Shao-Wen Sun

Rapid analysis of melamine in infant formula by sweeping-micellar electrokinetic chromatography

In the present study, an analytical method using capillary electrophoresis with on-line preconcentration technique was developed for rapid determination of melamine in infant formula. Both stacking and sweeping preconcentration techniques had been investigated for the comparison of their effectiveness in melamine analysis. The limit of detection of melamine standard was 0.5 ng/mL for the field amplified sample stacking (FASS) technique and 9.2 ng/mL for the sweeping technique. Although the FASS technique provided better concentration efficacy than the sweeping technique, the matrix effect was more profound with the former. Matrix effect was evaluated by comparing the enhancement factor (EF) of melamine standard and post-extraction spiked infant formula solution. The EF was changed from 429.86 +/- 9.81 to the level less than 133.31 with significant peak distortion in the FASS system, and it was remained unchanged in the sweeping system. Sweeping-micellar electrokinetic chromatography (sweeping-MEKC) was demonstrated to be most suitable for real sample analysis. Under optimum sweeping-MEKC conditions, melamine content in infant formulas could be determined within 6 min. The developed solid phase extraction (SPE) procedures coupled with the sweeping-MEKC method was subjected to method validation. Run-to-run repeatability (n = 3) and day-to-day reproducibility (n = 3) of peak area were within 3.6% and 4.8% RSD, respectively. The accuracy was tested by spiking 0.5 and 2 microg/mL of melamine standard in the melamine contaminated milk powder provided by the European Commission, and the recoveries were 93.4 +/- 0.5% and 98.7 +/- 0.4%, respectively. Results of this study show a great potential for the sweeping-MEKC method as a tool for the fast screening of melamine in infant formulas.

Optimization of capillary electrophoretic separation of quinolone antibacterials using the overlapping resolution mapping scheme

The capillary electrophoretic separation of fourteen quinolone antibacterials, viz., cinoxacin, ciprofloxacin, enoxacin, flumequine, lomefloxacin, nalidixic acid, norfloxacin, ofloxacin, oxolinic acid, pefloxacin, pipemidic acid, piromidic acid, rosoxacin and sparfloxacin, was optimized by using the overlapping resolution mapping scheme. Three relevant parameters to run buffer compositions, i.e., the concentrations of sodium cholate and sodium heptanesulfonate, and the volume percentage of acetonitrile, were chosen for optimization. Seven experiments were carried out to obtain the overlapped resolution diagram for locating the area of optimum separations. Following the predicted optimum condition, a baseline separation of the fourteen quinolones was achieved within 8 min.

Analysis of nine rhubarb anthraquinones and bianthrones by micellar electrokinetic chromatography using experimental design

An efficient micellar electrokinetic chromatography (MEKC) method has been developed for the analysis of nine anthraquinones and bianthrones in rhubarb. A chemometric approach was used to search for the optimum conditions of separation. Those factors which were found to be significant with a screening design were further optimized with a central composite face-centered (CCF) design. Acetonitrile concentration was found to be the most influential, not only in resolution, but also in analysis time and peak asymmetry. With the optimized conditions: 15 mM sodium tetraborate/15 mM sodium dihydrogenphosphate buffer, 30 mM sodium deoxycholate, pH 8.6, 17 vol.% acetonitrile and 28 kV, nine tested analytes were baseline-separated within 14 min. The method was validated to analyze the rhubarb material. Solid-phase extraction (SPE) was manipulated to remove interfering substances. Five anthraquinones and two glycosidic bianthrones were detected and quantificated. The method should be suitable for determining these major active principles in rhubarb crude drugs.

Validated HPLC method for determination of sennosides A and B in senna tablets.

