Comparison of high-speed counter-current chromatography and high-performance liquid chromatography on fingerprinting of Chinese traditional medicine

Active constituents of Chinese traditional medicine (CTM) are influenced by soils, climates, and growth stages. Therefore, fingerprint is important in quality control of CTM. Our studies showed for the first time that high-speed counter-current chromatography (HSCCC) could be applied in the development of fingerprint of CTM. Twelve components were separated from extracts of three crude samples of Salvia miltiorrhiza Bunge, which were collected from different growth locations. All 12 components of each sample were isolated within 13 h coming with good correspondence by using HSCCC. Relative standard deviation (R.S.D.) values of the retention time in HSCCC separation was less than 3% satisfied the precision requirements of national standards in the fingerprint development. As a new approach, HSCCC was compared to the conventional approach-HPLC in our experiments. The fingerprint developed by HPLC comprised 11 peaks that collected within 45 min. R.S.D. values of retention times of the corresponding peaks in HPLC analysis were very small (maximum 0.66% and average 0.10%). In conclusion, HSCCC was a feasible method to be used in the development of fingerprint of CTM.     

Comparison of microemulsion electrokinetic chromatography with high-performance liquid chromatography for fingerprint analysis of resina draconis

Microemulsion electrokinetic chromatography (MEEKC) has been developed for fingerprint analysis of resina draconis, a substitute for sanguis draconis in the Chinese market. The microemulsion as the running buffer was made up of 3.3% (w/v) sodium dodecyl sulfate (SDS), 6.6% (w/v) n-butanol, 0.8% (w/v) n-octane, and 10 mmol/L sodium tetraborate buffer (pH 9.2), which was also used as the solvent for ultrasonic extraction of both water- and fat-soluble compounds in the traditional Chinese medicine samples. Four batches of resina draconis obtained from different pharmaceutical factories located in different geographic regions were used to establish the electrophoretic fingerprint. MEEKC was performed using a Beckman PACE/MDQ system equipped with a diode-array detector and with monitoring at 280 nm. The fingerprint of resina draconis comprised 27 common peaks within 100 min. The relative standard deviations of the relative migration time of these common peaks were less than 2.1%. Through repetitive injection of the sample solution six times in 24 h, all relative standard deviations of the migration time and peak area of loureirin A and loureirin B were less than 2.5 and 3.8%, which demonstrated that the method had good stability and reproducibility. The relative peak areas of these common peaks in the electropherograms of four batches of resina draconis were processed with two mathematical methods, the correlation coefficient and the interangle cosine, to valuate the similarity. The values of the similarity degree of all samples were more than 0.91, which showed resina draconis samples from different origins were consistent. On the other hand, high-performance liquid chromatography (HPLC) coupled with photodiode-array detection was also applied to establish the fingerprint of resina draconis. The samples were separated with a LiChrospher C₁₈ column using acetonitrile (solvent A) and water containing 0.1% H₃PO₄ (solvent B) as the mobile phase in linear gradient elution mode at a flow rate of 0.6 mL/min and detection was at 280 nm. There were only 20 common peaks in the HPLC fingerprint, and the values of the similarity degree of all samples were also more than 0.91. Though the similarity results of fingerprint analysis seemed to be the same, MEEKC resulted in more common peaks and higher separation efficiency for a variety of polarities of the components than HPLC. So, MEEKC was more suitable for development of the fingerprint of resina draconis.     

Preparative isolation and purification of bergapten and imperatorin from the medicinal plant Cnidium monnieri using high-speed counter-current chromatography by stepwise increasing the flow-rate of the mobile phase

A high-speed counter-current chromatography (HSCCC) method was developed for the preparative separation and purification of bergapten and imperatorin from the Chinese medicinal plant Cnidium monnieri (L.) Cusson. The crude extract was obtained by extraction with ethanol from the dried fruits of Cnidium monnieri (L.) Cusson under sonication. Preparative HSCCC with a two-phase solvent system composed of n-hexane-ethyl acetate-ethanol-water (5:5:5:5, v/v/v/v) was successfully performed by increasing the flow-rate of the mobile phase stepwise from 1.0 to 2.0 ml min(-1) after 180 min. The components purified and collected were analyzed by high-performance liquid chromatography. The method yielded 45.8 mg of bergapten at 96.5% purity and 118.3 mg of imperatorin at 98.2% purity from 500 mg of the crude extract in a single run. The recoveries of bergapten and imperatorin were 92.1 and 93.7%, respectively.     

