The adsorptive properties of powdered carbon materials with a strongly differentiated porosity and their applications in electroanalysis and solid phase microextraction.

The adsorption of 4-chlorophenol from an aqueous solution on carbonaceous materials (one carbon black and two powdered activated carbons) with a strongly differentiated porosity was investigated. The kinetic data were fitted well to the pseudo-second order model. The amount of 4-chlorophenol adsorbed at equilibrium was increased with an increase in the specific surface area of the tested materials. The adsorption isotherms were analyzed using the Langmuir and Freundlich models. The Langmuir isotherm was slightly favorable (R(2)>0.99) rather than the Freundlich isotherm (R(2)>0.98). Carbon materials were also used for the modification of carbon paste electrodes as well as for the preparation of novel solid phase microextraction fibers. The peak current of the differential pulse voltammetry curves was increased along with the amount of added carbon paste electrode modifier. The signal response was closely related to the porosity of the materials used, and increased with the increase in the specific surface area. The amount of 4-chlorophenol extracted from the samples by the solid phase microextraction fiber's surface was also correlated with the specific surface area of the tested materials. All the novel fibers were better than the commercially available fibers prepared from polidimethylosiloxane.

Ultraviolet derivatization of low-molecular-mass thiols for high performance liquid chromatography and capillary electrophoresis analysis.

Thiols play an important role in metabolic processes of all living creatures and their analytical control is very important in order to understand their physiological and pathological function. Among a variety of methods available to measure thiol concentrations, chemical derivatization utilizing a suitable labeling reagent followed by liquid chromatographic or electrophoretic separation is the most reliable means for sensitive and specific determination of thiol compounds in real world samples. Ultraviolet detection is, for its simplicity, commonly used technique in liquid chromatography and capillary electrophoresis, and consequently many ultraviolet derivatization reagents are in used. This review summarizes HPLC and CE ultraviolet derivatization based methods, including pre-analytical considerations, procedures for sample reduction, derivatization, and separation of the primary biological aminothiols--cysteine, homocysteine, cysteinylglycine and glutathione, and most important thiol-drugs in pharmaceutical formulations and biological samples. Cognizance of the biochemistry involved in the formation of the analytes is taken.

Analysis of urine for cysteine, cysteinylglycine, and homocysteine by high-performance liquid chromatography.

A new analytical method is proposed for simultaneous determination, by liquid chromatography, of the three main urinary thiols-cysteine, cysteinylglycine, and homocysteine. To measure the total amount of these thiols urine is reduced with sodium borohydride, to convert disulfides to thiols which are then derivatized with 2-chloro-1-methylquinolinium tetrafluoroborate. Separation and quantitation of the 2-S-quinolinium thiol derivatives formed were achieved by high-performance liquid chromatography with detection at 355 nm. Validation showed the method enabled reliable simultaneous determination of these aminothiols in urine. The calibration graphs for each analyte, obtained by use of normal urine spiked with increasing amounts of cysteine, cysteinylglycine, and homocysteine, were linear (R2 > or = 0.997) over the range covering most practical situations. The recovery of the assay was 98-100% and sensitivity was 0.12-0.25 micromol L(-1). The method was applied to 91 different samples of normal urine to establish reference values for the aminothiols, normalized on creatinine.

Analysis of plasma thiols by high-performance liquid chromatography with ultraviolet detection.

The procedure for measurement of different forms of four plasma thiols cysteine, cysteinylglycine, glutathione and homocysteine is proposed. The analytes are derivatized with thiol-specific ultraviolet labeling reagent, 2-chloro-1-methylquinolinium tetrafluoroborate, and separated from each other, reagent excess and plasma matrix constituents by reversed-phase high performance liquid chromatography with detection at 355 nm. Oxidized forms are converted to their thiol counterparts by reductive cleavage with sodium borohydride prior to derivatization step. In order to circumvent the loss of reduced fraction of thiols due to oxidation during sample preparation, the derivatization reagent is added to whole blood immediately after collection and before separation of plasma from erythrocytes. The method measures total thiols, total free thiols, protein-bound thiols and reduced thiols. The method is linear within the physiological and pathological ranges of thiols and is applied for plasma samples donated by apparently healthy volunteers.