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.     

Simultaneous determination of antioxidants, preservatives and sweeteners permitted as additives in food by mixed micellar electrokinetic chromatography.

A micellar electrokinetic chromatography method was developed to simultaneously analyse commonly used food additives. The additive mixture, comprising propyl gallate, octyl gallate, dodecyl gallate, butylated hydroxyanisole, butylated hydroxytoluene, tertiary butylhydroquinone, p-hydroxybenzoic acid methyl ester, p-hydroxybenzoic acid ethyl ester, benzoic acid, sorbic acid, saccharin, aspartame and acesulfame-K, was not resolved using single surfactant micellar systems consisting of sodium dodecyl sulfate (SDS), sodium cholate (SC) or sodium deoxycholate (SDC). The separation of these additives using mixed micellar systems, involving SDS/SC, SDS/SDC and SC/SDC, was investigated. Organic solvents were added to the mixed micellar phases to optimise the separation. The mixture was successfully separated using a 20 mM borate buffer with 35 mM SC, 15 mM SDS and 10% methanol added at pH 9.3. Additives in cola beverages and low-joule jam were investigated and quantified using this method.     

Simultaneous determination of preservatives,sweeteners and antioxidants in foods by paired-ion liquid chromatography

Summary A paired-ion, reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of sweeteners (dulcin, saccharin-Na and acesulfame-K), preservatives (sodium dehydroacetate, sorbic acid, salicyclic acid, benzoic acid, succinic acid, methyl-para-hydroxybenzoic acid, ethyl-para-hydroxybenzoic acid, n-propyl-para-hydroxybenzoic acid, isopropyl-para-hydroxybenzoic acid, n-butyl-para-hydroxybenzoic acid, and isobutyl-para-hydroxybenzoic acid), and antioxidants (3-tertiary-butyl-4-hydroxyanisole and tertiary-butyl-hydroquinone). A mobile phase of acetonitrile-50 mM aqueous α-hydroxyisobutyric acid solution (pH 4.5) (2.2 : 3.4 or 2.4 : 3.6, v/v) containing 2.5 mM hexadecyltrimethylammonium bromide and a C₁₈ column with a flow rate at 1.0 mL/min and detection at 233 nm were used. This method was found to be very reproducible with detection limits ranged from 0.15 to 3.00 μg. The retention factor (k) of each additive could be affected by concentrations of hexadecyltrimethylammonium bromide and α-hydroxyisobutyric acid, and pH and ratio of mobile phase. The presence of additives in some food samples was determined.     

Quantitative determination of glucoraphanin in Brassica vegetables by micellar electrokinetic capillary chromatography

Glucoraphanin, a glucosinolate, is found naturally in plants and is present in relatively high concentrations in broccoli. Glucosinolates have received much attention as studies have indicated that a diet rich in them may provide some protection from certain cancers. A micellar electrokinetic chromatography (MEKC) method using sodium cholate as the micellar phase has been developed to quantify for glucoraphanin in broccoli (seeds and florets) and Brussels sprouts. The glucoraphanin peak elutes just under 5 min with a theoretical plate number of 380,000 per metre of capillary. The method is suitable for crude extracts of broccoli and Brussels sprouts. Glucoraphanin in broccoli seeds (1330 mg/100 g) broccoli florets (89 mg/100 g) and Brussels sprouts (3 mg/100 g) was determined and agreed with the data obtained by high performance liquid chromatography. The LODs were 10-100 times below the levels typically found in broccoli seeds (4 mg/100 g), broccoli florets (0.9 mg/100 g) and Brussels sprouts (0.1 mg/100 g).     

Specific determination of cysteine in human urine by capillary micellar electrokinetic chromatography

This paper describes a method for the analysis of cysteine in human urine using capillary micellar electrokinetic chromatography and on‐column reaction with 2,2′‐dipyridyl disulfide. In this reaction cysteine is quantitatively transformed into a mixed disulfide concomitantly with formation of an equimolar amount of 2‐thiopyridone that is further separated by capillary micellar electrokinetic chromatography and determined spectrophotometrically at 343 nm. The concentration of cysteine is thus estimated indirectly from the result of 2‐thiopyridone determination. The linear detection range for concentration versus peak area for the assay is from 0.05 to 5 mM (correlation coefficient 0.989) with a detection limit of 2.5 μM and a limit of quantitation of 8.5 μM. The inter‐day reproducibility of the peak area was 2.18% and the inter‐day reproducibility of the migration time 0.51%. The method is relatively rapid, simple, and can be easily automated. Moreover, its detection limit covers the concentration range at which cysteine is present in biological samples such as human urine.     