Mixed micellar electrokinetic capillary chromatography separation of depolymerized grape procyanidins

Oligomeric procyanidins are potent antioxidant polyphenols of potential interest as disease-preventing agents. Their efficiency depends on the size and composition of their oligomeric structures. The mean degree of polymerization of these compounds is usually estimated by thiolysis with thiol-alpha-toluene followed by analysis using high-performance liquid chromatography (HPLC). We show the development of a mixed micellar electrokinetic chromatography (MEKC) method for the separation of the major components obtained after thiolysis with cysteamine (catechins and their cysteamine conjugates). MEKC studies using sodium dodecyl sulfate (SDS as pseudostationary phase led to long migration times, e.g., with 100 mM SDS, at pH 7, the solutes were separated in about 40 min), while the use of sodium cholate (SC) produced an elution window relatively short. Using a mixed micellar SC-SDS system (50 mM phosphate at pH 7 containing 40 mM SC and 10 mM SDS), it is possible to separate these compounds in less than 15 min. The proposed method is useful to separate the major components of the thiolysate in effluents from food processing (e.g., skins and seeds from grape and apple) considered as potential procyanidin sources.     

Micellar electrokinetic chromatography profiles of human high-density lipoprotein phospholipids

A simple and fast micellar electrokinetic chromatography (MEKC) method was developed to investigate phospholipids isolated from human high-density lipoproteins (HDL). To optimize the MEKC conditions, several factors including bile salt concentration and organic modifier concentration in the separation buffer as well as temperature have been examined. The optimal separation buffer chosen was a mixture of 50 mM bile salts, 30% v/v 1-propanol and 10 mM sodium phosphate (pH 8.5). The applied voltage and temperature selected were 25 kV and 40°C, respectively. Meanwhile, high-salt stacking has been performed for sample pre-concentration to enhance peak sensitivity. Several factors including organic modifier concentration and salt concentration in the sample matrix as well as sample injection time have been optimized. The optimal sample buffer selected was a mixture of 100 mM NaCl and 20% 1-propanol, and the optimal sample injection time selected was 32 s under a pressure of 0.5 psi. Several phospholipid standards including lysophosphatidyl choline, phosphatidyl choline (PC), sphingomyelin, phosphatidyl ethanolamine, phosphatidyl inositol, phosphatidyl serine and phosphatidic acid have been studied using the optimal MEKC method. The MEKC profile of the mixed phospholipid standards showed good separation and reproducibility. The linear ranges for PC and sphingomyelin were 0.025-1.2 and 0.025-2.0 mg/mL, respectively. The concentration limits of detection of PC and sphingomyelin were 0.0156 and 0.0199 mg/mL, respectively. Using phosphatidic acid as an internal standard, precision and accuracy have been measured for PC and sphingomyelin. The intraday and interday quantitative analysis showed good results. The new MEKC method has been used to characterize native, in vitro oxidized and glycated human HDL phospholipids within 16 min. At absorbance 200 nm, two similar peaks were observed for native and oxidized HDL phospholipids, but three peaks were observed for glycated HDL phospholipids. Interestingly, at absorbance 234 nm, distinctively different MEKC profiles were observed for the three HDL phospholipids.     

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.     

