On-line Coupling Of Solid-phase Extraction Research Articles

On-line coupling of solid-phase extraction of phenols on porous graphitic carbon and LC separation on C18 silica gel column via subcritical water desorption

ABSTRACTAn approach to the on-line coupling of solid-phase extraction on porous graphitic carbon (PGC) column and high performance liquid chromatography (HPLC) separation on octadecyl silica column is proposed. The approach includes extraction of phenols from 10 ml of water sample on PGC column; desorption with subcritical water at 175°C, injection of the eluate to the HPLC column and separation at ambient temperature with acetonitrile–water eluent. Limits of detection for UV detection of phenols were 1–5 μg l−1, and analyte peaks were 20–50% narrower than for direct injection of 20 μl of sample.

A miniaturized transverse flow gating interface for the on-line coupling of solid-phase extraction with capillary electrophoresis.

A miniaturized transverse flow gating interface (μ-TFGI) is presented for the on-line coupling of solid-phase extraction with capillary electrophoresis (SPE-CE). The fabrication and operation procedures of the μ-TFGI are described in detail. After the operation conditions were investigated and selected, the μ-TFGI was evaluated on an SPE-CE-UV setup using clenbuterol (CLB) as the test analyte. The preconcentration factors obtained with the SPE-CE-UV system and the SPE-UV part were 600 and 620, respectively. The plate numbers obtained within 3 min were 100000 and 80000 for automatic injection via the μ-TFGI and manual direct injection, respectively. The precisions were 2.4 - 6.8% (RSD, %, n = 9) and 3.1% (RSD, %, n = 27) for the recovery (94.3 - 101.9%) and migration time of CLB spiked in urine samples, respectively. These results demonstrate that the μ-TFGI has the ability to exactly and reproducibly transfer nanoliters of fractions from SPE onto CE with no degradation of the efficiencies of SPE and CE.

A sheath flow gating interface for the on-line coupling of solid-phase extraction with capillary electrophoresis

A sheath flow gating interface (SFGI) is presented for the on-line coupling of solid-phase extraction (SPE) with capillary electrophoresis (CE). The design, construction and operation of the SFGI are described in detail. After operating conditions were investigated and selected, the SFGI was evaluated on a SPE–CE–UV setup using hydroxylated poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith as the absorbent and using three phenols as the test analytes. The preconcentration factors obtained with the SPE–CE–UV system and the SPE–UV part are 530 and 550, respectively. The plate numbers obtained using the SPE–CE–UV system are slightly better than or comparable to those with the CE–UV part. The precisions (RSDs) of 100 consecutive injections are 2.43%, 3.86%, and 4.25% for peak height, peak area and migration time, respectively. The measured recoveries for the river water samples spiked at three different levels are in the range of 93.6–102.8% with the interday RSD values ranging from 2.0 to 4.5% (n=3). These data collectively demonstrate that the SFGI has the ability to exactly and reproducibly transfer nanoliters of fractions from SPE onto CE with no degradation of the efficiencies of SPE and CE, suggesting a great potential to be routinely used for the coupling of SPE, microcolumn LC or FIA with CE.

On-line coupling of solid-phase extraction to gas chromatography–mass spectrometry to determine musk fragrances in wastewater

