Determination of phenolic whitening agents in cosmetics by micellar electrokinetic capillary chromatography with amperometric detection

A sensitive method for simultaneous determination of six phenolic whitening agents,including arbutin, phenol,resorcinol,hydroquinone,kojic acid,and salicylic acid in cosmetics has been developed using micellar electrokinetic capillary chromatography with amperometric detection（MECC-AD）.Effects of several factors,such as the pH value and concentration of running buffer,potential applied to the working electrode,separation voltage,and injection time were investigated to obtain optimum conditions for separation and detection.With a 75 cm long fused-silica capillary tube,well-defined separation of six phenolic compounds was achieved in 10mmol/L SDS/40 mmol/L H₃BO₃-Na₂B₄O₇ running buffer（pH 9.0）.Good linear relationship was obtained for each analyte over three orders of magnitude with correlation coefficients（r2） between 0.9985 and 0.9994,and the detection limit（S/N=3） ranged from 0.04μg/mL to 0.45μg/mL The proposed method has been successfully applied for the determination of phenolic whitening agents in real cosmetic samples with satisfactory results,providing an alternative monitoring method for cosmetics safety regulation.     

Determination of purine and pyrimidine bases in DNA by micellar electrokinetic capillary chromatography with electrochemical detection

A method based on micellar electrokinetic capillary chromatography with electrochemical detection was developed for the determination of cytosine, 5-methylcytosine (5-MC), thymine, adenine, and guanine in the hydrolysates of DNA. The working electrode was fabricated in a novel self-positioning carbon disc electrode system that can align the capillary outlet with the working electrode without a three-dimensional micromanipulator. The five analytes could be well separated within 10 min in a 40 cm length capillary at a separation voltage of 9 kV in a 40 mmol/l borate buffer (pH 10.0) containing 100 mmol/l sodium dodecyl sulfate. Good linearity was observed between peak current and concentration of bases over three orders of magnitude with the detection limits (SIN=3) ranging from 1.28 x 10(-6) to 5.02 x 10(-6) mol/l. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 5% for both migration time and peak current (n=7). It has been successfully applied to determine bases including 5-MC in the hydrolysates of fish sperm DNA, calf thymus DNA, and DNA isolated from spleen cells of female mice.     

Determination of phosphoamino acids by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection

A micellar electrokinetic capillary chromatography (MEKC) method with laser-induced fluorescence detection (LIF) was developed for analyzing three phosphoamino acids including phosphotyrosine (P-Tyr), phosphoserine (P-Ser), and phosphothreonine (P-Thr). 3-(2-Furoyl)quinoline-2-carboxaldehyde (FQ), a fluorogenic dye, was employed for derivatization of these phosphoamino acids. Results indicated that the complete baseline resolution of each phosphoamino acid was obtained within 10 min, using 20 mmol l⁻¹ sodium borate buffer (pH 9.35) containing 20 mmol l⁻¹sodium deoxycholate (SDC) and 10 mmol l⁻¹ Brij35. Other common amino acids, especially Glu and Asp, did not disturb the assay of these phosphoamino acids. There was a linear relationship between the peak area for analyte and its concentration, with correlation coefficients in the range of 0.9966-0.9996. The concentration detection limits (signal-to-noise = 3) for P-Tyr, P-Ser, and P-Thr were 10, 40, and 75 nmol l⁻¹, respectively. The developed method was successfully applied for determining phosphoamino acids in the hydrolysis sample of a phosphorylated protein kinase.     

Determination of plasma heparin by micellar electrokinetic capillary chromatography

The micellar electrokinetic capillary chromatography (MECC) method is reported for the separation of heparin, and for the possibility of direct determination of free heparin in plasma. The conditions for MECC were: pH 8.5, 25 mM sodium dodecyl sulfate (SDS), 25 mM borate buffer, with a 30 cmx50 mum ID fused-silica capillary. The sample was detected with a UV-detector at 270 nm with heparin as external standard. The recovery rate was 95.6-98.7%. This method was linear in the range 80-7000 U l(-1). The within-run and between-run relative standard deviations were lower than 3.1 and 4.5%, respectively. It is suggested that this MECC method may be used to determine blood samples containing high levels of heparin.     

