C. Pérez-Conde

Molecularly imprinted polymers: an analytical tool for the determination of benzimidazole compounds in water samples.

Molecularly imprinted polymers (MIPs) for benzimidazole compounds have been synthesized by precipitation polymerization using thiabendazole (TBZ) as template, methacrylic acid as functional monomer, ethyleneglycol dimethacrylate (EDMA) and divinylbenzene (DVB) as cross-linkers and a mixture of acetonitrile and toluene as porogen. The experiments carried out by molecularly imprinted solid phase extraction (MISPE) in cartridges demonstrated the imprint effect in both imprinted polymers. MIP-DVB enabled a much higher breakthrough volume than MIP-EDMA, and thus was selected for further experiments. The ability of this MIP for the selective recognition of other benzimidazole compounds (albendazole, benomyl, carbendazim, fenbendazole, flubendazole and fuberidazole) was evaluated. The obtained results revealed the high selectivity of the imprinted polymer towards all the selected benzimidazole compounds. An off-line analytical methodology based on a MISPE procedure has been developed for the determination of benzimidazole compounds in tap, river and well water samples at concentration levels below the legislated maximum concentration levels (MCLs) with quantitative recoveries. Additionally, an on-line preconcentration procedure based on the use of a molecularly imprinted polymer as selective stationary phase in HPLC is proposed as a fast screening method for the evaluation of the presence of benzimidazole compounds in water samples.

Assessment of the cross-reactivity and binding sites characterisation of a propazine-imprinted polymer using the Langmuir-Freundlich isotherm

In this paper, the Langmuir-Freundlich isotherm is used to model the interaction of several triazines (desethylatrazine, desisopropylatrazine, simazine, atrazine, propazine and prometryn) with a propazine-imprinted polymer and to explain the observed cross-reactivity. Different rebinding experiments (each herbicide alone or all together in a mixture) were carried out and the experimental binding isotherms were fitted to the Langmuir-Freundlich isotherm. The fitting coefficients obtained (total number of binding sites, mean binding affinity and heterogeneity index) allowed the description of the kind of binding sites present in the imprinted polymer under study. It was concluded that the recognition mechanism was mainly governed by the molecular size although slight differences in the molecular structure may also play an important role. The obtained results suggest that the use of this new methodology can open new pathways for understanding how molecular recognition in imprinted polymers takes place.

Microalgae fiber optic biosensors for herbicide monitoring using sol–gel technology

Three microalgal species (Dictyosphaerium chlorelloides (D.c.), Scenedesmus intermedius (S.i.) and Scenedesmus sp. (S.s.)) were encapsulated in silicate sol-gel matrices and the increase in the amount of chlorophyll fluorescence signal was used to quantify simazine. Influence of several parameters on the preparation of the sensing layers has been evaluated: effect of pH on sol-gel gelation time; effect of algae density on sensor response; influence of glycerol (%) on the membrane stability. Long term stability was also tested and the fluorescence signal from biosensors remained stable for at least 3 weeks. D.c. biosensor presented the lowest detection limits for simazine (3.6 microg L(-1)) and the broadest dynamic calibration range (19-860 microg L(-1)) with IC(50) 125+/-14 microg L(-1). Biosensor was validated by HPLC with UV/DAD detection. The biosensor showed response to those herbicides that inhibit the photosynthesis at photosystem II (triazines: simazine, atrazine, propazine, terbuthylazine; urea based herbicides: linuron). However, no significant increases of fluorescence response was obtained for similar concentrations of 2,4-D (hormonal herbicide) or Cu(II). The combined use of two biosensors that use two different genotypes, sensitive and resistant to simazine, jointly allowed improving microalgae biosensor specificity.

Speciation of inorganic selenium in environmental matrices by flow injection analysis-hydride generation-atomic fluorescence spectrometry. Comparison of off-line, pseudo on-line and on-line extraction and reduction methods

This paper reports several sensitive flow injection analysis-hydride generation-atomic fluorescence spectrometry (FIA-HG-AFS) analytical methods for inorganic selenium determination in waste waters and sewage sludge samples with different treatments: off-line, pseudo-on-line and on-line extraction and reduction to Se(IV). The on-line method, which combines Se extraction and Se reduction in a microwave oven (MW), requires the use of the standard additions method in real determinations. During the extraction steps no alteration of the Se oxidation states took place and it was possible to determine Se(IV) and total inorganic selenium. The proposed analytical methods were successfully applied to waste waters and sludge samples. Validation was performed by using reference materials (RM 602, 603 and Aquacheck 135, 143) and by recovery tests on spiked samples.

Development of a fluoroimmunosensor for theophylline using immobilised antibody

A flowthrough theophylline fluoroimmunosensor with an antibody covalently immobilised on a solid support has been developed. The immobilisation technique proposed in this paper used Protein-A on control pore glass (Protein A-CPG) in an immunoreactor and dimethylsuberimidate as a cross-linking agent. Several supports and cross-linking reagents were tested in order to obtain oriented immobilisation and thus efficiency of the immunological reaction and reusability of the immunosensor. The immunosensor performance characteristics were established. The precision expressed as RSD, was 1.6%; the detection limit was 3 mug l(-1); the immunoreactor lifetime was established in 80 assays and there were no interferences with structurally similar compounds such as aminophylline, dihydroxypropyltheophylline and caffeine in the determination of the analyte. This fluoroimmunosensor was applied to determine theophylline in human serum samples from patients of the Puerta de Hierro Hospital in Madrid. The results obtained show that there are no significant differences between the proposed immunosensor and the high-pressure liquid chromatographic method with UV detection used by the Hospital, thus demonstrating the validity of the method.