An on-line coupling solid-phase extraction (SPE) has been developed for the first time to preconcentrate trace amounts of 17 musk fragrances extensively used in personal care products (6 polycyclic musks, 3 nitro musks, 7 macrocyclic musks and 1 polycyclic musk degradation product) from wastewater samples, prior to analysis by gas chromatography and mass spectrometry through an on-column interface. A 10mm×2mm I.D. precolumn packed with Oasis HLB (60μm) or C18 (60μm) was compared for the optimization of 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) as well as SPE parameters (e.g. sample flow, sample volume, elution solvent, etc.) were optimized. An organic modifier such as methanol 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 low ngL−1 levels, preconcentrating only 10mL of sample, and the limits of detection were between 1 and 30ngL−1. The method was applied for the determination of musk fragrances in wastewater samples from three urban wastewater treatment plants (WWTPs). The analysis of influent urban wastewater revealed that galaxolide, tonalide and ambrettolide were the most abundant musk compounds with concentrations ranging between 18ngL−1 and 45,091ngL−1, 852ngL−1 and 49,904ngL−1 and 507ngL−1 and 21,528ngL−1 respectively. The remaining musks were present at lower concentrations and two of the macrocyclic musk studied (musk MC4 and civetone) were not detected. The analysis of effluent wastewater showed a decrease in the concentrations of all of the compounds present in influent samples, with the decrease being more significantly in the case of polycyclic and nitro musks than for macrocyclic musks. Only HHCB-lactone remained constant or increased its concentration.

Automated method for determination of olive oil phenols and metabolites in human plasma and application in intervention studies

The interest for olive oil phenols (OOPs) is a growing trend thanks to their contribution to prevent or improve diseases associated to oxidative damage. OOPs ingested in the diet are found at low concentrations in blood either as free forms (e.g. hydroxytyrosol, tyrosol, vanillin, ferulic acid, coumaric acid) or conjugated as sulfate and glucuronide derivatives. Therefore, the identification/quantitation of OOPs in plasma to study their biological effects and elucidate their metabolism requires selective and sensitive methods. The present research describes the development, validation and application of an automated method based on on-line coupling of solid-phase extraction and liquid chromatography–tandem mass spectrometry (SPE–LC–MS/MS) for quantitation of conjugated and free OOPs in human plasma. This approach minimizes sample handling—thus reducing analyte losses and degradation by contact with the atmosphere—and increases analysis throughput, which is crucial in intervention studies dealing with cohorts formed by numerous individuals. The fundamental of the approach is the retention of OOPs and metabolites in an SPE anionic cartridge with subsequent on-line elution to an LC–MS/MS system. Quantitative analysis of OOPs (relative quantitation for conjugated OOPs) was carried out by selected reaction monitoring mode that reported relative limits of detection and quantitation between 0.02–0.28ng/mL (16.6–232pg on-column) and 0.05–0.83ng/mL (41.5–689pg on-column), respectively. The accuracy of the method, estimated as recovery factor, ranged from 84.2 to 99.4%, and precision, expressed as relative standard deviation, was below 3.8%. The resulting method has been applied to the determination of OOPs and metabolites in plasma samples from individuals who ingested a breakfast prepared with virgin olive oil. The proposed method has an excellent potential for high-throughput use in both clinical and research laboratories.

Staggered multistep elution solid‐phase extraction capillary electrophoresis/tandem mass spectrometry: a high‐throughput approach in protein analysis

An approach based on staggered multistep elution solid-phase extraction (SPE) capillary electrophoresis/tandem mass spectrometry (CE/MS/MS) was developed in the analysis of digested protein mixtures. On-line coupling of SPE with CE/MS was achieved using a two-leveled two-cross polydimethylsiloxane (PDMS)-based interface. Multistep elution SPE was used prior to CE to provide an additional dimension of separation, thus extending the separation capacity for the peptide mixture analysis. By decreasing in the number of co-eluting peptides, problems stemming from ionization suppression and finite MS/MS duty cycle were reduced. As a result, sequence coverage increased significantly using multistep elution SPE-CE/MS/MS compared to one-step elution SPE-CE/MS/MS in the analysis of a single protein tryptic digest (49% vs. 18%) and a six protein tryptic digest (22-71% vs. 10-44%). A staggered CE method was incorporated to increase the throughput. The electropherograms of consecutive CE runs were partially overlapped by injecting the sample plug at a fixed time interval. With the use of a 5 min injection interval, slightly poor results were obtained in comparison with the sequential CE method while the total analysis time was reduced to 28%.

