Determination study of contaminants of emerging concern at trace levels in agricultural soil. A pilot study.

In this study, we aimed to develop and validate a quick, easy, and robust extraction method for the simultaneous determination of 30 organic contaminants of emerging concern (CECs) including some transformation products in soil samples. Three different extraction methods based on an ultrasonic cylindrical probe (UAE), a pressurized liquid extraction (PLE), and a QuEChERS method were compared. Ultra-performance liquid chromatography coupled with electrospray tandem mass spectrometry (LC-MS/MS) was used for identification and quantification of the target analytes. A modified QuEChERS method showed the best results in terms of extractability and accuracy. The extraction procedure developed provided adequate extraction performances (70% of the target analytes were recovered within a 70-99% range), with good repeatability and reproducibility (variations below 20%) and great sensitivity (LOQ < 0.1 ng/g in most cases). No matrix effects were observed for 70% of the compounds. Finally, the analytical methodology was applied in a pilot study where agricultural soil was irrigated with reclaimed water spiked with the contaminants under study. Of the 25 CECs added in irrigation water, a total of 13 pesticides and 5 pharmaceutical products were detected at concentration ranges from 0.1 to 1.2 ng/g (d.w) and from 0.1 to 2.0 ng/g (d.w), respectively.

Solid phase extraction of pesticides from environmental waters using an MSU-1 mesoporous material and determination by UPLC-MS/MS.

This paper describes the synthesis of a silica based MSU-1 mesoporous solid and its application as sorbent in solid-phase extraction to pre-concentrate thirteen pesticides of low-high polarity (methomyl, cymoxanil, carbofuran, monolinuron, isoproturon, methidathion, methiocarb, malathion, phosalone, diazinon, penconazole, neburon and chlorotoluron) in ground and river water. The synthesis was based in an H-bonding interaction assembling (I0N0) between two non-ionic components (the inorganic silica surface, I0 and the polyethylene oxide template, N0) by adding tetraethoxysilane to the non-ionic surfactant Brij®100, the latter previously dissolved in HCl 1 M. 50 mL water samples adjusted at pH= 3.5 were passed, at a flow rate of 5 mL/min, through a home-made cartridge containing 50 mg of MSU-1 sorbent, pre-conditioned with 5 mL of ultrapure water; then, the cartridge was washed with 5 mL of ultrapure water. Following elution with 5 mL of acetonitrile, the pesticides were determined by ultra performance liquid chromatography coupled to triple quadrupole-mass spectrometry. Two selected reaction monitoring transitions were monitored per compound, the most intense one being used for quantification and the second one for confirmation. Three points were used for identification, as established in the Directive 96/23/EC for LC-MS/MS analysis, which deals with confirmatory methods for organic residues and contaminants listed in the Group B (veterinary drugs and contaminants). Medium matrix effect (|20%||50%|). Therefore, the standard addition methodology was applied by adding an adequate amount of the pesticide standard mixture to the final sample extract. All pesticides were quantified using this approach for practical reasons, thus avoiding two different calibrations. The method quantification limit (MQL) of pesticides was 0.01 µg/L for all of them, except for diazinon (0.1 µg/L). Recoveries of the target pesticides at MQL and 0.25 µg/L concentration levels in blank river water were in the range 70.1-113.5% and 86.7-107.3%, respectively, with RSDs lower than 16.3% and 15.7%, respectively. Four ground water samples and three river water samples, taken from Almería (Spain), were analyzed by the proposed method and only phosalone at a concentration level of 0.05 µg/L was found in one river water sample.

Chemometric assisted solid-phase microextraction for the determination of anti-inflammatory and antiepileptic drugs in river water by liquid chromatography-diode array detection.

