Determination of pesticides in surface and ground waters by liquid chromatography-electrospray-tandem mass spectrometry

The sensitive multiresidual analytical method for simultaneous analysis of 14 most commonly used agricultural pesticides in Serbia was developed and optimized. The selected insecticides, fungicides and herbicides belong to seven chemical classes (organophosphates, neonicotinoids, carbamates, diacylhydrazines, benzimidazoles, triazines and phenylureas). The method was based on solid-phase extraction followed by liquid chromatography-tandem mass spectrometry. The following parameters that may affect the SPE procedure efficiency were optimized: the sorbent type in combination with different elution solvents, the sample pH and the sample volume. For each pesticide, MSⁿ analysis was performed and distinctive ions and transitions were selected for identification and quantification, as well as for confirmation purposes. External matrix-matched calibration method was used to eliminate variable matrix effect and ensure precise quantification. Good recoveries (72-129%), and low limits of detection (0.4-5.5 ng L⁻¹) and quantification (1.1-18.2 ng L⁻¹) were achieved for all selected pesticides. The developed and optimized method was successfully applied in the analysis of several river waters, as well as ground waters in Serbia, influenced by agriculture. The most frequently detected pesticide was carbendazim. Dimethoate, carbofuran and propazine were also found in the investigated samples.     

Supramolecular solvent-based extraction of benzimidazolic fungicides from natural waters prior to their liquid chromatographic/fluorimetric determination

A supramolecular solvent made up of vesicles of decanoic acid in the nano- and microscale regimes dispersed in a continuous aqueous phase is proposed for the extraction/preconcentration of benzimidazolic fungicides (BFs) from river and underground water samples prior to their determination by liquid chromatography (LC)/fluorimetry. The solvent is produced from the coacervation of decanoic acid aqueous vesicles by the action of tetrabutylammonium (Bu₄N⁺). Carbendazim (CB), thiabendazole (TB) and fuberidazole (FB) are extracted on the basis of hydrophobic and π-cation interactions and the formation of hydrogen bonds. The extraction provides high preconcentration factors (160 for CB and 190 for TB and FB), requires a short time (the procedure takes less than 20 min and several samples can be simultaneously processed) and a low sample volume (20 mL), and avoids the use of toxic organic solvents. Because of the absence of matrix interferences and the low viscosity of the extracts, these can be directly injected into the chromatographic system without the need of cleaning-up or diluting them. Recoveries are not influenced by the presence of salt concentrations up to 1 M. The proposed method provides detection limits for the determination of CB, TB and FB in natural waters of 32, 4 and 0.1 ng L⁻¹, respectively, and a precision, expressed as relative standard deviation (n = 11) of 5.5% for CB (100 ng L⁻¹), 4.0% for TB (80 ng L⁻¹) and 2.5% for FB (30 ng L⁻¹). Recoveries obtained by applying this approach to the analysis of river and underground water samples fortified at the ng L⁻¹ level are in the intervals 75–83, 95–102 and 97–101% for CB, TB and FB, respectively.     

Synthesis of amidinothioureido-silica gel and its application to flame atomic absorption spectrometric determination of silver, gold and palladium with on-line preconcentration and separation

A simple and highly selective flow injection (FI) on-line preconcentration and separation flame atomic absorption spectrometric (FAAS) method was developed for the determinations of trace amounts of silver, gold and palladium. The selective preconcentration of the noble metals was achieved in a wide range of sample acidity (0.1-6 M HNO₃ or HCl) on a microcolumn packed with amidinothioureido-silica gel (ATuSG). The analytes retained on the column were effectively eluted with 5.0% thiourea solution. The analytical procedure was optimized for sample acidity, elution, interferences, flow rate of sampling and eluting, and concentration of sample. Common co-existing cations and anions did not interfere with the preconcentration and determination of the three metals. At a sample loading flow rate of 4.5 ml min⁻¹ with 60 s preconcentration, detection limits (3σ) of 1.1 ng ml⁻¹ Ag, 13 ng ml⁻¹ Au and 17 ng ml⁻¹ Pd were obtained. The precisions (R.S.D., n=11) were 1.2% for Ag, 1.2% for Au and 1.7% for Pd, respectively. The detection limits can be further improved by increasing sample volume. The analytical results obtained by the proposed method for a number of standard reference materials were in good agreement with the certified values.     

