David Littlejohn

A CRITICAL EVALUATION OF THE THREE-STAGE BCR SEQUENTIAL EXTRACTION PROCEDURE TO ASSESS THE POTENTIAL MOBILITY AND TOXICITY OF HEAVY METALS IN INDUSTRIALLY-CONTAMINATED LAND

Cadmium, chromium, copper, lead, manganese, nickel, vanadium and zinc have been determined in samples of made-up ground from layers of a trial pit excavated on a recently derelict, industrially contaminated site. The pseudototal metal content of the layers was determined following a microwave-assisted digestion with aqua regia. Operational speciation was performed using the BCR three-step sequential extraction procedure. Analyses were carried out by flame or electrothermal atomic absorption spectrometry (FAAS or ETAAS). A suppressive interference (30%) was observed in the determination of cadmium in aqua regia digests by ETAAS, but not in 0.11 mol l ˇ1 acetic acid, 0.1 mol l ˇ1 hydroxylammonium chloride or 1.0 mol l ˇ1 ammonium acetate extracts. Agreement between duplicate samples was acceptable (i.e. within 10%) for most elements in most layers, but some large discrepancies were apparent, especially for lead. The amount of metal extracted in the sequential procedure (i.e. Step 1aStep 2aStep 3aresidual) did not generally agree well with pseudototal digestion. Various layers of the trail pit contained significant levels of contaminant metals, but these were not always in easily mobilized forms. For example, less than 0.2% of the lead (4000 m gg ˇ 1 ) at 65‐85 cm depth was present as exchangeable or acid-soluble species. The study illustrates the importance of considering metal speciation when assessing the mobility of potentially toxic elements in industrially-contaminated land. # 1998 Elsevier Science B.V.

Evaluation of a sequential extraction procedure for the speciation of heavy metals in sediments

The three-stage sequential extraction procedure for speciation of heavy metals, proposed by the Commission of the European Communities Bureau of Reference (BCR), has been applied to a freshwater sediment collected from the River Clyde, Lanarkshire, UK. Initial studies were carried out using flame atomic absorption spectrometry (FAAS). Iron, manganese and zinc could be determined in the sediment extracts by FAAS, but the technique proved insufficiently sensitive for the determination of chromium, copper, nickel and lead. Detection methods based on electrothermal AAS were therefore developed and applied. Furnace conditions were optimised for the determination of the four analytes mentioned, plus molybdenum and vanadium, in acetic acid, hydroxylammonium chloride and ammonium acetate matrices. Interferences by components in the sediment extracts necessitated analysis by the method of standard additions in most cases. The sequential extraction procedure was found to be both repeatable and reproducible. The amounts of analytes released by the sequential extraction procedure plus aqua regia digestion of the residue remaining after extraction were similar to those released by pseudo-total digestion of the sediment (using aqua regia).

Three-stage sequential extraction procedure for the determination of metals in river sediments

A three-stage sequential extraction procedure, following a protocol proposed by a European working group coordinated and supported by the Community Bureau of Reference (BCR), has been applied to two river sediments from an industrial region of East Catalonia, Spain. The extractant solutions were: Step One, acetic acid (0.11 mol l(-1)); Step Two, hydroxylammonium chloride (0.1 mol l(-1), pH 2); Step Three, hydrogen peroxide (8.8 mol l(-1)) oxidation followed by extraction with ammonium acetate (1 mol l(-1), pH 2). The six elements determined in the extracts were Cd, Cr, Cu, Ni, Pb and Zn. Analysis of the extracts was carried out by flame atomic absorption spectrometry (FAAS). There were slight differences in analyte sensitivity between calibrants prepared in the extractant matrices and acidified aqueous calibrants. No significant matrix interferences were found except for Cr in the acetic acid and hydroxylammonium chloride extracts, which required determination by the standard additions method. The other elements (plus all the elements in the ammonium acetate extracts) were determined by direct calibration against calibrant solutions prepared in the same matrices as the samples.

Evaluation of a slurry technique for the determination of lead in spinach by electrothermal atomic-absorption spectrometry

A simple method for the determination of lead in spinach involving minimum sample preparation is described. The powdered spinach is suspended in a thixotropic thickening agent, Viscalex HV30, and the slurry is injected directly into the electrothermal atomiser. Oxygen is introduced during the ashing stage to allow the use of higher ash temperatures and to avoid the build up of carbonaceous residue in the tube. Concentrations of powdered spinach up to 10%m/V can be tolerated in the suspension. Good agreement was achieved between results obtained by a standard additions procedure and by direct calibration with aqueous standards, and also by an alternative wet digestion procedure.

Process NMR spectrometry

A review is presented, covering the many advantages of NMR in process applications including the possibility of standardless quantitative analysis. The technique may provide a useful alternative for quantitative monitoring of batch and continuous reactions but it will not be suitable for trace analysis.