In the present work, an analytical method for the simultaneous determination of seven non steroidal anti-inflammatory drugs (naproxen, ketoprofen, diclofenac, piroxicam, indomethacin, sulindac and diflunisal) and the anticonvulsant carbamazepine is reported. The method involves preconcentration and clean-up by solid-phase microextraction using polydimethylsiloxane/divinylbenzene fibers, followed by liquid chromatography with diode array detection analysis. Parameters that affect the efficiency of the solid-phase microextraction step such as soaking solvent, soaking period, desorption period, stirring rate, extraction time, sample pH, ionic strength, organic solvent and temperature were investigated using a Plackett-Burman screening design. Then, the factors presenting significant positive effects on the analytical response (soaking period, stirring rate, stirring time) were considered in a further central composite design to optimize the operational conditions for the solid phase microextraction procedure. Additionally, multiple response simultaneous optimization by using the desirability function was used to find the optimum experimental conditions for the on-line solid-phase microextraction of analytes in river water samples coupled to liquid chromatography and diode array detection. The best results were obtained using a soaking period of 5 min, stirring rate of 1400 rpm and stirring time of 44 min. The use of solid-phase microextraction technique avoided matrix effect and allowed to quantify the analytes in river water samples by using Milli-Q based calibration graphs. Recoveries ranging from 71.6% to 122.8% for all pharmaceuticals proved the accuracy of the proposed method in river water samples. Method detection limits were in the range of 0.5-3.0 microgL(-1) and limits of quantitation (LOQs) were between 1.0 and 4.0 microgL(-1) for pharmaceutical compounds in river water samples. The expanded uncertainty associated to the measurement of the concentration ranged between 8.5% and 29.0% for 20 microgL(-1) of each analyte and between 9.0% and 29.5% for the average of different concentration levels. The main source of uncertainty was the calibration step in both cases.

Solving matrix-effects exploiting the second order advantage in the resolution and determination of eight tetracycline antibiotics in effluent wastewater by modelling liquid chromatography data with multivariate curve resolution-alternating least squares and unfolded-partial least squares followed by residual bilinearization algorithms I. Effect of signal pre-treatment.

The effect of piecewise direct standardization (PDS) and baseline correction approaches was evaluated in the performance of multivariate curve resolution (MCR-ALS) algorithm for the resolution of three-way data sets from liquid chromatography with diode-array detection (LC-DAD). First, eight tetracyclines (tetracycline, oxytetracycline, chlorotetracycline, demeclocycline, methacycline, doxycycline, meclocycline and minocycline) were isolated from 250 mL effluent wastewater samples by solid-phase extraction (SPE) with Oasis MAX 500 mg/6 mL cartridges and then separated on an Aquasil C18 150 mm x 4.6mm (5 microm particle size) column by LC and detected by DAD. Previous experiments, carried out with Milli-Q water samples, showed a considerable loss of the most polar analytes (minocycline, oxitetracycline and tetracycline) due to breakthrough. PDS was applied to overcome this important drawback. Conversion of chromatograms obtained from standards prepared in solvent was performed obtaining a high correlation with those corresponding to the real situation (r2 = 0.98). Although the enrichment and clean-up steps were carefully optimized, the sample matrix caused a large baseline drift, and also additive interferences were present at the retention times of the analytes. These problems were solved with the baseline correction method proposed by Eilers. MCR-ALS was applied to the corrected and uncorrected three-way data sets to obtain spectral and chromatographic profiles of each tetracycline, as well as those corresponding to the co-eluting interferences. The complexity of the calibration model built from uncorrected data sets was higher, as expected, and the quality of the spectral and chromatographic profiles was worse.

Determination of photoirradiated tetracyclines in water by high-performance liquid chromatography with chemiluminescence detection based reaction of rhodamine B with cerium (IV).

A simple, selective and sensitive method has been developed for the simultaneous determination of tetracycline, oxytetracycline, chlorotetracycline, demeclocycline, doxycycline and meclocycline based on reversed-phase high-performance liquid chromatography with chemiluminescence detection. The procedure was based on the chemiluminescent enhancement by photoirradiated tetracyclines of the cerium (IV)-rhodamine B system in sulphuric acid medium. The six tetracyclines were separated on an Aquasil-C18 column with a gradient elution using a mixture of acetonitrile and 0.1 mol L(-1) phosphate buffer as mobile phase, photoderivatized using a photoreactor consisting of a tube reactor coil of PFA and a 8W Xenon lamp. Under the optimized conditions, the method was validated with respect to linearity, precision, limits of detection and quantification and accuracy. The relative standard deviation (RSD) on intra-day precision was below 10% and detection limits ranged between 0.12 and 0.34 microg L(-1). The proposed method has been successfully applied to the determination of tetracyclines in surface water samples. A possible mechanism of the chemiluminescence in the system is discussed.

