On-line ionic imprinted polymer selective solid-phase extraction of nickel and lead from seawater and their determination by inductively coupled plasma-optical emission spectrometry

Nickel(II) and lead(II) ionic imprinted 8-hydroxyquinoline polymers were synthesized by a precipitation polymerization technique and were used as selective solid phase extraction supports for the determination of nickel and lead in seawater by flow injection solid phase extraction on-line inductively coupled plasma-optical emission spectrometry. An optimum loading flow rate of 2.25 mL min⁻¹ for 2 min and an elution flow rate of 2.25 mL min⁻¹ for 1 min gave an enrichment factor of 15 for nickel. However, a low dynamic capacity and/or rate for adsorption and desorption was found for lead ionic imprinted polymer and a flow rate of 3.00 mL min⁻¹ for 4-min loading and a flow rate of 2.25 mL min⁻¹ for 1-min elution gave a enrichment factor of 5. The limit of detection was 0.33 μg L⁻¹ for nickel and 1.88 μg L⁻¹ for lead, with a precision (n = 11) of 8% (2.37 μg Ni L⁻¹) for nickel and 11% (8.38 μg Pb L⁻¹) for lead. Accuracy was also assessed by analyzing SLEW-3 (estuarine water) and TM-24 (lake water) certified reference materials, and the values determined were in good agreement with the certified concentrations.     

LC–MS–MS determination of ibuprofen, 2-hydroxyibuprofen enantiomers,and carboxyibuprofen stereoisomers for application in biotransformation studies employing endophytic fungi

The purpose of this study was the development and validation of an LC–MS–MS method for simultaneous analysis of ibuprofen (IBP), 2-hydroxyibuprofen (2-OH-IBP) enantiomers, and carboxyibuprofen (COOH-IBP) stereoisomers in fungi culture medium, to investigate the ability of some endophytic fungi to biotransform the chiral drug IBP into its metabolites. Resolution of IBP and the stereoisomers of its main metabolites was achieved by use of a Chiralpak AS-H column (150 × 4.6 mm, 5 μm particle size), column temperature 8 °C, and the mobile phase hexane–isopropanol–trifluoroacetic acid (95: 5: 0.1, v/v) at a flow rate of 1.2 mL min⁻¹. Post-column infusion with 10 mmol L⁻¹ ammonium acetate in methanol at a flow rate of 0.3 mL min⁻¹ was performed to enhance MS detection (positive electrospray ionization). Liquid–liquid extraction was used for sample preparation with hexane–ethyl acetate (1:1, v/v) as extraction solvent. Linearity was obtained in the range 0.1–20 μg mL⁻¹ for IBP, 0.05–7.5 μg mL⁻¹ for each 2-OH-IBP enantiomer, and 0.025–5.0 μg mL⁻¹ for each COOH-IBP stereoisomer (r ≥ 0.99). The coefficients of variation and relative errors obtained in precision and accuracy studies (within-day and between-day) were below 15%. The stability studies showed that the samples were stable (p > 0.05) during freeze and thaw cycles, short-term exposure to room temperature, storage at −20 °C, and biotransformation conditions. Among the six fungi studied, only the strains Nigrospora sphaerica (SS67) and Chaetomium globosum (VR10) biotransformed IBP enantioselectively, with greater formation of the metabolite (+)-(S)-2-OH-IBP. Formation of the COOH-IBP stereoisomers, which involves hydroxylation at C3 and further oxidation to form the carboxyl group, was not observed.     

