Oxidized Multi-Walled Carbon Nanotubes as SPE Sorbent for Determination of Mefenacet and Its Degradation Products Residues in Water Samples by RRLC-UV-ESI-MS

A new method was developed for the analysis of herbicide mefenacet (MN) and its three photolysis degradation products namely hydroxylbenzothiazole (HBT), N-methylaniline (N-MA) and 2-benzothiazoloxyacetic acid (2-BAA) in water samples by rapid resolution liquid chromatography coupled with UV detection and electrospray ionization mass spectrometry. In the SPE pre-concentration step, the adsorptive potential of oxidized multi-walled carbon nanotubes for the extraction of these four target analytes was investigated for the first time. Parameters influencing the extraction efficiency, such as sample flow-rate, eluent volume and sample volume, were examined. The mean recoveries were between 85.6 and 101.4% and relative standard deviations were between 3.0 and 9.2%. The limits of detection obtained were 0.02 μg L^?1 for MN and 2-BAA and 0.04 μg L^?1 for HBT and N-MA. The proposed method was applied to monitor the residual concentrations of these four target analytes in 39 real water samples collected from April to July of 2009.     

Direct rapid analysis of multiple PPCPs in municipal wastewater using ultrahigh performance liquid chromatography–tandem mass spectrometry without SPE pre-concentration

Ultrahigh performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) was utilized to develop a rapid, sensitive and reliable method without solid phase extraction (SPE) pre-concentration for trace analysis of 11 pharmaceuticals and personal care products (PPCPs) in in?uent and ef?uent from municipal wastewater treatment plants (WWTPs). This method not only shortened the analysis time but also reduced analysis cost significantly by omitting SPE process and avoiding the consumption of SPE cartridge. Detection parameters for UHPLC–MS/MS analysis were optimized, including sample pH, eluent, mobile phase (solvent and additive), column temperature, and ?ow rate. Under the optimal conditions, all analytes were well separated and detected within 8.0 min by UHPLC–MS/MS. The method quantification limits (MQLs) for the 11 PPCPs ranged from 0.040 to 88 ng L⁻¹ and from 0.030 to 90 ng L⁻¹ for influent and effluent, respectively. The matrix effect was systematically investigated and quantified for different types of samples. The analysis of in?uent and ef?uent samples of two WWTPs in Hong Kong revealed the presence of 11 PPCPs, including acyclovir, benzophenone-3, benzylparaben, carbamazepine, ethylparaben, fluconazole, fluoxetine, methylparaben, metronidazole, propylparaben, and ranitidine. Their concentrations ranged from 9.1 to 1810 ng L⁻¹ in influent and from 6.5 to 823 ng L⁻¹ in effluent samples collected from Hong Kong WWTPs.     

On-line bi-directional electrostacking for As speciation/preconcentration using electrothermal atomic absorption spectrometry

A method using bi-directional electrostacking (BDES) in a flow system is presented for As preconcentration and speciation analysis. Some parameters such as electrostacking time and applied voltage, support buffers and their concentrations were investigated. Boric acid plus sodium hydroxide at 0.1 mol/l concentration was selected as support buffer to improve the pre-concentration factor (PF) for As(V). An analytical range from 2.0 to 50.0 μg l⁻¹, and 0.35 μg l⁻¹ as limit of detection, when applied 750 V for 20 min, were achieved. Under these conditions, a pre-concentration factor of 4.8 was obtained. The proposed method was applied to determine As(V) in mineral water and natural water samples (river, fountain and gold mine) from Ouro Preto city. Recoveries from 93.5 to 106.4% were achieved at 10 μg l⁻¹ added As level (R.S.D.s between 3 and 7%). Potassium permanganate (10 mg l⁻¹) was used for oxidising As species in order to determine total As, being established the concentration of As(III) from the difference between total As and As(V).     

