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.     

Quantitative determination of UV filters in sunscreen lotions using microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) has been applied to the separation of some UV filters (Eusolex 4360, Eusolex 6300, Eusolex OCR, Eusolex 2292, Eusolex 6007, Eusolex 9020, Eusolex HMS, Eusolex OS, and Eusolex 232) commonly used in sunscreen lotions. Use of a MEEKC buffer with a mixed surfactant system to stabilize the oil droplets and an organic modifier in the aqueous phase allowed separation of most of the selected analytes in a single run in a system fitted with a diode array detector recording three wavelengths (240 nm, 300 nm, and 380 nm) simultaneously. The microemulsion employed consisted of 2.25 g of SDS, 0.75 g of Brij 35, 6.6 g 1‐butanol, 0.8 g n‐octane, 17.5 g 2‐propanol, and 72.1 g of 10 mM borate buffer (pH 9.2). Detection limits from 0.65 to 6.0 μg/mL were obtained and the calibration plots were linear over at least one order of magnitude for all analytes. The developed method could be applied to the determination of UV filters in several sun protection products including lotions, milks, and oils. Comparison of the obtained data with those from an HPLC method described in the literature showed acceptable agreement.     

混合胶束电动毛细管色谱法分离测定妈富隆片剂中的炔雌醇含量

胆汁酸钠（SC）－十二烷基硫酸钠（SDS）混合胶束电动毛细管色谱法分离测定妈富隆片剂中的炔雌醇，分离缓冲液为SC（55mmol/L)-SDS(15mmol/L)-Tris磷酸（50mmol/L)(pH8.05),分离电压20kV，温度20℃,75μm（i.d)*57.5酮为内标，炔雌醇质量浓度在75．15－901．8μg/mL之间呈良好的线性关系，加样回收率96．4％－104．5％，RSD为3．6％－4．9％（n=3),可用于复方制剂中炔雌醇的含量测定。     

Enantioseparation of esbiothrin by cyclodextrin‐modified microemulsion and micellar electrokinetic chromatography

A comparison between chiral cyclodextrin‐modified microemulsion electrokinetic chromatography (CD‐MEEKC) and cyclodextrin‐modified micellar electrokinetic chromatography (CD‐MEKC) for the enantiomeric separation of esbiothrin was carried out. For both methods, the separation conditions were optimized by varying CD types and concentration, running buffer pH and compositions, organic modifiers, and temperature. The optimal CD‐MEEKC conditions were 0.8% n‐heptane, 2.3% SDS, 6.6% n‐butanol, 90.3% 10 mM sodium tetraborate containing 3% (w/v, the ratio of CD mass to microemulsion volume) methyl‐β‐cyclodextrin, pH 10, 25°C. The optimized CD‐MEKC conditions were 3.3% SDS, 96.7% 10 mM sodium tetraborate containing 5% (w/v) β‐CD, pH 10, 25°C. The difference in physicochemical properties of the buffer and CDs resulted in different optimal CD type. The competitive distribution between the microemulsion (or micelle) and chiral CD contributed to the chiral separation. Both methods provided excellent separation (R_s ～? 3) with similar migration time (ca. 15 min). CD‐MEEKC provided higher separation efficiencies (>300000) than CD‐MEKC (>200000). The LODs for CD‐MEEKC and CD‐MEKC were 4.7 μg/mL and 3.2 μg/mL, respectively. The RSDs of migration time and peak area for CD‐MEEKC were slightly higher than for CD‐MEKC. Both the demonstrated CD‐MEEKC and CD‐MEKC methods provided high efficiencies, low LODs, and reproducible enantioseparations of esbiothrin.     

Simultaneous determination of catecholamines and amino acids by micellar electrokinetic chromatography with laser-induced fluorescence detection

A selective and sensitive method was developed for separation and simultaneous determination of catecholamines and amino acids by MEKC with LIF. Interestingly enough, such work has been firstly performed on catecholamines derivatized with 4-chloro-7-nitro-2,1,3-benzoxadiazole and the detailed derivatization mechanism was discussed. After derivatization at 60 degrees C for 20 min, NBD-labeled catecholamines and amino acids were separated in a buffer system containing 10 mM sodium tetraborate-Na2HPO4, 20 mM SDS, and 10% v/v ACN at pH 9.75. SDS micelles were employed to improve the fluorescence intensity of catecholamine derivatives efficiently. Under optimum conditions, two catecholamines and 11 amino acids were separated in a short 13 min analysis time and the RSDs for migration time and peak area were less than 0.60 and 6.50%, respectively. The method was successfully applied for the quantification of catecholamines and amino acids in Portulaca oleracea L., human urine sample, and mixed injection sample.     