Improved method for kinetic studies in microreactors using flow manipulation and noninvasive Raman spectrometry

A novel method has been devised to derive kinetic information about reactions in microfluidic systems. Advantages have been demonstrated over conventional procedures for a Knoevenagel condensation reaction in terms of the time required to obtain the data (fivefold reduction) and the efficient use of reagents (tenfold reduction). The procedure is based on a step change from a low (e.g., 0.6 μL min(-1)) to a high (e.g., 14 μL min(-1)) flow rate and real-time noninvasive Raman measurements at the end of the flow line, which allows location-specific information to be obtained without the need to move the measurement probe along the microreactor channel. To validate the method, values of the effective reaction order n were obtained employing two different experimental methodologies. Using these values of n, rate constants k were calculated and compared. The values of k derived from the proposed method at 10 and 40 °C were 0.0356 ± 0.0008 mol(-0.3) dm(0.9) s(-1) (n = 1.3) and 0.24 ± 0.018 mol(-0.1) dm(0.3) s(-1) (n = 1.1), respectively, whereas the values obtained using a more laborious conventional methodology were 0.0335 ± 0.0032 mol(-0.4) dm(1.2) s(-1) (n = 1.4) at 10 °C and 0.244 ± 0.032 mol(-0.3) dm(0.9) s(-1) (n = 1.3) at 40 °C. The new approach is not limited to analysis by Raman spectrometry and can be used with different techniques that can be incorporated into the end of the flow path to provide rapid measurements.

Palladium as a chemical modifier for the determination of lead in food slurries by electrothermal atomisation atomic absorption spectrometry

Palladium is shown to be superior to ammonium dihydrogen phosphate as a modifier for lead in the analysis of food slurries by electrothermal atomisation atomic absorption spectrometry. A conventional autosampler was modified to permit magnetic stirring of the slurry samples in the autosampler cups. Stirred slurries can be accurately and precisely pipetted into a graphite furnace up to concentrations of 5%m/V. Above this, systematic errors occur. A method is described for the determination of lead in slurries up to a concentration of 4%m/V. The procedure involves calibration with aqueous standards, palladium matrix modification and platform atomisation.

A diffusion tube sampler for the determination of acetic acid and formic acid vapours in museum cabinets

A passive, diffusion-tube sampler has been developed for the quantification of acetic acid and formic acid vapours in ambient air. The sampling rates of the diffusion tube and the response times were calculated to be 0.88 ml min−1 and 3.8 min for acetic acid and 1.02 ml min−1 and 3.3 min for formic acid, respectively. The sampler has been deployed unobtrusively in museum environments to collect pollutants over a period of typically 1–2 weeks. Determination of the collected analytes was performed using ion chromatography. Under laboratory test conditions, the results of the sampler for replicate analyses were found to be repeatable and reproducible; typical RSD values were less than 5% for the collection of acetic and formic acid vapours from atmospheres of approximately 187 and 88 mg m−3, respectively. Detection limits of 44 and 13 μg m−3 were calculated for a two week sampling period for acetic acid and formic acid, respectively. The mass of acids collected by the passive sampler increased linearly with atmospheric acid concentrations up to approximately 386 mg m−3 acetic acid and 194 mg m−3 formic acid. In an atmosphere containing approximately 187 and 88 mg m−3 of acetic and formic acid vapours, respectively, the mass of acids collected by passive samplers increased linearly for exposure times between 2 and 75 h. The sampler has been used to investigate the concentration of acetic acid and formic acid vapours in museum cabinets where damage to artefacts by atmospheric pollution has been observed.

Quantitative assessment of surface-enhanced resonance Raman scattering for the analysis of dyes on colloidal silver

Factors that affect quantitative analysis by surface-enhanced resonance Raman scattering (SERRS) have been investigated using azobenzotriazol and reactive dyes. Preaggregation of the silver colloid was the most effective method to obtain repeatable and reproducible scattering. Aggregation by poly(l-lysine) or spermine provided better precision than aggregation by sodium chloride or nitric acid. Repeatable quantitative analysis was achieved with the azobenzotriazol dyes. A linear calibration graph was obtained over different concentration ranges below 10(-)(8) M, depending on the nature of the colloid. Calculations estimate that 10(-)(8) M is the concentration at which monolayer coverage of the dye on the silver colloid is achieved. Above 10(-)(8) M, there was only a minor increase in the scattering intensity from the azobenzotriazol dyes. In contrast, the reactive dyes did not give a response proportional to concentration over the range studied. The different responses obtained for the two types of dye are believed to be caused by differences in the nature of the interaction of the molecules with the silver surface. The conclusion reached is that control of the colloid preparation, aggregation process, and surface chemistry are essential for successful quantitative analysis of dyes on colloidal silver by SERRS.

Real-time monitoring of powder mixing in a convective blender using non-invasive reflectance NIR spectrometry

A convective blender based on a scaled down version of a high shear mixer-granulator was used to produce binary mixtures of microcrystalline cellulose (Avicel) and aspirin, citric acid, aspartame or povidone. Spectra of stationary Avicel or aspirin powder provided an indication of the information depth achieved with the NIR spectrometer used in the study, and confirmed previously reported effects of particle size and wavenumber. However, it was demonstrated that for 10% w/w aspirin in Avicel, the information depth at the C-H second overtone of aspirin (about 2.4 mm) was unaffected by changes in the particle size of aspirin and was determined by the major component. By making non-invasive NIR measurements as powders were mixed, it was possible to illustrate differences in the mixing characteristics of aspirin, citric acid, aspartame or povidone with Avicel, which were related to differences in the cohesive properties of the particles. Mixing profiles based on second overtone signals were better for quantitative analysis than those derived from first overtone measurements. It was also demonstrated that the peak-to-peak noise of the mixing profile obtained from the second overtone of aspirin changed linearly with the particle size of aspirin added to Avicel. Hence, measurement of the mixing profile in real time with NIR spectrometry provided simultaneously the opportunity to study the dynamics of powder mixing, make quantitative measurements and monitor possible changes in particle size during blending.