Simultaneous determination of preservatives,sweeteners and antioxidants in foods by paired-ion liquid chromatography

Summary A paired-ion, reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of sweeteners (dulcin, saccharin-Na and acesulfame-K), preservatives (sodium dehydroacetate, sorbic acid, salicyclic acid, benzoic acid, succinic acid, methyl-para-hydroxybenzoic acid, ethylpara-hydroxybenzoic acid, n-propyl-para-hydroxybenzoic acid, isopropyl-para-hydroxybenzoic acid, n-butyl-para-hydroxybenzoic acid, and isobutyl-para-hydroxybenzoic acid), and antioxidants (3-tertiary-butyl-4-hydroxyanisole and tertiary-butyl-hydroquinone). A mobile phase of acetonitrile-50 mM aqueous -hydroxy-isobutyric acid solution (pH 4.5) (2.2 3.4 or 2.4 3.6, v/v) containing 2.5 mM hexadecyltrimethylammonium bromide and a C₁₈ column with a flow rate at 1.0 mL/min and detection at 233 nm were used. This method was found to be very reproducible with detection limits ranged from 0.15 to 3.00 g. The retention factor (k) of each additive could be affected by concentrations of hexadecyltrimethylammonium bromide and -hydroxyisobutyric acid, and pH and ratio of mobile phase. The presence of additives in some food samples was determined.     

毛细管胶束电动色谱法分离测定中药半枝莲中的7种有效成分

建立了毛细管胶束电动色谱同时分析检测中药半枝莲药材及其膏剂中黄芩素、柚皮素、汉黄芩素、野黄芩苷、芹菜素、木犀草素和原儿茶酸7种有效成分的方法。半枝莲样品中7种有效成分经甲醇超声提取。实验考察了运行缓冲溶液的pH值和浓度、添加剂、检测波长、分离电压和进样时间等重要参数对目标物分离的影响。得到的优化条件为: 运行缓冲液50 mmol/L硼砂-0.20 mol/L硼酸溶液(pH 8.4),含8.5 mmol/L十二烷基硫酸钠(SDS),分离电压25 kV,检测波长260 nm和335 nm。在此条件下,7种组分于12 min内达到基线分离。各组分在8×10~6～3.2×10~4mol/L范围内呈良好的线性关系,相关系数(r2)为0.9965～0.9999;检出限为7.0×10~8～2.0×10~6mol/L;回收率均大于85%。该方法提取简便、准确可靠、重复性好、灵敏度高,可以用于中药半枝莲中7种有效成分的定量检测。     

Extraction of iridoid glycosides and their determination by micellar electrokinetic capillary chromatography

Several methods for the extraction of two iridoid glycosides, catalpol and aucubin, from the plant matrix (Veronica longifolia leaves) were compared. Pressurized hot water extraction and hot water extraction were the most efficient isolation techniques for both. Pressurized liquid extraction and maceration with various organic solvents were also tested. Relative to the amounts extracted with hot water, ethanol extracted only 22% of catalpol and 25% of aucubin and pressurized hot water extracted 83% of catalpol and 92% of aucubin. The lowest relative standard deviations, 22% for catalpol and 8% for aucubin, were achieved with hot water extraction (13 repetitions), and the highest relative standard deviations, 76% for catalpol and 73% for aucubin, with pressurized liquid extraction (five repetitions). A fast capillary electrophoretic method was developed for the quantitative determination of catalpol and aucubin.     

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.     

Simultaneous UV and electrochemical determination of the herbicide asulam in tap water samples by micellar electrokinetic capillary chromatography

