Joseph W. Lam

Strontium and barium uptake in aragonitic otoliths of marine fish

Abstract Minor and trace element analyses of fish otoliths (ear stones) may provide a high-resolution reconstruction of temperature histories and trace element compositions of aquatic systems where other environmental proxies are not available. However, before otoliths can be used to reconstruct water chemistry, it is essential to validate the assumption that trace metals in otoliths are deposited in proportion to dissolved concentrations in the ambient environment. We show, using a marine fish (Leiostomus xanthurus) reared in the laboratory under controlled experimental conditions, that otolith Sr/Ca and Ba/Ca ratios are deposited in proportion to their respective ratios in ambient waters. Temperature significantly affected Sr incorporation but did not affect Ba incorporation in otoliths. Sr/Ca partition coefficients (DSr) were 0.182 and 0.205 at 20°C and 25°C, respectively. The partition coefficients for Ba/Ca were 0.055 at 20°C and 0.062 at 25°C. A nonlinearity in the relationship between DBa and ambient Ba concentrations suggested that extrapolation beyond the Ba levels used in the experiment was not justified. On the basis of our results, it should be possible to reconstruct Sr/Ca and Ba/Ca levels in environments inhabited by fish based on otolith chemistry. Furthermore, Sr/Ca thermometry may also be possible using fish otoliths, but validation of the temperature dependence of Sr/Ca in otoliths will be required. We believe otoliths represent an excellent, and as yet underused, record of the physicochemical properties of both modern and ancient aquatic environments.

Certification of a fish otolith reference material in support of quality assurance for trace element analysis

Production and certification activities relating to the development of a new Certified Reference Material (FEBS-1) based on a fish otolith matrix are described. The material was prepared from 4.5 kg of dried saggital otolith harvested from the red snapper (Lutjanus campechanus), ball milled and sieved to <200 mesh, homogenized, irradiated, bottled into 1 g aliquots and certified for major, minor and trace element composition using inductively coupled plasma mass spectrometry (ICP-MS), isotope dilution-ICP-MS, neutron activation, ICP-optical emission spectrometry and X-ray fluorescence. Several laboratories participated in this activity, providing for a robust estimate of each measurand. Certified values for seven elements (Ba, Ca, Li, Mg, Mn, Na and Sr) are reported, accompanied by full GUM uncertainty estimates. Reference values for Cd, Cu, Ni, Pb and Zn are also provided; these elements were considered to be not certifiable because of the large component of uncertainty contributed by homogeneity. This CRM will be of interest to those laboratories requiring quality assurance of measurements of bulk elemental composition of otoliths and other marine aragonites.

Applications of ICP-MS in marine analytical chemistry

SummaryThe versatility of ICP-MS in marine analytical chemistry is illustrated with applications to the multielement trace analysis of two recently released marine reference materials, the coastal seawater CASS-2 and the non-defatted lobster hepatopancreas tissue LUTS-1, and to the determination of tributyltin and dibutyltin in the harbour sediment reference material PACS-1 by HPLC-ICP-MS. Seawater analyses were performed after separation of the trace elements either by adsorption on immobilized 8-hydroxy-quinoline or by reductive coprecipitation with iron and palladium. Simultaneous determination of seven trace elements in LUTS-1, including mercury, by isotope dilution ICP-MS, was achieved after dissolution by microwave digestion with nitric acid and hydrogen peroxide. Butyltin species in PACS-1 were separated by cation exchange HPLC of an extract of the sediment; method detection limits for tributyltin and dibutyltin in sediment samples are estimated to be 5 ng Sn/g and 12 ng Sn/g, respectively.

Chemical vapor generation characteristics of transition and noble metals reacting with tetrahydroborate(III)

The vapor generation characteristics of several transition and noble metals arising from reduction of their aquo-ions by tetrahydroborate(III) are presented. A modified parallel path Burgener Teflon nebulizer interfaced to an ICP-MS for detection was used to examine the effects of experimental variables. The influence of both hydrochloric and nitric acid as well as the nature of the surface exposed to the nascent species is of paramount importance to the overall efficiency of the generation process. Both glass and Ryton double pass spray chambers were examined, the latter providing superior performance with respect to sensitivity as well as memory effects. Data were presented for the generation of vapor phase species of Rh, Pd, Au and Cu that can be collected in a weakly acidic medium for subsequent release as a gaseous product.

Expanding the scope of chemical vapor generation for noble and transition metals

A modified Bergener parallel path nebulizer was used for the generation of volatile metal species of Pt, Co, Ag, Cu, Rh, Pd, Au, Ni, Ir, Ti and Mn through reaction with tetrahydroborate (III). Several physicochemical factors were identified which impact on their yield which, at present, is estimated to range from 0.02-2% absolute.