Development of liquid phase microextraction method based on solidification of floated organic drop for extraction and preconcentration of organochlorine pesticides in water samples

A simple and efficient liquid-phase microextraction (LPME) in conjunction with gas chromatography-electron capture detector (GC-ECD) has been developed for extraction and determination of 11 organochlorine pesticides (OCPs) from water samples. In this technique a microdrop of 1-dodecanol containing pentachloronitrobenzene (internal standard) is delivered to the surface of an aqueous sample while being agitated by a stirring bar in the bulk of solution. Following completion of extraction, the sample vial was cooled by putting it into an ice bath for 5 min. Finally 2 μL of the drop was injected into the GC for analysis. Factors relevant to the extraction efficiency were studied and optimized. Under the optimized extraction conditions (extraction solvent: 1-dodecanol; extraction temperature: 65 °C; sodium chloride concentration: 0.25 M; microdrop and sample volumes: 8 μL and 20 mL respectively; the stirring rate: 750 rpm and the extraction time: 30 min), figures of merit of the proposed method were evaluated. The detection limits of the method were in the range of 7-19 ng L⁻¹ and the RSD% for analysis of 2 μg L⁻¹ of OCPs was below 7.2% (n = 5). A good linearity (r² ≥ 0.993) and a relatively broad dynamic linear range (25-2000 ng L⁻¹) were obtained. After 30 min of extraction, preconcentration factors were in the range of 708-1337 for different organochlorine pesticides and the relative errors ranged from −10.1 to 10.9%. Finally the proposed method was successfully utilized for preconcentration and determination of OCPs in different real samples.     

Determination of antimony(III) and total antimony by single-drop microextraction combined with electrothermal atomic absorption spectrometry

A simple and sensitive method for using electrothermal atomic absorption spectrometry (ET AAS) with Rh as permanent modifier determination of Sb(III) and total Sb after separation and preconcentration by N-benzoyl-N-phenylhydroxylamine (BPHA)-chloroform single drop has been developed. Parameters, such as pyrolysis and atomization temperature, solvent type, pH, BPHA concentration, extraction time, drop size, stirring rate and sample volume were investigated. Under the optimized experimental conditions, the detection limits (3σ) were 8.0 ng L⁻¹ for Sb(III) and 9.2 ng L⁻¹ for total Sb, respectively. The relative standard deviations (R.S.Ds.) were 6.6% for Sb(III) and 7.1% for total Sb (c = 0.2 ng mL⁻¹, n = 7), respectively. The enrichment factor was 96. The developed method has been applied successfully to the determination of Sb(III) and total Sb in natural water samples.     

Stereoselective quantitation of mecoprop and dichlorprop in natural waters by supramolecular solvent-based microextraction,chiral liquid chromatography and tandem mass spectrometry

Liquid chromatography (LC)/tandem mass spectrometry (MS/MS) after supramolecular solvent-based microextraction (SUSME) was firstly used in this work for the enantioselective determination of chiral pesticides in natural waters. The method developed for the quantitation of the R- and S-enantiomers of mecoprop (MCPP) and dichlorprop (DCPP) involved the extraction of the herbicides in a supramolecular solvent (SUPRAS) made up of reverse aggregates of dodecanoic acid (DoA), analyte re-extraction in acetate buffer (pH = 5.0), separation of the target enantiomers on a chiral column of permethylated α-cyclodextrin under isocratic conditions, and detection of the daughter ions (m/z = 140.9 and 160.6 for MCPP and DCPP, respectively) using a hybrid triple quadrupole mass spectrometer equipped with an electrospray source operating in the negative ion mode. Similar recoveries (ca. 75%) and actual concentration factors (ca. 94) were obtained for both phenoxypropanoic acids (PPAs). The quantitation limits were 1 ng L⁻¹ for R- and S-MCPP, and 4 ng L⁻¹ for R- and S-DCPP, and the precision, expressed as relative standard deviation (n = 6) was in the ranges 2.4–2.7% ([R-MCPP] = [S-MCPP] = 5 ng L⁻¹ and [R-DCPP] = [S-DCPP] = 15 ng L⁻¹) and 1.6–1.8% (100 ng L⁻¹ of each enantiomer). The SUSME-LC–MS/MS method was successfully applied to the determination of the enantiomers of MCPP and DCPP in river and underground waters, fortified at concentrations between 15 and 180 ng L⁻¹ at variable enantiomeric ratios (ER = 1–9).     

