M.M. López Guerrero

On-line preconcentration using chelating and ion-exchange minicolumns for the speciation of chromium(III) and chromium(VI) and their quantitative determination in natural waters by inductively coupled plasma mass spectrometry

There are only a few analytical techniques available that have sufficient sensitivity and selectivity for the determination and speciation of chromium in environmental waters. In this work, a non-chromatographic system is developed for the simultaneous determination of chromium(III) and chromium(VI) by solid phase extraction and inductively coupled plasma mass spectrometry (ICP-MS). The system is based on the use of three minicolumns packed, respectively, with chelating and anionic ion exchange resins, which were placed in the injection valve of a simple flow manifold. By using this device, diverse advantages are attained: speciation and simultaneous determination of Cr(III) and Cr(VI) as well as increase of the sensitivity and reduction of the interferences by the preconcentration. The effects of chemicals and flow variables were investigated. Detection limits (2 min sample loading time) were 0.009 μg L−1 for Cr(VI) and 0.03 μg L−1 for Cr(III). The relative standard deviations (n = 10) for 0.3 μg L−1 of Cr(VI) and Cr(III) were 3.2% and 2.6%, respectively, demonstrating a good precision for the analysis. The accuracy of the proposed method was checked with certified reference materials. Values obtained were in accordance with those reported for the certified materials. The method was applied to the determination of chromium species in different seawater samples.

High resolution continuum source atomic absorption spectrometry and solid phase extraction for the simultaneous separation/preconcentration and sequential monitoring of Sb, Bi, Sn and Hg in low concentrations

A rapid method was developed for separation, pre-concentration and sequential determination of antimony, bismuth, tin and mercury by flow injection solid phase extraction coupled with on-line chemical vapor generation electrothermal atomic absorption spectrometry. The system is based on chelating/cationic retention of the analytes onto a mini-column filled with a mesoporous silica functionalized with 1,5 bis(di-2-pyridyl)methylene thiocarbohydrazide. Several variables (sample flow rate, eluent flow rate, eluent concentration and reductant concentration) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using three central composite designs. The optimized operating conditions were: sample pH = 2.2, sample flow rate 3 mL min−1, eluent flow rate 2.5 mL min−1, eluent 3.1% HCl for Sb, Bi and Sn, and 4.6% thiourea for Hg, and 0.6% NaBH4 reductant. The optimum conditions established were applied to the determination of Sb, Bi, Sn and Hg in sea water and river water by flow injection solid phase extraction coupled with on-line chemical vapor generation high resolution continuum source electrothermal atomic absorption spectrometry (FI-SPE-CVG-CS ETAAS). For the quality control of the analytical performance and the validation of the newly developed method, the analysis of two certified samples, TM 24.3 and TMDA 54.4, Fortified Lake Waters was addressed. The results showed good agreement with the certified values.

Synthesis and characterization of a novel mesoporous silica functionalized with [1,5 bis(di-2-pyridyl)methylene thiocarbohydrazide] and its application as enrichment sorbent for determination of antimony by FI-HG-ETAAS.

A simple, sensitive, low-cost and rapid flow injection (FI) on-line sorption preconcentration/hydride generation system has been synchronously coupled to an electrothermal atomic absorption spectrometer (ETAAS) for the determination of trace amounts of Sb in aqueous environmental samples (river and sea water samples). The system is based on retention of the analyte onto a micro-column filled with a novel mesoporous silica functionalised with [1,5 bis(di-2-pyridyl) methylene] thiocarbohydrazide placed in the injection valve of the FI manifold. The adsorption capacity of the resin for Sb was found to be 160.8 µmol g(-1). Chemicals and flow variables affecting the continuous preconcentration of antimony, the direct generation of antimony hydride and the final determination of this element by ETAAS were evaluated. The optimized operating conditions selected were: sample pH 5.0, sample flow rate 2.5 ml min(-1), eluent flow rate 5.4 ml min(-1), eluent 2.0% thiourea in 4.0% nitric acid. Under the optimum conditions, the calibration graph obtained was linear over the range 0.025-2.5 μg L(-1). At a sample frequency of 20 h(-1) and 120 s preconcentration time, the enrichment factor was 22. The detection limit of the method (3ơ) was 1 ng L(-1) for a 5.0 mL sample volume and the precision was 0.9% (RSD) for 11 replicate determinations at 1.0 μg L(-1) Sb. The preconcentration factor and detection limit can be improved by increasing the preconcentration time, which can be increased at least up to 5 min. The accuracy of the proposed method was demonstrated by analyzing two certified reference materials and by determining the analyte content in spiked environmental water samples. The results obtained using this method were in good agreement with the certified values of the standard reference materials and the recoveries for the spiked river and sea water samples were 91.3-109.9%.