This study developed an efficient and reliable ion-pair liquid chromatographic method for quantitation of sennosides A and B in commercial senna tablets. Separation was conducted on a Hypersil C 18 column (250 x 4.6 mm, 5 microm) at a temperature of 40 degrees C, using a mixture of 0.1 M acetate buffer (pH 6.0) and acetonitrile (70:30, v/v) containing 5 mM tetrahexylammonium bromide as mobile phase. Sennosides A and B were completely separated from other constituents within 14 min. The developed method was validated. Both run-to-run repeatability (n=10) and day-to-day reproducibility (n=3) of peak area were below 0.4% RSD. Linearity of peak area was tested in the range 30-70 microg/ml (r>0.9997). Accuracy was assessed with recovery and the recoveries for sennosides A and B were 101.73+/-1.30% and 101.81+/-2.18% (n=3 x 6), respectively. Robustness of the analytical method was tested using a three-leveled Plackett-Burman design in which 11 factors were assessed with 23 experiments. Eight factors (column, concentration of ion pair reagent, % of organic modifier (acetonitrile), buffer pH, column temperature, flow rate, time constant and detection wavelength) were investigated in a specified range above and below the nominal method conditions. It was found that: (1) column and % acetonitrile affected significantly resolution and retention time, (2) column, % acetonitrile, column temperature, flow rate and time constant affected significantly the plate number of sennoside A, and (3) column and time constant affected significantly the tailing factor.

Separation of aporphine alkaloids by micellar electrokinetic chromatography

The separation of nine aporphine alkaloids, lindcarpine, laurolitsine, N-methyllindcarpine, boldine, norpredicentrine, isocorydine, laurotetanine, N-methyllaurotetanine and isoboldine, was investigated by micellar electrokinetic chromatography. Optimization of separation was realized with the univariate approach by studying the effects of five factors relevant to run buffer on migration times. Quantitative analysis on a Lauraceous plant showed a similar result to that obtained with HPLC previously performed.

Optimization of the capillary electrophoretic separation of bisbenzylisoquinoline alkaloids by an overlapping resolution mapping scheme

The micellar electrokinetic chromatographic (MEKC) separation of eight bisbenzylisoquinoline (BBI) alkaloids, aromoline, berbamine, colorflammine, homoaromoline, isotetrandrine, obamegine, tetrandrine and thalrugosine, was optimized by using the overlapping resolution mapping (ORM) scheme. Three critical parameters of the electrophoretic media, i.e. surfactant (sodium cholate), organic modifier (acetonitrile) and pH, were chosen for optimization, with their working ranges being appropriately defined. Seven experiments were conducted to obtain the overlapped resolution diagram from which the area of maximum separations could be located. Using the conditions of a point in this area, the eight BBI compounds were baseline separated within 20 min. The elution order of the compounds was found to be related to their lipophilicity. The resolution, run time, efficiency and the limits of detection of the MEKC method were compared with those of the high-performance liquid chromatography method developed previously.

Determination of bisbenzylisoquinoline alkaloids by high-performance liquid chromatography (II).

After the earlier analysis of nine bisbenzylisoquinoline alkaloids with ion pair chromatography, seven other bisbenzylisoquinoline alkaloids were analyzed using gradient elution with an acetonitrile-phosphate buffer (pH 8.0) mixture, and UV detection. Four alkaloids were detected in the stem woods of a Lauraceous plant, Dehaasia triandra Merr. and their contents determined. LC-MS suggested that a major unknown compound in the plant was also a bisbenzylisoquinoline alkaloid.

Determination of ursodeoxycholic acid in pharmaceutical preparations by capillary electrophoresis with indirect UV detection.

A simple and rapid capillary electrophoretic method, with indirect UV detection, for the quantification of ursodeoxycholic acid (UDCA) in pharmaceutical preparations was developed in this study. Sodium p-hydroxy benzoate was used as background electrolyte (BGE) (5 mM, pH 8.0) and visualization agent. Separation was carried out on a fused-silica capillary (50 microm x 72 cm) at a potential of 25 kV under ambient temperature and detected at 250 nm. Glycocholic acid was used as internal standard for quantification. Both run-to-run repeatability and day-to-day reproducibility of migration time were below 0.1% relative standard deviation (R.S.D.). Repeatability and reproducibility of relative peak height were 3.3 and 3.8% R.S.D., respectively. Accuracy was tested by spiking two pharmaceutical tablets with standards and the recoveries were 101.9+/-9.87 and 99.6+/-9.60% (n=3), respectively. Linearity of relative peak height was tested in the range 20-100 microg/ml. Limit of detection (LOD) was 3 microg/ml. The method could be used to assay UDCA raw materials and formulation products.