Determination of low level methyl tert-butyl ether, ethyl tert-butyl ether and methyl tert-amyl ether in human urine by HS-SPME gas chromatography/mass spectrometry

Methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME) are oxygenated compounds added to gasoline to enhance octane rating and to improve combustion. They may be found as pollutants of living and working environments. In this work a robotized method for the quantification of low level MTBE, ETBE and TAME in human urine was developed and validated. The analytes were sampled in the headspace of urine by SPME in the presence of MTBE-d12 as internal standard. Different fibers were compared for their linearity and extraction efficiency: carboxen/polydimethylsiloxane, polydimethylsiloxane/divinylbenzene, and polydimethylsiloxane. The first, although highly efficient, was discarded due to deviation of linearity for competitive displacement, and the polydimethylsiloxane/divinylbenzene fiber was chosen instead. The analysis was performed by GC/MS operating in the electron impact mode. The method is very specific, with range of linearity 30-4600 ng L⁻¹, within- and between-run precision, as coefficient of variation, <22 and <16%, accuracy within 20% the theoretical level, and limit of detection of 6 ng L⁻¹ for all the analytes. The influence of the matrix on the quantification of these ethers was evaluated analysing the specimens of seven traffic policemen exposed to autovehicular emissions: using the calibration curve and the method of standard additions comparable levels of MTBE (68-528 ng L⁻¹), ETBE (<6 ng L⁻¹), and TAME (<6 ng L⁻¹) were obtained.     

Solvent-based de-emulsification dispersive liquid–liquid microextraction combined with gas chromatography–mass spectrometry for determination of trace organochlorine pesticides in environmental water samples

In this work, we propose solvent-based de-emulsification dispersive liquid–liquid microextraction (SD-DLLME) as a simple, rapid and efficient sample pretreatment technique for the extraction and preconcentration of organochlorine pesticides (OCPs) from environmental water samples. Separation and analysis of fifteen OCPs was carried out by gas chromatography–mass spectrometry (GC/MS). Parameters affecting the extraction efficiency were systematically investigated. The detection limits were in the range of 2–50 ng L⁻¹ using selective ion monitoring (SIM). The precision of the proposed method, expressed as relative standard deviation, varied between 3.5 and 10.2% (n = 5). Results from the analysis of spiked environmental water samples at the low-ppb level met the acceptance criteria set by the EPA.     

Multifunctional sorbents for the extraction of pesticide multiresidues from natural waters

In this work multifunctional sorbents, based on surfactant-coated mineral oxides, are assessed for the simultaneous extraction/preconcentration of pesticide multiresidues from aqueous environmental samples. Seventeen pesticides, representative of all the common groups (triazines, phenylureas, carbamates, azols, anilides, chloroacetanilides, organophosphorous, phenoxyacids, aryloxy acids and phenols), are selected for this study. The sorbents assessed are pure sodium dodecyl sulphate (SDS) and mixed tetrabutylammonium (TBA)-SDS hemimicelles and/or admicelles adsorbed onto alumina. Because of their multifunctional character, these sorbents provide different retention mechanisms (i.e. hydrophobic, ionic and/or π-cation interactions), which highly contribute to the efficient retention of pesticides with different polarities and acidities (bases, neutrals and acids). In addition, the low volume of eluent required for complete elution of analytes (typically 1-2 mL) avoided the need of using time-consuming and tedious evaporation steps that generally are needed when cross-linked polymeric resins or carbon materials are used as sorbents. The performance of two sorbents, i.e. SDS and TBA-SDS mixed hemimicelles/admicelles, for the admicellar solid-phase extraction (ASPE) of pesticide multiresidue was comparatively investigated. The latter was selected on the basis of the higher breakthrough volumes permitted, the lower volume of eluent required and the higher sample and eluent flow rates allowed. The proposed ASPE/LC/UV approach provided detection limits lower than 100 ng L⁻¹ for the determination of the 17 pesticides tested. Recoveries from spiked (at the ng L⁻¹ level) river and underground water samples was quantitative for most of the pesticides tested.     