Multi-wall carbon nanotube aqueous dispersion monitoring by using A4F-UV-MALS

In this work, the potentiality of asymmetrical flow field-flow fractionation (A4F) hyphenated to UV detector and multi-angle light scattering (MALS) was investigated for accurately determining multi-walled carbon nanotube (MWCNT) length and its corresponding dispersion state in aqueous medium. Fractionation key parameters were studied to obtain a method robust enough for heterogeneous sample characterization. The main A4F conditions were 10⁻⁵ mL min⁻¹ NH₄NO₃, elution flow of 1 mL min⁻¹, and cross flow of 2 mL min⁻¹. The recovery was found to be (94 ± 2)%. Online MALS analysis of eluted MWCNT suspension was performed to obtain length distribution. The length measurements were performed with a 4% relative standard deviation, and the length values were shown to be in accordance with expected ones. The capabilities of A4F-UV-MALS to size characterize various MWCNT samples and differentiate them according to their manufacturing process were evaluated by monitoring ball-milled MWCNT and MWCNT dispersions. The corresponding length distributions were found to be over 150–650 and 150–1,156 nm, respectively. A4F-UV-MALS was also used to evaluate MWCNT dispersion state in aqueous medium according to the surfactant concentration and sonication energy involved in the preparation of the dispersions. More especially, the presence or absence of aggregates, number and size of different populations, as well as size distributions were determined. A sodium dodecyl sulfate concentration of 15 to 30 mmol L⁻¹ and a sonication energy ranged over 20–30 kJ allow obtaining an optimal MWCNT dispersion. It is especially valuable for studying nanomaterials and checking their manufacturing processes, size characterization being always of high importance.     

Ultra-fast HPLC-ICP-MS analysis of oxaliplatin in patient urine

A novel method for rapid HPLC-ICP-MS analysis of oxaliplatin in human urine was developed implementing a stationary HPLC phase with a particle size of 1.8 μm. The method allowed a cycle time of <1 min at a HPLC flow rate of 0.9 mL min⁻¹. Procedural limits of detection of 0.05 μg L⁻¹ oxaliplatin (150 fg on column) were obtained. Analysis of oxaliplatin in patient urine showed that accurate quantification of the intact drug demanded for storage at −80 °C and rapid measurement after thawing.     

Spectrophotometric Determination of Chlorprothixene with Eriochrome Cyanine R

 Two spectrophotometric methods are described for the determination of chlorprothixene (CPT). The first method is based on the extraction of the ion-association compound of CPT with eriochrome cyanine R (ECR) into butanol. The extracted compound in the organic solvent obeys Beer’s law in the range 5–80 μg mL ⁻¹. The second method is based on the measuring of the absorbance of the aqueous solution of the compound of CPT with ECR in presence of methylcellulose. Conformity with Beer’s law was evident in the range 0.7–10 μg mL ⁻¹ of chlorprothixene. The methods were applied for the determination of chlorprothixene contents in pharmaceuticals. Received July 30, 1998. Revision July 20, 1999.     

Organosilica composite for preconcentration of phenolic compounds from aqueous solutions

A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO₂) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol) (TX). Under static conditions phenol was quantitatively extracted onto TX-SiO₂ in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO₂ for phenol is 2.4 mg g⁻¹ with distribution coefficients up to 3.4 × 10⁴ mL g⁻¹; corresponding data for 1-naphthol are 1.5 mg g⁻¹ and 3 × 10³ mL g⁻¹. The distribution coefficient does not change significantly for solution volumes of 0.025–0.5 L and adsorbent mass less than 0.03 g; 1–90 μg analyte can be easily eluted by 1–3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A ₅₄₀) and phenol concentration (C) in water was found according to the equation A ₅₄₀ = (6 ± 1) × 10⁻² + (0.9 ± 0.1)C (μmol L⁻¹) with a detection range from 1 × 10⁻⁸ mol L⁻¹ (0.9 μL g⁻¹) to 2 × 10⁻⁷ mol L⁻¹ (19 μL g⁻¹), a limit of quantification of 1 μL g⁻¹ (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical analysis. The detection limit of 1-naphthol with this method is 6 μL g⁻¹ while the quantification limit is 20 μL g⁻¹. A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08–3.2 mL g⁻¹.     