Simultaneous determination of chemical vapour generation forming elements (As, Bi, Sb, Se, Sn, Cd, Pt, Pd, Hg) and non-chemical vapour forming elements (Cu, Cr, Mn, Zn, Co) by ICP-OES

Silica-coated magnetic nanoparticles (MNPs) modified with [1,5-bis(2-pyridyl)-3-sulphophenyl methylene]thiocarbonohydrazide (PSTH-MNPs) were synthesized and characterized. These magnetic nanoparticles (PSTH-MNPs) were employed as a solid phase extraction (SPE) adsorbent for the separation and concentration of trace amounts of 14 elements (Pd, Cr, Mn, Zn, Cd, Hg, As, Sb, Bi, Cu, Pt, Sn, Se, Co) from environmental water samples. The main aim of this work was to develop a precise and accurate method for the simultaneous determination of the maximum possible number of elements by using this new absorbent and a multimode sample introduction system (MSIS). The MSIS acts as a system for the generation, separation and introduction of chemical vapours (CVG) and also as an introduction system for sample aerosols, in a simultaneous form, into an inductively coupled plasma-optical emission spectrometer. The on-line SPE-CVG-ICP-OES system developed was applied in the determination of the aforementioned metals in natural water samples (sea water, estuarine, lake and river water), with the least demanding and simple sample preparation procedure. The developed method was validated by analysing natural water certified reference materials (SLRS-4, TMDA 54.4, SW2 Batch 125, SRM 1643e). Sea water and well water samples collected from Malaga (Spain) were also analysed. The procedure has been demonstrated to be fast, easy, automatic, selective and economical, and the sensitivity was good. The main advantage of PSTH-MNPs is its very good stability and resistance because chemisorption of chelating molecules on the surface of solid supports provides immobility, mechanical stability and insolubility. The precision (RSD), accuracy (by standard addition or recovery) and limit of detection (LOD) were used to evaluate the characteristics of the procedure. The detection limits obtained were within 0.01 and 11.30 μg L−1, with RSDs of 1% to 7% and enrichment factors of between 1 and 385.5, which is adequate for the analyzed samples. Furthermore, the proposed method was applied in the simultaneous determination of the 14 elements mentioned above with a sample throughput of about 13 h−1, thereby, reducing the time of analysis and the volume of reagents and sample required.

Modulated anisotropy fluorescence for quantitative determination of carbaryl and benomyl.

Two individual components in mixtures have been resolved by frequency domain fluorescence technique by measuring the observable quantities which characterize the anisotropy decay; differential anisotropy phase and modulated anisotropy ratio (MAR), which in turn are related to the rotational correlation time. The method presented here is capable of directly resolving binaries mixtures of fluorophores on the basis of differences in their rotational diffusion rates. Our results demonstrate that modulation anisotropy ratio measurements can be used for quantitative determination of small analytes, carbaryl and benomyl, having identical or nearly identical fluorescence spectra. This methodology can be applied with good results when the fluorophores have a suitable MAR difference.

Simultaneous determination of V, Ni and Fe in fuel fly ash using solid sampling high resolution continuum source graphite furnace atomic absorption spectrometry

A green and simple method has been proposed in this work for the simultaneous determination of V, Ni and Fe in fuel ash samples by solid sampling high resolution continuum source graphite furnace atomic absorption spectrometry (SS HR CS GFAAS). The application of fast programs in combination with direct solid sampling allows eliminating pretreatment steps, involving minimal manipulation of sample. Iridium treated platforms were applied throughout the present study, enabling the use of aqueous standards for calibration. Correlation coefficients for the calibration curves were typically better than 0.9931. The concentrations found in the fuel ash samples analysed ranged from 0.66% to 4.2% for V, 0.23-0.7% for Ni and 0.10-0.60% for Fe. Precision (%RSD) were 5.2%, 10.0% and 9.8% for V, Ni and Fe, respectively, obtained as the average of the %RSD of six replicates of each fuel ash sample. The optimum conditions established were applied to the determination of the target analytes in fuel ash samples. In order to test the accuracy and applicability of the proposed method in the analysis of samples, five ash samples from the combustion of fuel in power stations, were analysed. The method accuracy was evaluated by comparing the results obtained using the proposed method with the results obtained by ICP OES previous acid digestion. The results showed good agreement between them. The goal of this work has been to develop a fast and simple methodology that permits the use of aqueous standards for straightforward calibration and the simultaneous determination of V, Ni and Fe in fuel ash samples by direct SS HR CS GFAAS.

Time-Resolved Spectroscopy for Selective Determination of Fluorescent Diuretics

The applicability of phase-resolved fluorescence spectroscopy has been shown for the resolution of mixtures of two diuretics (furosemide and triamterene) with closely overlapping fluorescence profiles. Phase-resolved intensity spectra were used to estimate the steady-state fractional intensities using a method based on nulling the contribution of one component in the total spectra of the mixture. The only requirements for the analysis are the knowledge of the steady-state spectra of the individual components and the precise phase angle for the suppression of each component in the mixture. This is a simple and rapid method that substitutes previous separation techniques that have normally been used for these compounds. One of the advantages of this work is that the information provided by the whole spectrum of the sample is not required. The detection limits are 9 ng mL−1 for triamterene and 8.5 µg mL−1 for furosemide. This procedure allowed the resolution of a two-component mixture at µg mL−1 level, with a relative standard deviation less than 8% (n = 7) and recoveries of the original drugs between 88% and 117%.