Determination of heterocyclic compounds by micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MECC) based on sodium cholate (NaCh) and sodium dodecyl sulphate (SDS) was developed for the determination of aromatic amino acids and heterocyclic legume constituents. The influence of temperature, voltage, micellar system, pH, zwitterion and modifier concentrations in the buffer on migration times, peak areas, resolution and number of theoretical plates was investigated. This MECC method makes possible the sensitive determination of the individual compounds with detection limits in the picomole range. Up to 300 000 theoretical plates per metre of capillary were obtained together with satisfactory linearity and repeatability of the NaCh method. The applicability of MECC to samples prepared from plant material, following a fast and simple technique of isolation, purification and group separation, is illustrated by selected examples.     

Determination of piribedil in pharmaceutical formulations by micellar electrokinetic capillary chromatography

A fast and simple micellar electrokinetic capillary chromatographic method was developed for the analysis of piribedil in pharmaceutical formulations. The effects of buffer concentration, buffer pH, sodium dodecyl sulphate (SDS) concentration, organic modifier, applied voltage and injection time were investigated. Optimum results were obtained with a 50 mM borate buffer at pH 8.0 containing 50 mM SDS by using a fused silica capillary (50 m internal diameter, 72 cm effective length). The sample was injected hydrodynamically for 4 s at 50 mbar pressure and the applied voltage was +30 kV. The detection wavelength was set at 205 nm. Diflunisal was used as an internal standard. The analysis was performed at 25 °C and the total run time was 14 min. The method was suitably validated with respect to linearity range, limit of detection and quantification, precision, accuracy, specificity and robustness. The linear calibration range was 5–100 g mL^–1 and the limit of detection was determined as 1 g mL^–1. The method developed was successfully applied to the determination of piribedil in pharmaceutical formulations. The results were compared with a spectrophotometric method reported in the literature and no significant difference was found statistically.     

Determination of pesticides in drinking water by micellar electrokinetic capillary chromatography

A new analytical procedure using a two-step sample preconcentration (solid-phase extraction (SPE) and field-amplified sample stacking) prior to separation by micellar electrokinetic capillary chromatography was developed for the determination of 14 pesticides such as aldicarb, carbofuran, isoproturon, chlorotoluron, metolachlor, mecoprop, dichlorprop, MCPA, 2,4-D, methoxychlor, TDE, DDT, dieldrin, and DDE in drinking water. Good recoveries of pesticides were obtained using SPE with sample pH adjusted to 2-3. Field-amplified sample stacking was found to give enrichment factors up to 30-fold preconcentration of various pesticides under reversed polarity at -2 kV for 50 s. The optimized background electrolyte (BGE) consisted of 50 mM sodium dodecyl sulfate (SDS), 10 mM borate buffer, 15 mM beta-cyclodextrin (beta-CD), and 22% acetonitrile at pH 9.6, running was under 25 kV and detection at 202 nm. Good linearity was obtained for all pesticides with detection limits down to 0.04-0.46 ng/mL and a working range of 0.1-40 ng/mL. The repeatabilities of migration time and peak area were satisfactory with relative standard deviations (RSDs) between 0.66 and 13.6% and 4.1 and 28%, respectively. All pesticides except dieldrin were found to be detected at concentrations at least tenfold lower than the World Health Organization (WHO) guideline values. The analytical procedure developed offers an economic method for fast screening of multiple pesticide residues in drinking water for health protection. It had been applied to determine carbofuran and MCPA in agricultural run-off water samples, giving satisfactory repeatabilities of 10 and 12%, respectively, with n=5 for the determination of pesticides in contaminated water samples.     

胶束电动毛细管色谱法测定植物中的水杨酸

建立了以胶束电动色谱为分离模式测定植物中水杨酸的新方法。在一定范围内，随着硼酸和甲醇浓度的升高，苯甲酸内标和水杨酸的分离度以近似线性关系升高；随缓冲液pH的升高分离度呈非线性升高；随十六烷基三甲基溴化铵浓度的升高分离度呈非线性下降。在优化的条件下，两可在12min内分离。测定了苹果和梨样品，并做了回收率试验，回收率在97.1%-102%之间。     

Determination of puerarin and daidzein in Puerariae radix and its medicinal preparations by micellar electrokinetic capillary chromatography with electrochemical detection

The use of micellar electrokinetic capillary chromatography (MECC) with electrochemical detection is described for the determination of puerarin and daidzein in Puerariae radix and its medicinal preparations. Operated in a wall-jet configuration, a 300 μm diameter carbon-disk electrode was used as the working electrode, which exhibits good responses at +900 mV (versus SCE) for the two analytes. Under the optimum conditions, the analytes were base-line separated within 11 min in a sodium dodecyl sulphate—borax (pH 7.8) running buffer, and excellent linearity was obtained in the concentration range from 5.0×10⁻⁴ to 5.0×10⁻⁶ mol/l. The detection limit (S/N=3) was 6×10⁻⁷ and 1.1×10⁻⁶ mol/l for puerarin and daidzein, respectively. This work provides a useful method for the analysis of traditional Chinese medicines.     