Catanionic surfactant ambient cloud point extraction and high-performance liquid chromatography for simultaneous analysis of organophosphorus pesticide residues in water and fruit juice samples

A mixed anionic–cationic surfactant cloud point extraction (CPE) has been developed using sodium dodecyl sulfate (SDS) and tetrabutylammonium bromide (TBABr) for the extraction and preconcentration of organophosphorus pesticides (OPPs) at ambient temperature before analysis by high-performance liquid chromatography. The studied OPPs were azinphos-methyl, parathion-methyl, fenitrothion, diazinon, chlorpyrifos, and prothiophos. The optimum conditions of the mixed anionic–cationic CPE were 50 mmol L⁻¹ SDS, 100 mmol L⁻¹ TBABr, and 10% (w/v) NaCl. The extracted OPPs were successfully separated within 11 min using the conditions of a Waters Symmetry C8 column, a flow rate of 0.8 mL min⁻¹, a gradient elution of methanol and water, and detection at 210 nm. Linearity was found over the range 0.05–5 μg mL⁻¹, with the correlation coefficients higher than 0.996. The enrichment factor of the target analytes was in the range 6–11, which corresponds to their limits of detection from 1 to 30 ng mL⁻¹. High precisions (intra-day and inter-day) were obtained with relative standard deviation <1.5% (t _R) and 10% (peak area). Accuracies (% recovery) of the different spiked OPP concentrations were 82.7–109.1% (water samples) and 80.3–113.3% (fruit juice samples). No contamination by the OPPs was observed in any studied samples.     

A thermogravimetic kinetic study of uncatalyzed diesel soot oxidation

Isothermal and non-isothermal thermogravimetric experiments (TG) with real and synthetic (Printex U) soot were performed at different O₂ concentrations (5–22%O₂/N₂), sample masses (0.5–10 mg), heating (5–20 °C min⁻¹) and flow rates (80–100 mL min⁻¹). The significance of the experimental and calculation uncertainties (i.e. experimental parameter dependencies, calculation method and mass transfer limitations), which are related to TG for the extraction of chemical kinetics, was explored. Finally, an intrinsic kinetic equation for soot oxidation is proposed.     

Solid Phase Extraction and Simultaneous Spectrophotometric Determination of Trace Amounts of Copper and Iron Using Mixture of Ligands

 A novel sensitive and simple method for rapid and selective extraction, preconcentration and determination of iron (as its bathophenanthroline complex) and copper (as its neocuproine complex) using octadecyl silica cartridges and dual wavelength spectrophotometry is presented. The dual wavelength method (533 nm for the iron-bathophenanthroline and 454 nm for the copper-neocuproine as the analytical wavelength) is used to eliminate spectral interferences. Extraction efficiency and the influence of flow rates of sample solution and eluent, pH, amount of neocuproine, bathophenanthroline and hydroxylamine hydrochloride, type and least amount of eluent for elution of iron and copper complexes from cartridge, break-through volume and limit of detection are evaluated. The effects of various cationic and anionic interferences on percent recovery of iron and copper are also studied. Extraction efficiencies >95% are obtained by elution of cartridges with minimal amount of organic solvent. Iron and copper were determined in the range of 3–100 ng mL⁻¹. The limits of detection are 0.98 and 1.13 ng mL⁻¹ for iron and copper, respectively. The proposed method is applied successfully to the determination of both analytes in river, tap and well water samples. Author for correspondence. E-mail: yyamini@modares.ac.ir Received September 18, 2002; accepted December 12, 2002 Published online May 5, 2003     

Solid Phase Extraction of Solanesol

The method of solid-phase extraction (SPE) for the concentration and clean-up of tobacco extract samples during solanesol analysis was proposed in this work. A column (200 mm × 4 mm i.d.) packed with 0.10 g silica gel (with particle size of 70 μm, porosity of 0.5 and surface area of 400 m² g⁻¹) was used as SPE cartridge. Several extraction parameters, such as sample loading flow (0.3–7 mL min⁻¹), sample volume (5–50 mL), the column adsorption capacity and elution were evaluated to provide a fast, quantitative and reproducible SPE method. A mean solanesol recovery was 97.5 ± 1.6% (mean ± sd) and mean intra- and inter-day reproducibility was higher than 97%. It can be used in the analysis of solanesol in tobacco extracts.     