Coacervative microextraction ultrasound-assisted back-extraction technique for determination of organophosphates pesticides in honey samples by gas chromatography–mass spectrometry

Coacervative microextraction ultrasound-assisted back-extraction technique (CME-UABE) is proposed for the first time for extracting and preconcentrating organophosphates pesticides (OPPs) from honey samples prior to gas chromatography–mass spectrometry (GC–MS) analysis. The extraction/preconcentration technique is supported on the micellar organized medium based on non-ionic surfactant. To enable coupling the proposed technique with GC, it was required to back extract the analytes into hexane. Several variables including, surfactant type and concentration, equilibration temperature and time, matrix modifiers, pH and buffers nature were studied and optimized over the relative response of the analytes. The best working conditions were as follows: an aliquot of 10 mL 50 g L⁻¹ honey blend solution was conditioned by adding 100 μL 0.1 mol L⁻¹ hydrochloric acid (pH 2) and finally extracted with 100 μL Triton X-114 100 g L⁻¹ at 85 °C for 5 min using CME technique. Under optimal experimental conditions, the enrichment factor (EF) was 167 and limits of detection (LODs), calculated as three times the signal-to-noise ratio (S/N = 3), ranged between 0.03 and 0.47 ng g⁻¹. The method precision was evaluated over five replicates at 1 ng g⁻¹ with RSDs ≤9.5%. The calibration graphs were linear within the concentration range of 0.3–1000 ng g⁻¹ for chlorpirifos; and 1–1000 ng g⁻¹ for fenitrothion, parathion and methidathion, respectively. The coefficients of correlation were ≥0.9992. Validation of the methodology was performed by standard addition method at two concentration levels (2 and 20 ng g⁻¹). The recoveries were ≥90%, indicating satisfactory robustness of the methodology, which could be successfully applied for determination of OPPs in honey samples of different Argentinean regions. Two of the analyzed samples showed levels of methidathion ranged between 1.2 and 2.3 ng g⁻¹.     

Dispersive liquid-liquid microextraction combined with high performance liquid chromatography-fluorescence detection for the determination of carbendazim and thiabendazole in environmental samples

A rapid and sensitive method for the determination of carbendazim (methyl benzimidazole-2-ylcarbamate, MBC) and thiabendazole (TBZ) in water and soil samples was developed by using dispersive liquid-liquid microextraction (DLLME) coupled with high performance liquid chromatography with fluorescence detection. The water samples were directly used for the DLLME extraction. For soil samples, the target analytes were first extracted by 0.1 mol L⁻¹ HCl. Then, the pH of the extract was adjusted to 7.0 with 2 mol L⁻¹ NaOH before the DLLME extraction. In the DLLME extraction method, chloroform (CHCl₃) was used as extraction solvent and tetrahydrofuran (THF) as dispersive solvent. Under the optimum conditions, the enrichment factors for MBC and TBZ were ranged between 149 and 210, and the extraction recoveries were between 50.8 and 70.9%, respectively. The linearity of the method was obtained in the range of 5-800 ng mL⁻¹ for water sample analysis, and 10-1000 ng g⁻¹ for soil samples, respectively. The correlation coefficients (r) ranged from 0.9987 to 0.9997. The limits of detection were 0.5-1.0 ng mL⁻¹ for water samples, and 1.0-1.6 ng g⁻¹ for soil samples. The relative standard deviations (RSDs) varied from 3.5 to 6.8% (n = 5). The recoveries of the method for MBC and TBZ from water samples at spiking levels of 5 and 20 ng mL⁻¹ were 84.0-94.0% and 86.0-92.5%, respectively. The recoveries for soil samples at spiking levels of 10 and 100 ng g⁻¹ varied between 82.0 and 93.4%.     

Solid phase extractive preconcentration coupled to gas chromatography-atomic emission detection for the determination of chlorophenols in water samples

Solid-phase extraction (SPE) followed by derivatization and gas chromatography-atomic emission detection (GC-AED) was evaluated for the determination of five chlorophenols (CPs) in water samples. The derivatization was based on the esterification of phenolic compounds with ferrocenecarboxylic acid. The determination of the derivatized phenols was performed by GC-AED in the iron selective detection mode at 302 nm. The described method was tested on spiked water samples.The overall method gave detection limits of 1.6-3.7 ng L⁻¹ and recoveries of 90.9-104.5% for the examined mono- to trichlorophenols in 10 mL water samples. The CPs extracted from a 10 mL water sample with SPE were concentrated into 100 μL of organic solvent, a preconcentration factor of 100. The method was applied to lake and tap water samples, and CP contents between 6 and 51 ng L⁻¹ in lake water and between below the detection limit and 8 ng L⁻¹ in tap water were found for different CPs. The method is quick, simple and gives excellent recoveries, limits of detection and standard deviations.     