Method development for gypenosides fingerprint by high performance liquid chromatography with diode-array detection and the addition of internal standard

In this paper, a new method for liquid chromatographic fingerprint of saponins in Gynostemma pentaphyllum (THUNB.) MAKINO was developed. The G. pentaphyllum powder was defatted by Soxhlet extraction with petroleum ether and then gypenosides were extracted from the residue with methanol by sonicating. Column chromatography with macro pore resin was then used to separate and enrich gypenosides. HPLC fingerprint analysis of gypenosides fraction was performed on a C18 column, with an isocratic elution of 34% acetonitrile for 60 min at 0.8 ml/min, sample injection volume was 20 microl and the wavelength was 203 nm. To cover the lack of standard compounds, the addition of an internal standard of ginsenoside Rb2 was employed in the gypenosides fingerprint profile. The relative retention time (RRT) and relative peak area (RPA) of the gypenosides peaks in the fingerprint were calculated by setting the ginsenoside Rb2 as the marker compound. The relative standard deviation (RSDs) of RRT of five common peaks vs. ginsenoside Rb2 in precision, repeatability and stability test were less than 1%, and the RSDs of RPA were less than 5%. The method validation data proved that the proposed method for the fingerprint with internal standard of G. pentaphyllum saponins is adequate, valid and applicable. Finally, three batches of crude drug samples collected from Shanxi province were tested by following the established method.     

Simultaneous micellar electrokinetic chromatography and liquid chromatography of adriblastina and tarabine PFS Their application to some biological fluids

The current work presents analytical procedures for simultaneous determination of tarabine PFS and adriblastina by micellar electrokinetic chromatography (MEKC) and liquid chromatography (LC). For MEKC analysis, separations and identifications were accomplished using uncoated fused-silica capillary with hydrodynamic injections in the presence of 50mM borate/phophate pH 8.7 and 100mM SDS. The migration times of tarabine PFS and adriblastina were found to be 2.70 and 6.40min, respectively. Calibration curves were established for 10-300ng/mL (r=0.998) tarabine PFS and for 8-120microg/mL (r=0.999) adriblastina. For LC analysis, separations were performed on teicoplanin stationary phase with reversed mobile phase containing methanol:buffer pH 4.05 (20:80%, v/v) at 285nm. The retention times of tarabine PFS and adriblastina were 5.18 and 7.20min, respectively. Calibration curves were established for 3-90microg/mL (r=0.998) tarabine PFS and for 10-120microg/mL (r=0.999) adriblastina. Both MEKC and LC methods were applied for the simultaneous determination of analytes in urine samples.     

Verification of statistical-overlap theory in micellar electrokinetic chromatography

The limited peak capacity of neutral compounds in micellar electrokinetic chromatography (MEKC) causes peak overlap in a simple 38-compound sample that is predicted by statistical-overlap theory (SOT). The low-concentration sample was prepared in-house from several compound classes to span the entire migration-time range and was resolved partially in a pH=7 phosphate buffer containing 50 mM sodium dodecyl sulfate. Peaks, singlets, doublets, and other multiplets were identified on the basis of known migration times and were counted at 13 voltages spanning 4 – 26 kV. These numbers agreed well with predictions of a simple SOT based on the assumption of an inhomogeneous Poisson distribution of migration times. Because the dispersion theory of MEKC is simple, the standard deviations of single-component peaks were modeled theoretically. As part of a new way to implement SOT, probability distributions of the numbers of peaks, singlets, and so on, were computed by Monte Carlo simulation. These distributions contain all theoretical information on peak multiplicity predictable by SOT and were used to evaluate the agreement between experiment and theory. The peak capacity of MEKC was calculated numerically and substituted into the simplest equations in SOT, affirming that peak overlap arises from limited peak capacity.     

Analysis of organic components of smokeless gunpowders: high-performance liquid chromatogaphy vs. micellar electrokinetic capillary chromatography

