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Amikacin, gentamicin and tobramycin are aminoglycoside antibiotics mostly used for the treatment of a wide range of aerobic Gram negative bacteria. Lack of a UV chromophore as well as their polar and non-volatile nature make direct determination of these aminoglycosides by conventional LC and GC very challenging. Existing analytical methodology is either expensive, complicated or time consuming. In this work, a thin layer chromatography – flame ionization method was developed for fast analysis of these aminoglycosides in pharmaceutical formulations. Paromomycin was used as internal standard for quantitation. Development of the rod with one single solvent mixture was sufficient to achieve the desired separation of target components. Good determination coefficients (>0.997) were achieved for all target analytes. Repeatability, recovery and detection limits were determined and reported. A total of 5 samples in duplicate can be analyzed simultaneously within 25 s. This method offers the advantage of being able to analyze these aminoglycosides without any need for derivatization or laborious coloration. The developed method was applied to the analysis of some pharmaceutical commercial samples.

Liquid chromatography (LC) hyphenated to mass spectrometry is currently the most widely used means of determining metabolic phenotypes via both untargeted and targeted analysis. At present a range of analytical separations, including reversed-phase, hydrophilic interaction and ion-pair LC are employed to maximise metabolome coverage with ultra (high) performance liquid chromatography (UHPLC) increasingly displacing conventional high performance liquid chromatography because of the need for short analysis times and high peak capacity in such applications. However, it is widely recognized that these methodologies do not entirely solve the problems facing researchers trying to perform comprehensive metabolic phenotyping and in addition to these "routine" approaches there are continuing investigations of alternative separation methods including 2-dimensional/multi column approaches. These involve either new stationary phases or multidimensional combinations of the more conventional materials currently used, as well as application of miniaturization or "new" approaches such as supercritical HP and UHP- chromatographic separations. There is also a considerable amount of interest in the combination of chromatographic and ion mobility separations, with the latter providing both an increase in resolution and the potential to provide additional structural information via the determination of molecular collision cross section data. However, key problems remain to be solved including ensuring quality, comparability across different laboratories and the ever present difficulty of identifying unknowns.

International audience; Individual molecular components of soil organic matter (SOM) have been studied since the early 19th century. Their characterization is essential, because knowledge of the molecular structures constituting SOM allows for the detailed understanding of its origin and the processes implicated in soil C sequestration. This provides the basis for target-oriented development of management practices to optimize ecosystem services provided by soil. The aim of this review is to give an overview about the major analytical developments and the information gain that could be achieved by application of molecular methods in SOM research. Up to the 1980s, studies concentrated on the characterization of the chemical nature of SOM. Analyses were mainly based on soluble OM compounds, which were fractionated chemically into humic and fulvic acids. During the 1990s, the focus changed and scientists were more interested in biological processes controlling SOM formation and its dynamics. Introduction of physical fractionation and combination of molecular and isotopic techniques allowed assessment of composition, origin, and turnover of SOM within specific localizations in the mineral soil matrix. Analyses of the dynamics of single molecules led to a massive change of paradigms. Long residence times of SOM are no longer explained by chemical recalcitrance but by microbial products being stabilized by the interaction with soil minerals and microbial inaccessibility. In recent years, techniques yielding results with high molecular and spatial resolution were introduced, which will allow the acquisition of much more detailed information, moving a step further toward elucidating the nature and properties of SOM.