Determination of benzoylureas in ground water samples by fully automated on-line pre-concentration and liquid chromatography-fluorescence detection.

An on-line pre-concentration method for the analysis of five benzoylureas (diflubenzuron, triflumuron, hexaflumuron, lufenuron and flufenoxuron) in ground water samples was evaluated using two C(18) columns, and fluorescence detection after photochemical induced fluorescence (PIF) post-column derivatization. The trace enrichment was carried out with 35 mL of ground water modified with 15 mL of MeOH on a 50 mm x 4.6 mm I.D. first enrichment column (C-1) packed with 5 microm Hypersil Elite C(18). Retention properties of pesticides and humic acids usually contained in ground water were studied on C-1 at concentration levels ranging between 0.04 and 14.00 microg/L in water samples. The results obtained in this study show that the pesticides are pre-concentrated in the first short column while the humic acids contained in the ground water samples are eluted to waste. Pesticides recoveries ranged between 92.3 and 109.5%. The methodology proposed was used to determine benzoylureas in ground water samples at levels lower than 0.1 microg/L (maximum levels established by the European Union).

Mesoporous silica based MCM-41 as solid-phase extraction sorbent combined with micro-liquid chromatography-quadrupole-mass spectrometry for the analysis of pharmaceuticals in waters.

This paper reports the first application of the silica based mesoporous material MCM-41 as a sorbent in solid phase extraction, to pre-concentrate pharmaceuticals of very different polarity (atenolol, nadolol, pindolol, timolol, bisoprolol, metoprolol, betaxolol, ketoprofen, naproxen, ibuprofen, diclofenac, tolfenamic acid, flufenamic acid and meclofenamic acid) in surface waters. The analytes were extracted from 100mL water samples at pH 2.0 (containing 10(-3) mol/L of sodium chloride) by passing the solution through a cartridge filled with 100 mg of MCM-41. Following elution, the pharmaceuticals were determined by micro-liquid chromatography and triple quadrupole-mass spectrometry. Two selected reaction monitoring transitions were monitored per compound, the most intense one being used for quantification and the second one for confirmation. Matrix effect was found in real waters for most analytes and was overcome using the standard addition method, which compared favorably with the matrix matched calibration method. The detection limits in solvent (acetonitrile:water 10:90, v/v) ranged from 0.01 to 1.48 µg/L and in real water extracts from 0.10 to 3.85 µg/L (0.001-0.0385 µg/L in the water samples). The quantitation limits in solvent were in the range 0.02-4.93 µg/L, whereas in real water extracts were between 0.45 and 10.00 µg/L (0.0045 and 0.1000 µg/L in the water samples). When ultrapure water samples were spiked at two concentration levels of each pharmaceutical (0.1 and 0.2 µg/L) and quantified using solvent based calibration graphs, recoveries were near 100%. However, recoveries for most pharmaceuticals were comparable or better than de described above, when river water samples (spiked at the same concentration levels) were quantified by the standard addition method and slightly worse using the matrix matched calibration method. Five real samples (two rivers, one dam and two fountain water samples) were analyzed by the developed method, atenolol, timolol, betaxolol, nadolol and diclofenac being found in some of them, at levels higher than their quantitation limits.

Evaluation of multiwavelength chromatograms for the quantification of mixtures of pesticides by high-performance liquid chromatography-diode array detection with multivariate calibration.

Three multivariate calibration methods, partial least squares (PLS-1 and PLS-2) and principal component regression, were applied to the simultaneous determination of the five pesticides iprodione, procymidone, chlorothalonil, folpet and triazophos by high-performance liquid chromatography with diode array detection. Such detection gives multiwavelength chromatograms from a single analysis of one sample. In this paper, calibration models at two different wavelengths were developed to resolve mixtures of five pesticides with overlapping chromatographic peaks. The first model, carried out at 220 nm as detector compromise wavelength, yielded satisfactory sensitivity for accurate estimation of the concentration of iprodione, procymidone, chlorothalonil and folpet and the second model, at 200 nm, was used for accurate estimation of triazophos. Both calibration models were evaluated using the chromatograms and first-derivative (1D) chromatograms by predicting the concentrations of independent test set samples. Finally, the proposed 1D calibration models were successfully applied to the determination of these pesticides in groundwater and soil samples. In all cases, the PLS-1 calibration method showed superior quantitative prediction ability than the PLS-2 or principal component regression methods.