LC/MS analysis of stratum corneum lipids: ceramide profiling and discovery

Ceramides (CERs) in the upper layer of the skin, the stratum corneum (SC), play a key role in the skin barrier function. In human SC, the literature currently reports 11 CER subclasses that have been identified. In this paper, a novel quick and robust LC/MS method is presented that allows the separation and analysis of all known human SC CER subclasses using only limited sample preparation. Besides all 11 known and identified subclasses, a 3D multi-mass chromatogram shows the presence of other lipid subclasses. Using LC/MS/MS with an ion trap (IT) system, a Fourier transform-ion cyclotron resonance system, and a triple quadrupole system, we were able to identify one of these lipid subclasses as a new CER subclass: the ester-linked ω-hydroxy fatty acid with a dihydrosphingosine base (CER [EOdS]). Besides the identification of a new CER subclass, this paper also describes the applicability and robustness of the developed LC/MS method by analyzing three (biological) SC samples: SC from human dermatomed skin, human SC obtained by tape stripping, and SC from full-thickness skin explants. All three biological samples showed all known CER subclasses and slight differences were observed in CER profile.

Sensitive determination of domoic acid in shellfish by on-line coupling of weak anion exchange solid-phase extraction and liquid chromatography–diode array detection–tandem mass spectrometry

An automated method based on the use of on-line solid-phase extraction (SPE) coupled to liquid chromatography with diode array detection and tandem mass spectrometry (LC–DAD–MS/MS) has been developed for the determination of domoic acid in shellfish. The on-line coupling of SPE and liquid chromatography was accomplished by a column switching approach. A weak anion exchange (WAX) sorbent was selected for the SPE procedure, allowing a selective cleanup of shellfish extracts. High sensitivity was achieved by on-line pre-concentration of large volume injections (50–1000μL). A simple protein precipitation cleanup with acetone was used to efficiently remove proteins from shellfish extracts, preventing possible column clogging during chromatographic separation.The proposed method showed good performance in terms of linearity, limits of detection (LODs), precision and accuracy. Quantitative recovery and satisfactory inter-day precision (RSD ⩽7%) was achieved. LODs in the in the sub-nanogram per gram level (0.23–0.32ngg−1) were obtained with MS/MS detection. Matrix effects were assessed by post-extraction addition method and no signal enhancement or suppression was observed during MS detection.This method was successfully applied to the determination of domoic acid in several shellfish samples, including scallops, oysters, mussels, Manila clams, common cockles and razor clams.

Analytical platform for verification and quantitation of target peptides in human serum: Application to cathelicidin

A selective and sensitive, fully automated platform for verification and quantitative determination of target peptides in biofluids is proposed and then validated by development of a method for analysis of cathelicidin in human serum. The method is based on the on-line coupling of solid-phase extraction (SPE) and tandem mass spectrometry with direct infusion. Mass spectrometry analysis was carried out by multiple reaction monitoring using three transitions (one for quantitative analysis and two for qualitative analysis), all them confirmed by in silico fragmentation of the target peptide. Samples were prepared in the SPE workstation on a polymeric divinylbenzene resin by preconcentration, deproteinization, and cleanup, removing salts and interferences after direct injection of human serum. The analytical process required 12 min. The limits of detection and quantitation were 2.5 and 8.25 μg/L, respectively (0.20 and 0.66 pg on column). Repeatability and within-laboratory reproducibility were 2.4% and 2.7%, respectively. A dual-cartridge configuration was used to test recovery of cathelicidin in serum, resulting in 80%. Because quantitative retention in the cartridge was assessed, determination of cathelicidin was validated without using synthetic peptides labeled with stable isotopes. The hyphenated system allows full automation, thereby improving reproducibility and accuracy, as demanded by clinical analysis.