GABA and glutamate sampled from the brain by microdialysis do not always fulfill the classic criteria for exocytotic release. In this regard the origin (neuronal vs. astroglial, synaptic vs. extrasynaptic) of glutamate and GABA collected by microdialysis as well as in the ECIF itself, is still a matter of debate. In this overview microdialysis of GABA and glutamate and the use of microsensors to detect extracellular glutamate are compared and discussed.During basal conditions glutamate in microdialysates is mainly derived from non-synaptic sources. Indeed recently several sources of astrocytic glutamate release have been described, including glutamate derived from gliotransmission. However during conditions of (chemical, electrical or behavioral) stimulation a significant part of glutamate might be derived from neurotransi-nission. Interestingly accumulating evidence suggests that glutamate determined by microsensors is more likely to reflect basal synaptic events. This would mean that microdialysis and microsensors are complementary methods to study extracellular glutamate. Regarding GABA we concluded that the chromatographic conditions for the separation of this transmitter from other amino acid-defivatives are extremely cfitical. Optimal conditions to detect GABA in microdialysis samples - at least in our laboratory - include a retention time of approximately 60 min and a careful control of the pH of the mobile phase. Under these conditions it appears that 50-70% of GABA in dialysates is derived from neurotransmission. (c) 2007 Elsevier Inc. All fights reserved.

A mathematical procedure using the Matlab (R) PDE toolbox to calculate the numerical constant appearing in the general Taylor-Aris expression for the dispersion in a laminar flow through open-tubular conduits with a variety of quasi-rectangular cross-sectional shapes is described. The procedure has been applied to assess the effect of some of the most frequently occurring etching imperfections (linear or curved tapering of the inter-pillar distance along the depth coordinate, occurrence of local notches) in etched pillar array columns. In addition, covering a broad range of possible geometries, a number of new shapes and optimal geometries to minimize the dispersion in open-tubular microchannels and pillar array columns have been proposed. Making a full shape-sensitivity study, it was also found that, whereas the proposed designs can theoretically reduce the dispersion up to a factor of 8, relatively small deviations from this ideal shape can however again dramatically increase the dispersion. Designers should therefore be very careful before implementing an optimized shape and should first aim at solving the etching imperfection problems. (C) 2014 Elsevier B.V. All rights reserved.

The study of radial and axial temperature profiles always has been an area interest both in liquid chromatography (LC) and supercritical fluid chromatography (SFC). Whereas in LC always an increase in temperature is observed due to the dominance of viscous heating, in SFC, especially for low modifier content, a decrease in temperature is found due to the much larger decompression cooling. However, for higher modifier content and higher operating pressure, the temperature effects become a trade-off between viscous heating and decompression cooling, since in SFC the latter is a strong function of operating pressure and mobile phase composition. At a temperature of 40 °C and for neat CO2, the effect of decompression cooling and viscous heating cancel each other out at a pressure 450 bar. This pressure decreases almost linearly with volume fraction of methanol to 150 bar at 25 vol%. As a result, both cooling and heating effects can be observed when operating at high back pressure, large column pressure drops or high modifier content. For example at a back pressure of 150 bar and a column pressure drop of 270 bar decompression cooling is observed throughout the column. However at 300 bar back pressure and the same pressure drop, the mobile phase heats up in the first part of the column due to viscous heating and then cools in the second part due to decompression cooling. When coupling columns (2.1 mm × 150 mm, 1.8 μm fully porous particles) at very high operating pressure (e.g. 750 bar for 8 vol%), the situation is even more complex. E.g. at a back pressure of 150 bar and using 8 vol% methanol, viscous heating is only observed in the first column whereas only decompression cooling in the second. Further increasing the inlet pressure up to 1050 bar resulted in no excessive temperature differences along the column. This implies that the inlet pressure of SFC instrumentation could be expanded above 600 bar without additional band broadening caused by excessive radial temperature differences.

The goal of this study was to monitor the anti-proliferative activity of Rosmarinus officinalis and Salvia officinalis extracts against cancer cells and to correlate this activity with their phytochemical profiles using liquid chromatography/diode array detection/electrospray ion trap tandem mass spectrometry (LC/DAD/ESI-MSn). For the quantitative estimation of triterpenic acids in the crude extracts an NMR based methodology was used and compared with the HPLC measurements, both applied for the first time, for the case of betulinic acid. Both extracts exerted cytotoxic activity through dose-dependent impairment of viability and mitochondrial activity of rat insulinoma m5F (RINm5F) cells. Decrease of RINm5F viability was mediated by nitric oxide (NO)-induced apoptosis. Importantly, these extracts potentiated NO and TNF-alpha release from macrophages therefore enhancing their cytocidal action. The rosemary extract developed more pronounced antioxidant, cytotoxic and immunomodifying activities, probably due to the presence of betulinic acid and a higher concentration of carnosic acid in its phytochemical profile. (C) 2012 Elsevier Ltd. All rights reserved. Food Chemistry