Determination of selenite and selenate in drinking water: a fully automatic on-line separation/pre-concentration system coupled to electrothermal atomic spectrometry with permanent chemical modifiers

A time-based flow injection (FI) separation pre-concentration system coupled to an electrothermal atomic absorption spectrometer (graphite furnace) has been developed for the direct ultra-trace determination of selenite and selenate in drinking water. The pre-concentration of both forms of selenium is carried out onto a micro-column packed with an anionic resin (Dowex 1X8) that is placed in the robotic arm of the autosampling device. Selenite and selenate are sequentially eluted with HCl 0.1 M and HCl 4 M, respectively. The interference of large quantities of chloride during selenium atomisation is prevented by using iridium as a “permanent” chemical modifier. The features of the pre-concentration separation system for both species are: 53% efficiency of retention and an enhancement factor of 82 for a pre-concentration time of 180 s (sample flow rate=3 ml min⁻¹) with HCl elution volumes of 100 μl. The detection limit (3 s) is 10 ng l⁻¹ for the two species and the relative standard deviation (n=10) at the 200 ng l⁻¹ level is 3.5% for selenite and 5.6% for selenate. The addition of selenite and selenate stock standard solutions to tap water samples yields a 97-103% recovery of both species.     

Development of a new multi-residue laser diode thermal desorption atmospheric pressure chemical ionization tandem mass spectrometry method for the detection and quantification of pesticides and pharmaceuticals in wastewater samples

A new solid phase extraction (SPE) method coupled to a high throughput sample analysis technique was developed for the simultaneous determination of nine selected emerging contaminants in wastewater (atrazine, desethylatrazine, 17β-estradiol, ethynylestradiol, norethindrone, caffeine, carbamazepine, diclofenac and sulfamethoxazole). We specifically included pharmaceutical compounds from multiple therapeutic classes, as well as pesticides. Sample pre-concentration and clean-up was performed using a mixed-mode SPE cartridge (Strata ABW) having both cation and anion exchange properties, followed by analysis by laser diode thermal desorption atmospheric pressure chemical ionization coupled to tandem mass spectrometry (LDTD-APCI-MS/MS). The LDTD interface is a new high-throughput sample introduction method, which reduces total analysis time to less than 15 s per sample as compared to minutes with traditional liquid-chromatography coupled to tandem mass spectrometry (LC–MS/MS). Several SPE parameters were evaluated in order to optimize recovery efficiencies when extracting analytes from wastewater, such as the nature of the stationary phase, the loading flow rate, the extraction pH, the volume and composition of the washing solution and the initial sample volume. The method was successfully applied to real wastewater samples from the primary sedimentation tank of a municipal wastewater treatment plant. Recoveries of target compounds from wastewater ranged from 78% to 106%, the limit of detection ranged from 30 to 122 ng L⁻¹ while the limit of quantification ranged from 90 to 370 ng L⁻¹. Calibration curves in the wastewater matrix showed good linearity (R² ≥ 0.991) for all target analytes and the intraday and interday coefficient of variation was below 15%, reflecting a good precision.     

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.     

Liquid-phase microextraction and GC for the determination of primary, secondary and tertiary aromatic amines as their iodo-derivatives

Presence of iodine in aromatic amines, introduced by their reaction with iodine, and other electron withdrawing substituents such as chlorine and nitro, has been found to afford excellent liquid-phase microextraction (LPME) in toluene and separation by gas chromatography in the determination of primary, secondary and tertiary aromatic amines. The effect is due to decreased basic nature of amines when electronegative substituents are present. Single drop microextraction (SDME) of the amines in 2 μl of toluene and injection of the whole extract into GC, or LPME into 50 μl of toluene and injection of 2 μl of extract, were used. LPME has been found more robust and to give better extraction in shorter period than SDME. In SDME-GC-FID, the average correlation coefficient was 0.9939 and average limit of detection 25 μg l⁻¹ (range 12-61 μg l⁻¹) whereas the corresponding values in LPME-GC-MS were, respectively, 0.9953 and 33 ng l⁻¹ (range 18-60 ng l⁻¹). The method has been applied to determine aromatic amines in river water, dye factory effluents and food dye stuffs. The LPME was found as robust, rugged and simple extraction method.     

Determination of non-ionic and anionic surfactants in environmental water matrices

