂的情况下,实现了7种脂肪醛的高效基线分离,检出限为0.37～0.87 μmol/L,线性范围为0.78～25 μmol/L。应用所建立的方法对实际样品进行了测定,结果令人满意。     

Study on the effects of electrolytes and solvents in the determination of quaternary ammonium ions by nonaqueous capillary electrophoresis with contactless conductivity detection

A study on the separation of lipophilic quaternary ammonium cations in NACE coupled with contactless conductivity detection (NACE‐C⁴D) is presented. The suitability of different salts dissolved in various organic solvents as running electrolytes in NACE‐C⁴D was investigated. A solvent mixture of methanol/acetonitrile at a ratio of 90%:10% v/v showed the best results. Deoxycholic acid sodium salt as BGE was found to provide exceptional high stability with low baseline noise that leads to highest S/N ratios for the target analytes among all BGEs tested. Under the optimum conditions, capillaries with different internal diameters were examined and an id of 50 μm was found to give best detection sensitivity. The proposed method was validated and showed good linearity in the range from 2.5 to 200 μM, low limits of detection (0.1–0.7 μM) and acceptable reproducibility of peak area (intraday RSD 0.1–0.7%, n = 3; interday RSD 5.9–9.4%, n = 3).     

Fast separation of selective serotonin reuptake inhibitors antidepressants in plasma sample by nonaqueous capillary electrophoresis

A simple, fast, and sensitive liquid–liquid extraction method followed by nonaqueous capillary electrophoresis (LLE/NACE) was developed and validated for simultaneous determination of four antidepressants (fluoxetine, sertraline, citalopram and paroxetine) in human plasma. Several experimental separation conditions using aqueous and nonaqueous media separation were tested by varying the electrolyte pH value (for aqueous medium) and the ionic strength concentration considering the similar mobility of the compounds. High-resolution separation was achieved with a mixture of 1.25 mol L⁻¹ of phosphoric acid in acetonitrile. The quantification limits of the LLE/CE method varied between 15 and 30 ng mL⁻¹, with a relative standard deviation (RSD) lower than 10.3%. The method was successfully applied in therapeutic drug monitoring and should be employed in the evaluation of plasma levels in urgent toxicological analysis.     

Development and validation method for determination of Paroxetine and its metabolites by nonaqueous capillary electrophoresis in human urine. Experimental design for evaluating the ruggedness of the method

A simple, rapid, and sensitive procedure using nonaqueous capillary electrophoresis (NACE) to measure Paroxetine (one of the mostly used antidepressants for mental diseases treatment) and three metabolites has been developed and validated. Optimum separation of paroxetine and metabolites was obtained on a 57 cm x 75 microm capillary using a nonaqueous buffer system of 9:1 methanol-acetonitrile containing 25 mM ammonium acetate and 1% acetic acid, with temperature and voltage of 25 degrees C and 15 kV, respectively, and hydrodynamic injection. Fluoxetine was used as an internal standard. Good results were obtained for different aspects including stability of the solutions, linearity, accuracy, and precision. Detection limits between 9.3 and 23.1 microg.L(-1) were obtained for paroxetine and its metabolites. A ruggedness test of the method was carried out using the Plackett-Burman fractional factorial model with a matrix of 15 experiments. This method has been used to determine paroxetine and its main metabolite B at clinically relevant levels in human urine. Prior to NACE determination, the samples were purified and enriched by means of an extraction-preconcentration step with a preconditioned C18 cartridge and eluting the compounds with methanol.