The present study investigates the validity of one of the key assumptions underlying the general plate height model of chromatography, i.e., the presumed independency of the individual band broadening contributions. More precisely, it is investigated under which conditions the mass transfer inside the stationary zone (e.g., porous pillars) is independent from the axial transport of species outside this zone, and how strongly any such dependency would affect the validity of the general plate height model of chromatography. For this purpose, detailed calculations of the species concentration distribution inside and outside the porous pillars of a computer-mimic of a porous pillar array column have been made. These simulations revealed a clear interplay between the mass transfer inside and outside the pillars, manifesting itself as an asymmetry of the species concentration distribution inside the pillars. The latter is in disagreement with the basic assumption used to calculate the value of the Cs-term of the general plate height model. The asymmetry-effect is largest at low reduced velocities, high retention factors and high intra-pillar diffusion coefficients. Fortunately, these are conditions where the Cs-term is relatively small, which might explain why the general plate height model of chromatography (and based on the symmetry assumption) can represent the band broadening in a porous pillar array within an accuracy on the order of some 1–2%.

Matrix solid-phase dispersion (MSPD) as a sample preparation method for the determination of two potential endocrine disruptors, linuron and diuron and their common metabolites, 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl) urea (DCPU) and 3,4-dichloroaniline (3,4-DCA) in food commodities has been developed. The influence of the main factors on the extraction process yield was thoroughly evaluated. For that purpose, a 3((4-1)) fractional factorial design in further combination with artificial neural networks (ANNs) was employed. The optimal networks found were afterwards used to identify the optimum region corresponding to the highest average recovery displaying at the same time the lowest standard deviation for all analytes. Under final optimal conditions, potato samples (0.5 g) were mixed and dispersed on the same amount of Florisil. The blend was transferred on a polypropylene cartridge and analytes were eluted using 10 ml of methanol. The extract was concentrated to 50 mu l of acetonitrile/water (50:50) and injected in a high performance liquid chromatography coupled to UV-diode array detector system (HPLC/UV-DAD). Recoveries ranging from 55 to 96% and quantification limits between 5.3 and 15.2 ng/g were achieved. The method was also applied to other selected food commodities such as apple, carrot, cereals/wheat flour and orange juice demonstrating very good overall performance. (C) 2008 Elsevier B.V. All rights reserved. Journal of Chromatography A

In this work, a preconcentration method for the simultaneous determination of the endocrine disrupting chemicals (EDCs), diuron (1-(3,4dichlorophenyl)-3,3-dimethylurea), and linuron (3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea), as well as their metabolites DCPU (1-(3,4dichlorophenyl) urea), DCPMU (1-(3,4-dichlorophenyl)-3-methylurea) and 3,4-DCA (3,4-dichloroaniline), present in natural waters was optimized and validated. Water was subjected to solid-phase extraction (SPE) and the influence of several experimental variables affecting the extraction efficiency of the target analytes was studied, including the sorbent material, elution solvents, pH and breakthrough volume, as well as some solution parameters that is, ionic strength and organic matter content. A high-performance liquid chromatography system coupled to UV-diode array detector (DAD) was used for the target analytes quantification at the optimum conditions described in Part 1. The fully nested experimental design, adapted to the new experimental parameters, was used to study the measurement uncertainty arising from trueness by estimating proportional bias (in terms of recovery). The overall recoveries of the target analytes were in the range of 71.6-90.2%, except 3,4-DCA for which a low overall recovery of 51.4% was obtained. The analytical procedure was shown to be linear over the studied range of concentration (25-400 ng/1), exhibiting satisfactory repeatability and reaching limits of detection in the 1.3-11.2 ngl range for all, quite different in nature, water types. The SPE method was further applied for the determination of the selected EDCs and their metabolites in water samples taken from selected study stations in the region of Epirus (N.W. Greece) corresponding to the sediment samples locations (Part 1). (c) 2007 Elsevier B.V. All rights reserved. Journal of Chromatography A