Solid-phase extraction (SPE) combined with liquid chromatography electrospray mass spectrometry (LC-(ESI)MS) was used to determine 16 non-ionic and anionic surfactants in different environmental water samples at ng L⁻¹ levels. The proposed method is sensitive and simple and has good linear range and detection limits (less than 50 ng L⁻¹) for most compound classes.The effect of ion suppression was studied in aqueous matrices from several treatment plants—including urban and industrial wastewater treatment plants (WWTPs), drinking-water treatment plants (DWTPs) and seawater desalination plants (SWDPs)—and it was considered when quantifying our samples. In addition, conventional treatments and tertiary treatments that use advanced membrane technologies, such as ultrafiltration (UF) and reverse osmosis (RO) were evaluated in order to determine their efficiency in eliminating these compounds.The concentrations of non-ionic surfactants in the raw waters studied ranged from 0.2 to 100 μg L⁻¹. In effluents, the concentrations ranged from 0.1 to 5 μg L⁻¹, which reflects consistent elimination. Anionic surfactants were present in all waters studied at higher levels. Levels up to 3900 μg L⁻¹ of linear alkylbenzene sulfonates (LASs) and 32,000 μg L⁻¹ of alkyl ethoxysulfates (AESs) were detected in urban WWTP influents, while levels up to 25 μg L⁻¹ of LASs and 114 μg L⁻¹ of AESs were found in drinking-water and desalination treatment plants.The results indicate that conventional processes alone are not sufficient to completely remove the studied surfactants from waste streams. Tertiary treatments that use advanced membrane technologies such as UF and RO can further reduce the amount of target compounds in the effluent water.     

Solid phase extraction vis-à-vis coprecipitation preconcentration of cadmium and lead from soils onto 5,7-dibromoquinoline-8-ol embedded benzophenone and determination by FAAS

This article compares the solid phase extraction (SPE) and coprecipitative preconcentration of cadmium and lead from dilute aqueous solutions as a function of pH and weight of chelating agent. SPE enriches cadmium and lead over a wider pH range (6.0-8.0) and requires lower weight of DBQ chelate embedded benzophenone. Among the quinoline-8-ol and its dihaloderivatives, DBQ embedded benzophenone allows quantitative enrichment over a wide pH range (6.0-8.0) for both cadmium and lead unlike DCQ (∼6.5 for Cd and 6.5-7.0 for Pb), DBQ was preferred. The calibration plots were rectilinear over the concentration range of 0.1-50 and 2.5-200 μg l⁻¹ of cadmium and lead with detection limits of 0.1 and 2.0 μg l⁻¹, respectively, which are 400 times lower than the direct FAAS method. The precision of the developed procedure is good as it provides relative standard deviation values of 2.20 and 2.45% during five replicate determinations of 2 and 25 μg l⁻¹ of cadmium and lead, respectively. The accuracy of the developed procedure was tested by analyzing certified reference materials (CRM's) of soil and marine sediment samples supplied by IAEA, Italy and NRC, Canada, respectively. Furthermore, the developed procedure has been successfully used for the speciative determination of cadmium and lead in soil samples collected from the vicinity of industries in India.     

Determination of traces of palladium in stream sediment and auto catalyst by FI-ICP-OES using on-line separation and preconcentration with QuadraSil TA

A flow injection analysis (FIA) method using on-line separation and preconcentration with a novel metal scavenger beads, QuadraSil™ TA, has been developed for the ICP-OES determination of traces of palladium. QuadraSil TA contains diethylenetriamine as a functional group on spherical silica beads and shows the highest selectivity for Pd(II) at pH 1 (0.1 mol l⁻¹ hydrochloric acid) solution. An aliquot of the sample solution prepared as 0.1 mol l⁻¹ in hydrochloric acid was passed through the QuadraSil TA column. After washing the column with the carrier solution, the Pd(II) retained on the column was eluted with 0.05 mol l⁻¹ thiourea solution and the eluate was directly introduced into an ICP-OES. The proposed method was successfully applied to the determination of traces of palladium in JSd-2 stream sediment certified reference material [0.019 ± 0.001 μg g⁻¹ (n = 3); provisional value: 0.0212 μg g⁻¹] and SRM 2556 used auto catalyst certified reference material [315 ± 4 μg g⁻¹ (n = 4); certified value: 326 μg g⁻¹]. The detection limit (3σ) of 0.28 ng ml⁻¹ was obtained for 5 ml of sample solution. The sample throughputs for 5 ml and 100 μl of the sample solutions were 10 and 15 h⁻¹, respectively.     

