Analysis of ephedra-alkaloids using sweeping and cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography methods

Two stacking methods of capillary electrophoresis (CE) were developed for the separation of very dilute solutions of ephedra-alkaloids, namely ephedrine, pseudoephedrine, methylephedrine, methylpseudoephedrine, norephedrine, and norpseudoephedrine. A sweeping method which uses a carrier comprised of phosphoric acid, sodium dodecyl sulfate (SDS), diethylamine and acetonitrile permits the detection of the alkaloids down to the 10(-1) microg/mL level, and the cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-Sweep-MEKC) method using phosphoric acid, SDS, and acetronitrile as electrolytes can detect down to the 10(-3) microg/mL level. The former requires the conductance of the sample solution to be adjusted beforehand, and only five peaks were observed, two of which were overlapped. The latter is capable of separating the six alkaloids but has a somewhat poorer reproducibility. Using an optimized injection time, it was found that the more diluted a solution is, the greater the sweeping effect will be. The CSEI-Sweep-MEKC method with a 600 s injection time and a 10(-1) microg/mL solution concentration provides an amplification effect of approximately 10(4). The method is suitable for analyses of dilute herb drug extracts and mouse sera. The effect of buffers on the separation and validation of the methods in this study are also discussed.     

Using cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography to determine selective serotonin reuptake inhibitors

We have employed a rapid and highly efficient on-line preconcentration method, cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-sweeping-MEKC), for the analysis of selective serotonin reuptake inhibitors (SSRIs) of antidepressant drugs. We monitored the effects of several of the CSEI-sweeping-MEKC parameters - including the pH, the concentrations of high-conductivity buffer (HCB), sodium dodecyl sulfate (SDS), and organic modifier, the injection length of the HCB, and the injection time of the sample - to optimize the separation process. The optimal background electrolyte was 50 mM citric acid/disodium hydrogenphosphate buffer (pH 2.2) containing 100 mM SDS and 22% isopropyl alcohol. The sensitivity enhancements of the SSRIs sertraline, fluoxetine, paroxetine, fluvoxamine, and citalopram ranged from 5.7 x 10(4) to 1.2 x 10(5); the coefficients of determination exceeded 0.9938 and the relative standard deviations of the peak heights were less than 3.2%; the detection limits ranged from 0.056 to 0.22 ng/mL. We employed the optimal conditions to analyze these five SSRIs in a plasma sample prepared using solid-phase extraction (SPE) to minimize the influence of the matrix. Although the limits of detection of the SSRIs in human plasma were higher than those in pure water, this present technique is more sensitive than other, more-conventional methods. The recovery of the SPE extraction efficiency was satisfactory (up to 89%). Our findings suggest that, under the optimal conditions, the CSEI-sweeping-MEKC method can be used successfully to determine these five SSRIs in human plasma.     

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.     

Determination of ephedrine and codeine in human urine by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

A sensitive method for the determination of ephedrine and codeine in human urine by capillary electrophoresis(CE)was described.In order to improve the sensitivity,two online concentration techniques including cation-selective exhaustive injection (CSEI)and sweeping micellar electrokinetic chromatography(sweeping-MEKC)were used.Under the optimum conditions,the detection limits(S/N=3)were 0.10μg/L for ephedrine and 0.80μg/L for codeine.This method was successfully applied to real urine sample analysis.     

Hair analysis for methamphetamine, ketamine, morphine and codeine by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

This article presents the state of the art of qualitative analysis in the framework of the chromatographic analysis. After establishing the differences between two main classes of qualitative analysis (analyte identification and sample classification/qualification) the particularities of instrumental qualitative analysis are commented on. Qualitative chromatographic analysis for sample classification/qualification through the so-called chromatographic fingerprint (for complex samples) or the volatiles profile (through the direct coupling headspace-mass spectrometry using the chromatograph as interface) is discussed. Next, more technical exposition of the qualitative chromatographic information is presented supported by a variety of representative examples.     

Analyses of tobacco alkaloids by cation-selective exhaustive injection sweeping microemulsion electrokinetic chromatography

In this study, an on-line concentration method which coupled cation-selective exhaustive injection (CSEI) sweeping technology with microemulsion electrokinetic chromatography (MEEKC) was used to detect and analyze several tobacco alkaloids (nornicotine, anabasine, anatabine, nicotine, myosmine and cotinine) that are commonly found in various tobacco products. First, the effects of microemulsion compositions (oil, cosurfactant and solution pH) were examined in order to optimize the alkaloid separations in conventional MEEKC. The pH value and the injection length of basic plug were found to be the predominant influences on the alkaloid stacking. This optimal CSEI sweeping MEEKC method provided approximately 180- to 540-fold increase in detection sensitivity in terms of peak height without any loss in separation efficiency when compared to normal MEEKC separation. Furthermore, this proposed CSEI sweeping MEEKC method was applied successfully for the detection of the minor alkaloids nornicotine, anabasine and anatabine in tobacco products.     