The simultaneous monitoring of malondialdehyde, pentanal and hexanal, final products of lipid peroxidation is reported, using a headspace solid-phase microextraction (HS-SPME) technique with on-fibre derivatisation. The aldehydes are extracted and subjected to on-sorbent derivatisation into stable hydrazones with 2,4,6-trichlorophenylhydrazine (TCPH) and analyzed. The degree of inhibition of oxidation is performed by monitoring the chlorinated hydrazones after thermal desorption, by gas chromatography-electron capture detection. The procedure was employed to evaluate in vitro the antioxidant activity of Hypericum perforatum L. extracts and of the well-known antioxidant vitamin E following induction of oxidation of sunflower oil, as a model lipid system. Prior to the measurement of antioxidant activity, the optimal process conditions, i.e. headspace volume, temperature, agitation, extraction/derivatisation time and desorption time and temperature were properly established. Aqueous extracts of H. perforatum L. exhibited the highest antioxidative effect. The method is shown to be promising for screening purposes for antioxidant substances and natural extracts. (C) 2007 Elsevier B.V. All rights reserved. Journal of Chromatography A

A multiresidue method for the determination of 20 organochlorine pesticides (aldrin, endrin, dieldrin, alpha-BHC, beta-BHC, gamma-BHC, delta-BHC, alpha-chlordane, gamma-chlordane, 4,4'-DDE, 4,4'-DDT, 4,4'-DDD, endosulfan 1, endosulfan 11, endosulfan sulfate, endrin aldehyde, heptachlor, heptachlor epoxide, endrin ketone and methoxychlor) and eight PCB congeners (PCB 20, 28, 52, 101, 118, 138, 153, 180) in chicken eggs has been developed and validated. The samples were extracted by a simple and fast matrix solid-phase dispersion (MSPD) method using Florisil as the sorbent material and dichloromethane/hexane (1: 1) as the eluting system. Further purification of the extracts was conducted using a conventional clean-up procedure with concentrated sulphuric acid. Determination and quantitation of PCBs and OCs residues was carried out using a gas chromatograph equipped with an electron capture detector (GC-ECD). A mass spectrometric detector (GC-MS) in the selected ion monitoring (SIM) mode was used for confirmation purposes. The method detection limits were < 0.7 ng g(-1) for all PCBs and OCs and the relative standard deviations for analyses of samples fortified over the range of 10-200 ng g(-1) were < 8%. All compounds provided average recoveries (spiked at five concentration levels) ranging from 82% to 110%. The proposed method was used to analyze 30 commercial products taken from local markets in the course of a 3-month sampling campaign. (c) 2006 Elsevier B.V. All rights reserved. Analytica Chimica Acta

The gas chromatographic determination of amino acids via their simultaneous extraction, preconcentration and pentafluorobenzylation is reported. Using phase-transfer catalysis (PTC), the amino acids under study were transformed to their pentafluorobenzyl adducts. The method was tested for different catalysts and tetrabutylammonium bromide provided favorable features in comparison to the other PTCs. The derivatization procedure was optimized and the best reaction conditions are given. With the exception of arginine, 19 amino acids were converted to volatile derivatives and analyzed with GC/MS and GC/FID at low concentration levels with acceptable sensitivity and good reproducibility. The LODs were found to range from 0.7 to 2.3 mu M for the GC/MS analyses and from 1.7 to 6.9 mu M for GC/FID analyses. The method practicability and applicability were confirmed by the analysis of urine, fruit juice and wheat flour for the determination of the amino acids under study. Protein-bound amino acids were analyzed after an alkaline hydrolysis step with 5 M NaOH applying this method to wheat flour with an overall procedure duration less than 12 h. The optimized protocol was applied to these samples without any pretreatment and their amino acid concentrations were calculated from the appropriate calibration plots. (c) 2006 Elsevier B.V. All rights reserved. Journal of Chromatography A