The aim of the present study was to verify the analytical performances of high-performance liquid chromatography (HPLC) and micellar electrokinetic capillary chromatography (MEKC) for the separation and qualitative determination of a selected group of organic components of smokeless gunpowders. The HPLC method was based on a gradient reversed-phase elution with a mobile phase composed of 0.17 M H(3)PO(4)/methanol; detection was performed by UV absorption at the wavelengths of 220, 254, and 270 nm. The MEKC experiments were carried out by using uncoated fused-silica capillaries (50 microm inside diameter, 50 cm effective length) and a running buffer composed of 10 mM sodium tetraborate at pH 9.24 added with 25 mM sodium dodecyl sulfate (SDS); the applied voltage was 25 kV; detection was either at a fixed wavelength UV of 214 nm or with a diode-array detector operating in the wavelength range from 190 to 350 nm. Both reversed-phase HPLC and MEKC techniques succeeded in resolving the tested standard mixtures of organic components of smokeless powders. Although the sequence of elution of the different analytes was slightly different between HPLC and MEKC, a statistical analysis based on the Spearman's rank correlation test showed that the two separation patterns were highly correlated. HPLC and MEKC were comparable in terms of elution/migration time precision, whereas MEKC showed higher reproducibility of peak areas. The interfacing of capillary electrophoresis with diode array UV detection provided distinct UV spectra of the individual analytes, thus improving, on the detection side, the analytical selectivity and identification power of capillary electrophoresis.     

Quality evaluation of Guan‐Xin‐Ning injection based on fingerprint analysis and simultaneous separation and determination of seven bioactive constituents by capillary electrophoresis

The purpose of this study was to develop a comprehensive, rapid and practical capillary electrophoresis (CE) method for quality control (QC) of Guan‐Xin‐Ning (GXN) injection based on fingerprint analysis and simultaneous separation and determination of seven constituents. In fingerprint analysis, a capillary zone electrophoresis (CZE) method with a running buffer of 30 mM borate solution (pH 9.3) was established. Meanwhile, ten batches of samples were used to establish the fingerprint electropherogram and 34 common peaks were obtained within 20 min. The RSD of relative migration times (RMT) and relative peak areas (RPA) were less than 5%. In order to further evaluate the quality of GXN injection, a micellar electrokinetic chromatography (MEKC) method was developed for simultaneous separation and determination of bioactive constituents. Seven components reached baseline separation with a running buffer containing 35 mM SDS and 45 mM borate solution (pH 9.3). A good linearity was obtained with correlation coefficients from 0.9906 to 0.9997. The LOD and LOQ ranged from 0.12 to 1.50 μg/mL and from 0.40 to 4.90 μg/mL, respectively. The recoveries ranged between 99.0 and 104.4%. Therefore, it was concluded that the proposed method can be used for full‐scale quality analysis of GXN injection.     

Simultaneous separation and purification of five bioactive coumarins from the Chinese medicinal plant Cnidium monnieri by high-speed counter-current chromatography

Cnidium monnieri (L.) Cusson is a well-known Chinese medicinal plant, which has been used for the treatment of impotence, frigidity, and skin-related diseases, and exhibits strong antipruritic, antiallergic, antidermatophytic, antibacterial, antifungal, and antiosteoporotic activities. A high-speed counter-current chromatography method was developed for the separation and purification of five bioactive coumarins from this plant. The crude coumarins were obtained by ethanol extraction from the dried fruits of Cnidium monnieri (L.) Cusson under sonication. High-speed counter-current chromatography with the two-phase solvent systems n-hexane-ethyl acetate-ethanol-water (5:5:4:6, v/v) and n-hexane-ethyl acetate-ethanol-water (5:5:6:4, v/v) was successfully performed with stepwise elution. The five relatively pure coumarins were obtained from 500 mg of the crude extract in a single run. Their purities were 90.6-98.9%, and the recoveries were 85.7-94.2%.     

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.     

Optimised separation of endogenous urinary components using cyclodextrin-modified micellar electrokinetic capillary chromatography

In this study both native and chemically modified cyclodextrins (CDs) were investigated as buffer additives to improve the micellar electrokinetic capillary chromatography (MEKC) separation of endogenous bioanalytes in human urine. The following CDs were investigated: alpha, beta, gamma-CDs; hydroxypropyl-alpha-CD, hydroxypropyl-beta-CD, methylated beta-CD, sulphated beta-CD, sulphobutyl ether-beta-CD and hydroxypropyl-gamma-CD. The separations were compared to MEKC without additives. The best improvement in peak resolution and separation of urine components was observed with the sulphated beta-CD. A four-factor three-level full factorial design study was conducted on voltage, temperature, pH and sulphated beta-CD molarity. The optimum conditions were 25 mM sodium tetraborate, pH 9.5, 75 mM sodium dodecyl sulphate (SDS) and 6.25 mM sulphated beta-CD and were able to resolve 70 peaks from a urine pool in 12 min. These optimum conditions have been successfully applied to a number of clinical samples.     