In vitro monitoring of clindamycin in human urine using flow injection chemiluminescence

A sensitive chemiluminescence method for the determination of clindamycin is presented. The method is based on the inhibitory effect of clindamycin on the chemiluminescence reaction between luminol and myoglobin in a flow-injection system. The decrement in chemiluminescence intensity is linear with the logarithm of the clindamycin concentration over the range of 0.1–70.0 ng mL⁻¹ (r ² = 0.9995), with a detection limit of 0.03 ng mL⁻¹ (3σ). At a flow rate of 2.0 mL min⁻¹, the complete analytical process could be performed within 0.5 min, including sampling and washing, with a relative standard deviation of less than 3.0% (n = 5). The procedure was applied to the determination of clindamycin in human serum and in monitoring the excretion of clindamycin in human urine samples without any pretreatment process. It was found that the excretive clindamycin concentration reached its maximum 3 hours after oral administration. The clindamycin excretive ratio in 9 hours was 10.84% in the body of the volunteer.     

First results on Fe solid-phase extraction from coastal seawater using anatase TiO2 nano-particles

This paper describes the application of TiO₂ nano-particles (anatase form) for the solid-phase extraction of iron from coastal seawater samples. We investigated the adsorption processes by infra-red spectroscopy. We compared in batch and on-(mini)column extraction approaches (0.1 and 0.05 g TiO₂ per sample, respectively), combined to external calibration and detection by inductively coupled plasma mass spectrometry at medium mass resolution. Globally, this titania phase was slightly more efficient with seawater than with ultra-pure water, although between pH 2 and pH 7, the Fe retention efficiency progressed more in ultra-pure water than in seawater (6.9 versus 4.8 times improvement). Different reaction schemes are proposed between Fe(III) species and the two main categories of titania sites at pH 2 (adsorption of [FeL _x ]^{(3 − x)+} via possibly the mediation of chlorides) and at pH 7 (adsorption of [Fe(OH)₂]⁺ and precipitation of [Fe(OH)₃]⁰). Under optimised conditions, the inlet system was pre-cleaned by pumping 6% HCl for ∼2 h, and the column was conditioned by aspirating ultra-pure water (1.7 g min⁻¹) and 0.05% ammonia (0.6 g min⁻¹) for 1 min. Then 3 g seawater sample was loaded at the same flow rate while being mixed on-line with 0.05% ammonia at 0.6 g min⁻¹ to adjust the pH to 7. The iron retained on the oxide powder was then eluted with 3 g 6% HCl (<0.002% residual salinity in the separated samples). The overall procedural blank was 220 ± 46 (2 s, n = 16) ng Fe kg⁻¹ (the titania was renewed in the column every 20 samples, with 2-min rinsing in between samples with 6% HCl at 1.5 g min⁻¹). The recovery estimated from the Canadian certified reference material CASS-2 was 69.5 ± 7.6% (2 s, n = 4). Typically, the relative combined uncertainty (k = 2) estimated for the measurement of ∼1 μg Fe kg⁻¹ (0.45 μm filtered and acidified to pH 1.5) of seawater was ∼12%. We applied our method to a similar sample, from the coastal region of the North Sea. The agreement well within stated uncertainties of our result with the value obtained independently by isotope dilution mass spectrometry further validated our method.     

Fast ultrasound-assisted extraction of copper,iron, manganese and zinc from human hair samples prior to flow injection flame atomic absorption spectrometric detection

A dynamic ultrasound-assisted extraction procedure utilizing diluted nitric acid was developed for the determination of copper, iron, manganese and zinc in human hair taken from workers in permanent contact with a polluted environment. The extraction unit of the dynamic ultrasound-assisted extraction system contains a minicolumn into which a specified amount of hair (5–50 mg) is placed. Once inserted into the continuous manifold, trace metals were extracted at 3 mL min⁻¹ with 3 mol L⁻¹ nitric acid under the action of ultrasound for 2 min for zinc and 3 min for copper, iron and manganese determination, and using an ultrasonic water-bath temperature of 70 °C for zinc and 80 °C for copper, iron and manganese determination. The system permits the direct analysis of hair and yields concentrations with relative standard deviations of <3% (n = 11). The applicability of the procedure was verified by analysing human hair samples from workers exposed to welding fumes, and its accuracy was assessed through comparison with a conventional sample dissolution procedure and the use of a certified reference material (BCR 397, human hair).     