Phase-transfer catalysis (PTC) has been a well-established technique on the synthesis of organic chemicals for more than three decades. Its scope and underlying mechanistic features have been the subject of numerous studies and appear to be recognized and understood. This review is intended to approach the subject by focusing on the extraction-preconcentration-derivatization/reaction prior to analysis and to chronicle recent progress made. We present the salient aspects of PTC modes followed by a brief review of mechanistic considerations including reaction mechanisms, selectivity, rates and kinetics pointing out to the potency of PTC in analytical chemistry. Specific guidelines are given on how to optimize a PTC-based analysis with respect to catalyst, solvent, reaction conditions and more, based on reaction characteristics. Finally, using the PTC principles as a framework, selected real-life applications are provided, the capabilities and limitations of PTC are addressed for the purpose of direct analysis of organic analytes and certain advantages are highlighted. (c) 2005 Elsevier B.V All rights reserved. Analytica Chimica Acta

The determination of commercial plasticizers (di-(2-ethylhexyl)adipate (DEHA) and acetyl tributyl citrate (ATBC)) in aqueous solutions is described. The newly proposed technique of applying microwaves to cloud point extracts in order to enable combination with gas chromatographic analysis has been used for this purpose. Both plasticizers were entrapped in the micelles of the non-ionic surfactant Triton X-114 and removed from the bulk phase by centrifugation. Micellization was enhanced by increasing the ionic strength of the solution with concentrated NaCl. Extraction recoveries of the proposed method were over 95% for water and 3% (w/v) aqueous acetic acid and over 85% for 10% (v/v) aqueous ethanol, respectively. The calibration curves obtained, following the proposed methodology have a linear range between 50 and 2000 mu g/L for each analyte while the detection limits were as low as 15 and 19 mu g/L for DEHA and ATBC, respectively, with an RSD below 5% even for low concentrations. As an analytical demonstration the proposed methodology was applied for the determination of the migration levels of the selected plasticizers from a PVC food packaging film into aqueous simulants. (c) 2005 Elsevier B.V. All rights reserved. Journal of Chromatography A

We present contemporary developments in the field of surfactants and micellar systems together with their applications in analysis, with the aim of highlighting some of the most important aspects of this area of research. We pay particular attention to speciation through cloud-point extraction (CPE), as well as to the differentiation of metallic species, oxidation states and complexes prior to their determination. We also present a theoretical background and a guide for experimentally optimizing CPE. We conclude by discussing some problems arising from the use of surfactant systems, while proposing future trends and potential new areas for their application. (c) 2005 Elsevier Ltd. All rights reserved. Trac-Trends in Analytical Chemistry

Peroxidation of lipids produces low-molecular-weight carbonyl compounds, which are reactive with biological nucleophiles. The analysis of these compounds is often difficult. A multicomponent method for the determination of 11 of them in biological samples is reported. The samples are subjected to a pretreatment-derivatization procedure followed by gas chromatographic analysis with either electron-capture detection (ECD) or mass-selective detection (MSD) in the selected-ion monitoring mode. The procedure involves derivatization of the analyte with 2,4,6-trichlorophenylhydrazine, extraction with n-hexane, and separation of the derivatization products on a nonpolar gas chromatographic column. The concentration of the derivatization reagent, pH, reaction time, temperature, and presence of extraneous ions were investigated to determine the optimal derivatization conditions. Under these conditions, the method allows for the selective detection of low-molecular-weight carbonyl compounds at femtomole levels in several biological materials such as plasma, urine, and bovine serum albumin without interferences. The limits of detection were in the ranges 0.01-0.2 muM for ECD and 0.15-1.5 muM for MSD. The mean procedural recoveries obtained during the method validation were within the range 85-95% and the intra- and interassay standard deviations do not exceed 4.6 and 6.1%, respectively. (C) 2004 Elsevier Inc. All rights reserved. Anal Biochem

