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The objective of this work was to study the effects of the following Ligands: Chelex-100, Dowex MAC-3 and Dowex 50WX-8 using Competing Ligand Exchange Method. This objective was achieved by investigating complex dissociation kinetics of trace metals: Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Mn(II) and Pb(II) of a well-characterized Laurentian Fulvic Acid (LFA) in model solutions and in a natural waters of Lake Heva (Quebec, Canada). The effects of variation in the competing ligands (including their quantities) on the complex dissociation kinetics were quantitatively characterized by their first-order dissociation rate coefficients. The kinetic lability of the metal complexes varied with the metal-to-LFA ratio, as expected from the theory of metal complexes of the chemically and physically heterogeneous complexants, LFA. The general trend in the metal-binding by the above competing ligands was: Dowex 50WX-8 > Chelex-100 > Dowex MAC-3. However, no difference was found between the Dowex 50WX-8 and Chelex-100 for Cd(II), Zn(II), and Co(II). The results revealed the importance of the quantity of Chelex-100 as a competing ligand in the metal(II)–LFA complexation, on the dissociation kinetics of these complexes in model solutions. By developing Competing Ligand Exchange Method as an analytical technique, for studying the relative affinities of the above competing ligands for metals complexation in natural waters this work has made a substantial contribution to analytical chemistry.

Kinetic speciation of uranium in model solutions containing uranium and humic acid (HA) and in natural waters has been investigated by Competitive Ligand Exchange Method (CLEM). In alkaline freshwaters, most of uranium species were uranium–carbonate species, which were labile in the CLEM experiment. The uranium speciation of every sample was characterized either as “labile” or “non-labile” uranium complexes depending on the dissociation rate coefficients of the complexes. The results showed that as the U(VI)/HA ratio was decreased, the dissociation rate coefficients decreased and the labile fraction decreased as well. When the U(VI)/HA ratio was 0.1, the labile fraction of the U(VI)-HA increased with increasing pH; however, there was no pH effect on the dissociation of U(VI)-HA complexes at lower U(VI)/HA ratios. Chelex-100 had some limitations in its use for the study of dissociation of U(VI)-HA complex at very low U(VI)/HA ratios. By developing an analytical method and procedure for quantitative determination of kinetic parameters for the dissociation of uranium-HA complexes in model solutions and natural waters, this work has made a substantial contribution to analytical chemistry.

A technique has been developed to study chemical speciation of copper in freshwaters by competing ligand exchange (CLE) method using anodic stripping voltammetry (ASV) in the differential pulse (DP) mode with ethylenediaminetetraacetic acid (EDTA) as a competing ligand. The voltammetric behavior of Cu(II)–EDTA complex has been investigated using DPASV. When DPASV is used at an appropriate deposition potential, the inert Cu(II)–EDTA complex becomes electroactive, and is reduced directly. Furthermore, at the same deposition potential, Cu(II)–fuvic acid and Cu(II)–humic acid complexes do not contribute significantly to the analytical signal, which makes EDTA a suitable competing ligand in the determination of copper speciation using CLE–ASV. This method has been applied to freshwater samples from Rideau Canal (Ottawa, ON, Canada). The analysis of the copper titration data of these freshwater samples has indicated the presence of a very strong copper-binding ligand with a conditional stability constant of approximately 1020 and a corresponding very high concentration (above 100 nM) of the ligand.

The competing ligand exchange method was used to investigate the competitive binding of Ni(II) by Al(III) and Fe(III) in model aqueous solutions and freshwaters. Graphite furnace atomic absorption spectrometry and adsorptive cathodic stripping voltammetry were used to monitor the rate of uptake of the Ni by Chelex 100 chelating resin and dimethylglyoxime as the competing ligands, respectively. The results have revealed that Ni(II)–humate complexes were more labile in presence of the mixture of Al(III) and Fe(III), compared to the lability of the Ni(II)–humate complexes when only one of the two, Al(III) or Fe(III), was present. The environmental significance of this work is that in model solutions simulating freshwater containing humic substances and the target trace metal Ni(II) and cations, Al(III) and Fe(III), the competitive binding of Ni(II), Al(III) and Fe(III) by humic substances makes Ni(II)–humate complexes labile, releasing free Ni2+–aqua complex, which reported to be toxic.