On-line Coupling of Solid-Phase Extraction to Liquid Chromatography--A Review

Solid-phase extraction (SPE) is an effective sample preparation method for removal of interfering compound and enrichment of analyte. Liquid chromatography (LC) with various detectors is a main separation and detection technique used in the analytical field. This article reviews the literatures about the on-line coupling of SPE with LC. The advantages of on-line coupling are reduction of analysis time, sample contamination, and analyte losses, as well as improvement of precision and accuracy. The SPE sorbents including traditional materials, such as chemically bonded silica, ion-exchange and carbon-based materials, and some novel sorbents, such as restricted access material, molecularly imprinted polymer, immunosorbent, and monolithic material, used in the on-line analysis are discussed in detail. The on-line coupling of SPE-LC to other sample preparation techniques, such as supercritical fluid extraction, subcritical water extraction, microwave-assisted extraction, ultrasound-assisted extraction, and derivatization technique are also reviewed.

On-line coupling of solid-phase extraction to liquid chromatography–tandem mass spectrometry for the determination of macrolide antibiotics in environmental water

An automated on-line solid-phase extraction–liquid chromatography–tandem mass spectrometry (SPE–LC–MS/MS) system was developed for the determination of macrolide antibiotics including erythromycin (ETM), roxithromycin (RTM), tylosin (TLS) and tilmicosin (TMC) in environmental water samples. A Capcell Pak MF Ph-1 column packed with restricted access material (RAM) was used as SPE column for the concentration of the analytes and clean-up of the sample. One milliliter water sample was injected into the conditioned SPE column and the matrix was washed out with 3 mL high purity water. By rotation of the switching valve, macrolides (MLs) were eluted in the back-flush mode and transferred to the analytical column by the chromatographic mobile phase. The matrix effect was evaluated by the directly injection LC–MS and on-line SPE–LC–MS methods. The limits of detection (LODs) and limits of quantification (LOQs) obtained are in the range of 2–6 and 7–20 ng L −1, respectively, which means that the proposed method is suitable for trace analysis of MLs at low level concentration. The intra- and inter-day precisions are in the range of 2.9–7.2% and 3.3–8.9%, respectively. In the three fortified levels (20, 200 and 2000 ng L −1), recoveries of MLs ranging from 86.5% to 98.3% are obtained.

On-line coupling of solid-phase extraction to high-performance liquid chromatography for determination of estrogens in environment

A method based on on-line solid-phase extraction (SPE) coupling to high-performance liquid chromatography (HPLC) for the determination of estrogens has been developed. This method can continuously perform extraction of estrone, estradiol, estriol and diethylstilbestrol from aqueous samples without any other pretreatment, which can then be analyzed by HPLC with a UV detector at 230 nm. A pre-concentration column was adapted with methanol/water for chromatographic separation and two kinds of sorbents were involved, which are octadecyl-bonded silica and cigarette filter. The condition of pH of samples, sample loading flow rate and desorption time were all optimized, and the performances of both two sorbents were satisfactory. The on-line SPE system requires very low maintenance and just involved a switching-valve-filter system and a flow-inject pump, and the operation of the whole SPE-HPLC instrumentation is quite simple. The detection limits for pre-concentrating 50 mL of standard solution using cigarette filter as sorbent ranged from 0.98 to 78.1 ng L −1. The enhancement factors were in the range of 197–326. The recoveries of estrogens spiked in real water samples ranged from 85 to 112%. The precisions for nine replicate measurements of a standard mixture (5.0 μg L −1) were in the range of 1.0–3.4%.

On-line coupling of solid-phase extraction, derivatization reaction and spectrophotometry by sequential injection analysis: Application to trifluoperazine assay in human urine