A fast screening method for the presence of atrazine and other triazines in water using flow injection with chemiluminescent detection

Atrazine is a triazine herbicide which contains two secondary aliphatic amine groups. Previous studies have shown that aliphatic amines react with tris(2,2′-bipyridyl)ruthenium(III) to produce chemiluminescence. This paper describes the application of tris(2,2′-bipyridyl)ruthenium(III) to the detection of atrazine and related triazine herbicides in water by flow injection chemiluminescence analysis. The optimised experimental conditions were determined to be: sample and carrier flow rates of 4.6 mL min⁻¹, sample at pH 9 buffered with 50 mM borax, and reagent concentration of 1 mM tris(2,2′-bipyridyl)ruthenium(III) in 20 mM H₂SO₄ (pH 1). Under these conditions, the logarithm of the chemiluminescence intensity versus concentration was linear in the range of 2.15-2150 μg L⁻¹ for samples in MilliQ water, and the limit of detection of atrazine in water was determined to be 1.3 ± 0.1 μg L⁻¹. Validation of the method was performed using direct injection HPLC. The presence of natural organic matter (NOM) significantly increased the chemiluminescence, masking the signal generated by atrazine. Isolating the target analyte via solid phase extraction (SPE) prior to analysis removed this interference and concentrated the samples, resulting in a greatly improved sensitivity with a detection limit of 14 ± 2 ng L⁻¹.     

An amperometric method for the detection of amitrole, glyphosate and its aminomethyl-phosphonic acid metabolite in environmental waters using passive samplers

The herbicides amitrole and glyphosate, and its metabolite aminomethyl-phosphonic acid (AMPA), in water samples have been directly analysed by high-performance liquid chromatography using an electrochemical (EC) detector. Limits of detection of 0.3 μg mL⁻¹ for glyphosate, 0.05 μg mL⁻¹ for AMPA and 0.03 μg mL⁻¹ for amitrole were comparable to those obtained by other authors using EC and also by liquid chromatography coupled to mass spectrometry, but the latter method requires derivatisation and pre-concentration of the sample whereas EC methods show similar sensitivity without the need of any derivatisation. The method was specifically designed to analyse extracts from passive samplers used for monitoring of polar herbicide residues in waters. To this purpose, three types of Empore^® disks were tested for their ability to adsorb and desorb these ionic, polar analytes. A procedure for their extraction from the membranes and reducing the interferences from other substances present in natural waters (i.e. humic acids) is described. The method is simple, does not require sophisticated equipment and is valid for the analysis and monitoring of herbicides residues using passive samplers.     

Improvement of analytical performances for mercury speciation by on-line derivatization, cryofocussing and atomic fluorescence spectrometry

A modified automated on-line hyphenated system for simultaneous inorganic ionic mercury (Hg²⁺) and monomethylmercury (MeHg⁺) analysis by hydride generation (HG) or ethylation (Eth), cryofocussing, gas chromatography (GC) separation and atomic fluorescence spectrometry (AFS) detection has been improved. Both derivatization methods are investigated with respect to the chromatographic and analytical performances. They can be both affected by interferences when the AFS detection system is used. Water vapor removal using a soda lime moisture trap improves significantly the chromatographic performances, the reproducibility and the detection limits for Hg²⁺ and MeHg⁺ analyzed with both methods. For ethylation (Eth) derivatization, a scattering interference generated from low-quality ethylation reagent has also been eliminated. For HG, improved detection limits are 0.13 ng l⁻¹ and 0.01 ng l⁻¹ for Hg²⁺ and MeHg⁺, respectively (0.1 l water sample), and reproducibility are 5% for Hg²⁺ (20 ng l⁻¹) and MeHg⁺ (5 ng l⁻¹). Improved detection limits for Eth are 0.22 ng g⁻¹ for Hg²⁺ and 0.02 ng g⁻¹ for MeHg⁺ (1 g dry sediment sample) and the reproducibility are 5-6% for Hg²⁺ and MeHg⁺ (1-2 ng g⁻¹).     

On-line electrochemical preconcentration and flame atomic absorption spectrometric determination of manganese in urine samples

A sensitive and selective method was developed for the determination of traces of manganese in urine using on-line electrochemical preconcentration followed by flame atomic absorption spectrometry detection. A home made flow-through polypropylene cell (4.5 cm long × 0.8 cm diameter filled with glass marbles) with an effective inner volume of 0.5 ml containing a working and a counter electrode, both of glassy carbon and a Pt pseudo reference electrode was located in a flow injection manifold specially designed for the purpose of this work. The manganese was deposited from buffer solution of NH₃/NH₄Cl at pH 9.00 through an oxidizing process at a current of 400 mA during 7 min. A flow of HCl 0.1 mol l⁻¹ at 4 ml min⁻¹ through the cell, chemically dissolved the deposit. A small portion (15 μl) of the concentrate was introduced in a continuously flowing system by means of a timing device and was then carried to the detector for the manganese quantification. All electrochemical and spectroscopic variables as well as possible interferences in both systems were systematically studied. The relative standard deviations for ten consecutive measurements of manganese solutions of 2.0 and 20 μg l⁻¹ were of 2.3 and 1.5%, respectively, while for a sample processed five times was less then 5%. The accuracy of the developed procedure was evaluated by adding known amounts of manganese standard to urine samples and following the whole procedure. Recoveries within the range 97.2-102.8% were obtained. To further prove the accuracy, a Seronorm Trace Elements in Urine, Batch 403125 sample with a reported concentration of 13 μg Mn l⁻¹ was also analyzed. The experimental value obtained was of 12.7 ± 0.1 μg l⁻¹, which does not differ significantly from the reported amount (p < 0.05). A preconcentration factor of 40, a linear range between 0.015 and 60 μg l⁻¹ and a limit of detection of 15 ng l⁻¹ permitted the determination of manganese in real urine samples from non-exposed subjects in the range 0.5-2.8 μg l⁻¹.     

