Separation of pharmaceutically important estrogens by micellar electrokinetic chromatography

Separation and online preconcentration by multistep stacking with large-volume injection of anabolic steroids by capillary electrokinetic chromatography using charged cyclodextrins and UV-absorption detection

The separation of three common anabolic steroids (methyltestosterone, methandrostenolone and testosterone) was performed for the first time by capillary EKC. Different charged CD derivatives and bile salts were tested as dispersed phases in order to achieve the separation. A mixture of 10 mmol/L succinylated-beta-CD with 1 mmol/L beta-CD in a 50 mmol/L borate buffer (pH 9) enabled the separation of the three anabolic steroids in less than 9 min. Concentration LODs, obtained for these compounds with low absorption of UV light, were approximately 5 x 10(-5) mol/L. The use of online reverse migrating sample stacking with large-volume injection (the effective length of the capillary) enabled to improve the detection sensitivity. Sensitivity enhancement factors (SEFs) ranging from 95 (for testosterone) to 149 (for methyltestosterone) were achieved by single stacking preconcentration. Then, the possibilities of multistep stacking to improve the sensitivity for these analytes were investigated. SEFs obtained by double stacking preconcentration ranged from 138 to 185, enabling concentration LODs of 2.79 x 10(-7) mol/L (for methyltestosterone), 3.47 x 10(-7) mol/L (for testosterone) and 3.56 x 10(-7) mol/L (for methandrostenolone). Although online triple stacking preconcentration was achieved, its repeatability was very poor and SEFs for the studied analytes were not calculated.

Sol–gel coated polydimethylsiloxane/β-cyclodextrin as novel stationary phase for stir bar sorptive extraction and its application to analysis of estrogens and bisphenol A

A sol-gel technique was used for the preparation of a stir bar coated with a composite composed of polydimethysiloxane and beta-cyclodextrin (PDMS/beta-CD). The sol-gel mechanism during coating procedure was discussed and successful binding of beta-CD to the sol-gel network was confirmed by the IR spectra. Scanning electron micrographs of the stir bars revealed a homogeneous surface with a film thickness of 30-150 microm attributing to different coating times. Good thermal stability and solvent-resistance of the stir bar were found thanks to chemical binding formed between the stationary phase and the glass substrate. The PDMS/beta-CD coated stir bar was proved to have better selectivity to polar compounds compared to the PDMS coated stir bar, and higher extraction capacity compared to the corresponding PDMS/beta-CD coated fiber. Methods for the determinations of estrogens in environmental water, bisphenol A in drinking water and in leachate of one-off dishware by the PDMS/beta-CD coated stir bar coupled with high-performance liquid chromatography (HPLC) were developed. The limits of detection were within the range of 0.04-0.11 microg l(-1) for estrogens using UV detection and 8 ngl(-1) for bisphenol A using fluorescence detection. Reproducibility with RSD less than 9.7% for extractions of real water samples at microg l(-1) or ngl(-1) level was obtained.

Determination of association constants of inclusion complexes of steroid hormones and cyclodextrins from their electrophoretic mobility

CE estimation of the association constants of several steroid hormones with beta-CD and gamma-CD and their hydroxypropyl derivative is presented. Estriol, 17beta-estradiol, ethynylestradiol, estrone, progesterone, mestranol and norethindrone are among the target analytes. The calculation of the cyclodextrin:analyte association constants were performed from the electrophoretic mobility values of steroids at different concentration of CDs in the run buffer. The reliability of the final data was ensured by employing three different linearisation plots (double reciprocal fit, Y-reciprocal fit and X-reciprocal fit). The highest inclusion affinity of target analytes was observed towards gamma-CD and its hydroxypropyl derivative, which is demonstrated by high association constant values and corresponding good linearity of the plots. The affinity of steroids towards a particular CD type based on physical and structural characteristics is explored.