Systematic optimization of exhaustive electrokinetic injection combined with micellar sweeping in capillary electrophoresis

The combination of exhaustive electrokinetic injection and sweeping micellar electrokinetic chromatography (sweeping-MEKC) in capillary electrophoresis often provides a several thousand-fold improvement in concentration detection limit. However, reproducibility of this method has been a major issue that often prevents its use as a quantitative tool for the analysis of ultra-trace analytes in complex matrices. In this paper, we demonstrate that such a technique can be systematically optimized with five key factors: the conductivity of the sample solution, the conductivities of the separation buffers, the fraction of the capillary that is filled with the high conductivity buffer, the electrokinetic injection time, and the surfactant concentration. By controlling the sample conductivity, we were able to achieve highly reproducible results, while still maintaining the sensitivity of field-amplified sample injection. At optimal conditions, we were able to analyze three amine drugs (amphetamine, methamphetamine, and methylenedioxymethamphetamine) with limits of detection of 6 to 8 pg ml(-1) (ppt), which is a several thousand-fold improvement over normal sample injection using CE with a photodiode array detector.     

Cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography for analysis of morphine and its four metabolites in human urine

A cation-selective exhaustive injection and sweeping micellar EKC (CSEI-Sweep-MEKC) was established to analyze morphine and its four metabolites, including codeine, normorphine (NM), morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G). After SPE, the urine samples were analyzed by this CE method. The phosphate buffer (75 mM, pH 2.5) containing 30% methanol was first filled into an uncoated fused-silica capillary (40 cm, 50 microm id), then a high-conductivity buffer (120 mM phosphate, 10.3 kPa for 99.9 s) followed. The pretreated urine sample was loaded by electrokinetic injection (10 kV, 600 s). The stacking and separation were performed by using phosphate buffer (25 mM, pH 2.5) containing 22% methanol and 100 mM SDS at -20 kV, and detected at 200 nm. During method validation, calibration plots were linear (r > or = 0.998) over a range of 30-3000 ng/mL for morphine, NM, and codeine, 100-2000 ng/mL for M6G, and 80-3200 ng/mL for M3G. The LODs (S/N = 5, sampling 600 s at 10 kV) were 10 ng/mL for morphine, NM, and codeine, 35 ng/mL for M6G, and 25 ng/mL for M3G. This stacking CE method could increase 2500-fold sensitivity of codeine, when comparing with CZE. Five addicts' urine specimens were analyzed. Their results were compared with those of LC-MS-MS, and showed good coincidence. This method could be feasible for monitoring morphine and its metabolites in forensic interest and pharmacokinetic investigations.     

场放大进样-胶束扫集毛细管电脉法测定痕量泼尼松

建立了胶束毛细管电动色谱在线富集技术测定药品中痕量的泼尼松的方法。在胶束扫集的基础上联用场放大进样,使泼尼松的富集倍数提高了136倍;检出限由原来的2.7mg/L降至20μg/L。胶束扫集毛细管电泳缓冲体系为120mmol/LSDS、10mmol/LNaH2PO4(pH2.5)10%乙腈(V/V)。分离电压-20kV,进样电压-20kV,进样时间70s,进水时间180s,检测波长250nm。同时讨论了SDS浓度、样品基质pH、进样电压、进水时间和进样时间对分离效果的影响。实验结果显示:在优化实验条件下,样品的检测仅需8min,泼尼松在0.05～10mg/L的范围内线性关系良好(r=0.998)。回收率在89.4%～106%之间,相对标准偏差在2.1%～2.6%之间,可用于各种中药制剂中泼尼松的含量测定。     

Direct and sensitive analysis of methamphetamine, ketamine, morphine and codeine in human urine by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

Cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-Sweep-MEKC) was directly used to test some abuse drugs in human urine, including morphine (M), codeine (C), ketamine (K) and methamphetamine (MA). First, phosphate buffer (50 mM, pH 2.5) containing 30% methanol was filled into uncoated fused silica capillary (40 cm, 50 microm I.D.), then high conductivity buffer (100 mM phosphate, 6.9 kPa for 99.9 s) was followed. Electrokinetic injection (10 kV, 500 s) was used to load samples and to enhance sensitivity. The stacking step and separation were performed at -20 kV and 200 nm using phosphate buffer (25 mM, pH 2.5) containing 20% methanol and 100 mM sodium dodecyl sulfate. Using CSEI-Sweep-MEKC, the analytes could be simultaneously analyzed and have a detection limit down to ppb level. It was unnecessary to have sample pretreatments. During method validation, calibration plots were linear (r>or=0.9982) over a range of 150-3,000 ng/mL for M and C, 250-5,000 n g/mL for MA, and 50-1,000 ng/mL for K. The limits of detection were 15 ng/mL for M and C, and 5 ng/mL for MA and K (S/N=3, sampling 500 s at 10 kV). Comparing with capillary zone electrophoresis, the results indicated that this stacking method could increase 6,000-fold sensitivity for analysis of MA. Our method was applied for analysis of 28 real urine samples. The results showed good coincidence with immunoassay and GC-MS. This method was feasible for application to detect trace levels of abused drugs in forensic analysis.     

