James W. McLaren

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.

Study of the effects of concomitant elements in inductively coupled plasmamass spectrometry

Abstract The effect of 0.01 M concentrations of several concomitant elements (Li, Na, K, Cs, Mg, Ca, B, Al and U) on the signal of 100 μg l concentrations of several test analytes (V, Cr, Mn, Ni, Co, Cu, Zn, Cd and Pb) has been studied at a single set of operating conditions used for multielement ICP-MS analysis. It appears that some concomitant elements (Na, K, Cs, Mg, Ca) induce an enhancement of the analyte signals while another (Li) does not have any significant effect and others (B, Al, U) cause a suppression. Since in all cases, the change of signal is in the same direction for all the analytes, internal standardization using some background lines was used to try to compensate for these effects. An accurate correction is realized in most cases, with the exception of the heavier elements Cd and Pb which need a separate, heavier internal standard. Overall, the data suggest that a key factor linked to the effects may be the rate of atom-electron collisions: when it increases substantially (as with easily ionized elements), the ionization of the analytes is favored more than their recombination with electrons; but if the concomitant elements form refractory oxides (B, Al and U) that can deposit on the interface, then the collisional rate is lower and the recombination is favored. When no effect is seen, the ionization induced by collisions is balanced by the recombination.

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.

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.

A novel inductively coupled plasma/selected-ion flow tube mass spectrometer for the study of reactions of atomic and atomic oxide ions

Abstract A novel inductively coupled plasma/selected-ion flow tube (ICP/SIFT) mass spectrometer has been constructed for the study of the kinetics and product distributions of reactions of atomic and atomic oxide ions with neutral molecules. The ICP essentially provides a universal source for atomic ions. The operation of the instrument is demonstrated with prototype reactivity and kinetic measurements.

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.

Evaluation of a membrane interface sample introduction system for inductively coupled plasma mass spectrometry

Its performance was assessed by a comparison of sensitivity for rhodium and uranium, and of oxide levels for uranium, with data obtained in a previous study of methods to reduce isobaric interferences by oxides. The results show that the device has considerable promise, but that further studies should be conducted with a new version optimized for maximum water removal, rather than maximum analyte transport efficiency

Physico-chemical characterization of metal binding proteins using HPLC-ICP-MS, HPLC-MA-AAS and electrospray-MS

A size exclusion HPLC method was developed and interfaced with ICP-MS detection for determining the metal profiles of commercially available rabbit liver metallothioneins (MT) and metallothionein-like proteins (MLP) extracted from fresh water mussels and hemolyzed osprey blood. The redox state of the cysteine residues was indirectly evaluated via a cadmium saturation approach in the presence or absence of a reducing agent, followed by HPLC-microatomization (MA)-AAS and HPLC-ICP-MS analyses. An electrospray-MS protocol was also developed to accurately measure the molecular weight of rabbit MT isoform II. Nanogram quantities of Cd-MT/MLP were poorly chromatographed on silica based supports. A copolymeric styrene-divinylbenzene size exclusion support provided a symmetrical peak (rabbit MT standard) and linear HPLC-MA-AAS calibration curves [r=0.9988; from the LOD (27 ng, as protein) to about 300×LOD], indicating negligible losses of Cd during the chromatography of trace quantities. Co-injection of Cd2+ saturated samples with beta-mercaptoethanol (BMSH) was essential to repress Cd2+-support interactions which otherwise induced an undesirable metalaffinity retention mechanism. In the presence of added Cd2+, 22 mmol/L BMSH did not significantly compete for Cd2+ specifically bound to MT, while preventing non-specific binding to non-thiolic complexing sites. Crude mussel and osprey blood MLP extracts (in cold, deoxygenated Tris-HCl buffer) were obtained by ultracentrifugation (145,000 g) and thermocoagulation/centrifugation, respectively. Incubation with BMSH was prerequisite to obtain a maximum saturation of mussel and osprey blood MLP by Cd2+, even for samples conserved (−80° C) in the presence of BMSH (22 mmol/L). These observations indicated that a major proportion of the cysteine residues present in these MLP were oxidized. The assumption of a fully reduced MT/MLP pool binding metals in a definite stoichiometry has been the basis of several quantitative metal binding assays involving the saturation of the thiolic complexing sites with a metallic marker (Ag+, Cd2+, or Hg2+). Since thiolic agents may interfere, the metal saturation protocols do not include a reducing step to ensure that all cysteines in a MT/MLP extract are available for co-ordination. Given that variations in the redox state of crude MT/MLP extracts may compromise the accuracy of metal saturation assays, it is concluded that the preparation of reference samples certified for total metallothionein content would be desirable.

An on-line method for the determination of lead and lead isotope ratios in fresh and saline waters by inductively coupled plasma mass spectrometry

Abstract A previously reported on-line ICP-MS method for the determination of lead and other trace elements in seawater has been re-examined to determine its suitability for the determination of lead isotope ratios (206Pb/207Pb and 207Pb/208Pb) in fresh and saline natural waters. A detection limit of 0.9 ng l for total lead (for a 5 ml sample) was achieved. Precision of isotope ratio data was 0.2–0.3% RSD at a Pb concentration of 1 μg l , and was still better than 2% at concentrations of only 10–40 ng l in seawater certified reference materials (CRMs). For all three natural water CRMs examined, measured precision was very close to the limit predicted by counting statistics.

The use of inductively coupled plasma mass spectrometry in the production of environmental certified reference materials

The use of inductively coupled plasma mass spectrometry (ICP-MS) in the production of environmental certified reference materials by the National Research Council of Canada is reviewed. Particular emphasis is placed on the use of isotope dilution ICP-MS. Results for fresh and saline natural waters, fish tissues and sediments are presented to illustrate the impressive capabilities of this technique.