Determination of benzoylureas in tomato by high-performance liquid chromatography using continuous on-line post-elution photoirradiation with fluorescence detection.

A photochemically induced fluorescence post-column method, with HPLC separation and fluorescence detection, was developed for the determination of five naturally non-fluorescent benzoylurea insecticides: diflubenzuron, triflumuron, hexaflumuron, lufenuron and flufenoxuron. The applicability of the method to the determination of insecticides in spiked tomato was evaluated. Samples were extracted into ethyl acetate and further cleaned-up by solid-phase extraction using an aminopropyl-bonded silica cartridge. The interferences due to the matrix effect were eliminated using matrix matched standards. Linear dynamic ranges were established over more than two orders of magnitude. The limits of detection ranged from 5 to 21 ng ml(-1) (or 0.5 and 2.1 microg kg(-1) in the vegetable samples), with relative standard deviations lower than 5.0%, using blank tomato extract. Mean recoveries ranged from 79 to 102%.

Cross-sections of spectrochromatograms for the resolution of overlapping peaks in diode-array high-performance liquid-chromatography.

Multi-wavelength detectors offer improved detection capabilities for liquid chromatographic methods, but require multivariate approaches to utilise all the available information. The photodiode-array detector in high-performance liquid chromatography (HPLC) generates a three-dimensional data matrix, which is conventionally presented as an isometric projection or a contour plot. In this work, a new graphical technique is described for improving the quantitative results obtained from HPLC, using the available spectrochromatographic information in both the time and wavelength domains. The technique consists of performing cross-sections through the data matrix to obtain the maximum analytical information for each of the analytes. Hence, the resolution of overlapping peaks and the sensitivity in the determination are optimised. In order to demonstrate the validity and simplicity of the approach, the method has been applied to the resolution of synthetic mixtures of iprodione, procymidone and chlorothalonil. Also, the method has been satisfactorily applied to the simultaneous determination of the pesticides in environmental groundwater samples.

Determination and degradation of methomyl in tomatoes and green beans grown in greenhouses.

A liquid chromatographic (LC) method using UV detection at 233 nm was used to study the degradation of methomyl in tomatoes and green beans grown in greenhouses. A liquid-liquid extraction with CH2Cl2-methanol (90 + 10, v/v) and a cleanup step with Florisil were combined with LC to isolate, recover, and quantitate the pesticide. Average recoveries obtained at spike levels of 0.03 and 0.40 mg/kg were 83.2-84.7% for tomatoes and 83.3-87.5% for green beans. Determination limits were 0.03 mg/kg for tomatoes and 0.01 mg/kg for green beans. Levels of methomyl residues were studied in tomatoes and green beans grown in an experimental greenhouse to establish the effect of the kind of greenhouse, application dose, species grown, and climatic conditions on the degradation of this pesticide. Analysis of variance showed that doses did not affect the response. The half-life, however, is greater in a flat-roof greenhouse than in an asymmetric-roof greenhouse and is significantly longer for green beans than for tomatoes and longer in winter than in spring. A preharvest time of about 5 days may be suitable for green beans sprayed with methomyl. Tomatoes show residue levels at the time of application lower than Spanish minimum residue levels.

Determination of binary and ternary mixtures of pesticides in wetland waters by gas chromatography using partial least-squares analysis.

Partial least-squares (PLS) analysis was applied for the first time to ternary and binary mixtures of pesticides producing overlapping peaks in gas chromatograms. Several preprocessing algorithms for pretreatment of data were tested for optimization of the PLS models, and the most advantageous were used in each case. Three different mixtures of pesticides were resolved with satisfactory results: parathion-methyl, chlorpyrifos-methyl, and vinclozolin; parathion-ethyl, chlorpyrifos, and triadimefon; and endosulfan sulfate and carbophenothion. The proposed models were applied to the determination of 3 mixtures of pesticides at levels of 0.02-1.00 ng/mL in wetland water samples after a preconcentration step with C18 cartridges, with recoveries ranging from 82.7 to 117.4%. The reported method is sufficiently sensitive to measure pesticide residues at the maximum allowable concentrations given in the European Union Drinking Water Directive.