A novel stacking method of repetitive large volume sample injection and sweeping MEKC for determination of androgenic steroids in urine

In this research, a novel stacking capillary electrophoresis method, repetitive large volume sample injection and sweeping MEKC (rLVSI-sweeping MEKC) were developed to analyze the presence of three androgenic steroids considered as sport doping drugs, testosterone (T), epitestosterone (E) and epitestosterone glucuronide (EG) in urine. This method provides better sensitivity enhancement than the traditional large volume sample stacking-sweeping strategies due to sensitivity enhancement by repetitive injections. This multiple sampling method enhances sensitivity of monitoring of urine samples by UV detection (254 nm). Firstly, the phosphate buffer was filled into an uncoated fused silica capillary and the samples were injected into the capillary at 10 psi for 20 s, and then stacked at −10 kV for 1 min using phosphate buffer containing SDS. The above injecting and stacking steps were repeated five times. Finally, separation was performed at −20 kV, using phosphate buffer containing methanol, SDS and (2-hydroxypropyl)-β-cyclodextrin. Method validation showed that calibration plots were linear (r ≧ 0.997) over a range of 5-200 ng mL⁻¹ for T, 20-200 ng mL⁻¹ for E and 0.5-500 ng mL⁻¹ for EG. The limits of detection were 1.0 ng mL⁻¹ for T, 5.0 ng mL⁻¹ for E and 200.0 pg mL⁻¹ for EG. When evaluating precision and accuracy, values of RSD and RE in intra-day (n = 3) and inter-day (n = 5) analysis were found to be less than 10.0%. Compared with the simple LVSS-sweeping, which is also a stacking strategy, this method further improves sensitivity up to 25 folds (∼2500 folds with MEKC without preconcentration). This method was applied to monitor 10 athletes’ urine, and did not detect any analyte. The novel stacking method was feasible for monitoring of doping by sportsmen.     

Validation of method for determination of different classes of pesticides in aqueous samples by dispersive liquid-liquid microextraction with liquid chromatography-tandem mass spectrometric detection

In this study, a simple, rapid and efficient method has been developed for the extraction and preconcentration of different classes of pesticides, carbofuran (insecticide), clomazone (herbicide) and tebuconazole (fungicide) in aqueous samples by dispersive liquid-liquid microextraction (DLLME) coupled with liquid chromatography-tandem mass spectrometric detection. Some experimental parameters that influence the extraction efficiency, such as the type and volume of the disperser solvents and extraction solvents, extraction time, speed of centrifugation, pH and addition of salt were examined and optimized. Under the optimum conditions, the recoveries of pesticides in water at spiking levels between 0.02 and 2.0 μg L⁻¹ ranged from 62.7% to 120.0%. The relative standard deviations varied between 1.9% and 9.1% (n = 3). The limits of quantification of the method considering a 50-fold preconcentration step were 0.02 μg L⁻¹. The linearity of the method ranged from 1.0 to 1000 μg L⁻¹ for all compounds, with correlation coefficients varying from 0.9982 to 0.9992. Results show that the method we propose can meet the requirements for the determination of pesticides in water samples. The comparison of this method with solid-phase extraction indicates that DLLME is a simple, fast, and low-cost method for the determination of pesticides in natural waters.     

Development, validation and application of a SDME/GC-FID methodology for the multiresidue determination of organophosphate and pyrethroid pesticides in water

