Fast assessment of bioaccessible metallic contamination in marine sediments.

A fast (16min) procedure to assess the bioaccessible metallic fraction of Cd, Cr, Cu, Ni, Pb and Zn simultaneously extracted (SEM) from marine sediments plus an indirect approach to determine acid volatile sulfides (AVS) are presented. For the extraction process magnetic agitation was compared with ultrasonic stirring (using a bath and a probe), and several stirring times were assayed. The proposed SEM procedure uses an ultrasonic probe and 1mL of HCl. It dramatically minimizes the turnaround time and the residues. AVS were evaluated as the difference between the amounts of sulphur in the solid residue after the extraction and total sulphur in the original sample. These procedures are fast, easy to implement and cost-effective to assess the potential risk posed by metals in marine sediments. They were tested using several CRMs and applied to sediments from two Galician Rias (NW Spain); their SEM-AVS differences indicated no biological risk.

Interpolation in the standard additions method.

The standard additions method (SAM) has traditionally been performed by using extrapolation. This practice is suboptimal because predictions are affected by even slight departures of calibration points from a straight line. Despite this, most textbooks and papers in analytical chemistry still refer exclusively to extrapolation. In contrast, the use of interpolation is recommended in this paper as a way to get predictions on the central part of the regression line and thus minimize the bias in the prediction and the variance associated with the analytical result. Several scenarios were studied, with concentration errors simulated in different calibration solutions. It was found that translational effects due to variations at the central part of the calibration caused the lowest disturbances on the predicted concentrations. The differences between the interpolated and extrapolated predictions can be as large as ±30%. The confidence interval associated with the extrapolation result is wider than that due to interpolation by as much as 100%. It is shown that commonly used equations underestimate the correct confidence intervals. Both, absence of bias and improved precision, are of relevance in quality assurance, method validation and error propagation.

3-Way characterization of soils by Procrustes rotation, matrix-augmented principal components analysis and parallel factor analysis.

Three different approaches for 3-way analyses, namely, Procrustes rotation, parallel factor analysis (PARAFAC) and matrix-augmented principal component analysis, have been compared considering a four-seasons study on soil pollution. Each sampling season comprised 92 roadsoil samples and 12 analytical variables (heavy metals, loss on ignition, pH and humidity). Results show that the three chemometric techniques lead to essentially the same conclusions. Hence, Procrustes rotation, a mathematical technique scarcely applied in analytical chemistry, revealed as a useful tool for 3-way data analysis with potential advantages, including its conceptual simplicity and straightforward interpretation of the results. A novel application of the consensus vectors allowed definition of "consensus scores" so that visualization of the samples and temporal patterns can be made. Results also suggested that the trilinearity assumption imbedded in PARAFAC is essentially fulfilled when studying the temporal evolution of an environmental system where no new pollution sources appear during the course of the study.

Temporal characterisation of river waters in urban and semi-urban areas using physico-chemical parameters and chemometric methods.

Three sampling campaigns were carried out in rivers located at two hydrographic basins affected by urban and semi-urban areas around the Metropolitan area of A Coruña (ca. 500,000 inhabitants, NW-Spain) to study local and temporal variations of 21 physicochemical parameters (pH, conductivity, Cl-, SO4(2-), SiO2, Ca2+, Mg2+, Na+, K+, hardness, NO3(-), NO2(-), NH4(+), COD, PO4(3-), Zn2+, Cu2+, Mn2+, Pb2+, alkalinity and acidity) in 23 sampling points. The temporal evolution of the water quality was assessed by matrix augmentation principal components analysis (MA-PCA) and parallel factor analysis (PARAFAC). Moreover, classical principal components analysis (PCA) (one per sampling campaign) was applied with exploratory and comparison purposes. The first factor of the different studies comprised variables associated to the mineral content and it differentiated the samples according to their hydrographic basins. The second factor was mainly associated to organic matter, from domestic wastes and decomposition of natural debris. The temporal evolution of the water quality was mostly related to seasonal increments of the physicochemical parameters defining the decomposition of the organic matter. The three models applied (PCA, MA-PCA and PARAFAC) led to similar conclusions, nonetheless, MA-PCA excelled, since the refolding of scores provided more straightforward and convenient overview of sample time and geographical variations than individual PCA and it is more flexible and adaptable to environmental studies than PARAFAC.

Handling complex effects in slurry-sampling-electrothermal atomic absorption spectrometry by multivariate calibration.

Analysis of solid samples by slurry-sampling-electrothermal atomic absorption spectrometry (SS-ETAAS) can imply spectral and chemical interferences caused by the large amount of concomitants introduced into the graphite furnace. Sometimes they cannot be solved using stabilized temperature platform furnace (STPF) conditions or typical approaches (previous sample ashing, use of chemical modifiers, etc.), which are time consuming and quite expensive. A new approach to handle interferences using multivariate calibrations (partial least squares, PLS, and artificial neural networks, ANN) is presented and exemplified with a real problem consisting on determining Sb in several solid matrices (soils, sediments and coal fly ash) as slurries by ETAAS. Experimental designs were implemented at different levels of Sb to develop the calibration matrix and assess which concomitants (seven ions were considered) modified the atomic signal mostly. They were Na+ and Ca2+ and they induced simultaneous displacement, depletion (enhancement) and broadening of the atomic peak. Here it is shown that these complex effects can be handled in a reliable, fast and cost-effective way to predict the concentration of Sb in slurry samples of several solid matrices. The method was validated predicting the concentrations of five certified reference materials (CRMs) and studying its robustness to current ETAAS problems. It is also shown that linear PLS can handle eventual non-linearities and that its results are comparable to more complex (non-linear) models, as those from ANNs.