Application of partial least-squares calibration to phosphorimetric data for determination of polycyclic aromatic hydrocarbons in spiked environmental samples.

A partial least-squares calibration method is proposed, for the first time, for phosphorescence signals. The proposed method is based on the determination of phenanthrene, fluoranthene, and benz[a]anthracene by room temperature phosphorimetry, using microemulsion solutions. The emission and first-derivative emission spectra of the ternary mixtures were tested to perform the calibration matrix. Improved recoveries were found for the prior differentiation step in the analysis of ternary mixtures of these polycyclic aromatic hydrocarbons in road dust samples. The proposed method yielded recoveries ranging from 93.2 to 115.3%, with relative standard deviations of < 6.8%.

Prediction of the processing factor for pesticides in apple juice by principal component analysis and multiple linear regression.

The main objective of this work was to establish a mathematical function that correlates pesticide residue levels in apple juice with the levels of the pesticides applied on the raw fruit, taking into account some of their physicochemical properties such as water solubility, the octanol/water partition coefficient, the organic carbon partition coefficient, vapour pressure and density. A mixture of 12 pesticides was applied to an apple tree; apples were collected after 10 days of application. After harvest, apples were treated with a mixture of three post-harvest pesticides and the fruits were then processed in order to obtain apple juice following a routine industrial process. The pesticide residue levels in the apple samples were analysed using two multi-residue methods based on LC-MS/MS and GC-MS/MS. The concentration of pesticides was determined in samples derived from the different steps of processing. The processing factors (the coefficient between residue level in the processed commodity and the residue level in the commodity to be processed) obtained for the full juicing process were found to vary among the different pesticides studied. In order to investigate the relationships between the levels of pesticide residue found in apple juice samples and their physicochemical properties, principal component analysis (PCA) was performed using two sets of samples (one of them using experimental data obtained in this work and the other including the data taken from the literature). In both cases the correlation was found between processing factors of pesticides in the apple juice and the negative logarithms (base 10) of the water solubility, octanol/water partition coefficient and organic carbon partition coefficient. The linear correlation between these physicochemical properties and the processing factor were established using a multiple linear regression technique.

Ultrasound-assisted ionic liquid dispersive liquid-liquid microextraction coupled with liquid chromatography-quadrupole-linear ion trap-mass spectrometry for simultaneous analysis of pharmaceuticals in wastewaters.

A simple, rapid, low environmental toxicity and sensitive ultrasound-assisted ionic liquid dispersive liquid-liquid microextraction (US-IL-DLLME) procedure was developed for the extraction of nine pharmaceuticals (paracetamol, metoprolol, bisoprolol, betaxolol, ketoprofen, naproxen, ibuprofen, flufenamic acid and tolfenamic acid) in wastewater, and their determination using high-performance liquid chromatography with a hybrid triple quadrupole-linear ion trap-mass spectrometer (LC-QqLIT-MS). The IL 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6]) and acetonitrile (ACN) were used as extraction and disperser solvent, respectively, for the DLLME procedure, instead of using toxic chlorinated solvent. The factors affecting the extraction efficiency, such as the type and volume of ionic liquid, type and volume of disperser solvent, cooling in ice-water, sonication time, centrifuging time, sample pH and ionic strength, were optimized. The ultrasound-assisted process was applied to accelerate the formation of the fine cloudy solution using a small volume of disperser solvent (0.5mL of acetonitrile), which increased the extraction efficiency and reduced the equilibrium time. A slight increase in the recoveries of pharmaceuticals was observed when an ice-water bath extraction step was included in the analytical procedure. In this way, enrichment factors between 255 and 340 were obtained. Data acquisition in selected reaction monitoring mode (SRM), allowed the simultaneous identification and quantification of the analytes using two transitions (SRM1 and SRM2). Additionally, the information dependent acquisition (IDA) scan was performed to carry out the identification of those analytes whose second transition was absent or was present at low intensity, also providing extra confirmation for the other analytes. The optimized US-IL-DLLME-LC-QqLIT-MS method showed a good precision level, with relative standard deviation values between 1.1% and 11.3%. Limits of detection and quantification were in the range 0.2-60ngL(-1) and 1.0-142ngL(-1), respectively. Good enrichment factors (255-340) and recoveries (88-111%) were obtained for the extraction of the target analytes in wastewater samples. This method has been successfully applied to analyze effluent wastewater samples from a municipal wastewater treatment plant located in Almería (Spain) and the results indicated the presence of flufenamic acid and metoprolol in concentration levels of 0.1 and 1.3µgL(-1), respectively.