Free metal ion concentration is generally considered a useful indicator of a metal’s bioavailability and ecotoxicity to aquatic biota. This article reports the speciation of nickel in mining and municipal effluents from Sudbury (Ontario, Canada), and also in model solutions containing a fully characterized laurentian fulvic acid (LFA) at environmentally relevant concentrations. A column ion exchange technique (IET) using a cation exchange resin (Dowex 50W-X8) was applied to determine free nickel ion concentrations. In model solutions, reasonable correlation was found between the predictions of an equilibrium-based computer speciation code, Windermere Humic Aqueous Model (WHAM) VI, and the results obtained by IET at low nickel-to-fulvic acid ratios. However at higher mole ratios, the WHAM VI predicted higher free nickel ion concentrations than IET. Only three out of six effluent samples showed reasonable agreement between the IET and the WHAM VI results, indicating the need for further development of IET for application to effluent waters.

This study presents the results of kinetic speciation of nickel in undiluted mining and municipal effluents and effluents diluted with receiving freshwaters from the surrounding environment. The dilution ratios used for the dilution of the effluents were arbitrarily chosen, but were representative of the prevailing mining practices. The purpose of the this dilution was to mimic dilution with natural waters that result from dilution of the mining and municipal effluents with receiving freshwaters, so that this study would reveal environmental realities that are of concern to the managers and regulators of water resources. Ligand exchange kinetics using the competing ligand exchange method (CLEM) was studied using two independent techniques: graphite furnace atomic absorption spectrometry (GFAAS) with Chelex 100 resin as the competing ligand, and adsorptive cathodic stripping voltammetry (AdCSV) with dimethylglyoxime (DMG) as the competing ligand to determine the percentage of Ni metal released from Ni(II)-DOC complexes and the rate of dissociation of Ni(II)-DOC complexes. Using a sample containing a mixture of 30% Copper Cliff Mine effluent, 40% Sudbury municipal effluent and 30% Vermillion River water, both techniques gave results showing that the dilution of the effluent samples increased the percentage of nickel released from Ni(II)-DOC complexes. This increase in the release of nickel from the Ni(II)-DOC complexes may be of concern to managers and regulators of water resources. Agreement between the results of these two techniques has enhanced the validity of the competing ligand exchange method used by both techniques.

The paper explores the lability of DOC complexes of Co, Ni, Cu, and Zn in the mining effluent, and investigates the effects of dilution of the effluent on the release of metals from the metal-DOC complexes. This study was done using competing ligand exchange method in conjunction with adsorptive cathodic stripping voltammetry on effluent samples from Copper Cliff Mine, Sudbury, Canada, using two samples of the effluent: one, undiluted (100%) effluent, and the other, diluted (45%) effluent. The dilution was done with tap water in order to determine the effects of dilution on the metal complexes in the effluents when they were discharged into receiving streams of freshwaters. The dilution of the effluent had a small effect on release of Cu from the Cu-DOC complexes, but had a much greater effect on the release of Zn from the Zn-DOC complexes. The release of Ni and Co from their DOC complexes decreased drastically on dilution of the effluent. The much greater release of Cu from the Cu-DOC complexes compared to the release of Ni, Co, and Zn from their DOC complexes in both the undiluted and the diluted effluent was probably due to the higher absolute concentration of Cu and the higher [Cu]/[DOC] ratio. The drastic decrease in the release of Ni and Co from the Ni- and Co-DOC complexes in the diluted (45%) effluent compared with the undiluted (100%) effluent probably resulted from strengthening of the metal-DOC bond due to the reduced screening of charges by a smaller concentration of Ca2+ in the diluted (45%) effluent. This work also shows that change in the ionic strength produces conformational changes in and in aggregation and precipitation of the DOC and also changes in electrostatic interactions between the metal cations and the humate polyanions.

An improved theoretical approach to Anodic Stripping Voltammetry with a Thin Mercury Film Rotating Disk Electrode for elucidating the nature of the interactions of Pb(II), Cd(II) and Zn(II) with humic substances in model solutions of Laurentian fulvic acid, and of Pb(II), Cd(II), Zn(II) and Cu(II) in freshwaters, is presented. Conditional stability constants of Pb(II), Cd(II) and Zn(II) complexes decreased with the ionic potential (z2/r) and increased with softness of the metal ion, indicating strong affinity of soft, polarizable donor ligands on humic substances for softer metal ions, resulting in an appreciable covalent character in electrostatic bonding between the metals and humic substances.