Validation of a micellar electrokinetic capillary chromatography method for the determination of imidurea, methyl and propylparabens in a pharmaceutical ointment

The quantitative aspects of a micellar electrokinetic chromatographic (MEKC) method for the determination of three preservatives (imidazolidinyl urea, methyl and propylparabens) in a pharmaceutical ointment are presented. Separation was carried out in a 31.2 cm long (21 cm to the detection window) × 50 μm i.d. fused silica capillary at an electric field of 960 V/cm and 25 °C. The electrolyte was 10 mM sodium dihydrogenophosphate containing 40 mM sodium dodecylsulfate (SDS) and adjusted to pH 6.1. Sample preparation consisted of a simple dispersion of the ointment in an internal standard solution (ethylparaben in the electrolyte). A 3.5 nl volume of the sample solution was introduced hydrodynamically into the capillary. The compounds detected at 200 nm were separated within 1.6 min. The method was validated with respect to specificity, linearity, accuracy, repeatability according to the International Conference on Harmonisation guidelines. Calibration curves were found to be linear for each compound (r²>0.999). Recovery studies performed by spiking an ointment placebo with the preservatives between 50 and 150% of their target concentration on 3 different days gave satisfactory results (mean recovery at each of the five concentrations ranging from 99.23 to 101.40%). The repeatability of sample preparation (n=6) was better than 2% for each of the preservatives.     

胶束电动色谱法分离与测定己烯雌酚片剂中的有效成分

建立了一种用来分离测定己烯雌酚的胶束电动色谱法,。通过对十二烷基硫酸钠、胆酸钠、脱氧胆酸钠3种表面活性剂进行比较,选定以60mmol/LSDS 10mmol/L硼砂的水溶液作为背景电解质溶液,研究了不同pH对分离己烯雌酚的影响。该方法被应用于测定己烯雌酚片剂中有效成分的含量。     

Precision of micellar electrokinetic capillary chromatography in the determination of seven antibiotics in pharmaceuticals and feedstuffs

Validation of analytical procedures is important for their efficient and reliable application. The International Conference on Harmonisation (ICH), Food and Drug Administration (FDA) and pharmacopoeia guidelines achieved a great deal in harmonising the definitions of the required validation characteristics. It is well known that poor reproducibility limits the practical implementation of capillary electrophoresis (CE). A precision study on four different MEKC methods was performed with 11 samples, containing seven antibiotics, by two analysts, in few days, on two capillary electrophoresis instruments. Five pharmaceutical preparations and three animal feeds were used. Precision was statistically analysed using migration time, peak area and height of each compound, as well as electroosmotic front (EOF). In 25 of 31 cases, the reproducibility of peak area, peak height and migration time was good (<5%). In most cases the reproducibility of peak area was much better than the reproducibility of peak height. The worst reproducibility that we observed was 12.7% for peak height and 7.6% for peak area.     

Sensitive determination of pyrrolizidine alkaloids in Tussilago farfara L. by field‐amplified,sample‐stacking,sweeping micellar electrokinetic chromatography

Pyrrolizidine alkaloids are the toxic components in Tussilago farfara L. Due to the lack of standard substances for quantitative analysis and traces of pyrrolizidine alkaloids in total alkaloids, the full quality control of Tussilago farfara L has been limited. In this study, we aimed to solve the difficulty of determination of pyrrolizidine alkaloids and identify more components in the total alkaloids. An on‐line preconcentration method has been applied to improve determining sensitivity of pyrrolizidine alkaloids in Tussilago farfara L. in which included field‐amplified sample stacking and sweeping in micellar electrokinetic capillary chromatography. The main parameters that affected separation and stacking efficiency were investigated in details. Under the optimal conditions, the sensitivity enhancement factors obtained by the developed method for the analytes were from 15‐ to 12‐fold, the limits of detection of senkirkine and senecionine were 2～5 μg/L. Senkirkine and senecionine have been detected in alkaloids ( c ) of Tussilago farfara L, along ferulic acid methyl ester and methyl caffeate. The developed method was also applied to the analysis of acid extraction ( a ) of Tussilago farfara L, and senkirkine could be detected directly. The results indicated that the developed method is feasible for the analysis of pyrrolizidine alkaloids in Tussilago farfara L with good recoveries.     

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.     

