Riansares Muñoz-Olivas

Screening analysis: an overview of methods applied to environmental, clinical and food analyses

Abstract It is important to emphasise that the analytical approach taken to making a measurement should be “fit for purpose” and that this criterion must be reflected in the analysis method proposed. A screening method is a process that extracts, isolates and identifies a compound or group of components in a sample with the minimum number of steps and the least manipulation of the sample. More basically, a screening method is a simple measurement providing a “yes/no” response. This article examines the interest in applying screening methods from several points of view, namely: the savings in time for a routine laboratory with a high number of samples to run; cost-effectiveness from using simpler and non-expensive instrumentation; the immediacy in decision-making (e.g., in clinical analysis); and, making measurements in the field. This article deals with all these aspects, as well as screening methods developed for many analytes and samples of interest, along with aspects concerning their traceability.

Determination of Cd in sonicate slurries and leachates of biological and environmental materials by FI-CV-AAS

An analytical method for Cd analysis in solid samples which combines the ultrasonic slurry formation with cold vapour generation and atomic absorption spectrometry is described. The samples are suspended in HCl and sonicated until homogeneous and reduced particle size slurry formation. Several aspects were studied: acidity of the medium, sonication time, and slurry formation in different matrices. The procedure described permits the use of direct calibration, with KCN addition as masking agent of interfering ions (Cu, Pb, Ni and Zn) present in the environmental matrices. Supernatant analysis of these last samples experimentally shown that preparation of the suspension with 6 mol l(-1) HCl concentration led to quantitative extraction of Cd. Biological materials analysis needed the use of the standard addition calibration method due to the high matrix effect observed. Supernatant analysis in biological samples does not give a total Cd recovery for all of them. The detection limits observed for Cd were 0.05 and 0.2 mug l(-1) for supernatant and slurry analysis respectively in environmental samples, while in biological samples were 0.2 and 0.6 mug l(-1) for supernatant and slurry analysis, respectively. In all case the better precision was obtained for supernatant analysis (3-6%) than slurry analysis (6-12%). The results obtained by analysing different reference materials (sewage sludge, city waste incineration, Antarctic krill and human hair) showed good agreement with the certified value confirming the validity of such a method for Cd determination instead to wet digestion procedures.

Alternative extraction methods for arsenic speciation in hair using ultrasound probe sonication and pressurised liquid extraction

The methods for arsenic speciation in hair currently available are scarce and highly time consuming, especially during sample preparation. This work presents alternative methods providing better recoveries and similar species distribution compared with established methods, but the extraction time is reduced from about 6 h to only a few minutes. First, several extraction media were studied and evaluated using ultrasound probe sonication. Either a solution of 0.5% performic acid or an enzymatic treatment (mixture of lipase and protease in aqueous media) was selected as the best treatment, which allowed us to reduce the extraction time to 5 or 10 min, respectively, achieving a slightly higher species recovery in the latter case. Second, a laboratory-made miniaturised device for pressurised liquid extraction is employed and compared with the previous methods. Initially, temperature, pressure and extraction time were optimised by applying chemometrics, in particular the use of a multivariate experimental design and analysis of variance. In order to improve the obtained results, additional variables such as type of solvent, particle size of dispersant medium and number of extraction cycles were further optimised. Optimum conditions were obtained using a mixture of 1% SDS and 5% isopropanol as extraction solvent at a temperature of 125 °C and an applied pressure of 6 MPa for two cycles of 5 min each. The optimal particle size of dispersant was 35 μm. Total arsenic was determined by ICP-MS and the species present in hair were quantified by HPLC-ICP-MS. For method validation a certified reference material (Human Hair GBW 07601) was used all throughout this study.

