Carme Aguilar

Solid-phase microextraction and gas chromatography with mass spectrometric detection for the determination of pesticides in aqueous samples

Abstract Solid-phase microextraction (SPME) is a fast, alternative method for extracting organochlorine, triazine and thiocarbamate pesticides. An 85-μm polyacrylate fiber was used to extract the analytes directly from aqueous samples and then thermal desorption was carried out in the hot injector of a gas chromatograph–mass spectrometer. To enhance the sensitivity of SPME, the temperature and the length of the extraction and desorption steps and the pH and salt concentration of the sample were optimized. The linearity of most of pesticides for real samples was found to be between 0.07 and 30 μg l−1 when GC–MS under full-scan acquisition was used and between 0.005 and 10 μg l−1 when selected-ion monitoring (SIM) acquisition was used. Limits of detection at the sub μg l−1 level were achieved with GC and MS under the full-scan acquisition mode and at the ng l−1 level for MS under SIM acquisition. The repeatability of the method for tap water spiked at a level of 0.5 μg l−1 (n=5) was below 25% (R.S.D.).

Determination of ciprofloxacin, enrofloxacin and flumequine in pig plasma samples by capillary isotachophoresis--capillary zone electrophoresis.

Quinolones are a group of synthetic antibiotics that are widely used in veterinary medicine. Their residues may remain in tissues, milk, etc. intended for human consumption. The European Union fixes the maximum residue limits (MRLs) of veterinary medicinal products in foodstuffs of animal origin. Analytical methods are therefore needed to determine them in biological samples. In this study, we describe capillary isotachophoresis-capillary zone electrophoresis (ITP-CZE) to analyze three quinolones, enrofloxacin (ENR), ciprofloxacin (CPR) and flumequine (FLU), in pig plasma samples. We used solid-phase extraction with Oasis HLB cartridges as a sample pretreatment clean-up step. Capillary zone electrophoresis (CZE) requires low amounts of sample and is not as sensitive as one would wish. ITP-CZE is an easy way to increase the sample loadability and sensitivity. With this system sensitivity increases 40-fold. The detection limits for CPR, ENR and FLU were 70, 85 and 50 microg l(-1), respectively, which were lower than their MRLs in different kinds of samples. This method is simple and sensitive, and is therefore an alternative tool to the existing HPLC methods for analyzing the residuals of these quinolones in biological samples.

Determination of pesticides in environmental waters by solid-phase extraction and gas chromatography with electron-capture and mass spectrometry detection

A group of pesticides with different chemical structures was determined by solid-phase extraction on LiChrolut EN cartridges and gas chromatography with electron-capture detection or mass spectrometry. The parameters affecting the solid-phase extraction process were optimized and the responses obtained by both GC detection systems were compared. The use of an electron-capture detector enabled the organochlorine pesticides studied to be determined at ng 1−1 levels whereas mass spectrometry under selective ion monitoring acquisition enabled levels of low μg 1−1 to be reached. The R.S.D. (n=6) of the method in tap water was lower than 8.1% for electron-capture and mass spectrometric detection. The methods developed were used to determine the pesticides studied in tap and river water and some pesticides could be found in Ebro river and Ebro delta water.

Sorbent preconcentration procedures coupled to capillary electrophoresis for environmental and biological applications.

Sorbent preconcentration offers good strategies to overcome the poor detection limits of capillary electrophoresis (CE). The present review focuses on the recent trends of the coupling between sorbent preconcentration techniques, namely solid-phase extraction (SPE) and solid-phase microextraction (SPME), to capillary electrophoresis (CE). Special attention is given to their environmental and biological application. We also discuss the most important advantages and disadvantages of the different methodologies and briefly outline the new trends of the coupling between sorbent preconcentration and CE.

Comparison of automated on-line solid-phase extraction followed by liquid chromatography–mass spectrometry with atmospheric pressure chemical ionization and particle beam mass spectrometry for the determination of a priority group of pesticides in environmental waters

Abstract Atmospheric pressure chemical ionization (APCI) in both positive and negative ionization modes and particle beam (PB) in electron impact (EI) and chemical ionization in positive (PCI) and negative (NCI) modes mass spectrometry (MS) coupled to high-performance liquid chromatography (HPLC) are compared in the determination of a group of pesticides. The method was combined with an automated on-line solid-phase extraction (SPE) step by preconcentrating 200 ml of sample through C18 pre-columns in order to perform the determination of these pesticides at low levels. Calibration graphs were constructed with time-scheduled selected ion monitoring (SIM) and using the internal standard method; for APCI under positive ion (PI) mode limits of detection (LODs) were between 0.8 and 4 ng l−1 and under negative ion (NI) mode of operation, between 4 and 20 ng l−1; for PB the LODs were between 0.05 to 0.2 μg l−1 under EI conditions and from 0.02 to 0.1μg l−1 under chemical ionization in both positive and negative acquisition modes. The study demonstrates the higher sensitivity of HPLC–APCI-MS compared with HPLC–PB-MS and the potential of both techniques for confirming the presence of contaminants in environmental matrices. The developed methods were validated by participating in Aquacheck inter-laboratory exercises.