A single-drop microextraction (SDME) procedure was developed for the analysis of organophosphorus and pyrethroid pesticides in water by gas chromatography (GC) with flame ionization detection (GC-FID). The significant parameters that affect SDME performance, such as the selection of microextraction solvent, solvent volume, extraction time, and stirring rate, were studied and optimized using a tool screening factorial design. The limits of detection (LODs) in water for the four investigated compounds were between 0.3 and 3.0 μg L⁻¹, with relative standard deviations ranging from 7.7 to 18.8%. Linear response data were obtained in the concentration range of 0.9-6.0 μg L⁻¹ (λ-cyhalothrin), 3.0-60.0 μg L⁻¹ (methyl parathion), 9.0-60.0 μg L⁻¹ (ethion), and 9.0-30.0 μg L⁻¹ (permethrin), with correlation coefficients ranging from 0.9337 to 0.9977. The relative recoveries for the spiked water ranged from 73.0 to 104%. Environmental water samples (n = 26) were successfully analyzed using the proposed method and methyl parathion presented concentration up to 2.74 μg L⁻¹. The SDME method, coupled with GC-FID analysis, provided good precision, accuracy, and reproducibility over a wide linear range. Other highlights of the method include its ease of use and its requirement of only small volumes of both organic solvent and sample.     

Determination of organophosphorous pesticides in wastewater samples using binary-solvent liquid-phase microextraction and solid-phase microextraction: a comparative study

A simple and efficient binary solvent-based two-phase hollow fiber membrane (HFM)-protected liquid-phase microextraction (BN-LPME) technique for moderately polar compounds was developed. Six organophosphorous pesticides (OPPs) (triethylphosphorothioate, thionazin, sulfotep, phorate, disulfoton, methyl parathion and ethyl parathion) were used as model compounds and extracted from 10-mL wastewater with a binary-solvent (toluene:hexane, 1:1) mixture. Some important extraction parameters, such as extraction time, effect of salt, sample pH and solvent ratio composition were optimized. BN-LPME combined with gas chromatography/mass spectrometric (GC/MS) analysis provided repeatability (R.S.D.s ≤ 12%, n = 4), and linearity (r ≤ 0.994) and solid-phase microextraction provides comparable of R.S.D.s ≤ 13%, n = 4 and linearity (r = ≤0.966) for spiked water samples. The limits of detection (LODs) were in the range of 0.3-11.4 ng L⁻¹ for BN-LPME and 3.1-120.5 ng L⁻¹ for SPME at (S/N = 3) under GC/MS selective ion monitoring mode. In addition to high enrichment, BN-LPME also served as a sample cleanup procedure, with the HFM act as a filtering medium to prevent large particles and extraneous materials from being extracted. To investigate and compare their applicability, the BN-LPME and SPME procedures were applied to the detection of OPPs in domestic wastewater samples.     

On-line preconcentration and separation of Co, Ni and Cd via capillary microextraction on ordered mesoporous alumina coating and determination by inductively plasma mass spectrometry (ICP-MS)

In this paper, an ordered mesoporous alumina coating was prepared and applied to capillary microextraction (CME) of trace Co, Ni and Cd for the first time. The coated capillary was used for on-line coupling CME with inductively plasma mass spectrometry (ICP-MS) for the determination of trace metals of Co, Ni and Cd. The porous structure of Al₂O₃ coating was examined by SEM and TEM. The effects of the extraction parameters including pH, sample flow rate and volume, elution solution and interfering ions on the recovery of analytes have been investigated and optimized. Under the optimized conditions, the limits of detection were 0.33, 1.5 and 1.4 ng L⁻¹ for Co, Ni and Cd, respectively, with a preconcentration factor of 10 times. The precisions for all investigated elements were 2.7, 4.1 and 2.5% (c = 0.05 ng L⁻¹, n = 7), for Co, Ni and Cd, respectively, and the sample frequency was 8 h⁻¹.The proposed method was successfully applied for the analysis of trace metals in water, rice and urine samples with the recovery of 94-105%. In order to validate the proposed method, two certified reference materials of GBW 0913 human urine and NIES No.10-b rice flour were analyzed, and the determination values are in good agreement with the certified values. The ordered mesoporous Al₂O₃ coated capillary can be used more than 20 times without decreasing the extraction efficiency.     

