An approach for arsenic in a contaminated soil: speciation, fractionation, extraction and effluent decontamination.

The fractionation and speciation of As in a contaminated soil were investigated, and a remediation strategy was tested. Regarding speciation, we found that As(V) prevails over As(III) whereas more than 40% of total arsenic is in organic form. The fractionation of As was investigated with two sequential extraction methods: a low mobility was found. Then we tested the possibility of using phosphoric acid to extract As from the soil and cleaning the washing effluents by sorption onto montmorillonite. The efficiency of the extraction and of the adsorption onto the clay were also investigated for Cr, Cu, Fe, Mn, Ni, Pb and Zn, whose total concentrations and fractionation in the soil are reported here. The extraction percentages for As and metals ranged from 30 to 65%; the residual proportions in the soil are presumably in very unreactive forms. Montmorillonite showed a good uptake capacity towards the investigated pollutants.

Adsorption of heavy metals on vermiculite: influence of pH and organic ligands.

The sorption behaviour of vermiculite has been studied with respect to cadmium, copper, lead, manganese, nickel, and zinc as a function of pH and in the presence of different ligands. The continuous column method was used in order to evaluate the feasibility to use the clay in wastewater purification systems. The total capacity of vermiculite was found to decrease in the following order: Mn > Ni > Zn > Cd > Cu > Pb. The adsorption of metal ions on vermiculite decreases with decreasing pH and increasing ionic strength. In general, the metal uptake on the clay was hindered by the presence of strong complexing agents in solution and it decreases with increasing of the complexation constants of the ligands with exception of cysteine and tiron. It is necessary, hence, to consider all these factors to effectively predict the uptake efficiency of this sorbent. However, it is possible to conclude that the vermiculite has good potentialities for cost-effective treatments of metal-contaminated wastewaters.

Adsorption of heavy metals on Na-montmorillonite. Effect of pH and organic substances.

Clays (especially montmorillonite and bentonite) are widely used as barriers in landfills to prevent contamination of subsoil and groundwater by leachates containing heavy metals. For this reason it is important to study the adsorption of metals by these clays. The sorption of seven metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) on Na-montmorillonite was studied as a function of pH and in the presence of ligands, forming complexes of different stabilities with the metals of interest. The continuous column method was used as it better simulates natural conditions. The total capacity of Na-montmorillonite towards these metals was determined. The pH variations influence to a higher extent the concentrations of Cu, Pb and Cd in the effluent. Moreover the results suggest that complex formation hinders the sorption of the metals on the clay, with an increasing influence in the order: Mn < or = Pb < or = Cd < or = Zn < Ni < Cu < Cr. The evaluation of the total capacity of Na-montmorillonite shows that this clay is a good sorbent towards all examined metals.

Heavy metals in agricultural soils from Piedmont, Italy. Distribution, speciation and chemometric data treatment.

The distribution and speciation of heavy metals in five agricultural soils of Piedmont Region (north-western Italy) were investigated. Ten metals, namely Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Ti and Zn were considered. Analytical determinations were performed by atomic emission or atomic absorption spectroscopy after microwave sample dissolution in acid solution. Total metal concentrations fit in the typical concentration ranges for unpolluted soils, with the exception of cadmium and lead content in some horizons. The effect of sampling depth on concentrations was discussed. Speciation studies were carried out by applying Tessier's procedure, which allows to subdivide the total metal content into five fractions, representing portions bound to different components of the soil. Moreover, the element labilities in two soils were evaluated by extraction with EDTA. Correlations among the variables and/or similarities among the sampling points were identified by principal component analysis and hierarchical cluster analysis.

Effect of ion-exchange site and eluent modifiers on the anion-exchange of carboxylic acids.

The chromatographic behavior of carboxylic acids has been investigated, on three different latex-based anion-exchange columns, in order to define the effect of the ion-exchange site structure on selectivity. The analytical columns produced are characterized by alkyl amines containing zero, one or two hydroxyl groups on the anion-exchange functional site. Divalent carboxylic acids, namely fumaric, maleic, trans-beta-hydromuconic, trans,trans-muconic, oxalic, malonic, succinic, glutaric, adipic, malic, tartaric and mucic acids, have been chosen as test solutes. The performance of the three stationary phases has been studied employing NaOH eluents and has been discussed with respect to the different hydrophilicity of the ion-exchange sites and analytes. Considering on previous results obtained using organic solvents (methanol and acetonitrile) with carbonate eluents on a highly hydrophilic column, the performance of the three exchangers has also been studied using acetonitrile, methanol and n-propanol. The chromatographic behavior was similar for the three columns studied, but the different organic solvents gave variations in selectivity. In order to characterize these differences, particle size measurements of the latices were performed both in pure water and in the presence of each organic solvent studied.

Liquid chromatographic methods for chloral hydrate determination.