Recent trends in analytical methods and separation techniques for drugs of abuse in hair

Hair analysis of drugs of abuse has been a subject of growing interest from a clinical, social and forensic perspective for years because of the broad time detection window after intake in comparison to urine and blood analysis. Over the last few years, hair analysis has gained increasing attention and recognition for the retrospective investigation of drug abuse in a wide variety of contexts, shown by the large number of applications developed. This review aims to provide an overview of the state of the art and the latest trends used in the literature from 2005 to the present in the analysis of drugs of abuse in hair, with a special focus on separation analytical techniques and their hyphenation with mass spectrometry detection. The most recently introduced sample preparation techniques are also addressed in this paper. The main strengths and weaknesses of all of these approaches are critically discussed by means of relevant applications.

Optimization of solid-phase microextraction conditions using a response surface methodology to determine organochlorine pesticides in water by gas chromatography and electron-capture detection.

A response surface methodology was applied to optimise the solid-phase microextraction (SPME) conditions using a polyacrylate-coated fiber to determine thirteen organochlorine pesticides from water. Analyses were performed using gas chromatography-electron-capture detection. Variables affecting absorption in both the headspace and immersion extraction were optimised by using a response surface generated with a Doehlert design, and the results were compared. The immersion SPME method was selected since higher recoveries were obtained for most of the compounds studied. The method developed was applied to the analysis of tap and Ebro river water samples. The linear range of most pesticides for real samples was found to be between 0.001 and 2.5 micrograms l-1 and the limits of detection were between 0.15 and 0.35 ng l-1. The repeatability and the reproducibility between days of the method (n = 6), expressed as relative standard deviation, for tap water spiked at a level of 1 ng l-1 were between 5.7 and 25.6% and between 7.6 and 26.5%, respectively.

On-line coupling of solid-phase extraction to gas chromatography with mass spectrometric detection to determine pesticides in water

A group of pesticides with different chemical structures was determined in water by on-line coupling of solid-phase extraction to gas chromatography with mass spectrometric detection through an on-column interface. A 10 mm x 2 mm I.D. precolumn packed with PLRP-S was selected for the solid-phase extraction process. The parameters affecting the transfer of the analytes from the precolumn to the GC system (e.g. flow-rate, temperature and solvent vapor exit time) were optimized. An organic modifier was added to the sample before the extraction process to avoid adsorption problems. The use of the MS detector under selected ion monitoring acquisition enabled the analytes to be quantified at sub microgram-per-litre levels preconcentrating only 10 ml of sample, and the limits of detection (S/N = 3) were between 2 and 20 ng l-1. The method was applied to the determination of the pesticides in tap and river water, and molinate was determined in Ebro river water.

Use of large-volume sample stacking in on-line solid-phase extraction-capillary electrophoresis for improved sensitivity

We present a new system for the sensitive analysis of cephalosporins by CE using both on‐line SPE and large‐volume sample stacking (LVSS). Sample volumes of 250 μL were loaded onto the SPE microcolumn which was then desorbed with 426 nL of ACN. The SPE elution plug was injected into the CE system via an in‐line valve interface filling approximately 60% of the volume of the separation capillary. Subsequently, LVSS was performed by applying a voltage of −5 kV, which resulted in the simultaneous removal of the elution solvent and the preconcentration of the analytes in a narrow zone. This way the amount of analyte loaded into the capillary could be considerably increased without serious loss of CE separation efficiency. LODs for cefoperazone and ceftiofur were in the ng/L range which represents an improvement of a factor of 8450 and 11 450 when compared with direct CE injection. The cephalosporin test compounds presented a good linear response (corrected peak area) between 0.5 and 10 μg/L with correlation coefficients higher than 0.995. The final method is compared with previously reported LVSS‐CE and SPE‐CE systems for the analysis of cephalosporins.

Sensitivity enhancement for the analysis of naproxen in tap water by solid‐phase extraction coupled in‐line to capillary electrophoresis

SPE coupled in-line to CE, as the strategy to enhance the concentration sensitivity in CE, has been used to enrich naproxen in tap water samples. In this study, a microcartridge containing an octadecyl silica (C18) sorbent was placed near the inlet within the separation capillary column. The optimum conditions were obtained when naproxen in an acidic aqueous solution (pH 3.5) was loaded into the capillary at 930 mbar for 30 min, and 20 mM ammonium acetate in methanol/water (70:30 v/v) was used as both an elution solution and a separation BGE. Under these conditions, the sensitivity was enhanced 1820-fold with respect to normal hydrodynamic injection, and the LOD achieved was 0.2 microg/L. To show the capability of the in-line SPE-CE method, tap water samples were analysed after a pretreatment consisting in an off-line C18-SPE procedure. The recovery of this procedure was higher than 80%. Under these conditions, naproxen could be detected at a concentration of 10 ng/L; so the potential of the procedure for the sensitive analysis of this type of drugs in water samples was demonstrated. Afterwards, these results were compared with those previously obtained for naproxen in water samples using different sample stacking techniques.