Use of aerosol processing and nitrogen-argon plasmas for reduction of oxide interference in inductively coupled plasma mass spectrometry

The results of a detailed study carried out for uranium suggest that the addition of 8% of nitrogen to the outer gas is often a more effective means of reducing oxide interferences in inductively coupled plasma mass spectrometry than reduction of the water loading of an all-argon plasma by spray-chamber cooling or partial desolvation of the aerosol. The beneficial effect of the addition of nitrogen is enhanced, however, by combination with reduction of the water loading. A dramatic reduction in the argon oxide background peak is also observed. The practicality of this approach has been demonstrated by applications to difficult determinations in marine sediment and freshwater reference materials.

Insights into the mechanism of chemical vapor generation of transition and noble metals

The mechanisms of chemical vapor generation (CVG) of transition and noble metals by reaction with tetrahydroborate(III) have been investigated in an effort to reconcile fundamental properties of compounds containing metal–hydride bonds with the experimental evidence collected in the present work and in the recent analytical literature on CVG. Silver, gold and rhodium were investigated in detail. Various materials constituting the wetted surfaces of the reaction apparatus (Ryton, glass, silanized glass) were examined for their effect on the overall process, as was the presence of surface-active agents (Triton X-100TM, antifoam B). Two types of reactions contribute to the formation of volatile species. The first (primary reaction) occurs through homogeneous liquid phase reactions between aqueous analyte complexes (MLn) and hydroboron species (BH4− and its hydrolysis products). The second (secondary reaction) is a surface mediated reaction between reaction intermediates, mostly formed in the primary reaction and chemisorbed by active sites on surfaces, and hydroboron species. The participation of active surface sites generally improves the efficiency of CVG compared with use of an inert surface, but this feature cannot always be usefully employed in analytical applications due to slow reaction kinetics producing memory effects. Reaction intermediates which can be classified as hydrido metal complexes, LnMHx, possess complex chemistry, making interpretation of experimental results difficult. Hydrido metal complexes, in addition to free atoms and nanoparticles, may constitute the volatile species leaving the solution and/or reaching the atomizer.

Determination of iron and ten other trace elements in the Open Ocean Seawater reference material NASS-3 by inductively coupled plasma mass spectrometry

Iron and ten other trace elements were determined in the Open Ocean Seawater certified reference material NASS-3 by inductively coupled plasma mass spectrometry (ICP-MS) after separation and concentration on silica-immobilized 8-hydroxyquinoline (I-8-HOQ). Iron and molybdenum were separated from sea-water samples adjusted to pH 3 prior to passage through the column, whereas for the other nine elements preconcentration was performed at pH 8. Determination of iron in the concentrates by isotope dilution, with 56Fe as the reference isotope and 57Fe as the spike, required the use of a nitrogen–argon mixed-gas plasma with partial aerosol desolvation. The detection limits of the method, based on a 90-fold preconcentration, range from 0.04 ng dm–3 for U to 6.3 ng dm–3 for zinc.

On-line method for the analysis of sea-water for trace elements by inductively coupled plasma mass spectrometry. Plenary lecture

A commercially available chelation concentration system for the on-line preconcentration of trace metals from saline solutions was modified to permit the simultaneous determination of Fe, Mn, Co, Ni, Cu, Zn, Cd and Pb in 5 ml sea-water samples in less than 10 min by inductively coupled plasma mass spectrometry. Modifications were necessary in order to obtain acceptably low blanks for several elements. The system was operated both with columns provided by the manufacturer and with columns containing silica-immobilized 8-hydroxyquinoline. Detection limits in sea-water ranged from 1.6 ng l–1(for Pb) to 55 ng l–1(for Ni) for the former columns, and from 0.3 ng l–1(for Cd) to 47 ng l–1(for Fe) for the latter. Accurate analyses of coastal and open-ocean sea-water certified reference materials were achieved with at least one of the column types for all elements except Fe and Co.

Continuous-flow microwave-assisted digestion of environmental samples using atomic spectrometric detection

A continuous-flow microwave-assisted digestion technique was tested with a view to the evaluation of its effectiveness for decomposition of environmental samples. A CEM SpectroPrep system was used at moderate powers and pressures of up to 2413 kPa to perform on-line digestion of slurried samples of biological tissues (0.5% m/v) and marine sediment (1% m/v). The efficiency of oxidation of biological matrices, as characterized by the residual carbon content of the solutions, was 64%. Recovery of trace elements averaged 90±1% and was accommodated with the use of suitable internal standards. Accuracy was verified by analysis of certified reference materials from the National Research Council of Canada, marine sediment BCSS-1 and lobster hepatopancreas tissue LUTS-1. Precision of measurement, as reflected in the determination of the trace metal content in replicate solutions, using a variety of atomic spectrometric techniques, was better than 1% RSD (relative standard deviation).