This work continues an evaluation of a previously developed capillary electrophoresis (CE) method to determine the distribution of Fe, Zn, Cu, Mn, and Cd in airborne particulate matter (PM) after sequential extraction. A three-stage extraction procedure following the BCR protocol was used to chemically fractionate metals between (F1) “exchangeable water and acid-extractable” (0.11 M acetic acid), (F2) “reducible” (0.1 M hydroxylamine hydrochloride acidified to pH 2.0 with nitric acid) and (F3) “oxidizable” (1.0 M ammonium acetate extraction after oxidation by 8.8 M hydrogen peroxide) PM fractions. The reliability and applicability of the developed procedure were tested using NIST 1648 Urban Air Particulate Matter. Small-scale extractions (10 mg mass in 1 ml extractant) have been used. The work has been focused on (i) the optimization of CE experimental conditions for sensitivity measuring trace metals in the BCR extractants and (ii) speeding up BCR extraction by finding a set of sonication conditions giving recoveries similar to conventional extraction for the metals of interest. The CE method was validated with respect to linearity, detection limits, precision, and accuracy. Detection limits were at low-μg/l (μg/g) and mid-μg/l (tens of μg/g) levels using electrokinetic and pressure injection modes, respectively. The efficiency of the accelerated BCR extraction method using an ultrasonic bath was evaluated, for each metal in each fraction, as a percent recovery of the conventional method. With the exception of iron (45.0 and 55.2%, respectively, in F1 and F2 fractions), the results attempted from ultrasonic extraction for all metals were reasonably comparable with those obtained using the conventional BCR procedure. The optimized procedure was found to be precise (typically R.S.D.

Effect of competition of major cations, Ca2+, Mg2+, and trace metals, Cu2+, Ni2+ and Zn2+, on the stability of the Pb(II)-fulvic acid (FA) complexes in model systems at constant pH and ionic strength was investigated by square-wave anodic stripping voltammetry (SWASV). The results show that the trace metals compete with the target trace metal, Pb(II), for binding sites of the FA even when they are present in the same concentration as that of Pb(II), whereas the major cations compete with Pb(II) only when they are present in massive excess.

Publications on the binding characteristics of metals with humic acid (HA) are sparse. Here we investigated the release of nickel from Ni(II)–HA complexes using model solutions of three different [Ni(II)]/[HA] mole ratios at three different pH values; we also compared the results with those of [Ni(II)]/[FA] complexes from previous work in this laboratory. Ligand exchange kinetics using the competing ligand exchange method (CLEM) were studied using two different techniques: graphite furnace atomic absorption spectrometry (GFAAS) with Chelex 100 resin as the competing ligand, and adsorptive cathodic stripping voltammetry (AdCSV) with dimethylglyoxime as the competing ligand to measure the rate of dissociation of Ni(II)–HA complexes. The results of the kinetic studies showed that as the [Ni(II)]/[HA] mole ratio was decreased, the rate of dissociation of Ni(II)–HA complexes decreased, and the proportion of free Ni2+ ions plus very labile nickel complexes decreased while the proportion of the less labile kinetically distinguishable components increased. Generally, the rate of dissociation of Ni(II)–HA complexes was slower than that of Ni(II)–FA complexes. Studies on the validity of the kinetic model showed that the concentrations of chemical species varied in a reasonable way with pH and the [Ni(II)]/[HA] mole ratios, indicating that the kinetically distinguishable components have chemical significance and the kinetic model is valid.

The effectiveness of NH 3 gas used in a Dynamic Reaction Cell (DRC) in reducing or eliminating carbon-based polyatomic ions in electrothermal vaporization (ETV) inductively coupled plasma mass spectrometry is reported. Ammonia gas was found effective in reducing interfering polyatomic ions on both Cr and Mg isotope ions. The use of NH 3 as a reaction gas for the reduction of polyatomic ion interferences on Si was not fully successful. However, the LODs for 28 Si + and 29 Si + were greatly improved over conventional ICP-MS. Ammonia was found to be unsuitable as a reaction gas for the determination of 30 Si + . Results of signal to background studies indicate that the experimental conditions required to optimize the DRC were close for solution nebulization and ETV for Cr only. For Mg and Si, different optimization conditions were required.