Simultaneous speciation of arsenic (As(III), MMA, DMA, and As(V)) and selenium (Se(IV), Se(VI), and SeCN−) in petroleum refinery aqueous streams

High-performance liquid chromatography (HPLC) coupled to an ICP-MS with an octapole reaction system (ORS) has been used to carry out quantitative speciation of selenium (Se) and arsenic (As) in the stream waters of a refining process. The argon dimers interfering with the ⁷⁸Se and ⁸⁰Se isotopes were suppressed by pressurizing the octapole chamber with 3.1 mL min⁻¹ H₂ and 0.5 mL min⁻¹ He. Four arsenic species arsenite—As(III), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)—and three inorganic Se species—selenite Se(IV), selenate Se(VI), and selenocyanate (SeCN⁻)—were separated in a single run by ion chromatography (IC) using gradient elution with 100 mmol L⁻¹ NH₄NO₃, pH 8.5, adjusted by addition of NH₃, as eluent. Repeatabilities of peak position and of peak area evaluation were better than 1% and about 3%, respectively. Detection limits (as 3σ of the baseline noise) were 81, 56, and 75 ng L⁻¹ for Se(IV), Se(VI), and SeCN⁻, respectively, and 22, 19, 25, and 16 ng L⁻¹ for As(III), As(V), MMA, and DMA, respectively. Calibration curve R ² values ranged between 0.996 and 0.999 for the arsenic and selenium species. Column recovery for ion chromatography was calculated to be 97 ± 6% for combined arsenic species and 98 ± 3% for combined selenium species. Because certified reference materials for As and Se speciation studies are still not commercially available, in order to check accuracy and precision the method was applied to certified reference materials, BCR 714, BCR 1714, and BCR 715 and to two different refinery samples—inlet and outlet wastewater. The method was successfully used to study the quantitative speciation of selenium and arsenic in petroleum refinery wastewaters.     

HPLC determination of cefotaxime and cephalexine residues in milk and cephalexine in veterinary formulation

An HPLC method was developed and validated for the determination of the cephalosporins cefotaxime and cephalexine in skimmed bovine milk. The analytical column, Kromasil C₁₈ (250 mm × 4.0 mm, 5 μm) was operated at ambient temperature. Mobile phase consisted of CH₃OH-acetate buffer (pH = 4.0) and it was delivered isocratically at a flow rate of 1.0 mL · min⁻¹. Total analysis time was less than 5 min. Caffeine was used as internal standard (5 ng · μL⁻¹). UV detection was performed at 265 nm. Method validation was performed by means of intra-day (n = 5) and inter-day accuracy and precision (n = 8), sensitivity and linearity. Limits of detection (LOD) and limits of quantification (LOQ) were 0.1 and 0.3 ng · μL⁻¹, respectively. The method was applied to the analysis of a veterinary drug (CEPOREX) containing cephalexine. The results were quite accurate with the relative error varying from −8.0 to −3.5%. Solid-phase extraction was applied to remove all matrix interference from milk samples. High extraction recoveries (average 84–121%) were achieved by using Abselut NEXUS cartridges with acetonitrile as eluent and a rinsing step with water and n-butanol. A pre-concentration step was necessary in a 1/10 level to reach the EU MRL concentration level (100 μg · kg⁻¹). RSD values were less than 7% for both cephalosporins. Correspondence: Ioannis N. Papadoyannis, Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece     

A Weak Cation-Exchange Monolithic SPE Column for Extraction and Analysis of Caffeine and Theophylline in Human Urine