Liquid chromatographic methods, based on reversed-phase (RP) and anion-exchange mechanisms, have been developed for chloral hydrate determination. Both methods are preceeded by derivatization of chloral hydrate. For RP separations, different reagents [namely dansylhydrazine and o-(4-nitrobenzyl)hydroxylamine] have been studied, but the best results have been achieved using 1,2-benzenedithiol with UV detection at 220 nm. The anion-exchange method is based on derivatization with NaOH to form sodium formate that is then analyzed by anion-exchange, with suppressed conductivity detection. Derivatization conditions were optimized in order to reach the best yield of reaction. The optimization of the procedure allowed to determine chloral hydrate with detection limits as low as 0.2 microg/l with good linearity and reproducibility. The anion-exchange method was also applied for chloral hydrate determination in a drinking water sample. A preconcentration procedure has also been studied.

Determination of epichlorohydrin by ion chromatography.

In this work we developed a new method for epichlorohydrin determination with suppressed ion chromatography. The technique is based on a reaction between the analyte and sulfur(IV) to form a product with a terminal sulfonate group that can be analyzed by anion-exchange chromatography. The reaction conditions were optimized as a function of temperature, type and concentrations of reagents and pH. Due to the characteristics of the product formed, the columns used were an lonPac AS 11 and AS II-HC with a NaOH eluent. The eluent concentration was optimized in order to achieve a complete separation of epichlorohydrin, chloride and nitrate ions, commonly occurring in drinking waters. In order to improve the detection limits, a preconcentration step, using reversed-phase materials, has been optimized. The method developed was suitable for epichlorohydrin determination in drinking water.

Preconcentration of contaminants in water analysis.

Among the environmental areas, in this review attention will be focused on water matrices and both on organic (e.g., pesticides, herbicides, phenols, polycyclic aromatic hydrocarbons), inorganic species and anion pollutants, since these kinds of substances include a wide number of compounds with different physical and chemical properties and different effects on human health. Analytical methods for control of quality of waters are required to be highly specific and possibly highly sensitive for the determination of even low amounts of pollutants. The main problems encountered during the analysis are the separation of matrix components from the pollutants of interest and the achievement of low detection limits. Therefore an overview on different materials and techniques available for sample concentration and/or matrix removal will be provided and discussed according to the chemical characteristics of the pollutant that has to be enriched.

Preconcentration and separation of haloacetic acids by ion chromatography.

A comparative study was made of the chromatographic behaviour of five haloacetic acids (mono-, dibromoacetic and mono-, di-, trichloroacetic acids). The techniques investigated included reversed-phase ion interaction chromatography with UV detection, suppressed and non-suppressed anion-exchange chromatography. The systems are discussed studying the retention as a function of the mobile phase parameters and the stationary phases used (LiChrospher 100 RP-18, IonPac AS9, AS10 and AS11). A preconcentration step, performed on different substrates, namely LiChrolut-EN and activated vegetal carbon, has been optimized in order to reduce the method detection limits. Results obtained for drinking water samples are shown.

Carboxylic acids: prediction of retention data from chromatographic and electrophoretic behaviours.

A review of the main results reached in the prediction of retention data of carboxylic acids, inferred by their chromatographic and electrophoretic behaviour, is presented. Attention has been focused on the main separation methods used in carboxylic acids analysis, that is ion-exclusion, anion-exchange, reversed-phase (RP) liquid chromatography and capillary electrophoresis. Papers proposing mechanistic models as well as chemometric and multilayer feed-forward neural network analysis of ion chromatography (IC) and RP chromatographic retention data were reviewed. Principal component analysis, PCA, sequential simplex method and simultaneous modelling of response surfaces through simple nonlinear models (not related to equilibria involved in retention) have been considered. Computer simulations for the prediction of retention data have also been discussed. A quick overlook on the prediction of capacity factors of analytes by less common determination methods such as thin-layer, gas chromatography and supercritical fluid chromatography has also been done.

Flow injection determination of Pb and Cd traces with graphite furnace atomic absorption spectrometry.

The preconcentration and recovery of lead and cadmium traces at ng l(-1) level were evaluated in standard solutions and natural aqueous samples using a FIAS (Flow Injection Atomic Spectrometry) apparatus. The method is based on retention of the complex formed between Pb or Cd and 1,2-dihydroxy-3,5-benzendisulphonic acid (Tiron) on a macroporous anion-exchange resin. The recovery of the analytes was obtained by elution with 0.1 M HCl and their determination was performed by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). The detection limits were 9 and 7 ng l(-1) for Pb and Cd respectively. The effects of sample solution pH and composition and of interfering agents as well as reagent purity are discussed. The technique was applied to the analysis of natural waters.

Evaluation of stability constants of metal complexes with sulphonated azo-ligands.

An ion-exchange procedure is described for the determination of the stability constants for cadmium, copper, nickel and manganese complexes with three sulphonated azo ligands: calmagite, alizarin violet N and palatine chrome black. The results, log K values, show a good agreement with those obtained by a spectrophotometric technique.

Determination of plasma tocopherols by high-performance liquid chromatography with coulometric detection.