Application of generalized artificial neural networks coupled with an orthogonal design to optimization of a system for the kinetic spectrophotometric determination of Hg(II)

A simple and sensitive kinetic method for the determination of traces of mercury (70-760 ng ml⁻¹) based on its inhibitory effect on the addition reaction between methyl green and sulfite ion is proposed. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of methyl green at 596 nm between 2 and 4 min using a fixed time method. Artificial neural networks with back propagation algorithm coupled with an orthogonal array design were applied to the modeling of the proposed kinetic system and optimization of experimental conditions. An orthogonal design was utilized to design the experimental protocol, in which pH, concentration of sulfite, temperature, and concentration of methyl green were varied simultaneously. Optimum experimental conditions in term of sensitivity were generated by using ANNs. The rate of decrease in absorbance is inversely proportional to the concentration of Hg(II) over entire concentration range tested (100-550 ng ml⁻¹) with a detection limit of 45 ng ml⁻¹ and a relative standard deviation at 200-400 ng ml⁻¹ Hg(II) of 3.2% (n=5). A simple preconcentration step improved the limit of detection and linear dynamic range of the method to about 8 and 12-760 ng ml⁻¹, respectively, by about 10 times enrichment of mercury between 12 and 75 ng ml⁻¹. The method was based on enrichment of Hg(II) from dilute samples on an anionic ion exchanger fixed on a plastic strip and was applied to the determination of Hg(II) in environmental samples with satisfactory results.     

Non-porous membrane-assisted liquid–liquid extraction of UV filter compounds from water samples

A method for the determination of nine UV filter compounds [benzophenone-3 (BP-3), isoamyl methoxycinnamate, 4-methylbenzylidene camphor, octocrylene (OC), butyl methoxydibenzoylmethane, ethylhexyl dimethyl p-aminobenzoate (OD-PABA), ethylhexyl methoxycinnamate (EHMC), ethylhexyl salicylate and homosalate] in water samples was developed and evaluated. The procedure includes non-porous membrane-assisted liquid–liquid extraction (MALLE) and LC–atmospheric pressure photoionisation (APPI)–MS/MS. Membrane bags made of different polymeric materials were examined to enable a fast and simple extraction of the target analytes. Among the polymeric materials tested, low- and high-density polyethylene membranes proved to be well suited to adsorb the analytes from water samples. Finally, 2 cm length tailor-made membrane bags were prepared from low-density polyethylene in order to accommodate 100 μL of propanol. The fully optimised protocol provides recoveries from 76% to 101% and limits of detection (LOD) between 0.4 ng L⁻¹ (OD-PABA) and 16 ng L⁻¹ (EHMC). The interday repeatability of the whole protocol was below 18%. The effective separation of matrix molecules was proved by only marginal matrix influence during the APPI-MS analysis since no ion suppression effects were observed. During the extraction step, the influence of the matrix was only significant when non-treated wastewater was analysed. The analysis of lake water indicated the presence of seven UV filter compounds included in this study at concentrations between 40 ng L⁻¹ (BP-3) and 4381 ng L⁻¹ (OC). In non-treated wastewater several UV filters were also detected at concentration levels as high as 5322 ng L⁻¹ (OC).     

Rapid and accurate determination of thallium in seawater using SF-ICP-MS

We present a method for the rapid and direct determination of dissolved Thallium (Tl) using high resolution sector field inductively coupled mass spectrometry (SF-ICP-MS) suitable for the measurement of large time series (e.g. during monitoring). Thallium data are presented for a series of natural sea water samples, which were validated with sea water standards CASS-4 and NASS-5. The sea water samples and standards were diluted 10 times prior to measurement with SF-ICP-MS in low resolution mode (R = 300, LR). For both CASS-4 and NASS-5 (salinity of 30.5) we calculated a concentration of about 11 ng L⁻¹ when using Tl values of 14 ± 2 ng L⁻¹ (at salinity of 35 ± 1) published by Flegal and Patterson [1] for Atlantic and Pacific sea water. For CASS-4 we report a Tl value of 10.6 ± 0.7 ng L⁻¹ (n = 70), for NASS-5 a Tl value of 10.3 ± 0.8 ng L⁻¹ (n = 11). For Tl in both CASS-4 and NASS-5, the overall error in accuracy and precision is less than 4% and 8% (2 s), respectively. Further, values of 7.7 ± 0.3 and 6.7 ± 0.2 ng L⁻¹ Tl were found for the estuarine standard SLEW-3 (salinity of 15) and the river water standard SLRS-4, respectively, for which no certified value exists so far. The detection and quantification limits of our method are 0.1 and 0.3 ng L⁻¹, respectively. Slight differences in the accuracy of our method and other published methods for the determination of Tl in sea water are discussed. Time-series of natural coastal water samples gave Tl values (6-12 ng L⁻¹), which correspond to determined salinities, and hence, appear realistic and oceanographically consistent.