Simultaneous separation of nitrofuran antibiotics and their metabolites by using micellar electrokinetic capillary chromatography

Mixtures comprising nitrofuran antibiotics (NFA) and nitrofuran metabolites (NFM) were resolved for the first time by using MEKC. Sodium deoxycholate (SDC) was chosen as the micelle-forming surfactant. Optimization of separation conditions was achieved by using a central composite experimental design (CCD) approach. Experimental parameters such as concentration ratio of borate to phosphate in the buffer, pH of the running electrolyte and voltage were investigated. The effect of concentration of the surfactant on resolution was significant. Under optimal conditions of 80 mM SDC, pH 9.0, (20 mM borate + 20 mM phosphate) and 16 kV, the resolution between eight consecutive peak pairs ranged from 1.9 to 11.8. Due to the absence of a UV-active chromophore in the metabolites, they were derivatized with 2-nitrobenzaldehyde (2-NBA). In order to mimic a proposed extraction procedure for the analysis of both NFA and/or derivatized NFM in a sample, aqueous samples (prederivatized with 2-NBA) were extracted by using C(18) SPE cartridges. After washing with H(2)O, the cartridges were eluted with a small portion of organic solvent with weak elution characteristics to remove excess 2-NBA (hexane was chosen). Target analytes were then recovered with ACN. Excellent reproducibility of migration time (t(mig)) was achieved for all analytes using the developed MECC approach, with absolute t(mig) <1% RSD and t(mig) ratio <0.2% RSD, and peak area ratio was 4% RSD. The LOD for each compound, calculated by extrapolating to an S/N of 3, were found to be 0.19-2.0 microg/mL.     

Separation and determination of epinephrine and dopamine in traditional Chinese medicines by micellar electrokinetic capillary chromatography with laser induced fluorescence detection

A micellar electrokinetic capillary chromatography method with laser-induced fluorescence detection was developed for the analysis of epinephrine and dopamine after derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole. The optimum derivatization conditions were: 30 mM sodium borate (pH adjusted to 8.0 with 1.0 M HCl), reaction time 30 min at 60 degrees C. Baseline separation was achieved within 14 min with a running buffer composed of 10 mM sodium borate + 25 mM sodium dodecyl sulfate (pH adjusted to 9.5 with 0.1 M NaOH) and an applied voltage of 15 kV. Good linearity relationships (correlation coefficients: 0.9991 for epinephrine and 0.9985 for dopamine) between peak areas and concentrations of the analytes were obtained. The detection limits and quantification limits for epinephrine and dopamine were 0.0038 mg/L and 0.013 mg/L, and 0.065 mg/L and 0.020 mg/L, respectively. The method was applied to the analysis of the two compounds in two Chinese medicines with recoveries in the range of 92.6-108.7%.     

Development of a micellar electrokinetic capillary chromatography method for the determination of four naphthalenediols in cosmetics and a comparison with a HPLC method

A micellar electrokinetic capillary chromatography (MEKC) method with ultraviolet visible (UV) detection was used for the determination of 1,7-naphthalenediol, 2,3-naphthalenediol, 1,5-naphthalenediol, and 2,7-naphthalenediol in cosmetics. The current method for their determination in various cosmetics is high-performance liquid chromatography (HPLC). Separation conditions affecting the MEKC method were optimized as 20 mM Na₂B₄O₇–50mM SDS, pH 9.8, with 22 kV applied voltage and UV detection at 230 nm. Under optimal conditions, electrophoretic analysis was completed in less than 6 min, with limit of detection (LOD) of 0.070–0.19 μg/mL and limit of quantitation (LOQ) of 0.23–0.63 μg/mL. A good linear relationship (r² > 0.99) was obtained at the range of 0.75–20 μg/mL. Recoveries for the four naphthalenediols in lotion, loose powder, and sun cream are between 91.2–107.2% with relative standard deviation (RSD) less than 4.04%. The method has been successfully applied to the determination of the four naphthalenediols in different kinds of cosmetics. A comparison with HPLC-UV method was also carried out according to the National Standards of the People's Republic of China. The results obtained by MEKC and HPLC methods are comparable, but the proposed MEKC method can help us obtain a much shorter detection time and low cost.     

Concentration and determination of cotinine in serum by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

Micellar electrokinetic chromatography (MEKC), combined with on-line concentration techniques, cation-selective exhaustive injection (CSEI) and sweeping, was developed for the analysis of cotinine, the primary biomarker for exposure to secondhand smoke. Experimental parameters including sample matrix, surfactant concentration, injection length and concentration of high-conductivity buffer, and sample electrokinetic injection time were optimized for electrophoretic enrichment and separation processes. Under the optimal conditions, the detection sensitivity of cotinine was enhanced by about 5000-fold using CSEI-sweeping MEKC compared to normal MEKC. The limit of detection for cotinine was found to be 0.2 ng/mL using ultraviolet absorbance detection. Furthermore, the developed method was successfully applied to the detection of cotinine in mouse serum samples.     

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%.     