Determination of cadmium in aqueous media by flow injection cold vapour atomic absorption spectrometry. Application to natural water samples

A simple, sensitive and rapid flow injection system for Cd cold vapour generation coupled to atomic absorption spectrometry (FI–CV-AAS) was developed. A vesicular medium of didodecyldimethylammonium bromide (DDAB) was investigated in order to understand the possible mechanisms occurring in Cd cold vapour generation and the influence of this surfactant as a catalyst. Similar experiments in an aqueous medium were carried out with optimization of the physical and chemical parameters. Identical analytical characteristics such as linearity and precision, and similar detection limits (0.15 and 0.05 µg l–1 for DDAB and aqueous media, respectively), were found for both reaction media; hence, the use of surfactants was not necessary for Cd cold vapour generation. Validation of the method was carried out by determining the Cd content in several certified waters. The method was applied to the analysis of some natural waters by the standard additions calibration method.

Comparison of bioconcentration of ionic silver and silver nanoparticles in zebrafish eleutheroembryos.

The production of silver nanoparticles has reached nowadays high levels. Bioconcentration studies, information on persistence and toxicity are fundamental to assess their global risk and thus necessary to establish legislations regarding their use. Previous studies on silver nanoparticle toxicity have determined a clear correlation between their chemical stability and toxicity. In this work, experimental conditions able to assure silver nanoparticles stability have been optimized. Then, zebrafish (Danio rerio) eleutheroembryos were exposed to ionic silver and to Ag NPs for comparison purposes. A protocol alternative to the OECD 305 technical guideline was used. To determine silver concentration in both the eleutheroembryos and the exposure media, an analytical method consisting in ultrasound assisted extraction, followed by inductively coupled plasma mass spectrometry and graphite furnace atomic absorption spectrometry, was developed. Then, bioconcentration factors were calculated. The results revealed that ionic silver was more accumulative for zebrafish eleutheroembryos than nanoparticles at the levels tested.

Interference removal for cadmium determination in waste water and sewage sludge by flow injection cold vapour generation atomic absorption spectrometry

Cold vapour generation coupled to atomic absorption spectrometry with using flow injection (FI-CVAAS) was evaluated as a rapid and simple method for the determination of cadmium in waste water and sewage sludge. Waste water samples did not need a pre-treatment before analysis. The sewage sludge was digested in a high pressure microwave oven in order to ensure good solubilisation of the samples. Some elements present in the sample (Cu, Pb, Ni, Zn) showed important interferences in the FI-CVAAS method. Elimination of such interferences by adding KCN to the borohydride solution is discussed. Validation of the method was achieved by analysing a sewage sludge sample used in an interlaboratory exercise organised by the WRC (Water Research Centre, UK) and by comparing the results with those obtained by electrothermal atomic absorption spectrometry (ETAAS) by use of a graphite furnace. Finally, waste waters and sewage sludge samples were analysed by both FI-CVAAS and ETAAS methods.

Zebrafish larvae as a model for the evaluation of inorganic arsenic and tributyltin bioconcentration

The European REACH legislation establishes the need to study the toxicity, persistence and bioaccumulation of those chemicals with an exceeding production of 100tons and/or chemicals considered PBTs substances (Persistence, Bioaccumulation and Toxicity). Currently, the OECD technical guideline 305 is the most used protocol to determine bioconcentration factors of contaminants in aquatic environments. However, this procedure implies high cost and amount of adult fishes. Zebrafish (Danio Rerio) has been selected since this animal model has several advantageous features over other vertebrates, mainly fast embryonic development and easy growth. The analytical methodology here developed has been applied to calculate the bioconcentration factors (BCFs) of two contaminants: inorganic arsenic and tributyltin (measured as arsenic and tin). The method is based on the use of an ultrasonic probe assisted extraction for accelerating the sample treatment followed by detection using graphite furnace atomic absorption spectrometry with Zeeman correction (ZGFAAS). Results obtained for the BCFs values are in good agreement with previously reported data on freshwater aquatic organisms. In the case of arsenic, after exposing larvae to concentrations of 5 and 50μgL(-1), very low BCFs were observed (between 2.2 and 9.5); while for tributyltin, the BCFs observed were within the range 840-1280 after exposure to concentrations of 0.2 and 2.0μgL(-1), respectively. This study shows the use of zebrafish larvae together with the proposed analytical approach as a promising alternative to the OECD 305 test to evaluate the BCFs of classical and emergent contaminants.