Complementary on-line preconcentration strategies for steroids by capillary electrophoresis

Complementary on-line preconcentration strategies are needed when analyzing different classes of solutes in real samples by capillary electrophoresis (CE) with UV detection. The performance of three different on-line preconcentration (focusing) techniques under alkaline conditions was examined in terms of their selectivity and sensitivity enhancement for a group of steroids, including classes of androgens, corticosteroids and estrogens. Electrokinetic focusing of large sample injection plugs (up to 28% of effective capillary length or 22.1 cm) directly on-capillary can be tuned for specific classes of steroids based on changes in their mobility (velocity) using a multi-section electrolyte system in CE. A dynamic pH junction was applied for the selective resolution and focusing of weakly acidic estrogens using borate, pH 11.0 and pH 8.0 in the background electrolyte and the sample, respectively. Sweeping, using an anionic bile acid surfactant and neutral gamma-cyclodextrin (gamma-CD) under alkaline conditions (pH 8), resulted in focusing and separation of the moderately hydrophobic (non-ionic) classes of steroids, such as androgen and corticosteroids. Optimal focusing and resolution of all test steroids under a single buffer condition was realized by a dynamic pH junction-sweeping format using borate, pH 11.0 and bile acid surfactant with gamma-CD in the BGE, whereas the sample is devoid of surfactant at pH 8.0. The design of selective on-line focusing strategies in CE is highlighted by the analysis of microgram amounts of ethynyl estradiol derived from a female contraceptive pill extract using the dynamic pH junction method, which resulted in over a 100-fold enhancement in concentration sensitivity.

Quantitative analysis of estrogens in human urine using gas chromatography/negative chemical ionisation mass spectrometry

A sensitive procedure for the determination of estrogens in urine has been developed, using enzymatic hydrolysis and ether extraction followed by capillary gas chromatography with negative chemical ionisation mass spectrometry (GC/NCI-MS) of the pentafluorobenzoyl derivatives. These derivatives were superior for GC/NCI-MS to trifluoroacetyl, heptafluorobutyl, pentadecafluorooctanoyl and perfluorotolyl derivatives, giving characteristic negative molecular ions as the base peak for each of the naturally occurring estrogens estrone, estradiol and estriol, and for the synthetic estrogen ethynylestradiol used in contraceptive pills. The method was also suitable for determination of some metabolites of estrone and estradiol. The specificity and sensitivity of the GC/NCI-MS method simplifies sample preparation. Recovery of spiked samples was in the range 84-101% for the natural estrogens based on additions to increase the concentration by 5 and 1 microg L(-1). The repeatability of the method was 1-8% for all estrogens.

Capillary electrophoresis of drugs: current status in the analysis of pharmaceuticals

The current status of capillary electrophoresis (CE) in pharmaceutical analyses is reviewed with about 300 references, mainly from 1996 until 1999. This article covers the use of CE for assay and purity determination of the main component, analysis of natural medicines, antisense DNA, peptides, and proteins. Analysis of hydrophobic and/or electrically neutral drugs by electrokinetic chromatography, capillary electrochromatography and nonaqueous CE is critically evaluated. Detailed techniques for the separation of enantiomers are given in the text with some actual applications. Furthermore, this review includes sensitivity and regulatory aspects for the actual use of CE in new drug applications (NDA). The analytical validation required for CE in NDA is also treated.

Selectivity in capillary electrophoresis in the presence of micelles, chiral selectors and non-aqueous media

In addition to high efficiency, short analysis times and small sample volumes, a further attractive feature of capillary electrophoretic techniques is the possibility to achieve, high selectivities. Usually, selectivity control also allows improvement in the resolution. A simple way to enhance the selectivity of capillary electrophoretic separations is to add one or more surfactants above their critical micelle concentration, or in the case of chiral separations to add a chiral selector to the background electrolyte. Because of the dynamic structure of micelles, the aggregation of monomers and size of the micelles can be easily adjusted. This review describes the various type of surfactants used in micellar electrokinetic capillary chromatography, and the chiral selectors employed in enantiomeric separations by capillary electrophoresis. Factors affecting the selectivity are noted. A brief discussion is included of the selectivity enhancement obtainable in non-aqueous media.