Development of an ultrasensitive stacking technique for 5‐nitroimidazole determination in untreated biological fluids by micellar electrokinetic chromatography

Cation‐selective exhaustive injection and sweeping followed by a MEKC separation is evaluated for the sensitive analysis of 5‐nitroimidazoles in untreated human serum and urine. Deproteinized serum and urine samples were diluted 76 and 143 times, respectively, in a low‐conductivity solvent (5.00 mM orthophosphoric acid containing 5.0% v/v methanol). Samples were electrokinetically injected at 9.8 kV for 632 s in a previously conditioned fused‐silica capillary (65.0 cm × 50 μm id). Separation was performed at –30 kV and 20°C using 44 mM phosphate buffer (pH 2.5), 123 mM SDS, and 8% v/v tetrahydrofurane as BGE. Signals were monitored at 276 nm and peak area was selected as analytical response. Good linearity (R² ≥ 0.988) and LODs lower than 1.5 and 1.8 μg/mL were achieved in serum and urine, respectively.     

Rapid determination of aniline metabolites of chlorpropham in potatoes by micellar electrokinetic chromatography using negative-charged mixed micelles and laser-induced fluorescence detection

A rapid, reliable method has been developed for the multi-residue analysis of aniline metabolites of chlorpropham in potato samples. The method involves the precolumn derivatization of aniline metabolites with 5-(4,6-dichloro-s-triazin-2-ylamino) fluorescein (DTAF) and their subsequent separation and determination by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection (MEKC-LIF). The optimum procedure includes a derivatization step of the aniline metabolites (3-chloroaniline, 3-chloro-4-hydroxyaniline and 3-chloro-4-methoxyaniline) at 40 degrees C for 40 min and a 5-fold dilution prior to MEKC analysis, which is conducted within about 7 min using negative-charged mixed micelles (SDS/Triton X-100) in the running buffer. Under these conditions, the DTAF-anilines were readily detected at 0.3-3.1 microg/L level with a precision of 4.8-6.4%. These results indicate that negative-charged mixed surfactant MEKC-LIF is useful as a selective, rapid, and sensitive tool for the determination of these anilines and surpasses other electrophoretic alternatives based on the use of fluorescein-isothiocyanate (FITC) as label reagent. Finally, the potato matrix showed no significant effects on the derivatization and determination of these analytes, since the analytical figures of merit for the real samples were similar to those obtained in aqueous solutions, and the average recovery at fortification levels of 10-250 microg/kg was over 97%.     

Characterization of poly(4-vinylpyridine 1-oxide) by free-solution capillary electrophoresis and micellar electrokinetic chromatography

The migration characteristics of poly(4-vinylpyridine 1-oxide) (PVP-NO) in phosphate buffers of acidic pH (20 mM H3PO4 or NaH2PO4) have been studied using both free-solution capillary electrophoresis (FSCE) and MEKC. To inhibit adsorption, 250 mM o-phosphoethanolamine (2-aminoethyl dihydrogen phosphate) was used. In FSCE, PVP-NO showed a narrow peak and a broader band, both having anionic behavior. These peak and band were attributed to the free and aggregated or micellized PVP-NO forms, respectively. According to surface tension measurements, the CMC of SDS in the BGE was 1.8 and 0.48 mM in the absence and in the presence of 1000 microg/mL PVP-NO, respectively, and the association of the polymer with SDS was completed at 9.7 mM SDS. Using MEKC, a narrow peak and a broader band also appeared at SDS concentrations of ca. 1 mM, and their intensity increased with the SDS concentration. These peak and band were attributed to the formation of mixed micelles constituted by both free PVP-NO/SDS and aggregated PVP-NO/SDS, respectively. The determination of PVP-NO by FSCE in commercial additives for laundry was demonstrated.     

Determination of neonicotinoid insecticides in environmental samples by micellar electrokinetic chromatography using solid‐phase treatments

A sensitive and reliable method based on MEKC has been developed and validated for trace determination of neonicotinoid insecticides (thiamethoxam, acetamiprid, and imidacloprid) and the metabolite 6‐chloronicotinic acid in water and soil matrices. Optimum separation of the neonicotinoid insecticides was obtained on a 58 cm long capillary (75 μm id) using as the running electrolyte 40 mM SDS, 5 mM borate (pH 10.4), and 5% (v/v) methanol at a temperature of 25°C, a voltage of 25 kV and with hydrodynamic injection (10 s). The analysis time was less than 7 min. Prior to MEKC determination, the samples were purified and enriched by carrying out extraction‐preconcentration steps. For aqueous samples, off‐line SPE with a sorptive material such as Strata‐X (polymeric hydrophobic sorbent) and octadecylsilane (C₁₈) was carried out to clean up and preconcentrate the insecticides. However, for soil samples, matrix solid‐phase dispersion (MSPD) was applied with C₁₈ used as the dispersant. Good linearity, accuracy, and precision were obtained and the detection limits were in the range between 0.01 and 0.07 μg mL^?1 for river water and 0.17 and 0.37 μg g^?1 for soil samples. Recovery levels reached greater than 92% for all of the assayed neonicotinoids in river water samples with Strata‐X. In soil matrices, the best recoveries (63–99%) were obtained with MSPD.