Different formats of imprinted polymers for determining organotin compounds in environmental samples.

Organotin compounds and their degradation products enter the environment mainly as a result of their use as biocides and antifouling paints. Analysis of these compounds in environmental samples has to be very sensitive and selective so that their concentrations corresponding to the low environmental target values can also be detected. Generally, analysis of a complex matrix leads to high interferences during the different process steps; clean-up procedures are recommended to overcome this problem. For the past many years, solid phase extraction by employing imprinted materials has been extensively used for many organic substances that are used for pre-concentration and clean-up purposes with excellent results. Here, we present three different imprinted polymers prepared via bulk, precipitation, and emulsion polymerization methods that use similar compositions. The synthesized polymer particles were characterized morphologically by employing scanning electron microscopy and Brunauer-Emmett-Teller analysis. Binding properties were calculated using the Langmuir-Freundlich isotherm. Depending on the properties of the materials, different analytical applications for complex matrices are proposed. These applications are mainly used on tributyltin and its degradation products for environmental analysis.

Zebrafish (Danio rerio) Eleutheroembryo-Based Procedure for Assessing Bioaccumulation

This paper reports on the development and preliminary evaluation of a new bioaccumulation test based on the use of zebrafish (Danio renio) eleutheroembryos (72 h after hatching, corresponding to 144 h post fertilization, hpf) as an alternative to adult fish-based procedures for regulatory purposes regarding REACH application. The proposed test accomplished the OECD 305 guideline and consists of a 48 h uptake period followed by a 24 h depuration step. Bioaccumulation experiments were performed for a selected of hyper hydrophobic chemicals (log Kow> 7.6), that is, PCB 136 and PBDE 154 at two concentration levels corresponding roughly to 1% and 0.1% the chemicaĺs LC50(nominal concentrations of 4.0 and 12.0 μg/L for PCB 136, and 1.0 and 5.0 μg/L PBDE 154, respectively). Toxicokinetic models were used to calculate the bioconcentration factors (BCFs) based on of the chemical concentrations found in the contaminated eleutheroembryos and their surrounding media. The experimentally determined accumulation profiles show bioaccumulation by zebrafish eleutheroembryos of both chemicals, and that the process is more complex than simple water-lipid partition. Calculated log BCFs using a first-order accumulation model(3.97 and 3.73 for PCB 136, and 3.95 and 4.29 for PBDE 154) were in the range of those previously reported in the literature. The suitability of this new nonprotected life stage bioaccumulation protocol for BCF estimation was evaluated by application to widely divergent micropollutants with different accumulation mechanisms. The results were compared with those in the MITE-NITE database for adult rice fish (Oryzias latipes).

Synthesis of a pH dependent covalent imprinted polymer able to recognize organotin species

The covalent imprinting approach has for the first time been successfully applied for the synthesis of an imprinted polymer able to recognize organotin species. The synthesis has been accomplished by co-polymerization of the complex Bu(2)SnO-m-vinylbenzoin as the imprinting template plus co-monomer sodium methacrylate, and ethylene glycol dimethacrylate as cross-linker. The imprinting effect has been evidenced within the narrow pH range 2.5< pH< 3.5. At lower pH values, the imprinting effect is prevented by the exclusive existence of non-specific interactions, whereas pH>3.5 provokes a strong rebind of the template in both imprinted and non-imprinted polymers. This pH dependency can be explained as a selective chemical modification which reduces bind diversity following a model based on enolization by protonation of the specific cavities. Characterization of the adsorption isotherms showed good agreement with the Langmuir-Freundlich (LF) model, presenting quite homogeneous binding sites for a bulk material and high capacity in the imprinting pH range. In addition, the affinity spectrum (AS) method has been represented showing the typical profiles of LF isotherm for both sub-saturation and saturation levels, being in general agreement with the encountered values for fitting coefficients. The covalent molecular imprinted polymer has been successfully evaluated in a SPE process for further OTC determination in the certified mussel tissue (CRM 477).