Analysis of estrogens in water by magnetic octadecylsilane particles extraction and sweeping micellar electrokinetic chromatography

A method based on magnetic separation was developed for the extraction of several estrogens (including diethylstilbestrol, estrone and estriol) in water followed by sweeping micellar electrokinetic chromatography (MEKC) analysis with UV detection. Novel magnetic octadecylsilane (ODS) particles were prepared using a silanization method with octadecyl trimethoxysilane as the surface modification reagent of magnetic Fe₃O₄ particles. Octadecyl trimethoxysilane was covalently immobilized on the magnetic iron oxide particles. The particles were used as the sorbents in the magnetic separation for the extraction of trace amounts of estrogens from water. The extraction condition and efficiency of the particles for the estrogens were investigated. Combining the magnetic ODS particles extraction and sweeping MEKC with UV detection, the estrogens at concentrations as low as ng/mL in water can be detected without interference from other substances in the sample matrix.     

Cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography for the analysis of methadone and its metabolites in serum of heroin addicts

Methadone (MET) metabolism has been largely demonstrated with a high inter-individual variability and, therefore, quantification of MET is very important for therapeutic drug monitoring. A cation-selective exhaustive injection and sweeping MEKC (CSEI-Sweeping) was first developed to analyze MET and its two metabolites, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) and 2-ethyl-5-methyl-3,3-diphenyl-1-pyrroline (EMDP), in human serum. After pretreatment, the samples were electrokinetically injected into capillary (10 kV, 500s) and swept by the separation phosphate buffer (100 mM, pH 4.0) containing 20% tetrahydrofuran and 100 mM SDS at -15 kV. The LODs were 200 pg/mL for MET and EMDP, and 400 pg/mL for EDDP. Ten volunteers were administered MET (5.0-120.0 mg/day) orally for 84 days and serum samples were taken after the daily dose of MET (days 1, 2, 7, 14, 28, 56 and 84) individually. This method was used for monitoring MET and its metabolites in heroin addicts and for pharmacokinetic investigations.     

结合阳离子选择性耗尽-扫集的微乳毛细管电泳法测定吴茱萸生物碱

本文建立了一种毛细管在线富集技术,通过将阳离子选择性耗尽(CSEI)-扫集(sweeping)技术与微乳毛细管电泳相结合,实现了吴茱萸中四种生物碱(1.吴茱萸碱;2.吴茱萸次碱;3.吴茱萸新碱;4.1-甲基-2-十一烷基-4(1H)-喹诺酮)的同时定量检测和分析。通过表面活性剂、有机改性剂、p H等条件的考察得到最佳微乳体系组成为:100 mmol·L-1SDS,1%(体积比)乙酸乙酯,15%(体积比)正丁醇,15%(体积比)乙腈,2.5%(体积比)甲酸,p H 2.00。通过基底缓冲p H和长度、水塞长度考察,CSEI-sweeping最佳富集条件为,水塞0.5psi水动引入2 s,p H 9.00基底缓冲0.5 psi水动引入90 s,+10 k V电动进样90 s。富集倍数达到了8~30倍。将此方法应用于实际样品中四种生物碱的定量,获得满意结果。研究结果表明,所建立CSEI-sweeping与MEEKC联用法能快速、准确地应用于吴茱萸四种生物碱的定量分析。     

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.     

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.     

Determination of brompheniramine enantiomers in rat plasma by cation‐selective exhaustive injection and sweeping cyclodextrin modified electrokinetic chromatography method