Determination of drugs in river and wastewaters using solid-phase extraction by packed multi-walled carbon nanotubes and liquid chromatography-quadrupole-linear ion trap-mass spectrometry.

The present paper describes a solid-phase extraction by packed multi-walled carbon nanotubes, followed by liquid chromatography-mass spectrometry, method for the determination of some of the most consumed drugs including four ß-blockers and eight non-steroidal anti-inflammatory drugs, in river and wastewater samples. High extraction efficiency was found for most drugs due to the large specific surface area and high adsorption capacity of this nanomaterial compared with other conventional solid-phase extraction sorbents, and matrix effect was present only for two of the twelve studied drugs. Only 20mg of carbon nanotubes was enough to preconcentrate the analytes with recoveries from 68% to 107% for most of them. The pharmaceuticals were analyzed by liquid chromatography coupled to a hybrid triple quadrupole-linear ion trap-mass spectrometer at ultra-trace levels. Data acquisition was carried out in selected reaction monitoring mode, using two transitions for simultaneous identification and quantification of the analytes. Additionally, an information dependent acquisition scan was performed to carry out the identification of those analytes whose second transition was absent or was present at low intensity. The analytical performance of the whole method was evaluated in two environmental water matrices (river and wastewaters). Matrix effect was not found in river water, quantitation being carried out with calibration graphs built with solvent based standard. On the contrary, matrix effect was present in wastewater for some of the target drugs and, therefore, quantitation was carried out using the standard addition method. Limits of detection and quantitation in river waters were in the range of 9-36 and 23-121ngL(-1), respectively and the relative standard deviation of the full method was less than 17%. The proposed methodology was applied to the analysis of three river water and two wastewater (influent and effluent) samples, all of them from Almería (Spain). Some pharmaceuticals were found in river water at concentration levels near to or lower than their quantitation limits, whereas the most consumed pharmaceuticals were found at high concentration levels in influent wastewater and were not detected or were found at lower levels in the effluent wastewater sample.

Determination of pharmaceuticals in river water by column switching of large sample volumes and liquid chromatography-diode array detection, assisted by chemometrics: an integrated approach to green analytical methodologies.

An analytical method for the simultaneous determination of nine beta-blockers (sotalol atenolol, nadolol, pindolol, metoprolol, timolol, bisoprolol, propanolol and betaxolol) and two analgesics (paracetamol and phenazone) in river water by liquid chromatography and diode array detection is reported. The method involves a modified precolumn switching methodology replacing the small precolumn with a short C18 liquid chromatography column (50 mm x 4.6 mm, 5 microm particle size), thus allowing the preconcentration of large water sample volumes whereas interferences eluting at the first of the chromatogram were discarded to waste. This approach allowed to preconcentrate 30 mL river water samples, modified with 0.4% MeOH, achieving univariate method detection and determination limits ranged between 0.03 and 0.16 microg L(-1) and between 0.2 and 0.5 microg L(-1), respectively, with precision values lower than 9.4% for spiking levels at the quantitation limits of each analyte and lower than 4.0%, except bisoprolol (8.3%), for higher spiking levels (1.0 microg L(-1) of all analytes). Matrix background was reduced in three way data by a baseline correction following the Eilers methodology, whereas multivariate curve resolution and alternating least squares in combination with the standard addition calibration method, applied to these data, coped with overlapping peak, systematic (additive) and proportional (matrix effect) errors. The method was successfully applied for the determination of the target pharmaceuticals in river water from three places in a river stream with acceptable recoveries and precision values, taking into account the complexity of the analytical problem. The joint statistical test for the slope and the intercept of the linear regression between the nominal concentration values versus those predicted, showed that the region computed contained the theoretically expected values (0) for the intercept and (1) for the slope (at a confidence level of 95%), which indicates the absence of both constant and proportional errors in the predicted concentrations.