An HPLC procedure has been developed for tocopherol determination with coulometric detection in human serum samples. Eluent optimization and foreign peak identification (bilirubin) by mass spectrometry are described. An extraction procedure gave yields around 98% with 1.3% coefficient of variation, and the calibration ranged from 0.1 to 200 mg/l with a correlation coefficient of 0.999. The detection limit achieved for vitamin E was 60 pg (3 ng/ml).

An NMR study of the interaction between melanin free acid and Mn2+ ions as a model to mimic the enhanced proton relaxation rates in melanotic melanoma.

The interaction of a soluble Melanin Free Acid (MFA) from Sepia melanin with Mn2+ ions is investigated by measuring the proton water relaxation rates. The similarity between MFA and the parent melanin is assessed by means of their high resolution 13C cross polarization magic angle spinning NMR spectra. The observed marked increase in longitudinal proton relaxation rates and the characteristic 1/T1 NMRD profile are associated to the formation of a macromolecular metal complex. The presence of similar paramagnetic species is expected to cause the high contrast shown by melanotic tissues in MRI.

Ion chromatographic determination of plasma oxalate in healthy subjects, in patients with chronic renal failure and in cases of hyperoxaluric syndromes.

An ion chromatographic procedure for the determination of plasma oxalate is proposed, in which the ultrafiltered sample is injected into an ion-chromatographic system. Sample processing appears effective in avoiding spontaneous oxalogenesis. Sensitivity (down to 1.0 mumol/l) allows determinations in normal and pathological samples; recoveries from plasma ultrafiltration are 94.6 +/- 11.7%. Protein binding was investigated and precautions to improve recoveries from plasma ultrafiltration are proposed. The technique is simple to perform from healthy controls averaged 6.75 +/- 2.62 mumols/l (mean +/- S.D. n = 18); samples from patients with primary hyperoxaluria and chronic renal failure undergoing regular dialysis were also analysed and some of the data obtained are reported and discussed.

Derivatization and high-performance liquid chromatographic determination of urinary glycolic acid.

A high-performance liquid chromatographic method for the determination of urinary glycolic acid is proposed, based on pre-column derivatization with phenylhydrazine coupled with the enzymatic oxidation of glycolate to glyoxylate. The phenylhydrazone formed is separated by liquid chromatography and detected at 324 nm. The minimum detectable concentration of glycolate was 10.0 mumol/l. The recovery of glycolate added to urine averaged 96.1%. The day-to-day coefficients of variation calculated by analysis of two urine samples with normal and high glycolate contents were 4.6 and 7.5%, respectively. Results of analyses of urine samples from healthy persons, idiopathic calcium stone formers and Type I primary hyperoxaluria patients are reported.

Ion-pair liquid-solid extraction for the preconcentration of trace metal ions Optimization of experimental conditions.

Cu(II) has been recovered from dilute solutions (0.1 mug/ml) by adsorbing the ion-pairs formed between different quaternary ammonium salts and the Cu-8-hydroxyquinoline-5-sulphonic acid complex on adsorbent resins, namely XAD 8 and S 862. Both batch and column techniques have been used, the first of which gave superior recovery and precision. It has also been shown that XAD 8 resin can be transformed into an ion-exchanger suitable for preconcentration of Cu(II). The results obtained have been compared with those of reversed-phase ion-pair chromatography and a model is proposed.

High-performance liquid chromatographic determination of glyoxylic acid and other carbonyl compounds in urine.

A high-performance liquid chromatographic method for the determination of carbonyl compounds, namely aldehydes, ketones and keto acids in urine, has been developed. Pre-column derivatization with 2,4-dinitrophenylhydrazine offers sufficient sensitivity for the determination of glyoxylic acid in urine with a detection limit of 0.5 mg/l. The separation is performed on a C18 10-micron column and with an acetonitrile-aqueous buffer mobile phase, which also allows the resolution of the syn and anti geometric isomers. Matrix effects, precision, accuracy, limits of detection and structural selectivity of the method are discussed.

Preconcentration and determination of ultratraces of lead and bismuth.

The recovery and preconcentration of Pb(II) and Bi(III) by coupling ion-exchange and precomplexation with 1,2-dihydroxy-3,5-benzenedisulphonic acid and 3,3',4'-trihydroxyfuchsone-2''-sulphonic acid has been investigated. Metal recoveries at 0.1-mg l . concentrations are better than 99% in the presence of cationic, anionic and non-ionic detergents, or an organic sequestering agent such as NTA, and at high ionic strength. Experiments with radiotracers show total recovery even at 15-ng l . concentrations. In the light of the results the procedure is proposed as a simple and rapid analytical method to preconcentrate Pb(II) and Bi(III).

Binding properties of aminopolycarboxylato ligands bound to cellulose.

The uptake of metal ions by EDTA bound to cellulose niters has been examined and compared with the corresponding uptake by iminodiacetic acid and N-methyliminodiacetic acid bound to cellulose. The results are interpreted in terms of steric hindrance, geometric factors, electrostatic interactions and thermodynamics.