Microwave-assisted extraction and ultrasonic slurry sampling procedures for cobalt determination in geological samples by electrothermal atomic absorption spectroscopy.

Slurry sampling is compared to microwave-assisted acid digestion for cobalt determination in soil/sediment samples by electrothermal atomic absorption spectrometry (ETAAS). Furnace temperature programs and appropriate amounts of three chemical modifiers were optimised in order to get the highest signals and good separations between the atomic and background signals. Using nitric acid (0.5% (v/v)) as liquid medium, no chemical modifier was needed. The detection limit, based on integrated absorbance, was 0.04mugg(-1) for digests and slurries. Within-batch precision and analytical recoveries were satisfactory for both procedures. Accuracy was tested by analysing a reference soil and a sediment from IRMM. The methods were further compared employing a set of roadside soils and estuarine sediments. As no significant differences (95% confidence) were found, practical analytical properties were suggested in order to select one of them.

Slurry sampling for direct analysis of solid materials by electrothermal atomic absorption spectrometry (ETAAS). A literature review from 1990 to 2000.

The determination of trace metals in solid samples has traditionally been performed by acid digestion and subsequent measurement by a suitable instrumental technique. This dissolution step is time-consuming and it shows important drawbacks. For these reasons, in the past years many efforts have been focused on the direct analysis of solid samples. Among the developed methodologies, slurry sampling-electrothermal atomic absorption spectrometry combines the significant advantages of the solid and liquid sampling methods, and it can be already considered as a mature technique, that is widely utilized for metal determination in both organic and inorganic matrices, even for routine analysis. Accordingly, this work gives a retrospective view of the progresses of this technique during the past decade (1990-2000).

Chemical modifiers for direct determination of cobalt in coal combustion residues by ultrasonic slurry-sampling-ETAAS.

Five modifiers were tested for the direct determination of cobalt in coal fly ash and slag by ultrasonic slurry-sampling electrothermal atomic absorption spectrometry (USS-ETAAS). The furnace temperature programs and the appropriate amount for each modifier were optimized to get the highest signal and the best separation between the atomic and background signals. Nitric acid (0.5% v/v) was the most adequate chemical modifier for cobalt determination, selecting 1,450 degrees C and 2,100 degrees C as pyrolysis and atomization temperatures, respectively. This modifier also acts as liquid medium for the slurry simplifying the procedure. The remaining modifiers enhanced the background signal, totally overlapped with cobalt peak. The method optimized gave a limit of detection of 0.36 microg g(-1), a characteristic mass of 13 +/- 1 pg and an overall-method precision which is highly satisfactory (<7%, RSD). The method was validated by analyzing two certified coal fly ash materials, and satisfactory recoveries were obtained (83-90%) and no statistical differences were observed between the experimental and the certified cobalt concentrations. Additionally, certified sediment, soil and urban particulate matter were assayed; again good results were obtained. The developed methodology was used to determine cobalt in several coal combustion residues from five Spanish power plants.

Classification of edible vegetables affected by different traffic intensities using potential curves.

Heavy metals in soils have largely been used to evaluate the impact of motorised traffic in the vicinity of motorways. Also in this field of work it is of paramount importance to analyse the vegetables grown in these areas since their consumption is one of the main sources of metal intake by people; not in vain human food is directly or indirectly derived from plants. Accordingly, a set of edible vegetable samples were first analysed and, then, classified employing different multivariate chemometric techniques; among them, SIMCA and a simplified mode of potential curves. The analytical variables were selected after a comprehensive study of roadside soil pollution where Pb, Cd and Cu were found to be the main metallic pollution tracers. Different groups of vegetables were obtained which were explained as a function of both the agricultural conditions (private versus commercial) and the different traffic intensities supported by the cultivated areas.

Searching for heavy metals grouping roadside soils as a function of motorized traffic influence.

Ninety two soil samples were collected in four sampling seasons in La Coruña, NW of Spain, and its surroundings to study the impact of vehicular traffic onto the metallic content of roadside soils in a medium-size city. Samples exhibited different levels of exposure and, therefore, sample groups should arise as a function of this anthropogenic impact. Surprisingly, this was not so when all the nine metals initially considered were subjected to multivariate analyses. Then, different unsupervised multivariate statistical techniques were used to discover those elements able to group the samples according to the level of road traffic. Such an objective was achieved only after removing the natural variability. Accordingly, Pb, Cd, Cu and Zn were found to satisfactorily conduct to this end, Pb being the most discriminant one.

Cadmium analysis in soil by microwave acid digestion and graphite furnace atomic absorption spectrometry.

The need to determine micronutrients and toxic elements in soils has grown in recent years and cadmium is of special interest. A method has been developed for the determination of cadmium in soils based on a prior acid digestion of the samples with nitric acid in closed Teflon vessels, into a microwave over. The cadmium determination was carried out by graphite furnace atomic absorption spectrometry (GFAAS) with L'vov platform. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. The best matrix modifier was found to be ammonium dihydrogen phosphate. The interferences are greatly reduced under these operating conditions and calibration can be performed with simple aqueous solutions of the metal standard. The method is rapid and provides accurate and precise results that agree with certified values for two reference materials: BCR 141 (calcareous loam soil) and BCR 277 (estuarine sediment).