Ramón J. Barrio

Simultaneous determination of citalopram, fluoxetine and their main metabolites in human urine samples by solid-phase microextraction coupled with high-performance liquid chromatography

A liquid chromatography method was developed for the determination of some frequently prescribed selective serotonin re-uptake inhibitors (SSRI) - citalopram and fluoxetine - and its main metabolites - demethylcitalopram, didemethylcitalopram and norfluoxetine - in human urine samples, using a previous stage of solid-phase microextraction. All the extraction parameters influencing adsorption (extraction time, temperature, pH, ion strength and organic modifier addition) and desorption (desorption time and desorption solvent mixture composition) of the analytes on the fiber have been studied. A satisfactory reproducibility for extraction from urine samples (R.S.D.<10%) was obtained. The linearity for urine ranged from 0.05 to 2 mg l(-1) with limits of detection close to 0.01 mg l(-1), which cover the typical urinary concentrations obtained for citalopram, fluoxetine and their metabolites.

Coupling solid-phase microextraction and high-performance liquid chromatography for direct and sensitive determination of halogenated fungicides in wine

A solid-phase microextraction (SPME) method coupled to high-performance liquid chromatography with diode array detection (HPLC-DAD) for the analysis of six organochlorine fungicides (nuarimol, triadimenol, triadimefon, folpet, vinclozolin and penconazole) in wine was developed. For this purpose, polydimethylsiloxane-divinylbenzene-coated fibers were utilized and all factors affecting throughput, precision, and accuracy of the SPME method were investigated and optimized. These factors include: matrix influence, extraction and desorption time, percentage of ethanol, pH, salt effect and desorption mode. The performed analytical procedure showed detectability ranging from 4 to 27 microg l(-1) and precision from 2.4 to 14.2% (as intra-day relative standard deviation, RSD) and 4.7-25.7% (as inter-day RSD) depending on the fungicide. The results demonstrate the suitability of the SPME-HPLC-DAD method to analyze these organochlorine fungicides in red wine.

Sensitive determination of triazines in underground waters using stir bar sorptive extraction directly coupled to automated thermal desorption and gas chromatography-mass spectrometry.

An automated thermal desorption-gas chromatography-mass spectrometry method for the determination of triazin herbicides in aqueous solution with excellent sensitivity was developed. The method is based on the use of stir bar sorptive extraction. The main parameters such as extraction time, sample volume, the addition of salt and organic modifiers, desorption temperature, desorption flow and desorption time which affect the efficiency of the proposed methodology are fully discussed. The proposed method is sensitive and shows a good linearity within a range of 10-10000 ng L(-1) with correlation coefficients higher than 0.998. Quantitation limits are, in all cases, below the limits accepted by European legislation for human waters consumption and ranging between 11.3 ng L(-1) and 0.7 ng L(-1). The repetitivity, expressed as a relative standard deviation, has values of lower than 8% for all analytes. Using this method, determination of 10 triazines in underground water samples was successfully performed. The average concentrations obtained in the analysis of the spiked samples at two different levels of concentration correspond to mean recoveries ranging from 94.4+/-5.1% to 106.0+/-6.3% for a significance level of 0.05.

Paracetamol voltammetric microsensors based on electrocopolymerized–molecularly imprinted film modified carbon fiber microelectrodes

A molecularly imprinted polymer is presented as a carbon fiber microelectrode coating for determining the presence of paracetamol. The polymeric film was obtained by electrocopolymerization of o-phenylenediamine and aniline in the presence of the template molecule, through the use of cyclic voltammetry. After removing the template, the signals of the microsensor were converted into physical ones by a voltammetric transductor using square wave voltammetry. Various parameters influencing the electropolymerization and voltammetric determination processes were examined and optimized. The response of the imprinted microsensor to paracetamol was linearly proportional to its concentration over the range 6.5 x 10(-6) to 2.0 x 10(-3) mol l(-1), with good stability and reproducibility (RSD < 5.6%). The detection limit was 1.5 microM. Under the experimental conditions used the voltammetric microsensor was able to differentiate between paracetamol and other closely structurally-related compounds present in biological fluids, such as certain catecholamines.

Development of a stir bar sorptive extraction based HPLC-FLD method for the quantification of serotonin reuptake inhibitors in plasma, urine and brain tissue samples.

The aim of this article is to present an analytical application of stir bar sorptive extraction (SBSE) coupled to HPLC-fluorescence detection (FLD) for the quantification of fluoxetine (FLX), citalopram (CIT) and venlafaxine (VLF) and their active metabolites - norfluoxetine (NFLX), desmethyl- (DCIT) and didesmethylcitalopram (DDCIT) and o-desmethylvenlafaxine (ODV) - in plasma, urine and brain tissue samples. All the parameters influencing adsorption (pH, ion strength, organic modifier addition, volume, extraction time and temperature) and desorption (desorption solvent composition, time, temperature and desorption mode) of the analytes on the stir bar have been optimized. For each matrix, the analytical method has been assessed by studying the linearity and the intra- and interday accuracy (89-113%) and precision (RSD<13%). The improvement of the quantification limits (0.2-2 microg l(-1) for plasma, 2-20 ng g(-1) for brain tissue and 1-10 microg l(-1) for urine, depending on the respective response for analytes) and the development of a procedure for all the matrices make this method useful in clinical and forensic analysis.