Adsorptive cathodic stripping voltammetry (AdCSV) in conjunction with the competing ligand-exchange method (CLEM) was investigated as a tool for measuring dissociation rate coefficients of nickel complexes in model systems. Dimethylglyoxime (DMG) was used as the competing ligand. Citric acid (CA) and a well-characterized fulvic acid (FA) were used as model ligands. The rate coefficients were calculated, and the consistency of equilibrium and kinetic data was discussed. The contributions of the disjunctive pathway (proceeding by the dissociation of the initial complex) and the adjunctive pathway (proceeding by the formation of an intermediate complex as a result of direct attack of the competing ligand on the initial complex) on the overall reactions were investigated. The reactions of Ni-CA or Ni-FA complexes with DMG were demonstrated to proceed by both disjunctive and adjunctive pathways. The predominant pathway for the overall reaction depends on the nickel-to-initial ligand and the DMG-to-initial ligand ratios. The reactions follow predominantly the disjunctive pathway for [DMG] > or = 3 mM and Ni-to-dissolved organic carbon (DOC) ratios greater than 10 nM Ni 2+/g of DOC. Since free nickel ion in freshwaters is reported to be toxic, its rate and pathway of formation are of environmental concern.

The speciation of lead and cadmium in model solutions of a well characterized fulvic acid (FA), Laurentian FA, was investigated by anodic stripping voltammetry (ASV) using a thin mercury film-rotating disk electrode (TMF-RDE) and a Nafion-coated TMF-RDE. Pseudopolarograms were fitted to a model that accounted for differences in the diffusion coefficients between the free metal ion, M, and the metal complexes, ML, and the heterogeneity of naturally-occurring organic complexants, L, such as fulvic acid. The pseudopolarograms were used for each metal system to determine the differential equilibrium function which is independent of the experimental conditions and allows the stability constants for other metal loading conditions to be predicted. The experiments were done using linear-scan anodic stripping voltammetry (LSASV), differential pulse anodic stripping voltammetry (DPASV), and square wave anodic stripping voltammetry (SWASV) with an uncoated TMF-RDE and a Nafion-coated thin mercury film-rotating disk electrode (NCTMF-RDE). The NCTMF-RDE was investigated to determine its usefulness in preventing adsorption of surface-active organic complexants such as fulvic acid on the mercury electrode surface. LSASV was found to be the least susceptible to adsorption. DPASV was affected by adsorption in the lead-FA model solutions, and SWASV was strongly affected by adsorption in both the lead-FA model solutions and the cadmium-FA model solutions. The Nafion-coated TMF-RDE did not prevent adsorption when DPASV or SWASV was used. However, the results suggest that the Nafion-coated TMF-RDE may be useful in preventing adsorption when LSASV is used.

Competition of Ca(II) and Mg(II) with Ni(II) ions for binding sites of a well-characterized fulvic acid (FA) in model solutions at constant pH and ionic strength was investigated. The Competing Ligand Exchange Method with Chelex-100 and dimethyl glyoxime as the competing ligands was employed to measure the rate of free Ni 2+ ion release using graphite furnace atomic absorption spectrometry and adsorptive cathodic stripping voltammetry, respectively. The Windermere Humic Aqueous Model was used to predict the effect of competition of Ca(II) and Mg(II) on the binding of Ni(II) by the FA. The results show that the presence of high concentrations of Ca(II) and Mg(II) in model solutions has considerable effects on the binding of Ni(II) by the FA. Since the concentrations of Ca(II) and Mg(II) used are 4 orders of magnitude higher than those of Ni(II), Ca(II) and Mg(II) can outcompete Ni(II) for sites where electrostatic interactions dominate, resulting in Ni(II) forming weak Ni(II)-FA complexes that are labile. The significance is that in freshwaters containing humic substances and trace quantities of nickel and major cations, Ca 2+ and Mg 2+ , the competition of Ca 2+ and Mg 2+ with Ni 2+ for binding sites of humic substances produces weak Ni(II)-humate complexes that are labile, releasing free Ni 2+ ions.