Speciation analysis of inorganic arsenic by magnetic solid phase extraction on-line with inductively coupled mass spectrometry determination

Arsenic, one of the main environmental pollutants and potent natural poison, is a chemical element that is spread throughout the Earths crust. It is well known that the toxicity of arsenic is highly dependent on its chemical forms. Generally, the inorganic species are more toxic than its organics forms, and As(III) is 60 times more toxic than As(V). In environmental waters, arsenic exists predominantly in two chemical forms: As(III) and As(V). In view of these facts, fast, sensitive, accurate and simple analytical methods for the speciation of inorganic arsenic in environmental waters are required. In this work, a new magnetic solid phase extraction with a hydride generation system was coupled on line with inductively coupled plasma mass spectrometry (MSPE-HG-ICP-MS). The new system was based on the retention of As(III) and As(V) in two knotted reactors filled with (Fe3O4) magnetic nanoparticles functionalized with [1,5-bis (2-pyridyl) 3-sulfophenylmethylene] thiocarbonohydrazide (PSTH-MNPs). As(III) and total inorganic As were sequentially eluted in different reduction conditions. The concentration of As(V) was obtained by subtracting As(III) from total As. The system runs in a fully automated way and the method has proved to have a wide linear range and to be precise, sensitive and fast. The detection limits found were 2.7 and 3.2 ng/L for As(III) and total As, respectively; with relative standard deviations (RSDs) of 2.5% and 2.7% and a sample throughput of 14.4 h-1. In order to validate the developed method, several certified reference samples of environmental waters including sea water, were analyzed and the determined values were in good agreement with the certified values. The proposed method was successfully applied to the speciation analysis of inorganic arsenic in well-water and sea water.

Simultaneous determination of traces of Pt, Pd, Os, Ir, Rh, Ag and Au metals by magnetic SPE ICP OES and in situ chemical vapour generation

Herein, a chelating sorbent that employs magnetic nanoparticles (MNPs) functionalized with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide (DPTH-MNPs) has been used to develop a simple method for the analysis of trace amounts of metal ions present in environmental samples; the method combines on-line magnetic solid phase extraction (MSPE) with atomic spectrometry. Thus, a flow injection FI-MSPE/cold vapour generation system coupled to an inductively coupled plasma optical emission spectrometry (ICP OES) method for the determination of trace amounts of noble metals, platinum group elements (PGEs: Ir, Pd, Pt, Os, and Rh), and Au and Ag in environmental samples has been developed. A magnet-based reactor designed to contain DPTH-MNPs was placed in the injection valve of the FI manifold. Several chemical and flow variables were considered as factors in the optimization process using two central composite designs; with the optimized method, the experimental detection limits for simultaneous determination, calculated as the concentration of analyte giving signals equivalent to three times the standard deviation of the blank plus the net blank intensity (LOD, peak height), were 1.5 μg L−1, 0.03 μg L−1, 0.65 μg L−1, 0.62 μg L−1, 0.57 μg L−1, 0.03 μg L−1, and 100 μg L−1 for Pd, Ag, Os, Au, Ir, Pt, and Rh, respectively. The method offers relatively good precision (RSD 1.8–7.2%). The accuracy of the proposed method was verified using certified reference materials (CMRs, NIST 2557 autocatalyst, TMDA 54.4 fortified lake water, and SRM 1643e trace elements in fresh water) and by determining the analyte contents in spiked aqueous samples. Sea water and tap water samples obtained from Malaga (Spain) were also analysed. The determined values were in good agreement with the certified values, and the recoveries for the spiked samples were in the range of 91.8–108.1%. Additionally, the proposed method was applied in the simultaneous determination of the abovementioned 7 elements with a sample throughput of about 17 h−1, thereby reducing the time of analysis and the volumes of reagents and sample required.

Development of a new FT-IR method for the determination of iron oxide. Optimization of the synthesis of suitable magnetic nanoparticles as sorbent in magnetic solid phase extraction

In the last few years, there is a clear increasing trend in the number of works dealing with magnetic nanomaterials for pre-concentration and/or separation of ions, organic compounds and inorganic compounds, as well as for use as tools for biomedical purposes because of their low toxicity, biocompatibility and biodegradability. The excellent properties of these nanomaterials are strongly influenced by the particle size and the amount of iron or iron oxide present. In order to obtain the appropriate feature of the magnetic nanoparticles (MNPs), in this work the optimization of the synthesis of magnetite MNPs has been developed. Thus, a simple, rapid and inexpensive method is presented to determine the concentration of Fe3O4 in magnetic nanoparticles (MNPs) by Fourier Transform Infrared Spectroscopy (FTIR). The optimization of the synthesis was accomplished using a multiple response surface methodology based on central composite design (CCD). Three independent factors namely the reaction time, volume and concentration of NH3 were investigated using two response variables, the iron concentration (% w/w) and the nanoparticle size (nm). Spherical MNPs with an iron concentration of 70% (w/w) and a size of 13 ± 1 nm were obtained by the optimized method. This method was validated by comparison with High Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry (HR CS GFAAS).