Application of ABTS radical cation for selective on-line detection of radical scavengers in HPLC eluates

The radical cation 2,2 ' -azinobis-(3 -ethylbenzothiazoline-6-sulfonate), (ABTS(.+)) was utilized in an on-line HPLC method for the detection of radical scavengers in complex matrixes. The HPLC-separated analytes react postcolumn with the preformed ABTS(.+), and the induced bleaching is detected as a negative peak by an absorbance detector at 734 nm, An optimized instrumental and experimental setup is presented. The method is suitable for both isocratic and gradient HPLC runs using mobile phases containing 100% organic solvent or,its solution in water, weak acids, or buffers (pH 3-7.4), The method is sensitive, selective, relatively simple, applicable to compounds of different chemical natures; uses common instruments and inexpensive reagents; and has a time-saving, non-laborious experimental protocol. It can also be used for quantitative analysis. The method was applied to several pure natural antioxidants and plant extracts. The minimum detectable concentration varied from 0.02 to 0.13 mug/mL, depending on the compound tested, The method can be applied to perform kinetic studies, which is illustrated by determination of Trolox equivalent antioxidant capacities (TEAC) of several known antioxidants in now injection mode

On-line coupling of solid-phase extraction with mass spectrometry for the analysis of biological samples. II. Determination of clenbuterol in urine using multiple-stage mass spectrometry in an ion-trap mass spectrometer

Solid-phase extraction (SPE) was coupled to ion-trap mass spectrometry to determine clenbuterol in urine. For SPE a cartridge exchanger was used and, after extraction, the eluate was directly introduced into the mass spectrometer, For two types of cartridges, i.e. C-18 and polydivinylbenzene (PDVB), the total SPE procedure (including injection of 1 mL urine, washing, and desorption) has been optimised, The total analysis, including SPE, elution, and detection, took 8.5 min with PDVB cartridges, while an analysis time of 11.5 min was obtained with C-18 cartridges. A considerable amount of matrix was present after extraction of urine over C-18 cartridges, resulting in significant ion suppression. With PDVB cartridges, the matrix was less prominent, and less ion suppression was observed, For single MS, a detection limit (LOD) of about 25 ng/mL was found with PDVB cartridges. With Cls cartridges an LOD of only about 50 ng/mL could be obtained. Applying tandem mass spectrometry (MS/MS) did not lead to an improved LOD due to an interfering compound, However, a considerable improvement in the LOD was obtained with MS3. The selectivity and sensitivity were increased by the combination of efficient fragmentation of clenbuterol and reduction of the noise. Detection limits of 2 and 0.5 ng/mL were obtained with C18 and PDVB cartridges, respectively. The ion suppression was 4 to 45% (concentration range: 250 to 1.0 ng/mL) after extraction of urine using PDVB cartridges, and up to 70% ion suppression was observed using Cls cartridges. With MS4, no further improvement in selectivity and sensitivity was achieved, due to inefficient fragmentation of clenbuterol and no further reduction of noise. Copyright (C) 2000 John Wiley & Sons, Ltd

Fast, high-efficiency peptide separations on a 50-mu m reversed-phase silica monolith in a nanoLC-MS set-up

Proteomic studies have stimulated the development of novel stationary phases in miniaturised chromatographic columns that permit high linear flow velocities and exhibit high resolving power. In this work, a 50-mu m reversed-phase silica-based monolith was chromatographically characterised for its use in proteomics applications using a nanoLC-MS set-up. It showed high efficiency for the separation of tryptic peptides under isocratic elution conditions (HETPmin = 5-10 mu m at 2.4 mm/s). Flow rates up to 1.95 mu L/min (18.4 mm/s) and gradient slopes up to an unusually fast 9% could be used. This resulted in rapid separations of peptide mixtures, with peak widths at half height of between 5 and 10 s. The 50-mu m monolithic column was used to analyse depleted serum from a cervical cancer patient at a throughput of one sample per 30 min. (c) 2006 Elsevier B.V. All rights reserved

Ultra-rapid non-equilibrium solid-phase microextraction at elevated temperatures and direct coupling to mass spectrometry for the analysis of lidocaine in urine

Solid-phase microextraction (SPME) has been directly coupled to an ion-trap mass spectrometer (MS) for the determination of the model compound lidocaine in urine, hereby applying MS/MS [fragmentation of [M + H](+) (m/z 235) to a fragment with m/z 86]. The throughput of samples has been increased using non-equilibrium SPME with polydimethylsiloxane (PDMS) fibers. The effect of temperature on the sorption and the desorption was studied. Elevated temperatures during sorption (65degreesC) and desorption (55degreesC) had a considerable influence on the speed of the extraction. The desorption was carried out with a home-made desorption chamber allowing thermostating. Only 1 min sorption and 1 min desorption were performed, after which IMS detection took place, resulting in a total analysis time of 3 min. Detection limits below 1 ng/mL could be obtained despite yields of only 2.1 and 1.5% for a 100- and a 30-mum PDMS-coated fiber, respectively. Furthermore, the determination of lidocaine in urine had acceptable reproducibilities, i.e., relative standard deviations (RSDs) below 10%. A limit of quantitation (RSD <15%) of about 1 ng/mL was obtained. No extra wash step of the extraction fiber was required after desorption if a 30-μm coating was used, whereas not all the analyte was desorbed from the 100-μm coating in a single desorption. Therefore, the SPME-MS/MS system with a 30-μm PDMS-coated fiber for rapid non-equilibrium SPME at elevated temperatures has interesting potential for high-throughput analysis of biological samples

Methods for reactive oxygen species (ROS) detection in aqueous environments

This review summarizes direct and indirect analytical methods for the detection and quantification of the reactive oxygen species (ROS): 1O2, O2·−/HOO·, H2O2, HO·, and CO3·− in aqueous solution. Each section briefly describes the chemical properties of a specific ROS followed by a table (organized alphabetically by detection method, i.e., absorbance, chemiluminescence, etc.) summarizing the nature of the observable (associated analytical signal) for each method, limit of detection, application notes, and reaction of the probe molecule with the particular ROS