Separation of natural pyrethrum extracts using micellar electrokinetic chromatography

The separation of the six pyrethrin esters in a technical pyrethrum extract (Riedel-de-Ha?n, Cresent Chemical Co. Inc. Hauppauge, NY, USA) by micellar electrokinetic chromatography (MEKC) using both sodium dodecyl sulfate (SDS) and a polymerized surfactant as pseudo-stationary phases has been investigated and optimized. Parameters such as pH, SDS and polymerized sodium N-undecyl sulfate (poly-SUS) concentration, type and concentration of background electrolyte and organic modifier, as well as the acetonitrile/water ratio in the sample were studied to optimize the resolution, efficiency, and analysis time. An optimized separation of the six pyrethrin esters was achieved in 25 min with 25 mM Tris, buffered at pH 9, containing 30 mM SDS, 25% (v/v) acetonitrile, and an equal volume ratio of acetonitrile/water sample matrix at a voltage of 25 kV. The use of 0.5% (w/v) poly-SUS enhanced resolution of the pyrethrin esters and shortened the total analysis time from 25 to 20 min, compared to the SDS mediated separation. The optimized MEKC results are compared to the HPLC separation of these esters and show an improvement in efficiency and total analysis time.     

Chemical fingerprint and quantitative analysis of fructus psoraleae by high-performance liquid chromatography

Fructus Psoraleae, a widely used traditional Chinese medicine, is well known as a health supplement ingredient. In our study, an improved and comprehensive HPLC fingerprint of Fructus Psoraleae was established. Two important new benzofuran glycosides, psoralenoside and isopsoralenoside, were identified as characteristic constituents for the first time. HPLC separation was performed on an RP-C8 column. The mobile phase was acetonitrile and 0.1% acetic acid solution with linear gradient change of acetonitrile from 10 to 82% in 40 min. The flow rate was 1.0 mL/min, and the detection wavelength was set at 310 nm. The HPLC chromatograms of twenty-six samples from different regions of China showed a similar pattern. Twelve peaks were selected as characteristic peaks and further identified as psoralenoside, isopsoralenoside, psoralen, isopsoralen, bavachromene, corylifolin, corylin, psoralidin, isobavachalcone, bavachinin, corylifol A, and bakuchiol, respectively. Nine of them were simultaneously quantitatively analyzed for the first time. A more comprehensive analytical method was established for the fingerprint of Fructus Psoraleae. It is very useful for authentication and quality assessment of the crude drug.     

Separation of Compounds in Traditional Chinese Medicines Using Comprehensive Two Dimensional Chromatography

Traditional Chinese medicine is an invaluable treasure of the Chinese nationalities. Thousands of natural species that are of pharmaceutical importance have been accumulated. Most of them are plants. Traditional Chinese medicines generally are of unusual complexity. Even a single medicinal material may contain hundreds of compounds. Since these compounds play cooperative roles pharmacologically, it is essential to analyze all compounds as a whole. It is also important for quality controls in each step of productions, such as raw material collection, processing, and manufacturing. A comprehensive two-dimensional separation system coupling capillary high performance liquid chromatography with fast capillary electrophoresis (μ-HPLC-CE) is developed to provide a powerful means to separate such complex samples. In the first dimensional separation, a home-packed micro-HPLC column was used to reduce the consultation of sample injection and avoid sample dilution. The second dimensional analysis was carried out by micellar electrokinetic chromatography(MEKC) considering the fact that most compounds in Chinese medicine are neutrals. In order to achieve high-speed separation^ theory of fast MEKC was extensively studied. Models of the fast MEKC migration behaviors were established. Relationships of theoretical plates vs. electric field strength and column length were derived. It is concluded that maintaining certain column length and applying high-voltage at the ends of the capillary simultaneously are the key points to achieving fast MEKC separation. A pulse-contacting interface was developed for the 2-D μ-HPLC-CE system. CE sampling was carried out in an instant contact of HPLC and CE columns in an optimized timing program. During the short contact period, a certain fraction of HPLC effluent was introduced into the CE capillary. Injection efficiency for such an interface was up to 81%. Relative standard deviation (RSD) of migration times and peak heights for 100 consecutive MEKC. separation were 3.0% and 1.8%, respectively. With this novel 2-D μ-HPLC-CE system, some traditional Chinese medicines were analyzed and hundreds of peaks were observed. For liquorice, over 110 components were fairly resolved. More than 250 peaks were obtained for a compound mixture of Cheng-Qi-Tang. The peak capacity of this novel comprehensive 2-D HPLC-CE system was estimated to be about 2400 in 80 min.     