A method consisting of cation‐selective exhaustive injection and sweeping (CSEI‐sweeping) as online preconcentration followed by a cyclodextrin modified electrokinetic chromatography (CDEKC) enantioseparation has been developed for the simultaneous determination of two brompheniramine enantiomers in rat plasma. In this method, analytes were electrokinetically injected at a voltage of 8 kV for 80 s in a fused‐silica capillary. Prior to the injection, the capillary was rinsed with 50 mM phosphate buffer of pH 3.5, followed by a plug of a higher conductivity buffer (150 mM phosphate pH 3.5, 20 psi, 6 min) and a plug of water (0.5 psi, 5 s). Separation was carried out applying –20 kV in 50 mM phosphate buffer, pH 3.5, containing 10% v/v ACN and 30 mg/mL sulfated‐β‐cyclodextrin (S‐β‐CD). Analytical signals were monitored at 210 nm. The detection sensitivity of brompheniramine enantiomers was enhanced by about 2400‐fold compared to the normal injection mode (hydrodynamic injection for 3 s at 0.5 psi, with a BGE of 50 mM phosphate buffer containing 20 mg/mL S‐β‐CD at pH 3.5), and LLOQ of two enantiomers were both 0.0100 μg/mL. In addition, this method had fairly good repeatability and showed promising capabilities in the application of stereoselective pharmacokinetic investigations for brompheniramine enantiomers in rat.     

Simultaneous determination of the herbicides diquat and paraquat in water

A method based on solid-phase extraction (on silica cartridges) and high-performance liquid chromatography (HPLC) followed by diode array UV detection is presented as an analytical tool for screening diquat (DQ) and paraquat (PQ) in drinking waters. The method is useful for quality control laboratories of water companies and beverage industries. Absolute recoveries of DQ and PQ from drinking water (25 mL in all cases), spiked at levels between 0.1, 1.0, and 5.0 microg/L, range from 91% to 103%. Relative standard deviation percentages are between 3% and 11%. Quantitation and detection limits are 70 and 40 ng/L for DQ and 90 and 60 ng/L for PQ, respectively; therefore, these herbicides can be detected and quantitated at levels below the limits established by the European Union.     

The separation of herbicides by micellar electrokinetic capillary chromatography

Summary A method for the separation of a number of herbicides consisting of chlorophenoxy acids by micellar electrokinetic capillary chromatography (MECC) was developed. Sodium dodecyl sulphate (SDS), Brij 35, cetyltrimethylammonium bromide (CTAB) and methanol were introduced into the buffers to investigate their effects on the separation of the herbicides. SDS combined with Brij 35 as the micellar agent was found to provide the best overall separation of these components.     

Determination of some sulfonylurea herbicides in soil by a novel liquid-phase microextraction combined with sweeping micellar electrokinetic chromatography

A novel method for the determination of five sulfonylurea herbicides in soil was developed by a dispersive solid-phase extraction (DSPE) clean-up followed by dispersive liquid–liquid microextraction (DLLME), prior to sweeping micellar electrokinetic chromatography (MEKC). In the DSPE-DLLME, 10 g of soil sample was first extracted with 10 mL of acetonitrile containing 5% formic acid (pH 3.0). The extract was then cleaned-up by a DSPE with C₁₈ as sorbent. A 1 mL aliquot of the resulting extract was then added into a centrifuge tube containing 5 mL of water adjusted to pH 2.0 and 60.0 μL chlorobenzene (as extraction solvent) for DLLME procedure. Then, the organic sample extraction solution was evaporated to dryness, and reconstituted with 20.0 μL of 1.0 mmol L⁻¹ Na₂HPO₄ (pH 10.0) for sweeping-MEKC analysis after DLLME. Under optimized conditions, the method provided as high as 3,000- to 5,000-fold enrichments factors. The linearity of the method was in the range of 3.3–200 ng g⁻¹ for chlorimuron ethyl and bensulfuron methyl, and in the range of 1.7–200 ng g⁻¹ for tribenuron methyl, chlorsulfuron and metsulfuron methyl, with the correlation coefficients (r) ranging from 0.9965 to 0.9983, respectively. The limits of detection (LODs) ranged from 0.5 to 1.0 ng g⁻¹. The intraday relative standard deviations (RSDs, n = 5) were below 5.3% and interday RSDs (n = 15) within 6.8%. The recoveries of the method for the five sulfonylureas from soil samples at spiking levels of 5.0, 20.0, and 100.0 ng g⁻¹ were 76.0–93.5%, respectively. The developed method has been successfully applied to the analysis of the target sulfonylurea herbicide residues in soil samples with a satisfactory result.     

Analysis of proguanil and its metabolites by application of the sweeping technique in micellar electrokinetic chromatography

The method of applying large sample volumes in micellar electrokinetic chromatography termed sweeping is applied to determine the conservative limits of detection of some basic drugs in plasma and urine. The biguanides proguanil, 4-chlorophenylbiguanide and cycloguanil are used as models of basic drugs and the limits of detection obtained compared with those previously reported for capillary zone electrophoresis using field-amplified sample injection (FASI) and also by LC using off-line preconcentration. It is found that the sweeping method can be applied to extracts of such biological matrices. The limits of detection obtained by sweeping are improved over FASI for plasma but not for urine and the limits of detection are higher than those reported for LC, for these compounds.