Introduction: This study deals with a new methodology of on-line solid-phase extraction (SPE), derivatization reaction and spectrophotometric measurement utilizing sequential injection analysis (SIA) technique. The method was applied for the assay of trifluoperazine in human urine. Methods: An SPE procedure was automated to perform sample clean-up, extraction and preconcentration into a homemade microcolumn connected to a SIA manifold. Unlike previous SIA methods, a simple SIA manifold included one syringe pump and one multi-position valve was constructed. This offered simplicity and rapidity to the proposed method (sampling frequency 11 sample h − 1 ). Spectrophotometric measurement was based on a fast oxidation of trifluoperazine by Ce(IV) in sulfuric acidic media resulting in a spectrophotometrically detectable chromophore measured at wavelength 500 nm. The SPE procedure was optimized by the univariate method while the derivatization reaction and spectrophotometric measurement were optimized by multivariate methods. Results: The method was linear in a range of 70–200 ng ml − 1 and accurate with a recovery of 92.7%. Relative standard deviation of repeatability ( n = 10 in a day) and intermediate precision ( n = 5 over a week) did not exceed 4.3% indicating satisfactory precision. The limits of detection and quantification were 18.2 and 55.2 ng ml − 1 , respectively. The sensitivity of the method was improved by the preconcentration, the use of extended pathlength in the detection device and the optimization of absorbance measurement. The method is selective in the presence of chlordiazepoxide, which is sometimes taken in combination with trifluoperazine. Discussion: The method is suitable for the application of overdose and therapeutic drug monitoring in human urine.

On-line coupling of solid-phase extraction and capillary electrophoresis for the determination of cefoperazone and ceftiofur in plasma

We present a method for determining two cephalosporins (cefoperazone and ceftiofur) in plasma by on-line solid-phase extraction (SPE)—capillary zone electrophoresis (CZE) with a T-split interface. Using this interface, a part of the SPE elution plug containing the cephalosporins is injected while the rest of the sample is flushed to waste. SPE was carried out using a C 18 micro-precolumn and the cephalosporins presented good retention properties with breakthrough volumes above 1 ml. Using a desorption volume of 426 nl of acetonitrile, recoveries were 75 and 90%, for cefoperazone and ceftiofur, respectively. The resulting elution volume was about 1.8 μl. A deproteinization step was included prior to SPE for the analysis of plasma samples with recoveries of 90 and 57% for cefoperazone and ceftiofur, respectively. With UV detection at 254 nm, linear relationships between the injected concentration and peak area was measured between 10 and 500 ng ml −1 for standards, and 200 and 1500 ng ml −1 for plasma samples. Intra-day ( n = 5) and inter-day ( n = 5) peak area repeatability were lower than 12% RSD. The detection limits obtained for spiked plasma (100 ng ml −1 cefoperazone and ceftiofur) are sufficient for applying the method to pharmacokinetic studies.

Integrated multilayer microfluidic device with a nanoporous membrane interconnect for online coupling of solid-phase extraction to microchip electrophoresis

An integrated microfluidic device was developed for online coupling of solid-phase extraction to microchip electrophoresis (chip SPE-CE). With a nanoporous membrane sandwiched between two PDMS substrates, SPE preconcentration and electrophoretic separation can be carried out in upper and lower fluidic layers, separately and sequentially. During the SPE process, the thin membrane can act as a fluid isolator to prevent intermixing between two fluidic channels. However, when a pulse voltage is applied, the membrane becomes a gateable interconnect so that a small plug of concentrated analytes can be online injected into the lower channel for subsequent separations. This multilayer design provides a universal solution to online SPE-CE hyphenation. Both electroosmotic flow and hydrodynamic pumps have been adopted for SPE operation. SPE was performed on a 2.5 mm long microcolumn, with two weirs on both sides to retain the C(18)-coated silica beads. Rhodamine 123 and FITC-labelled ephedrine were used to test the operational performance of the hyphenation system. High separation efficiency and thousand-fold signal enhancement were achieved.