Micellar electrokinetic chromatography for the analysis of D-amygdalin and its epimer in apricot kernel

We have developed a simple, rapid and reproducible method for the determination of D-amygdalin and its epimer by using micellar electrokinetic chromatography (MEKC). Separation of D-amygdalin was performed in a 20 mM sodium borate buffer (pH 8.5) containing 300 mM sodium dodecyl sulfate using a bare fused-silica capillary. The eluates were monitored by the absorbance at 210 nm. The applied electric field was 278 V/cm, and the time needed for the separation of D-amygdalin did not exceed 6 min. The calibration curve for D-amygdalin showed excellent linearity in the concentration range of 5-500 microg/ml. The migration time and the corrected peak area show relative standard deviations (n=6) of 0.86% and 1.48%, respectively. The limit of detection (S/N=3) for D-amygdalin was 2 microg/ml. Under acidic and neutral conditions, amygdalin exists only as the D-form; however, under basic conditions, it shows both the D- and L-forms with a concentration ratio of 1:1.3 (D-amygdalin/L-amygdalin). Results of HPLC, UV-Vis spectrophotometry, and mass spectrometry reconfirmed the identification of D-amygdalin and its epimer. The number of theoretical plates of D-amygdalin is about 100,000 in MEKC, which is significantly higher than approximately 8,000 of HPLC. This method has been successfully applied to the determination of amygdalin epimers in various apricot kernel extracts and pharmaceutical products.     

A comparative study of microemulsion electrokinetic capillary chromatography and micellar electrokinetic capillary chromatography for the analysis of UV-absorbing compounds in human urine

Separations of human urine by microemulsion electrokinetic chromatography (MEEKC) and micellar electrokinetic capillary chromatography (MEKC) with respect to resolution, migration times and efficiencies were optimized and compared. The optimised MEEKC and MEKC methods were simple and fast, both of which are excellent characteristics for the complex separations required in clinical and biomedical studies. However, resolution in MEKC was significantly greater than in MEEKC although migration times were 30% faster for the optimised MEEKC method. In addition, a faster analysis method (short-end injection) specifically for routine screening purposes was also investigated. With both MEEKC and MEKC modes, this provided short separations (less than 4 min for urine) with no major compromise in resolution. In conclusion, we found that MEEKC offered no real advantage over MEKC for urine analysis.     

Preparative isolation of osthol and xanthotoxol from Common Cnidium Fruit (Chinese traditional herb) using stepwise elution by high-speed counter-current chromatography

Preparative high-speed counter-current chromatography (HSCCC) was successfully used for isolation and purification of osthol and xanthotoxol from Cnidium monnieri (L.) Cusson (Common Cnidium Fruit) using stepwise elution with a pair of two-phase solvent systems composed of n-hexane-ethyl acetate-methanol-water at (1:1:1:1, v/v), and (5:5:6:4, v/v), which had been selected by analytical high-speed counter-current chromatography. Using a preparative unit of the HSCCC centrifuge, about a 308 mg amount of the crude extract was separated, yielding 88.3 mg of osthol and 19.4 mg of xanthotoxol at a high purity of over 98%.