A weak cation-exchange monolithic column has been prepared in stainless steel tubing and used as the solid-phase extraction material in quantitative analysis of caffeine and theophylline in urine. Column switching, with water as mobile phase, was used for on-line cleaning and screening of human urine samples. Reversed-phase high-performance liquid chromatography was then performed on a C₁₈ column with methanol–water 30:70 (v/v) as mobile phase at a flow rate of 0.5 mL min⁻¹. Ultraviolet detection was performed at 274 nm. Good linear relationships were obtained between response and concentrations of caffeine and theophylline in the range 0.1–50 μg mL⁻¹. Absolute recovery ranged from 77.4 to 82.3% and inter-day and intra-day relative standard deviations were less than 5%. The method was suitable for analysis of caffeine and theophylline in human urine, because it eliminated tedious pretreatment and enabled rapid, economic, repeatable, and effective assay of traces of the drugs in biological samples.     

Effect of organic load on the performance and methane production of an AnSBBR treating effluent from biodiesel production

Currently, there is an increasing demand for the production of biodiesel and, consequently, there will be an increasing need to treat wastewaters resulting from the production process of this biofuel. The main objective of this work was, therefore, to investigate the effect of applied volumetric organic load (AVOL) on the efficiency, stability, and methane production of an anaerobic sequencing batch biofilm reactor applied to the treatment of effluent from biodiesel production. As inert support, polyurethane foam cubes were used in the reactor and mixing was accomplished by recirculating the liquid phase. Increase in AVOL resulted in a drop in organic matter removal efficiency and increase in total volatile acids in the effluent. AVOLs of 1.5, 3.0, 4.5 and 6.0 g COD L⁻¹ day⁻¹ resulted in removal efficiencies of 92%, 81%, 67%, and 50%, for effluent filtered samples, and 91%, 80%, 63%, and 47%, for non-filtered samples, respectively, whereas total volatile acids concentrations in the effluent amounted to 42, 145, 386 and 729 mg HAc L⁻¹, respectively. Moreover, on increasing AVOL from 1.5 to 4.5 g COD L⁻¹ day⁻¹ methane production increased from 29.5 to 55.5 N mL CH₄ g COD⁻¹. However, this production dropped to 36.0 N mL CH₄ g COD⁻¹ when AVOL was increased to 6.0 g COD L⁻¹ day⁻¹, likely due to the higher concentration of volatile acids in the reactor. Despite the higher concentration of volatile acids at the highest AVOL, alkalinity supplementation to the influent, in the form of sodium bicarbonate, at a ratio of 0.5–1.3 g NaHCO₃ g COD_fed⁻¹, was sufficient to maintain the pH near neutral and guarantee process stability during reactor operation.     

Screen-printed sensor for batch and flow injection potentiometric chromium(VI) monitoring

A disposable screen-printed electrode was designed and evaluated for direct detection of chromium(VI) in batch and flow analysis. The carbon screen-printed electrode was modified with a graphite–epoxy composite. The optimal graphite–epoxy matrix contains 37.5% graphite powder, 12.5% diphenylcarbohydrazide, a selective compound for chromium(VI), and 50% epoxy resin. The principal analytical parameters of the potentiometric response in batch and flow analysis were optimized and calculated. The screen-printed sensor exhibits a response time of 20 ± 1 s. In flow analysis, the analytical frequency of sampling is 70 injections per hour using 0.1 M NaNO₃ solution at pH 3 as the carrier, a flow rate of 2.5 mL·min⁻¹, and an injection sample volume of 0.50 mL. The sensor shows potentiometric responses that are very selective for chromium(VI) ions and optimal detection limits in both static mode (2.1 × 10⁻⁷ M) and online analysis (9.4 × 10⁻⁷ M). The disposable potentiometric sensor was employed to determine toxicity levels of chromium(VI) in mineral, tap, and river waters by flow-injection potentiometry and batch potentiometry. Chromium(VI) determination was also carried out with successful results in leachates from municipal solid waste landfills.     