Pesticide analysis by micellar electrokinetic capillary chromatography

On-capillary sample concentration using sample stacking for the improvement of detection limits for various pesticides separated by micellar electrokinetic capillary chromatography was examined. The dependence of the stacking on different parameters was investigated. An approximately 30-fold preconcentration was achieved by applying sample stacking. Employing a two-step enrichment process (solid-phase extraction combined with sample stacking), detection limits were improved and the sample volume for SPE was reduced. In addition, the total time for the analysis was considerably reduced. Detection limits were between 0.01 and 0.1 ng/ml under these enrichment conditions.     

Determination of shikimate in crude plant extracts by micellar electrokinetic capillary chromatography

A method based on micellar electrokinetic capillary chromatography (MECC) has been developed for the determination of shikimate in water and crude plant extracts. The analytes are separated in a cholate-taurine buffer by MECC at pH 7.3 and measured by direct UV detection at 206 nm. Shikimate showed linearity up to 12.5 mM, with a squared correlation coefficient (r(2)) of 0.9997. The method has concentration limit of detection (cLOD) and concentration limit of quantification (cLOQ) at 24.4 and 67.8 microM, respectively, corresponding to detection in the femtomol range. The number of theoretical plates (N) was estimated to 245,000 for the optimized system using a capillary with an effective length of 560 mm. The method was tested on plant samples by measuring the shikimate content in leaves of rapeseed plants grown in hydroponic solutions containing the herbicide glyphosate, a well-known inhibitor of the shikimate pathway. In crude extracts of these plants, shikimate was found to accumulate in the leaves, confirming earlier reports of shikimate as a potential biomarker for glyphosate treatment. The method now developed was also able to detect shikimate-3-phosphate, but this compound was not accumulated in glyphosate inhibited plants as found for shikimate.     

Separation of coumarins by micellar electrokinetic capillary chromatography

Nine coumarins were successfully separated simultaneously using micellar electrokinetic capillary chromatography with 4-hydroxybenzoic acid as an internal standard. A carrier composed of buffer solution (20 mM sodium dodecyl sulfate-15 mM sodium borate-15 mM sodium dihydrogenphosphate)-acetonitrile (24:1) was found to be the most suitable electrolyte for this separation. The analysis time (22 min) was shorter than that using high-performance liquid chromatography (47 min). Contents of coumarins in the crude drug of Angelicae Tuhou Radix could be easily determined by the proposed method.     

Determination of antitubercular drugs by micellar electrokinetic capillary chromatography (MEKC)

A method for the determination of isoniazid (ISO), pyrazinamide (PYR) and rifampicin (RIF) in pharmaceutical products, by micellar electrokinetic capillary chromatography (MEKC) with ultraviolet detection is described. The influence of pH, concentration of surfactants, buffer and organic solvents, over the separation were studied as experimental variables. The optimal separation was carried out at 30 degrees C and 20 kV, using a 40 mM borate buffer and 100 mM sodium dodecylsulphate (SDS) adjusted to pH 8.5. Under these conditions, the analysis is accomplished in about 8 min. The method was applied to the determination of these compounds in different pharmaceuticals with good results when compared with a reference liquid chromatographic (LC) method.     

Serum iohexol analysis by micellar electrokinetic capillary chromatography

A simple and rapid ( approximately 4 min) method for the measurement of iohexol in serum for assessing the glomerular filtration rate is described. It is based on direct serum injection on the capillary by MEKC. The method is linear between 8 and 260 mg/L, with an RSD of peak height of 2.9%. Several simple steps have contributed to an improved daily precision, such as choosing a high pH buffer, increasing the SDS concentration, frequent standardization, and eliminating any sample pretreatment.     