18 páginas, 5 figuras, 5 tablas., Pesticides are applied widely to protect plants from disease, weeds and insect damage, and usually come into contact with soil, where they undergo a variety of transformations that provide a complex pattern of metabolites. This article reviews the most relevant analytical methods for determining pesticides and their transformation products in soils. We address some recent advances in sampling and sample-preparation technologies for soil analysis. We discuss and critically evaluate procedures, such as liquid extraction methods (pressurized liquid extraction or microwave-assisted extraction) and solid-phase based methods (headspace solid-phase microextraction, solid-phase microextraction or matrix-solid-phase dispersion). Analysis of pesticides is generally carried out by gas chromatography (GC) or liquid chromatography (LC) coupled to different detectors, especially to mass spectrometers (MSs). However, alternative and/or complementary methods, using capillary electrophoresis (CE), biosensors and bioassays have emerged recently. We also consider the advantages and the disadvantages of the various methodologies., This study has been supported by the EU (ECOSLOPES QLRT-2000-00289) and the Spanish Ministry of Science and Education (CICYT REN2001-1716).

The first amperometric biosensing method for the determination of L-fucose is described. L-Fucose is the objective of much current research, as it is considered as a potential marker for various pathologic disorders. Recombinant L-fucose dehydrogenase, having as cofactor beta-nicotinamide adenine dinucleotide phosphate (NAD(+)P), was cross-linked in a water-soluble photosensitive polymer matrix, that is, polyvinyl alcohol (PVA) modified with styrylpyridinium (SbQ), in the presence of BSA and glutaraldehyde. The resulting membrane was sandwiched between two polycarbonate membranes and was mounted in an amperometric cell. The oxidation of the enzymatically produced NADPH was monitored at a platinum anode at +0.25 V versus a silver pseudoreference electrode in the presence of ferricyanide. The system was fully optimized with respect to various analytical parameters. Regarding to the mechanical properties of the membrane and the storage stability of the immobilized enzyme, various parameters were also optimized. Several methods for the pretreatment of urine samples were investigated. Treatment of the samples with PbO2 found to eliminate the interference effect of various electroactive species exist in urine; optimum incubation time was determined since at prolonged incubation times L-fucose is also affected. Calibration curves for the direct and the mediated monitoring of NADPH were liner over the concentration ranges 0.04-1.0 mM (r(2) = 0.9995) and 0.03-3.0 mM (r(2) = 0.9997) fucose, respectively. The detection limits (S/N 3) were 2 and 1.5 muM fucose, respectively. The R.S.D. of the mediated biosensor is better than 1.5% (n = 10, 0.5 mM fucose). The proposed biosensor correlates well with a reference enzymatic method and exhibits very good working and storage stability. (C) 2004 Elsevier B.V. All rights reserved. Biosens Bioelectron

An in-vial simple method for the combined derivatization and extraction of phenolic acids and flavonoids from plant extracts and their direct determination with GC-MS, is described. The method is taking advantage of the beneficial potentials of phase transfer catalysis (PTC). Catalysts in soluble and polymer-bound form were tested with the latter being the format of choice due to its high reaction yield and facile separation from the rest of the reaction system. Optimization of experimental conditions was established. Chromatographic separation of eight phenolic acids and four flavonoids methylated via the PTC derivatization step was achieved in 45 min. The detection limits for the described GC-MS(SIM) method of analysis ranged between 2 and 40ng/ml whereas limits of quantitation fall in the range 5-118 ng/ml, with flavonoids accounting for the lowest sensitivity due to their multiple reaction behavior. Four methanolic extracts from Tilia europea, Urtica dioica, Mentha spicata and Hypericumperforatum grown wild in north-westem Greece and four aquatic infusions from commercially available Mentha spicata, Origanum dictamnus, Rosemarinus officinalis and Sideritis cretica were analyzed. Good trueness of the method was demonstrated as no matrix effects were found for the analytes concerned. (C) 2004 Elsevier B.V. All rights reserved. Journal of Chromatography A