The stability of nickel, lead, copper, cadmium, aluminium and zinc in the dissolved phase of environmental aqueous samples stored in common containers made of various materials was investigated. The samples were Rideau River surface water, rainwater and snow collected at Carleton University, Ottawa, Canada, and had concentrations of the above metals ranging from 0.5 to 90 ng l −1 , and the samples were not acidified. The container materials studied were high-density polyethylene (HDPE), polypropylene (PP) and Teflon. The rate and the extent of metal loss were dependent on the container material, and the metal. Significant losses were observed in both polyethylene and PP containers even over periods as short as 30 min. The time taken for the concentration of the metals in the dissolved phase to be reduced to half was in the high-density polyethylene containers: 5, 15, and 20 min, for lead, copper and cadmium, respectively. With PP containers, only 15% lead, 25% copper, and 20% cadmium were lost in 2 h of storage. Teflon containers show no loss of dissolved metals from aqueous environmental samples over periods of 24 h, and hence, Teflon is the most suitable container material for the storage of environmental aqueous samples for trace metals for periods up to 24 h. The loss was the same for all environmental aqueous samples, river water, rainwater and snowmelt. This study shows the importance of the container material in preserving the sample integrity of environmental aqueous samples. Dissolved zinc was found to be stable in all the container materials studied. This aspect needs further experimental verification before any generalization is justified.

The kinetics of dissociation of Ni(II), Pb(II), Cu(II), and Cd(II)–fulvic acid (FA, Armadale), and Al(III)–FA (Suwannee River) complexes in aqueous model solutions was studied by the competing ligand exchange method (CLEM). Chelex-100 cation exchange resin was used as the competing ligand and inductively-coupled plasma mass spectrometry (ICP-MS) or graphite furnace atomic absorption spectrometry (GFAAS) was used to determine the rate of dissociation of the metal–FA complexes in the model solutions. At low metal concentrations and at very low [metal]/[FA] mole ratios, the metals formed inert complexes (dissociation rate coefficient k d ≈ 10 −5 s −1 ) with the FAs. The percentage of inert complexes increased as the [metal]/[FA] mole ratio was decreased at a constant concentration of the metal. The percentage of labile metal–FA complexes (dissociation rate coefficient k d ≈ 10 −2 –10 −3 s −1 ) increased as the [metal]/[FA] mole ratio in the model solutions was increased. The results were similar for all the metals studied. The two well-characterized FAs showed similar behavior despite their marked differences in the binding capacity and in the source and nature of the two FAs — the Armadale FA is pedogenic, and the Suwannee River FA is aquogenic. The results have special significance for the natural environment in which potentially toxic metals are often present at trace levels. In such a situation, experiments at the environmentally relevant [metal]/[FA] mole ratios are necessary to determine the effect of the [metal]/[FA] mole ratios on dissociation of metal–FA complexes and release of metal–aquo complexes which are reported to be toxic.

Competitive ligand exchange/adsorptive cathodic stripping voltammetry (CLE/AdCSV) using rotating disk electrode voltammetry/square wave voltammetry (RDEV/SWV) has been developed and applied to the kinetic speciation of nickel in aqueous environmental samples containing heterogeneous, macromolecular, organic complexants. Dissociation rate coefficients were obtained for nickel complexes in nitrilotriacetic acid (NTA) model solutions, model solutions of a well-characterized fulvic acid (Armadale fulvic acid) and Rideau river surface water (RRSW). The results demonstrated that the dissociation of nickel complexes formed by organic complexants was slow in comparison with the rate of formation of the Ni(DMG)2 complex. Two kinetically distinguishable components were observed in the NTA model solutions: the first with dissociation rate coefficient >10−3 s−1, and the second with a dissociation rate coefficient ≈10−5 s−1. Nickel complexes of the Armadale FA in the model solution yielded two kinetically distinguishable nickel complexes, including an inert component that did not dissociate within the time scale of the experiment. The proportion of the inert component increased as the [FA] to [Ni] mole ratio was increased. The nickel complexes in the RRSW sample yielded one kinetically distinguishable component: an extremely slowly-dissociating component with a first-order dissociation rate coefficient ≈10−6 s−1. The results are in agreement with the earlier results obtained by our laboratory on the lability/inertness of the Ni–FA complexes formed with the Armadale FA and studied by the competing ligand exchange method (CLEM) using Chelex 100 as the competing ligand and inductively-coupled plasma – mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS) for measurement of the kinetics of metal complex dissociation.