A simple end-column electrochemical detector was designed and attached to an available commercial capillary electrophoresis instrument with UV detection to detect different kind of herbicides and to determinate methyl-4-aminophenyl-sulfonylcarbamate (asulam) in water samples. The designed cell is very easy to assemble and disassemble in a short period of time; the working electrode positioning is also quickly achieved without micropositioners. The alignment between working electrode and capillary outlet was very reproducible for the all checked electrodes; the R.S.D. obtained was lower than 6.0% for 100 μm gap distance. In this mode, the non-electroactive and electroactive compounds could be detected by UV and electrochemical detection, respectively at the same time. The electrochemical determination of asulam using micellar electrokinetic capillary chromatography (MEKC) is the first time that is reported. In both detection systems, a linear range was obtained for asulam concentrations lower than 25.0 mg l⁻¹, in boric acid 0.020 mol l⁻¹ at pH 8.20 and containing 0.025 mol l⁻¹ of sodium dodecyl sulfate, to obtain selectivity additional separation by the micellar distribution process. Under these conditions, an experimental detection limit of 0.4 mg l⁻¹ was achieved. A new experimental scheme is also described for asulam determination in tap waters with a previous preconcentration step. Using both, UV and electrochemical detection, with a previous extraction procedure, the detection limits of asulam in tap water samples were of 1.0 and 0.8 μg l⁻¹, respectively.     

Simultaneous and rapid determination of main lignans in different parts of Schisandra sphenanthera by micellar electrokinetic capillary chromatography

Lignans are imporant active ingredients of Schisandra sphenanthera. A micellar electrokinetic chromatography method was developed for the simultaneous determination of eight lignans--schizandrin, schisandrol B, schisantherin A, schisanhenol, anwulignan, deoxyschizandrin, schizandrin B and schizandrin C--in different parts of S. sphenanthera. The key factors for separation and determination were studied and the best analysis conditions were obtained using a background electrolyte of 10 mM phosphate-37.5 mM SDS-35% v/v acetonitrile (pH 8.0) at the separation voltage of 28 kV and detection at 214 nm, whereby the plant samples could be analyzed within 9.0 min. Analysis yielded good reproducibility (RSD between 1.19-2.28%) and good recovery (between 92.2-103.8%). The detection limits (LOD) and limit of quantification (LOQ) were within 0.4-1.2 mg/L and 1.5-4.0 mg/L. This method is promising to improve the quality control of different parts of S. sphenanthera.     

Separation and determination of isoflavones in red clover by micellar electrokinetic capillary chromatography

A micellar electrokinetic capillary chromatography (MECC) method has been developed for the determination of the four isoflavones, i.e. biochanin A, formononetin, genstein and daidzein in red clover (Trifolium Pratense L.). The effect of running buffer pH and concentration were investigated. An electrolyte composed of 30 mm borate, 20 mm sodium dodecyl sulfate (SDS) and 4 mg/mL HP-beta-CD containing 5% (v/v) ethanol at pH 10.1 provides a satisfactory separation for all the analytes. The applied voltage was 25 kV, and the capillary temperature was kept constant at 25 degrees C with a UV detection at 254 nm. The relative standard deviations (RSD) of the migration time and peak area were less than 1.73 and 3.94% (intra-day), and 2.29 and 4.38% (inter-day), respectively, under the optimized separation conditions. Regression equations revealed a good linear relationship between the peak area of each compound and its concentration. The contents of the four compounds in red clover were successfully determined with satisfactory repeatability and recovery.     

Separation and determination of acrylamide in potato chips by micellar electrokinetic capillary chromatography

A simple and rapid method using micellar electrokinetic capillary chromatography (MEKC) was developed for the separation and determination of acrylamide in potato chips at low levels for the first time. The experimental conditions for the separation and quantification of acrylamide were optimized at first. The optimized conditions were: 50 mmol/L Na₂B₄O₇ and 40 mmol/L SDS at pH 10.0, 12 kV applied voltage, 76 cm total length (67 cm effective length) and 75 μm i.d. capillary, 198 nm wavelength, 15 cm high 25 s hydrodynamics sample injection, 20 °C air-cooling. The linear response of acrylamide concentration ranges from 0.5 to 100 μg/mL with high correlation coefficient (r = 0.9986, n = 9). The LOD and LOQ were estimated to be 0.1 and 0.33 μg/mL based on S/N = 3 and 10. The precision values (expressed as R.S.D.) of intra- and inter-day were 0.86-4.35% and 2.61-9.65%, respectively. Recoveries spiked at levels 2, 20, 60 μg/mL ranged between 90.86% and 99.6% with R.S.D. less than 6.5%. Finally, the developed method has been applied to the analysis of real samples and has achieved satisfactory results. All of these indicated that it was a reliable method for the quantification of acrylamide in potato chips.     