A derivatization-extraction method that avoids tedious preconcentration steps is established in order to determine amino acids accurately at nanogram levels. The method involves conversion of the analytes of concern to N(O,S)-ethoxycarbonyl amino acid ethyl esters and subsequent extraction by single-drop microextraction (SDME) followed by GC analysis. The reaction proceeds smoothly and rapidly under ultrasonication which removes the bubbles from the bulk solution. Precision is acceptable and 12 non-hydrolyzed amino acids can be determined in urine in this manner. As long as the extraction conditions are consistently applied, quantitative analysis can be performed accurately. The limits of detection were satisfactory in the range 0.010-0.025 mug/ml for GC-FID and 0.26-68 ng/ml for GC-MS(SIM) with 1 ml sample volume. (C) 2004 Elsevier B.V. All rights reserved. Journal of Chromatography B-Analytical Technologies in the Biomedical and Life Sciences

The photochemical behavior of the sunscreen agent octyl-dimethyl-p-aminobenzoic acid (ODPABA) was studied in different aqueous solutions and under different conditions. ODPABA photolysis was performed under laboratory conditions using a xenon light source and under natural sunlight conditions in sea, swimming pool as well as in distilled water. The influence of dissolved organic matter (DOM) on the degradation kinetics was also studied in the presence of various concentrations of humic acids (HA). The phototransformation was shown to proceed via pseudo-first-order reaction in all cases and the reaction rates followed the order: distilled water > swimming pool water > seawater, depending mainly on the presence of dissolved organic matter that retarded the photolysis reaction. Kinetic experiments were monitored with HPLC/UV-DAD and the half-lives (t(1/2)) varied between 1.6 and 39 h in simulated solar irradiation and between 27 and 39 h in natural sunlight conditions. The product distribution during illumination was strongly dependent on the constitution of the irradiated media. Irradiation of the aqueous ODPABA solutions gave rise to several transformation products that were isolated by means of solid-phase extraction (SPE) and identified using GC-MS techniques. These were formed mainly through dealkylation and hydroxylation reactions and were detected in all aqueous solutions investigated. In the case of swimming pool water some additional byproducts were isolated and were tentatively identified as chlorinated intermediates, formed by the subsequent chlorination of the parent molecule as well as other intermediates. (C) 2003 Elsevier B.V. All rights reserved. Journal of Chromatography A

A method has been developed for the trace determination of two sunscreen constituents (2-hydroxy-4-methoxybenzophenone and octyldimethyl-p-aminobenzoic acid) in water samples, which are commonly used in commercial formulations. The method employs solid-phase microextraction (SPME) and gas chromatography with flame ionization and mass spectrometric detection. The technique was developed with headspace and direct sampling in order to demonstrate the applicability of these SPME extraction modes for the identification of these two UV absorbing compounds in waters. The main parameters affecting the SPME process, such as desorption time, extraction time profile, salt additives, pH, and temperature, were investigated, The poly(dimethylsiloxane) 100-mum and polyacrylate 85-mum fiber coatings were found to be the most efficient for the extraction of these compounds from aqueous matrices, Linear calibration curves in the wide range of 10-500 mug/l were obtained for both compounds yielding typical RSD values of 5-9% for both extraction modes, ne recoveries were relatively high, 82-98%, with quantitation limits below I mug/l. A comparison between the proposed methods and the conventional multiresidue solid-phase extraction revealed that the proposed technique(s) can be reliably used for sunscreen residue measurement in water samples with satisfactory results. (C) 2002 Elsevier Science B.V. All rights reserved. Journal of Chromatography A

