Dynamically coated capillaries improve the identification power of capillary zone electrophoresis for basic drugs in toxicological analysis.

In systematic toxicological analysis (STA), analytical methods should have a high identification power. This can be suitably expressed by parameters such as mean list length (MLL) or discriminating power (DP). The reproducibility of a method has a great impact on its identification power, and should be as high as possible. In this study, two separation methods based on capillary zone electrophoresis (CZE) were evaluated towards STA applications. Besides a normal phosphate buffer, the commercially available buffer CElixir was used, which is a double-layer dynamic coating system. The coating stabilizes the endoosmotic flow, is independent of the pH, and is claimed to be more reproducible and faster at low pH than with normal buffers. A test set of 73 basic pharmaceutical compounds was analyzed by the two CZE methods. The total analysis time, including rinsing steps, was 8 min when the coating was used and 18 min without the coating. Effective mobilities were calculated and the reproducibilities were a factor of 2 better when the coating was used (between-days SD 0.020 and 0.040 m2/V s with and without the coating, respectively). MLL and DP were calculated for the two CZE methods and for combinations with standardized liquid and gas chromatography systems. CZE with CElixir coating clearly has a high potential for STA applications, as it was shown to have a higher identification power and shorter analysis times than normal CZE.

Screening for the presence of drugs in serum and urine using different separation modes of capillary electrophoresis.

Capillary electrophoresis (CE) is a modern separation technique that has some distinct advantages for toxicological analysis, such as a high efficiency, fast analysis, flexibility, and complementary separation mechanisms to chromatographic methods. CE can be applied in various modes, which each have a different separation mechanism or selectivity. The most common mode is capillary zone electrophoresis (CZE), in which charged analytes migrate in a buffer under the influence of an electric field. In micellar electrokinetic chromatography (MEKC), micelles are added to the buffer which interact with the analytes. MEKC can also be used for the separation of neutral compounds. In non-aqueous CE (NACE), the aqueous buffer is replaced by a background of electrolytes in organic solvents. A sample that needs to be screened can easily be analyzed subsequently by these CE modes using the same instrumentation. The aim of the study was to develop procedures for the analysis of basic and acidic drugs in serum and urine using CZE, MEKC, and NACE. A test mixture that consisted of six basic and six acidic compounds was used to study the separation behavior of five CE methods. The results showed that three methods (based on CZE, MEKC, and NACE) were suitable for the analysis of basic compounds and three methods (based on CZE and MEKC) for the analysis of acidic compounds. For the extraction of analytes from serum and urine, a solid-phase extraction (SPE) and a liquid-liquid extraction (LLE) method were compared. Both SPE and LLE methods provided clean extracts after extraction of the basic compounds from serum and urine. The extracts of acidic compounds contained more matrix interferences, especially for urine. The SPE method had some advantages compared to LLE, as it lead to cleaner extracts and higher peaks, and as it elutes basic and acidic compounds in one fraction. The potentials and pitfalls of the various methods for screening purposes in analytical toxicology are discussed.

Intra- and interinstrument reproducibility of migration parameters in capillary electrophoresis for substance identification in systematic toxicological analysis.

The intra- and interinstrument reproducibilities of four capillary electrophoresis instruments were studied for identification purposes in systematic toxicological analysis (STA). A test set of 20 acidic test compounds and 5 reference compounds were analyzed for five days on each instrument using capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC). The buffers consisted of 90 mM borate set at pH 8.4 (CZE) and 20 mM phosphate and 50 mM sodium dodecyl sulfate set at pH 7.5 (MEKC). All analyses were carried out using fused silica capillaries at an electric field strength of 52.6 kV/m. The use of a reproducible identification parameter is very important in STA. To deal with the poor reproducibility of the migration time, we recently introduced the corrected effective mobility. In this study, we investigated the intra- and interinstrument reproducibility of the migration time, the effective mobility, and the corrected effective mobility. Large differences in intra-instrument reproducibility were found when the migration time was used. The calculation of the effective mobility and the corrected effective mobility diminished these differences and enhanced the interinstrument reproducibility roughly by a factor 3. For (corrected) effective mobilities, intrainstrument reproducibilities were between 0.8-2.6% and interinstrument reproducibilities were between 3.2-3.9%.

Structural characterisation of lipo-chitin oligosaccharides isolated from Bradyrhizobium aspalati, microsymbionts of commercially important South African legumes.

The shoots of the South African legume Aspalathus linearis spp. linearis (A. linearis) are used in the manufacture of an increasingly popular beverage that has acclaimed beneficial effects on health; this important export product is known as Rooibos (or Redbush) tea. Three strains of Bradyrhizobium aspalati, which are the nitrogen-fixing symbionts of Aspalathus carnosa, A. hispida and A. linearis, were tested for the production of lipo-chitin oligosaccharide signal molecules using thin-layer chromatographic analysis after induction with different inducers, including Rooibos tea extract, and radioactive labelling. Large-scale separation, using high-performance liquid chromatography, of lipo-chitin oligosaccharides from B. aspalati isolated from A. carnosa was performed for structural characterisation using fast-atom bombardment mass spectrometry and chemical modifications followed by gas chromatography-mass spectrometric analysis. The strain was shown to secrete a family of unusual lipo-chitin oligosaccharides that are highly substituted on the nonreducing-terminal residue but unsubstituted on the reducing-terminal residue. They have a backbone of three to five beta-(1-->4)-linked N-acetyl-D-glucosamine residues substituted on the nonreducing terminus with a C16:0, C16:1, C18:0, C18:1, C19:1cy, or C20:1 fatty acyl chain, and are both N-methylated and 4,6-dicarbamoylated.

Evaluation of capillary electrophoretic techniques towards systematic toxicological analysis.

Two capillary electrophoresis (CE) methods were evaluated for their suitability in systematic toxicological analysis (STA). A test set of 25 barbiturates was analysed using capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC). Buffers used consisted of 90 mM borate set at pH 8.4 (CZE) and 20 mM phosphate, 50 mM sodium dodecyl sulphate set at pH 7.5 (MEKC). All analyses were carried out using fused silica capillaries using an electric field strength of 52.6 kV/m. The use of a reproducible identification parameter is very important in STA as it influences the identification power (IP). To deal with the poor reproducibility of the migration time, we introduced the corrected effective mobility. Inter-day reproducibilities of the latter parameter were < 0.6% for CZE and < 0.5% for MEKC, using daily prepared buffers. The IP of the methods was expressed by calculation of the discriminating power and the mean list length. Data obtained were compared to gas chromatographic and high-performance liquid chromatographic data, and correlations between all methods were calculated. It was shown that little correlation exists between chromatographic and electrophoretic techniques. The results indicated that CE has a good identification power for the application in STA, especially when a combination of methods having a low correlation is used.

Capillary electrophoresis as a versatile tool for the bioanalysis of drugs--a review.

This review article presents an overview of current research on the use of capillary electrophoretic techniques for the analysis of drugs in biological matrices. The principles of capillary electrophoresis and its various separation and detection modes are briefly discussed. Sample pretreatment methods which have been used for clean-up and concentration are discussed. Finally, an extensive overview of bioanalytical applications is presented. The bioanalyses of more than 200 drugs have been summarised, including the applied sample pretreatment methods and the achieved detection limits.