Chemometric tools improving the determination of anti-inflammatory and antiepileptic drugs in river and wastewater by solid-phase microextraction and liquid chromatography diode array detection.

An analytical method for the simultaneous determination of seven non-steroidal anti-inflammatory drugs (naproxen, ketoprofen, diclofenac, piroxicam, indomethacin, sulindac and diflunisal) and the anticonvulsant carbamazepine in river and wastewater is reported. The method involves pre-concentration and clean-up by solid-phase microextraction using polydimethylsiloxane/divinylbenzene fibers, followed by liquid chromatography with diode array detection analysis. Owing to the fact that river water samples did not contain interferences and no sensitivity changes due to sample matrix were observed, external calibration was implemented. Standardization was also applied in order to carry out the prediction step by preparing only two diluted standards that were subjected to the pre-concentration step and a set of standards prepared in solvent. For the analysis of wastewater samples, in contrast, it was necessary to implement standard addition calibration in combination with the multivariate curve resolution-alternating least squares (MCR-ALS) algorithm, which allowed us to overcome matrix effect and exploit the second order advantage. Recoveries ranging from 72% to 125% for all pharmaceuticals proved the accuracy of the proposed method in river water samples. On the other hand, wastewater sample recoveries ranged from 83% to 140% for all pharmaceuticals, showing an acceptable performance - considering this sample contains no modeled interferences.

Application of the Doehlert design to optimize the signal obtained in photochemically induced fluorescence for the determination of eight phenylureas.

This work describes the optimization of a photochemically induced method for the detection of eight phenylureas has been developed by response surface methodology (RSM). These pesticides do not show native fluorescence but they were photolyzed into strongly fluorescent photoproducts under UV irradiation. The effect of the main variables affecting the yield of the photoderivatization reaction, and hence the fluorescence intensity, such as solvent, UV irradiation time and pH were optimized for each pesticide. A Doehlert design was applied in order to obtain maximum intensity fluorescence using response surface methodology. In general, a maximum was found for all pesticides using MeOH as organic solvent, except for diuron, whereas the effect of pH and irradiation time was different, according to each pesticide. Finally, the addition of beta-cyclodextrin upon the photochemically induced fluorescence intensity was investigate. The fluorescence intensity was only improved for monolinuron at a concentration of 4 x 10(-3) M of beta-cyclodextrin.

New method for the photo-chemiluminometric determination of benzoylurea insecticides based on acetonitrile chemiluminescence.

The viability of tandem photochemical reaction-chemiluminescence detection has been studied for the determination of five benzoylurea insecticides, namely, diflubenzuron, triflumuron, hexaflumuron, lufenuron and flufenoxuron. The 'on-line' photochemical reaction of benzoylurea pesticides provides an enhanced chemiluminescence response of the pesticides during their oxidation by potassium hexacyanoferrate(III) and sodium hydroxide, whose signal increases with the percentage of acetonitrile in the reaction medium. The determination was performed using a photoreactor consisting of a PFA (perfluoroalkoxy) tube reactor coil (5 mx1.6-mm O.D. and 0.8-mm I.D.) and an 8-W xenon lamp. As the yield of the photoderivatization process and the chemiluminescent signals depend on the percentage of acetonitrile, the chromatographic column (a Gemini C18, Phenomenex 150 mmx4.6 mm, 5-microm particle size) was chosen with the aim of using high percentages of this organic solvent in the mobile phase. Previous studies showed that the rate of the chemiluminescent reaction was very fast. Therefore, a modification was carried out in the detector in order to mix the analytes and reactants as near as possible to the measure cell. The optimised method was validated with respect to linearity, precision, limits of detection and quantification accuracy. Under the optimised conditions, linear working range extends three orders of magnitude with the relative standard deviation of intra-day precision below 10% and detection limits between 0.012 and 0.18 microg mL-1, according to the compound. The proposed method has been successfully applied to the determination of benzoylureas in cucumber with good results.