Multiwalled carbon nanotubes as sorbent for on-line coupling of solid-phase extraction to high-performance liquid chromatography for simultaneous determination of 10 sulfonamides in eggs and pork

The sulfonamides (SAs) have been widely used as effective chemotherapeutics and growth promoters in animals’ feeding, but their residues could be a potential danger to human health due to their carcinogenic potency and possible antibiotic resistance. Development of a simple and sensitive method for the determination of SAs residues in food of animal origin, therefore, is of great significance. An on-line solid-phase extraction (SPE) method using multiwalled carbon nanotubes as sorbent coupled with high-performance liquid chromatography (HPLC) for simultaneous determination of 10 sulfonamides (SAs) in eggs and pork was developed. The adsorptive potential of carbon nanotubes for solid-phase extraction of sulfonamides was investigated for the first time in the present paper. To on-line interface solid-phase extraction with HPLC, a conventional sample loop on the six-port injector valve of the HPLC was replaced by a preconcentration column packed with carbon nanotubes. The analytes in water solution were preconcentrated onto the preconcentration column and subsequently eluted with mobile phase of methanol–water (22:78). The developed on-line solid-phase extraction method for HPLC permitted the current HPLC separation and the next preconcentration proceeded in parallel, and thus allows one determination finished within 35 min. The RSD of 10 SAs for nine replicate measurements of a standard mixture of 1 μg l −1 were in the range of 2.5–7.8%. The method was applied to the determination of trace sulfadiazin (SDZ), sulfamerazine (SMR), sulfadimidine (SDMD), sulfathiazole (STZ), sulfamoxol (SMO), sulfamethizole (SMT), sulfamethoxypyridazine (SMP), sulfachlorpyridazine (SCP), sulfadoxin (SDX) and sulfisoxazole (SIA) in eggs and pork. The results indicated that the proposed method was simple, cost-effective and sensitive.

Cigarette filter as sorbent for on-line coupling of solid-phase extraction to high-performance liquid chromatography for determination of polycyclic aromatic hydrocarbons in water

An on-line solid-phase extraction (SPE) protocol using the cigarette filter as sorbent coupled with high-performance liquid chromatography (HPLC) was developed for simultaneous determination of trace naphthalene (NAPH), phenanthrene (PHEN), anthracene (ANT), fluoranthene (FLU), benzo( b)fluoranthene (BbF), benzo( k)fluoranthene (BkF), benzo( a)pyrene (BaP), and benzo( ghi)perylene (BghiP) in water samples. To on-line interface solid-phase extraction to HPLC, a preconcentration column packed with the cigarette filter was used to replace a conventional sample loop on the injector valve of the HPLC for on-line solid-phase extraction. The sample solution was loaded and the analytes were then preconcentrated onto the preconcentration column. The collected analytes were subsequently eluted with a mobile phase of methanol–water (95:5). HPLC with a photodiode array detector was used for their separation and detection. The detection limits (S/N = 3) for preconcentrating 42 mL of sample solution ranged from 0.9 to 58.6 ng L −1 at a sample throughput of 2 samples h −1. The enhancement factors were in the range of 409–1710. The developed method was applied to the determination of trace NAPH, PHEN, ANT, FLU, BbF, BkF, BaP and BghiP in local river water samples. The recoveries of PAHs spiked in real water samples ranged from 87 to 115%. The precisions for nine replicate measurements of a standard mixture (NAPH: 4.0 μg L −1, PHEN: 0.40 μg L −1, ANT: 0.40 μg L −1, FLU: 2.0 μg L −1, BbF: 1.6 μg L −1, BkF: 2.0 μg L −1, BaP: 2.0 μg L −1, BghiP: 1.7 μg L −1) were in the range of 1.2–5.1%.

On-line coupling of solid-phase extraction with mass spectrometry for the analysis of biological samples: III. Determination of prednisolone in serum