Competitive binding of Cu2+, Co2+ and Ni2+ ions by naturally-occurring organic complexants in the Rideau River surface water (RRSW) samples has been investigated employing the competing ligand exchange method (CLEM). It is well known that the reaction rate between a metal ion and a ligand is dependent on the rate of exchange of the coordinated water, which varies greatly for metals, being 3×104 s−1 for Ni2+ ion, 1×109 s−1 for Cu2+ ion and 2×106 s−1 for Co2+ ion. Naturally-occurring, heterogeneous, organic complexants in freshwaters are mainly humic substances, which are polyfunctional, and are ubiquitous in freshwaters and constitute ∼70–90% of the dissolved organic carbon. They have minor (∼1–10%) strong binding sites and major (∼99–90%) weak binding sites. The above metals first occupy strong binding sites and after all the strong binding sites are occupied, the remaining metals are bound to the weak binding sites of the organic complexants. Since the RRSW contains the above metals in concentrations below their limits of quantification by graphite furnace atomic absorption spectrometry (GFAAS), the RRSW samples have been spiked with various concentrations of Ni(II), Cu(II), and Co(II). In CLEM, a cation-exchange resin Chelex-100 has been used as the competing ligand, and GFAAS has been employed for monitoring the rate of uptake of the metals by Chelex-100. The results have revealed that in the absence of Cu(II) and Co(II), Ni(II) occupies strong binding sites of the naturally-occurring organic complexants, forming strong complexes, which are inert. When Cu(II) and Co(II) are present in sufficient concentrations, they occupy all the strong binding sites, with the result that Ni(II) binds to the weak binding sites, forming weak complexes, which are labile. The lability of the nickel complexes in the presence of Cu(II) and Co(II) is thus the result of successful competition of Cu(II) and Co(II) with Ni(II) for strong binding sites of the organic complexants (humic substances). The lability of nickel-complexes is enhanced more by copper than by cobalt. The environmental significance of this work for freshwaters is that even at relatively low nickel loadings, the metals usually associated with nickel in nickel ores, such as copper and cobalt, may successfully compete with nickel for strong binding sites of the naturally-occurring organic complexants in freshwaters with the consequence that nickel may exist as free nickel ions i.e. Ni(II)–aquo ions, which are reported to be toxic.

The competitive binding of Cu(II), Co(II) and Ni(II) ions by a well-characterized fulvic acid (FA) in model aqueous solutions has been investigated by employing the competing ligand exchange method (CLEM) with Chelex-100 as the competing ligand. The reaction rate between a metal ion and a ligand is dependent on the rate of exchange of the coordinated water, which varies greatly for the above metals. Fulvic acid is a polyfunctional, polyelectrolytical, physically-heterogeneous, organic complexant having binding sites that can be roughly classified into two categories: minor (∼1–10%), strong sites, and major (∼99–90%), weak sites. The strong binding sites are first occupied, and after all the strong binding sites are occupied, the weak binding sites are occupied. Experiments have been done using model aqueous solutions containing various concentrations of Cu, Co and Ni, and the above well-characterized FA. Graphite furnace atomic absorption spectrometry and inductively-coupled plasma mass spectrometry were employed to monitor the rate of uptake of the metals by Chelex-100. The above metals, in the metals/FA mole ratios used in this study, have been found to compete with one another for the relatively small number of strong binding sites of the FA, and Cu(II) and Co(II) which have much greater rate constant for water exchange than that of Ni(II) win the competition over Ni(II). In the absence of Cu(II) and Co(II), the strong binding sites of the FA are occupied by Ni(II), forming strong complexes, which are inert, whereas, in the presence of Cu(II) and Co(II), the strong binding sites of the FA are occupied by Cu(II); Co(II), Ni(II), and the remaining Cu(II) occupy the weak binding sites of the FA, forming weak complexes, which are labile. The enhanced lability of the Ni–FA complexes in the presence of Cu(II) and Co(II) indicates that Cu(II) and Co(II) successfully compete with Ni(II) for the strong binding sites of the FA.

A shadow spectral digital imaging technique (SSDI) with charge coupled device (CCD) camera detection was used to investigate the spatial and temporal distribution of condensation clouds of analyte species generated in a graphite furnace during the atomization of 5–40-μg masses of metals. Complex, non-uniform structures of aerosol species located away from both the graphite tube axis and walls are prevalent. Species giving rise to observed signals are likely clusters of metals in the case of Ag, Au and Pd, and oxide aerosols for elements such as Al, Ca and Mg. Source scatter often arises during the atomization of relatively large masses of analytes (or during the atomization of real samples containing high concentrations of concomitant matrix species) in the graphite furnace due to such aerosol formation. The SSDI technique is an extremely useful aid to the elucidation of this phenomenon and imaging at several wavelengths using both line and continuum sources in combination with (thermal, incandescent) emission from these structures permits a more complete picture to be developed.