Simultaneous determination of eleven preservatives in cosmetics by micellar electrokinetic chromatography

A new method for the simultaneous quantitation of 11 preservatives-imidazolidinyl urea, benzyl alcohol, dehydroacetic acid, sorbic acid, phenoxyethanol, benzoic acid, salicylic acid, and four parabens (methyl, ethyl, propyl, and butyl)-in cosmetics by micellar electrokinetic capillary chromatography was established and validated. The separation was performed using an uncoated fused-silica capillary (50 pm id x 60.2 cm, effective length 50 cm) with a running buffer consisting of 15 mmol/L sodium tetraborate, 60 mmol/L boric acid, and 100 mmol/L sodium dodecyl sulfate. A 1:10 dilution of the running buffer was used as the sample buffer to extract the cosmetic samples. The key factors, such as the concentration and pH of the running and sample buffers, which influence quantitative analysis of the above 11 preservatives in cosmetic samples, were investigated in detail. The linear ranges of the calibration curves for imidazolidinyl urea and the other 10 preservatives were 50-1000 and 10-200 mg/L, respectively. The correlation coefficients of the standard curves were all higher than 0.999. The recoveries at the concentrations studied ranged from 93.0 to 102.7%. RSDs were all less than 5%. The new method with simple sample pretreatment met the needs for routine analysis of the 11 preservatives in cosmetics.     

Determination of doxycycline in pharmaceuticals and human urine by micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MEKC) was performed at 25 °C and 30 kV (under a pressure of 15 mbar), using 30 mM borate buffer containing 60 mM sodium dodecysulfate (SDS) and 5% (v/v) methanol as background electrolyte (pH 9.0) to determine doxycycline. UV detection was at 350 nm. The method was shown to be specific, accurate (recovery was 100.3 ± 1.0%), linear over the tested range (correlation coefficient 0.9995) and precise (RSD <1.9%). The method was used to determine doxycycline in tablets, capsules and human urine after oral application.     

Determination of neutral and cationic herbicides in water by micellar electrokinetic capillary chromatography

The separation and determination of two s-triazines and two quats in water samples by MEKC was described. The influence of pH, type and concentration of buffer, concentration and type of surfactant, organic modifier and the added salt on the separation of the two neutral and the two cationic herbicides was studied. Simazine and atrazine (neutral compounds at the working pH) were little influenced by the chemical variables, while the cationic paraquat and diquat were more influenced. In the optimisation on the separation voltage, the total concentration of salt in the run buffer and the repeatability of the separation were taken into consideration. The composition of dissolution, in which the analytes were dissolved, was also studied.A solid-phase extraction method to retain and to elute the four analytes in a single step was also developed. Recoveries between 80 and 95% and R.S.D. between 6 and 10% was obtained in the analysis of a well-water sample spiked with 2 and 5 ppb of triazines and quats, respectively. Detection limits were between 0.6 and 1.9 ppb.     

Analysis of B6 vitamers by micellar electrokinetic capillary chromatography with laser-excited fluorescence detection

Micellar electrokinetic capillary chromatography (MECC) involves the application of a high voltage (10 to 40 kV) across a capillary column (25 to 75 microns i.d.) that is filled with a solution containing micelles. The mobile phase in this work consists of sodium dodecyl sulfate in an aqueous phosphate/borate buffer system. Pyridoxine (vitamin B6) and five of its metabolites are separated, with efficiencies as high as 60,000 theoretical plates/meter. Pyridoxic acid, a metabolite of B6, is separated and quantitated in human urine using laser-excited fluorescence detection. Limits of detection are less than a picogram injected.     

Determination of triazine compounds in ground water samples by micellar electrokinetic capillary chromatography

In this work, a capillary electrophoresis (CE) method for the determination of a group of eleven triazine compounds by micellar electrokinetic capillary chromatography (MEKC) with diode array detection was developed. The eleven herbicides studied were: desethylatrazin-2-hydroxy (DEA), simazine, prometon, atrazine, simetryn, ametryn, propazine, prometryn, trietazine, terbutylazine, and terbutryn The separation of these compounds was optimised as a function of buffer concentration and pH, concentration of sodium dodecyl sulphate (SDS) and voltage applied. To increase the selectivity of the separation and the resolution of the solutes, different organic solvents were tested as buffer additives, obtaining the best results when 1-propanol was used. The optimised buffer (24 mM of sodium borate, 18 mM of disodium hydrogen phosphate, 25 mM of SDS, pH 9.5, and 5% of 1-propanol) provides the best separation in terms of resolution and migration time. This method allowed the determination of these compounds at concentrations of 0.05 μg l⁻¹ in ground water samples pretreated using solid-phase extraction (SPE).