Solid-phase extraction (SPE) was directly coupled to mass spectrometry (MS) to assess the feasibility of the system for the rapid determination of prednisolone in serum. A C 18 stationary phase allowed washing of the cartridge with 25% methanol. Elution was performed by switching the methanol percentage from 25% in the washing step to 50% during elution. The high flow-rates during the extraction (5.0 ml/min) combined with ion-trap MS detection resulted in a total analysis time of 4 min. Some tailing of the prednisolone peak was observed. However, the tailing was found acceptable, since by this elution procedure most matrix compounds were prevented from eluting from the cartridge. Some matrix interference was still observed with a triple-quadrupole MS, even in the multiple reaction monitoring mode. This resulted in a detection limit (LOD) of about 10 ng/ml. The matrix interference and the LOD were similar for atmospheric pressure chemical ionisation and atmospheric pressure photo ionisation. Applying an ion-trap MS in the MS–MS mode resulted in cleaner chromatograms. Due to extensive fragmentation of prednisolone, the LOD was not lower than about 5 ng/ml prednisolone in serum, and a limit of quantitation of about 10 ng/ml (relative standard deviation <15%) was observed.

Column-switching high-performance liquid chromatographic analysis of carbamazepine and its principal metabolite in human plasma with direct sample injection using an alkyl-diol silica (ADS) precolumn

In this paper, the on-line coupling of solid-phase extraction, based on a restricted-access support with high-performance reverse phase chromatography for the analysis of carbamazepine (CBZ) and carbamazepine-10,11-epoxide (CBZ-E) in human plasma samples is described. A precolumn packed with 25 μm C 18 alkyl-diol support is used for direct plasma injection. Using column-switching techniques, the analytes were enriched on the precolumn by a 5 mM phosphate buffer (pH 7) with 2% of methanol solution at a flow-rate of 0.8 ml min −1, while proteins and endogenous hydrophilic substances in plasma were washed off to waste. The enriched analytes were then back-flushed onto the analytical C 18 column, separated by a mixture of 10 mM phosphate buffer (pH 7) acetonitrile (70:30 v/v) solution at a flow-rate of 1.0 ml min −1 and detected by the ultraviolet absorbance set at 212 and 285 nm and without transfer loss. Linear calibration graphs were obtained for sample injection volumes of 50 (0.2–4.0 of μg of CBZ ml −1 and 0.1–5.0 μg of CBZ-E ml −1, respectively), and 20 μl (5.0–20.0 μg of CBZ ml −1); in either case the r-value was >0.9963. Recoveries from spiked plasma samples were quantitative for both analytes and the coefficients of variation were below 3.83%. The lowest samples concentrations that can be quantified with acceptable accuracy and precision was 0.2 μg CBZ ml −1 and 0.1 μg CBZ-E ml −1 when a sample volume of 50 μl was injected. Concentrations of 0.08 and 0.05 μg ml −1 of CBZ and CBZ-E were considered the limit of detection for a signal-to-noise ratio of 3. Furthermore, the developed column-switching method was successfully applied to the determination of CBZ and CBZ-E in plasma samples of patients submitted to CBZ therapy.

Monitoring of antifouling agents in water samples by on-line solid-phase extraction–liquid chromatography–atmospheric pressure chemical ionization mass spectrometry

An automatic method for determining diuron, irgarol 1051, folpet and dichlofluanid in seawater samples have been developed. This method is based on the on-line coupling of solid-phase extraction (SPE) with a highly crosslinked polymeric sorbent, LiChrolut EN, to liquid chromatography followed by atmospheric pressure chemical ionization (APCI) and mass spectrometry. The operational parameters affecting the APCI interface have been studied in both positive and negative ionization modes. The use of LiChrolut EN in the SPE produced recoveries of over 85% for all the compounds when 100 ml of seawater sample was preconcentrated. Calibration was carried out in both ionization modes and in full-scan and selected-ion monitoring (SIM). The method allowed all the analytes to be detected at 5 ng l −1 in SIM acquisition mode except folpet, which, because of its low response, could only be detected at 250 ng l −1. The method was used to analyse water samples taken from five different marina and fishing ports along the coast of Tarragona, Catalonia (Spain), over a 5-month period. Diuron and irgarol 1051 were detected and quantified in most samples at concentration levels ranging from 27 to 420 ng l −1 for diuron and from 15 to 511 ng l −1 for irgarol 1051.