Trace-level determination of triazines and several degradation products in environmental waters by disk solid-phase extraction and micellar electrokinetic chromatography.

An analytical method combining disk solid-phase extraction with micellar electrokinetic chromatography has been developed for the determination of atrazine, simazine, hydroxyatrazine, deisopropylatrazine, deethylatrazine, propazine and prometryn in water samples. The influence of the buffer and sodium dodecyl sulfate (SDS) concentration, pH and organic modifier on the separation has been studied. Baseline separation of the seven triazines was achieved under the following conditions: 10 mM borate buffer, 60 mM SDS, 20% methanol and pH 9.2. C18-bonded silica and poly(styrene-divinylbenzene) (PS-DVB) disks were evaluated for solid-phase extraction of the selected pesticides (11 of water sample). Using two PS-DVB disks, quantitative recoveries were obtained for all pesticides tested. The method was successfully applied for the determination of the seven triazines in drinking and well water at the 0.1 microg l(-1) and 0.5 microg l(-1) concentration levels, respectively. The detection limits for these analytes using the proposed analytical method were within the 0.02-0.06 microg l(-1) range in drinking water and the 0.06-0.30 microg l(-1) range in well water.

On-line concentration in micellar electrokinetic chromatography for triazine determination in water samples: evaluation of three different stacking modes

Three different stacking modes for the on-line concentration of seven selected triazines (desisopropylatrazine, desethylatrazine, simazine, hydroxyatrazine, atrazine, propazine and prometryn) by micellar electrokinetic chromatography (MEKC) were evaluated, namely the normal stacking mode, field enhancement sample injection and reverse electrode polarity stacking mode (REPSM). The best results were obtained using REPSM at –20 kV for 90 s. Concentration factors from 4 to 10 were achieved and the detection limits varied within the range 3.3–8.5 μg l−1. This methodology was combined with a solid-phase extraction (SPE) procedure to allow the determination of these analytes at trace levels. The SPE-REPSM-MEKC method developed was validated with a certified reference material of pesticides in drinking water (CRM 606) and was applied to the determination of the selected triazines in drinking waters at the level required by the European Union (0.1 μg l−1).

Determination of lead in natural waters using flow injection with on-line preconcentration and flame AAS detection

A rapid and sensitive method has been developed for the determination of lead in water samples by flame atomic absorption spectrometry using on-line preconcentration on a microcolumn packed with silica gel treated with a mixture of Aliquat 336 and nitroso-R-salt. The lead is retained at pH 5.5. The preconcentrated lead is directly eluted from the column to the nebulizer-burner system using 150 μL of 0.1 mol/L hydrochloric acid. The optimum preconcentration conditions are given and the retention efficiency achieved is higher than 80%. The enrichment factor is 37 and 100 for sample volumes of 5 and 30 mL, respectively. The limits of detection are 10.0, 6.0 and 4.0 ng/mL when 5, 10 and 30 mL of water is preconcentrated.

On-line preconcentration of aluminium with immobilized Chromotrope 2B for the determination by flame atomic absorption spectrometry and inductively coupled plasma mass spectrometry

Abstract A new and rapid on-line preconcentration and matrix separation method is described for the determination of aluminium by flame atomic absorption spectrometry (FAAS) and inductively coupled plasma mass spectrometry (ICP-MS). The method is based on selective retention of aluminium in a microcolumn packed with Chromotrope 2B immobilized on AG 1-X8 ion exchange resin. All the variables that affect the efficiency of aluminium retention and elution from the microcolumn have been investigated. The resulting method is rapid, sensitive and selective. For collection times of 10 and 2 min at a flow rate of 1 ml min −1 the detection limits are 10 and 0.1 ng ml −1 for FAAS and ICP-MS, respectively. The proposed method, which is highly sensitive and selective, was successfully applied to determine aluminium in tap water and dialysis solutions.

A novel flow injection chemiluminescence determination of Cr(VI) with Dichlorotris(1,10-phenanthroline)ruthenium(II).

A selective novel reverse flow injection system with chemiluminescence detection (rFI-CL) for the determination of Cr(VI) in presence of Cr(III) with Dichlorotris (1,10-phenanthroline)ruthenium(II), (Ru(phen)(3)Cl(2)), is described in this work. This new method is based on the oxidation capacity of Cr(VI) in H(2)SO(4) media. First, the Ruthenium(II) complex is oxidized to Ruthenium(III) complex by Cr(VI) and afterwards it is reduced to the excited state of the Ruthenium(II) complex by a sodium oxalate solution, emitting light inside the detector. The intensity of chemiluminescence (CL) is proportional to the concentration of Cr(VI) and, under optimum conditions, it can be determined over the range of 3-300 μg L(-1) with a detection limit of 0.9 μg L(-1). The RSD was 8.4% and 1.5% at 5 and 50 μg L(-1), respectively. For the rFI-CL method various analytical parameters were optimized: flow rate (1 mL min(-1)), H(2)SO(4) carrier concentration (20% w/V), Ru(phen)(3)Cl(2) concentration (5mM) and sodium oxalate concentration (0.1M). The effect of Cr(III), Fe(III), Al(III), Cd(II), Zn(II), Hg(II), Pb(II), Ca(II) and Mg(II), was studied. The method is highly sensitive and selective, allowing a fast, on-line determination of Cr(VI) in the presence of Cr(III). Finally, the method was tested in four different water samples (tap, reservoir, well and mineral), with good recovery percentage.