M. Aranzazu Goicolea

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.

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.

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.

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.

A retention time locked gas chromatography–mass spectrometry method based on stir-bar sorptive extraction and thermal desorption for automated determination of synthetic musk fragrances in natural and wastewaters

A stir-bar sorptive extraction (SBSE) method followed by automated thermal desorption (ATD) coupled to gas chromatography-mass spectrometry was optimized for determining trace levels of 18 synthetic fragrances (musks). Using the method developed a retention time locked library is created and converted to a screening database. This homebuilt database can be combined with deconvolution software for the identification of musks. A factorial design was provide to evaluate the main parameters and interactions between the factors affecting the process of SBSE. Operating with de MS-detector in the full-scan mode, high sensitivity with detection limits in the low ng L(-1) range, and good linearity and repeatability were achieved for all musks. The applicability of the method developed was tested in natural waters (surface and groundwater) and wastewater of a plant treatment (WWPT). The results obtained confirmed the usefulness of the proposed method for the determination and unequivocal identification of musks. This approach enables the developed method to be used for routine screening of environmental samples and posterior rapid quantitation of the positive samples.

Screening and quantification of antipsychotic drugs in human brain tissue by liquid chromatography-tandem mass spectrometry: Application to postmortem diagnostics of forensic interest

A quantitative LC-MS/MS method has been developed for the simultaneous determination of 17 antipsychotic drugs in human postmortem brain tissue. Sample preparation was performed using Hybrid Solid Phase Extraction-Precipitation technology for the removal of endogenous protein and phospholipid interferences. The chromatographic separation was performed for 16 min on a C8 column, which used a gradient elution of formate ammonium and acetonitrile, and a flow rate gradient. Triple quadrupole mass spectrometry was employed to generate tandem mass spectrometric (MS/MS) data of the target analytes to select the ion m/z signals. Quantitation of the analytes was performed by operating in the dynamic multiple reaction monitoring (dMRM) mode using an electrospray ionization interface. Calibration curves prepared in the spiked brain tissue were linear in the range 20-8000 ng/g (r(2)>0.993) for all drugs (except olanzapine). Within- and between-day coefficients of variation were lower than 25% for all drugs at the LOQ. The LOQ in the matrix ranged between 2 ng/g and 80 ng/g. The method was successfully applied to the unequivocal identification and accurate quantification of antipsychotic drugs in human postmortem brain tissues: therefore, this method can be used in forensic investigations.

Characterization of organic gunshot residues in lead-free ammunition using a new sample collection device for liquid chromatography–quadrupole time-of-flight mass spectrometry

The identification of characteristic organic gunshot residues (OGSR) provides conclusive evidence in the elucidation of elemental profiles when lead-free ammunition is fired. OGSR also prevents false negatives. Toward this aim, a quick and efficient method based on liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF) was developed to detect and identify 18 gunpowder additives in gunshot residues (GSR). The unequivocal identification of target analytes was assured by using MS/MS mode. Swabs were compared with home-modified tape lift supports covered with a PTFE layer to determine the better sampling technique. The modified tape lift provided better extraction recoveries and enabled the analysis of inorganic and organic GSR simultaneously. The developed method was applied to the analysis of GSR from four different lead-free ammunitions. Diphenylamine and its nitrated degradation products and centralites were identified in all samples, providing strong evidence of GSR.

Multimembrane carbon fiber microelectrodes for amperometric determination of serotonin in human urine

An electrochemical sensor for the determination of serotonin in urine was prepared using Ni(II)-phthalocyanine and Nafion to modify the surface of a 4 mm length carbon fiber microelectrode. The resultant sensor was found to improve the response towards this neuronal amine versus the microelectrode without the polymer films. Different polymerization conditions, as well as different conditioning solutions and buffer systems, were investigated in order to optimize the response of the electrodes. Square wave voltammetry (SWV) is proposed as a direct method for determination of serotonin in human urine, after a solid-liquid extraction process. The proposed method enables a detection limit for serotonin of 0.80 +/- 0.04 microgram L-1 to be achieved at a reduction potential of 0.35 V, with an overall prediction error of 2.2% and recoveries of 93%.