Molecularly imprinted polymer solid-phase extraction coupled to square wave voltammetry at carbon fibre microelectrodes for the determination of fenbendazole in beef liver

A molecularly imprinted polymer was developed and used for solid-phase extraction (MISPE) of the antihelmintic fenbendazole in beef liver samples. Detection of the analyte was accomplished using square wave voltammetry (SWV) at a cylindrical carbon fibre microelectrode (CFME). A mixture of MeOH/HAc (9:1) was employed both as eluent in the MISPE system and as working medium for electrochemical detection of fenbendazole. The limit of detection was 1.9 × 10⁻⁷ mol L⁻¹ (57 μg L⁻¹), which was appropriate for the determination of fenbendazole at the maximum residue level permitted by the European Commission (500 μg kg⁻¹ in liver). Given that the SW voltammetric analysis could not be directly performed in the sample extract as a consequence of interference from some sample components, a sample clean-up with a MIP for selectively retaining fenbendazole was performed. The MIP was synthesized using a 1:8:22 template/methacrylic acid/ethylene glycol dimethacrylate ratio. A Britton–Robinson Buffer of pH 9.0 was selected for retaining fenbendazole in the MIP cartridges, and an eluent volume of 5.0 mL at a flow rate of 2.0 mL min⁻¹ was chosen in the elution step. Cross-reactivity with the MIP was observed for other benzimidazoles. The synthesized MIP exhibited a good selectivity for benzimidazoles with respect to other veterinary drugs. The applicability of the MISPE-SWV method was tested with beef liver samples, spiked with fenbendazole at 5,000 and 500 μg kg⁻¹. Results obtained for ten different liver samples yielded mean recoveries of (95 ± 12)% and (96 ± 11)% for the upper and lower concentration level, respectively.     

Dispersive liquid–liquid microextraction coupled to liquid chromatography for thiamine determination in foods

A miniaturized dispersive liquid–liquid microextraction (DLLME) procedure coupled to liquid chromatography (LC) with fluorimetric detection was evaluated for the preconcentration and determination of thiamine (vitamin B₁). Derivatization was carried out by chemical oxidation of thiamine with 5 × 10⁻⁵ M ferricyanide at pH 13 to form fluorescent thiochrome. For DLLME, 0.5 mL of acetonitrile (dispersing solvent) containing 90 μL of tetrachloroethane (extraction solvent) was rapidly injected into 10 mL of sample solution containing the derivatized thiochrome and 24% (w/v) sodium chloride, thereby forming a cloudy solution. Phase separation was carried out by centrifugation, and a volume of 20 μL of the sedimented phase was submitted to LC. The mobile phase was a mixture of a 90% (v/v) 10 mM KH₂PO₄ (pH 7) solution and 10% (v/v) acetonitrile at 1 mL min⁻¹. An amide-based stationary phase involving a ligand with amide groups and the endcapping of trimethylsilyl was used. Specificity, linearity, precision, recovery, and sensitivity were satisfactory. Calibration graph was carried out by the standard additions method and was linear between 1 and 10 ng mL⁻¹. The detection limit was 0.09 ng mL⁻¹. The selectivity of the method was judged from the absence of interfering peaks at the thiamine elution time for blank chromatograms of unspiked samples. A relative standard deviation of 3.2% was obtained for a standard solution containing thiamine at 5 ng mL⁻¹. The esters thiamine monophosphate and thiamine pyrophosphate can also be determined by submitting the sample to successive acid and enzymatic treatments. The method was applied to the determination of thiamine in different foods such as beer, brewer’s yeast, honey, and baby foods including infant formulas, fermented milk, cereals, and purees. For the analysis of solid samples, a previous extraction step was applied based on an acid hydrolysis with trichloroacetic acid. The reliability of the procedure was checked by analyzing a certified reference material, pig’s liver (CRM 487). The value obtained was 8.76 ± 0.2 μg g⁻¹ thiamine, which is in excellent agreement with the certified value, 8.6 ± 1.1 μg g⁻¹.