Determination of pharmaceuticals in soils and sediments by pressurized liquid extraction and liquid chromatography tandem mass spectrometry

The present work describes the development of a sensitive analytical method based on pressurized liquid extraction (PLE) and pre-concentration by solid-phase extraction (SPE), followed by liquid chromatography–electrospray tandem mass spectrometry (LC–ESI-MS/MS) for the determination of seventeen pharmaceuticals in soils and sediments. The method is based on sample homogenisation using Na₂–EDTA washed sand and extraction with water at 90 °C. Special emphasis was placed on the optimization of the extraction procedure to develop a green method that reduces, at a maximum, the use of organic solvents in order to eliminate matrix components during the clean-up. The proposed method was linear in a concentration range from 0.3 to 333 ng g⁻¹, with correlation coefficients higher than 0.993. Method detection (MDLs) and quantification (MQLs) limits ranged from 0.1 to 6.8 ng g⁻¹ and from 0.25 to 23 ng g⁻¹, respectively. Absolute recoveries were analyte dependent, varying between 50% and 105% at the MQL level, except for fenofibrate (40%) and diclofenac (34%). The intra-day and inter-day precision was given by RSD values from 0.7% to 7.9% and from 1.6% to 14.5%, respectively. Acetaminophen, carbamazepine, ciprofloxacin, clofibric acid, codeine, diazepam, fenofibrate, metropolol, ofloxacin and propanolol were detected at concentrations from MDL to 35.62 ng g⁻¹ in soils and sediments from marsh areas. Due to the low recoveries, results for fenofibrate and diclofenac can only be considered as semi-quantitative. The method was fully suitable for the other 15 pharmaceuticals.     

Speciation of organotin compounds in waters and marine sediments using purge-and-trap capillary gas chromatography with atomic emission detection

A procedure for the simultaneous determination of six organotin compounds, including methyl-, butyl- and phenyltins, in waters and marine sediments is developed. The analytes were leached from the solid samples into an acetic acid:methanol mixture by using an ultrasonic probe. The organotins were derivatized with sodium tetraethylborate (NaBEt₄) in the aqueous phase, stripped by a flow of helium, pre-concentrated in a trap and thermally desorbed. This was followed by capillary gas chromatography with microwave-induced plasma atomic emission spectrometry as the detection system (GC-AED). Each chromatographic run took 22 min, including the purge time. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were at least 0.9991. Detection limits ranged from 11 to 50 ng Sn l⁻¹ for tributyltin and tetramethyltin, respectively. The seawater samples analyzed contained variable concentrations of mono-, di- and tributyl- and monophenyltin, ranging from 0.05 to 0.48 μg Sn l⁻¹, depending on the compound. Some of the sediments analyzed contained concentrations of dibutyl- and tributyltin of between 6.0 and 13.0 ng Sn g⁻¹. Analysis of the certified reference material PACS-2, as well as of spiked water and sediment samples showed the accuracy of the method. The proposed method is selective and reproducible, and is considered suitable for monitoring organotin compounds in water and sediment samples.     