Separation and determination of aminophenols and phenylenediamines by liquid chromatography and micellar electrokinetic capillary chromatography

The separation and determination of aminophenols and phenylenediamines were investigated by liquid chromatography (LC) and micellar electrokinetic chromatography (MEKC) in this study. Aminophenols and phenylenediamines are commonly used components in commercial hair colorants. The problem of tailing peaks in LC was improved by the technique of using mobile phase containing 15 mM triethylamine at pH 8.0. The analysis of o-aminophenol was not succeeded with LC even though the modifier of triethylamine was added. But it could be quantitative successfully by MEKC. The optimum separation condition of MEKC was achieved by employing 55 mM cetyltrimethyl ammonium chloride in 50 mM borate buffer (pH 9.2) with electric field strength of −145 V cm⁻¹. Finally, the commercial hair dyes were analyzed by developing methods of LC and MEKC. From both the results, there is no significant difference presence at 99.5% confidence level. These two methods could give the complementary results.     

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.     

Separation of preservatives in cosmetic products by micellar electrokinetic chromatography.

This paper describes the methodological optimization and validation of a simple micellar electrokinetic chromatography for the rapid simultaneous separation of 2-methyl-4-isothiazolin-3-one, methylparaben, ethylparaben, propylparaben, and butylparaben. By using a 30 mM phosphate buffer (pH 7.2) containing 30 mM sodium dodecyl sulfate (SDS), an applied voltage of 10 kV and a separation temperature of 40 degrees C, a quantitative determination was achieved, resulting in an analysis time of approximately 4 min. Only dilution and filtration are needed before analysis. The parameters for validation, such as linear ranges, detection limits, accuracy, and precision, are also reported.     

Simultaneous determination of nine acetylcholinesterase inhibitors using micellar electrokinetic chromatography

MEKC was used for the separation of nine acetylcholinesterase inhibitors (AChEIs). AChEIs are an important group of drug compounds that are used medicinally to treat Alzheimer's disease and Myasthenia Gravis. At the time of the experiment, this is the first time that nine AChEIs are used simultaneously in a study. Several chromatographic parameters, such as buffer concentration, pH, surfactants and their concentration, background electrolyte composition, etc., were evaluated to optimize the separation. The optimum separation of the nine AChEIs was achieved in less than 15 min by using 12.5 mM Na(2)HPO(4), 12.5 mM Na(2)B(4)O(7) and 20 mM SDS at pH 10, an applied voltage of 30 kV and a temperature of 25 °C. The reproducibility of the method was also evaluated by computing the RSDs of the migration times and the areas of the nine analyte-peaks, and the migration time and the area of the peak that corresponds to rivastigmine added in the blood sample. The RSD values of the migration times and the peak areas were less than 2% and 6%, respectively, in most cases. The limits of detection and quantification were 0.5 μg/mL and 1.7 μg/mL, respectively. The MEKC method developed was applied to a real blood sample that was obtained from a patient who was not under any of this medication. The sample was spiked with rivastigmine in order to establish the ability of the method to separate the drug from other components that might exist in the blood sample.     

Identification and determination of active anthraquinones in Chinese teas by micellar electrokinetic capillary chromatography

The simultaneous determination of emodin, aloe-emodin and rhein, in Semen Cassiae, Qinghai Wild Dahuang tea, Ningxia Juemingzi tea, Lanzhou Juemingzi tea and Surong Juemingzi tea, has been investigated by micellar electrokinetic capillary chromatography for the fi rst time. With an electrolyte containing 15 mm borax, 30 mm SDS, 10% (v/v) ethanol, at pH 9.60 and 20 kV applied voltage, the three analytes were completely separated within 12 min. The effects of the concentration of borax, electrolyte pH, the concentrations of SDS and organic modifier and the applied voltage on electropheoretic behavior and separation were studied. The linear calibration range was 4-120 micro g/mL (r = 0.9921) for emodin, 10-200 micro g/mL (r = 0.9970) for aloe-emodin and 2-100 micro g/mL (r = 0.9971) for rhein, respectively. Under the optimum conditions, the relative standard deviation (RSD) values (n = 6) of the migration time and the peak area of each peak was 0.59-0.80% and 1.30-3.22%, respectively. The contents of the analytes in Rheum, Qinghai Wild Dahuang tea, Semen Cassiae and three other kinds of teas were easily determined with recoveries ranging from 95.3 to 104.4%.     

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.