2,5-Hexanedione (2,5HD) is the principle metabolite of n-hexane and methyl ethyl ketone in human urine. In this paper, a rapid and highly sensitive method for the determination of urinary 2,5HD by gas chromatography-electron capture detection and gas chromatography-mass selective detection is described. The method comprises, optionally, acid hydrolysis before the analyte is being derivitized with 2,4,6-trichlorophenyl hydrazine (TCPH) towards the formation of a chlorinated hydrazone derivative for 2,5HD analysis. The reaction conditions such as temperature, time, reagent concentration and pH were optimized properly. The detection limit of the method - defined as signal to noise ratio = 3 - is as low as 0.4 and 1.5 muM using the ECD and MSD (SIM mode), respectively. The linearity of the detection systems extends up to 50 muM of 2,5HD with correlation coefficients better than 0.9995. The within-day and between-day reproducibility for a urine sample of 10 muM in 2,5HD were 2.6 and 3.2%, respectively. Spiked pooled samples with various concentrations in the range 5-10 muM were processed following the proposed procedure. The recovery was satisfactory enough ranging from 92 to 104%. The method was applied to the analysis of urine samples received from people working in a chemical laboratory and the results revealed variable, yet low concentrations of 2,5HD in the hydrolyzed samples. (C) 2001 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta

Kefalograviera cheeses (five trials) of different sodium content were made from split lots of curd by varying the salting processes, i.e, brine - and dry - salting, with NaCl (control) or a mixture of NaCl/KCl (3:1 or 1:1, w/w basis). The extent and characteristics of proteolysis in the cheeses were monitored during aging by Kjeldahl determination of soluble nitrogen fractions (water-soluble nitrogen [WSN], trichloroacetic acid [TCA]-SN, phosphotungstic acid [PTA]-SN), the cadmium-ninhydrin method for the determination of total free amino acids (FAA), urea-polyacrylamide gel electrophoresis of cheese proteins, followed by densitometric analysis of the alpha (s1)- and beta -casein fractions, reverse-phase high-performance liquid chromatography (HPLC) analysis of the water-soluble extracts of cheeses, and ion-exchange HPLC analysis of FAA. The results showed that proteolysis was similar in control and experimental cheeses at all sampling ages, indicating that the partial substitution of NaCl by KCI in the manufacture of Kefalograviera cheese did not significantly influence the extent and characteristics of proteolysis during cheese aging. (C) 2001 Elsevier Science Ltd. All rights reserved. Food Chemistry

A simple procedure is described for I he simultaneous extraction and HPLC determination of phenols and tocopherols in virgin olive oil. The extraction was carried out using methanol and an isopropanol- methanol mixture. Separation was achieved on a reversed phase C-18 column with acetic acid/water-methanol-acetonitrile-isopropanol mixture under gradient elution. Detection was accomplished with UV detection at lambda==280 nm. Using this method, simple and complex phenols as well as alpha -tocopherol can be determined in one run. Phenolic compounds were totally extracted whereas an average recovery of 80% was achieved for alpha -tocopherol. Validation of method is reported for olive oil samples with varying concentrations of alpha -tocopherol and phenolic compounds. (C) 2001 Elsevier Science Ltd. All rights reserved. Food Chemistry

A series of polymeric membranes have been employed as outer barriers in an amperometric malate dehydrogenase (MDH)/diaphorase (DI) or MDH/DI/NAD(+)/mediator enzyme electrode for the determination of malate in undiluted neutral or acidic media. MDH/DI were physically entrapped with NAD(+) and mediator in a mixed ester cellulose membrane. Outer membranes such as non-anionic surfactant-modified cellulose acetate/Tween-80 and unplasticised spin coated PVC/polycarbonate (PC) resin in conjunction with an ascorbate oxidase (AOD) layer were utilised. Mechanical strength, thickness studies and diffusional properties of the membranes were investigated. Hexacyanoferrate(III), 2,4-dichlorophenolindophenol (DCPI) and naphthoquinone (NQ) were tested as mediators for enzymatically produced NADH using cyclic voltammetry. Analytical utility of the sensors is demonstrated. (C) 2000 Elsevier Science B.V. All rights reserved. Analytica Chimica Acta