Synthesis and application of a functionalized resin for flow injection/F AAS copper determination in waters

This paper reports the development of a new strategy for low-level determination of copper in water samples by using a flow-injection system coupled to solid-phase extraction (SPE) using flame atomic absorption spectrometry (F AAS) as detector. In order to preconcentrate copper from samples, a minicolumn packed with a styrene-divinylbenzene resin functionalized with (S)-2-[hydroxy-bis-(4-vinyl-phenyl)-methyl]-pyrrolidine-1-carboxylic acid ethyl ester was used and the synthesis procedure is described. System operation is based on the on-line retention of Cu(II) ions at pH 9.0 ± 0.2 in a such minicolumn with posterior analyte elution with 2 mol l⁻¹ HCl directly to the F AAS nebulizer. The influence of several chemical (sample pH, buffer concentration, HCl eluent concentration and effect of the ionic strength) and flow (sample and eluent flow rates and preconcentration time) variables that could affect the performance of this system were investigated as well as the possible interferents. At optimized conditions, for 2 min of preconcentration time (13.2 ml of sample volume), the system achieved a detection limit of 1.1 μg l⁻¹, a R.S.D. 1% at 20 μg g l⁻¹ and an analytical throughput of 25 h⁻¹, whereas for 4 min of preconcentration time (26.4 ml of sample volume), a detection limit of 0.93 μg l⁻¹, a R.S.D. 5.3% at 5 μg l⁻¹ and a sampling frequency of 13 h⁻¹ were reported.     

Pre-concentration of trace elements in short chain alcohols using different commercial cation exchange resins prior to inductively coupled plasma-optical emission spectrometric detection

Chelex-100, Dowex 50W-x8 and Dowex MAC-3 exchange resins were investigated for separation and pre-concentration of trace amounts of Cd, Cr, Cu, Fe, Mn, Pb, Ti and Zn in alcohols with respect to retention and desorption characteristics. Dowex 50W-x8 was found to be the best sorbent with percentages recoveries >95%. In addition, Chelex-100 appeared to be suitable for the pre-concentration of Cu, Fe and Zn, whereas Dowex MAC-3 was selective for Cu and Fe. Therefore, Dowex 50W-x8 was used for further investigations. The relative standard deviations <4% (n = 20), limits of detection and quantification were 0.1–1.2 μg L⁻¹ and 0.3–1.5 μg L⁻¹, respectively. The SPE method was validated against a certified reference material and the results were in agreement with certified values. The accuracy of the optimized method was verified by the recovery test in the spiked alcohol samples. The accuracy and spike recovery test for different metal ions were in the range 98–102% and 95–105%, respectively. The optimized method was applied to the separation and pre-concentration of metal ions in different commercial alcohol samples.     

At-line microextraction by packed sorbent-gas chromatography–mass spectrometry for the determination of UV filter and polycyclic musk compounds in water samples

An at-line analysis protocol is presented that allows the determination of four UV filters, two polycyclic musk compounds and caffeine in water at concentration level of ng L⁻¹. The fully automated method includes analytes enrichment by Microextraction by packed sorbent (MEPS) coupled directly to large volume injection-gas chromatography–mass spectrometry. Two common SPE phases, C8 and C18, were examined for their suitability to extract the target substances by MEPS. The analytes were extracted from small sample volumes of 800 μL with recoveries ranging from 46 to 114% for the C8-sorbent and 65–109% for the C18-sorbent. Limits of detection between 34 and 96 ng L⁻¹ enable the determination of the analytes at common environmental concentration levels. Both sorbents showed linear calibration curves for most of the analytes up to a concentration level of 20 ng mL⁻¹. Carryover was minimized by washing the sorbents 10 times with 100 μL methanol. After this thorough cleaning, the MEPS are re-used and up to 70 analyses can be performed with the same sorbent. The fully automated microextraction GC–MS protocol was evaluated for the influence of matrix substances typical for wastewater. Dilution of samples prior to MEPS is recommended when the polar caffeine is present at high concentration. Real water samples were analyzed by the MEPS-GC–MS method and compared to standard SPE.     

Solid-phase molecularly imprinted pre-concentration and spectrophotometric determination of isoxicam in pharmaceuticals and human serum

A selective molecularly imprinted polymer (MIP) has been synthesized for isoxicam pre-concentration, followed by its spectrophotometric determination based on hydrogen bonding interactions between examined drug and alizarin yellow GG. This method is able to evaluate isoxicam in range of 1.0 × 10⁻³ to 20.0 μg mL⁻¹, with a limit of determination of 1.0 ng mL⁻¹. The retention capacity and pre-concentration factor of prepared sorbent are 18.5 mg g⁻¹ and 200, respectively; and the prepared MIPs can be reused at least for five times. The MIP capability for isoxicam selection and extraction from the solution is higher than non-imprinted polymer (NIP). Under optimum conditions, this procedure can be successfully applied to assay trace amounts of isoxicam in pharmaceutical and biological samples.