Multi-residue analysis of pharmaceutical compounds in wastewaters by dual solid-phase microextraction coupled to liquid chromatography electrospray ionization ion trap mass spectrometry

The aim of this article is to present a new procedure based on dual solid-phase microextraction (dSPME) for the simultaneous extraction of 16 pharmaceutical compounds with acidic and basic characteristics in urban wastewaters. Water samples are divided into two aliquots of 2 mL each extracted by two CW-TPR fibers at different pH values (pH 3 and 11) and with a NaCl concentration of 300 g L(-1) at 75 degrees C for 30 min. The analytes in both fibers are desorbed one after the other in the desorption chamber in static mode with mobile phase for 10 min. The extracts are injected into an LC system coupled to an ion trap mass spectrometer, leading to the accurate quantification of 16 pharmaceutical compounds in wastewaters, in MS(2) mode. All the target compounds found in wastewaters provide good signals corresponding to the protonated precursor ion [M+H](+). The parameters influencing adsorption and desorption of the analytes on fiber were optimized. The assessment of the analytical method was performed by studying the linearity (LOQ to 10 ng mL(-1)) and the intra- and interday accuracy (89.2-109.7%) and precision (RSD <13.6%). The quantification limits obtained ranged between 0.005 and 0.05 microg L(-1). The application of the method to real samples proves its effectiveness in identifying and detecting naproxen, valsartan, bezafibrate, torasemide, diclofenac, carbamazepine, citalopram, lorazepan, fluoxetine, imipramine and amitriptyline in influent and effluent wastewater treatment plant samples.

Direct potentiometric quantification of histamine using solid-phase imprinted nanoparticles as recognition elements.

A new potentiometric sensor based on molecularly imprinted nanoparticles produced via the solid-phase imprinting method was developed. For histamine quantification, the nanoparticles were incorporated within a membrane, which was then used to fabricate an ion-selective electrode. The use of nanoparticles with high affinity and specificity allowed for label-free detection/quantification of histamine in real samples with short response times. The sensor could selectively quantify histamine in presence of other biogenic amines in real wine and fish matrices. The limit of detection achieved was 1.12×10(-6)molL(-1), with a linear range between 10(-6) and 10(-2)molL(-1) and a response time below 20s, making the sensor as developed a promising tool for direct quantification of histamine in the food industry.

Chiral imprinted polymers as enantiospecific coatings of stir bar sorptive extraction devices

This paper reports the design of Molecularly Imprinted Polymers (MIP) with affinity towards (S)-citalopram using computational modeling for the selection of functional monomers and monomer:template ratio. Acrylamide was selected as functional monomer and the final complex functional monomer/template resulted in a 3:1 ratio. The polymer was synthesized by radical polymerization initiated by UV onto magnetic stir-bars in order to obtain a stir bar sorptive extraction (SBSE) device capable of selective enantiomeric recognition. After successful template removal, the parameters affecting the SBSE procedure (sample volume, ionic strength, extraction time and pH) were optimized for the effective rebinding of the target analyte. The resultant chirally imprinted polymer based stir-bar was able to selectively extract (S)-citalopram from a racemic mixture in an aqueous media with high specificity (specificity factor 4) between 25 and 500 μgL(-1). The MIP coated stir-bars can have significance for enantiospecific sample pre-concentration and subsequent analysis without the need for any chiral chromatographic separation.

Solid-phase microextraction for the determination of systemic and non-volatile pesticides in river water using gas chromatography with nitrogen-phosphorous and electron-capture detection.

A solid-phase microextraction (SPME) method combined with gas chromatography with nitrogen-phosphorous and electron capture detection for the analysis of the pesticides terbumeton, metribuzine, isomethiozine, pyridafenthion and triadimenol in river water has been developed. For this purpose, polyacrylate and polydimethylsiloxane coated fibres have been utilised and the factors affecting throughput, precision and accuracy of the SPME method have been investigated and optimised. These factors include: matrix influence, adsorption time, pH, salt effect, desorption time, temperature and also the lapse of time between sampling and injection. The performed analytical procedure showed detectability ranging from 2.0 ng l(-1) to 3.0 microg l(-1) and precision from 1.9 to 27.7% (as relative standard deviation) depending on the pesticide, the fibre and the detector used. The results demonstrate the suitability of the SPME method to analyse these non-volatile pesticides in river water.

Determination of imidacloprid and its major metabolite in soils by liquid chromatography with pulsed reductive amperometric detection

Abstract A liquid chromatography method assay for imidacloprid insecticide and its major metabolite 6-chloronicotinic acid was developed to monitor both compounds in soils. The electrochemical study of the compounds proves the reduction and adsorption processes on the mercury electrodes. Pulsed amperometric detection overcomes electrode fouling problems by repeatedly and continuously applying cleaning potentials to the working electrode. The measurement potential was −1300 mV and the cleaning and conditioning potentials were −500 and −1150 mV, respectively. The Chromatographic separation was achieved on a Spherisorb CN column 5 μm (4.1 × 250 mm). Samples were eluted with a mobile phase containing 5 × 10 −3 M phosphate buffer-acetonitrile (75 : 25), pH 2.5 at a flow rate of 1.0 ml min −1 . The limit of detection for this method was 2.7 ng of imidacloprid and 8.1 ng of 6-chloronicotinic acid.