Reported is a method for the removal of silica for the direct analysis of solid geological samples high in silica content using slurry sampling electrothermal vaporization-inductively coupled plasma-mass spectrometry (ETV-ICP-MS). The ETV-ICP-MS vaporization curve for SiO2, sampled as a slurry, is reported for temperatures ranging from 810–2600 °C. This curve showed that silica was completely vaporized at a temperature of 2200 °C. The effect of using HF as a chemical modifier to remove silica as the tetrafluoride was studied. It was found that HF could completely remove any Si attributed to silica if sufficient modifier were added and an adequate reaction time allowed. At reaction hold times that were less than optimal, two Si signals were observed. The first signal, which appears at an earlier time and at a temperature less than 480 °C, is attributed to the volatilization of silicon tetrafluoride. The second signal, which appears at a later time and at a temperature of about 2500 °C, is attributed to the vaporization of residual unreacted SiO2 remaining in the graphite tube, or to the vaporization of a mixture of SiO2 and SiC. 20 µl of 50% HF is effective in completely removing 0.125 µg of SiO2. No adverse effects including corrosive degradation of the graphite tube were observed over the lifetime of the tube, which exceeded 200 firings. Hydrofluoric acid chemical modifier was successful in removing virtually all the silica content in natural silicate standard reference materials.

Trace amounts of phosphorus have been determined in high purity iron using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). The iron matrix was largely removed using solvent extraction with 4-methyl-2-pentanone. Zirconium was used as a chemical modifier to avoid interference arising from the residual iron present after solvent extraction. The use of Zr modifier did not result in P signal suppression as was observed when Ni and La were used as chemical modifiers. External calibration with aqueous standards yielded results in good agreement with reference values. The detection limit achieved using this method was 0.008 ppm P in iron.

A method for the analysis of exponential decay curves involving several kinetic components has been evaluated using simulated data. The method was originally developed for determination of fluorescence lifetimes and is applied here to data similar to those obtained in the measurement of rates of dissociation of metal–fulvic acid complexes in aqueous solutions. The method allows for a distribution of rate constants for dissociation of complexes instead of the single value for each complex obtained from the analysis used in previous studies from this laboratory. The signal-to-noise ratio of the data was a crucial factor in the distribution of the rate constants recovered from the analysis. Complexes with rate constants for dissociation differing by a factor of five were easily recovered, but when the difference was only a factor of two the resolution was not achieved even with a low level of noise. These tests were made with equal concentrations of each kinetic component. When the concentration of one kinetic component was reduced by a factor of 10, this species was not recovered in the analysis. These results clearly show the limits of resolution for individual kinetic components and the uncertainty expected in the values of the rate constants obtained by statistical analysis.

Rotating disk electrode voltammetry (RDEV) in conjunction with anodic stripping voltammetry (ASV) with a thin mercury film electrode (TMFE) or with a Nafion-coated thin mercury film electrode (NCTMFE) has been evaluated for the direct determination (i.e., without preconcentration) of lead and cadmium speciation in aqueous solutions containing dissolved organic matter. The RDEV technique has been used to estimate dissociation rate constants and diffusion coefficients; pseudopolarograms have indicated the identity of the metal complexes undergoing electrode reductions at the corresponding plateaus of the pseudopolarograms in a number of model solutions containing Cd or Pb and known amounts of fulvic acid. It has been found that the effect of dissolved organic material is measurable when the concentrations of fulvic acid are equal to or less than 20 μg/mL (which is below the concentration of naturally occurring dissolved organic carbon in most freshwaters). The effective electrode surface area has been found to be considerably less than the geometric surface area, and if this fact is not explicitly taken into consideration, the result would be an erroneous estimation of dissociation rate constants and diffusion coefficients. Pseudopolarograms of aqueous samples containing Cd or Pb and fulvic acid and samples of Rideau river surface water clearly show that NCTMFEs effectively block the transport of large inert metal-FA complexes to the electrode surface, resulting in interference-free determination, and giving well-defined pseudopolarograms, and yet do not hinder the transport of small metal-FA complexes to the electrode surface. It is concluded that RDEV/ASV offers promise of being a valuable technique for determining chemical speciation of lead and cadmium in river surface waters.

The mechanisms by which the platinum group elements (PGEs) are vaporized in the graphite furnace have been investigated using electrothermal vaporization-inductively coupled plasma-mass spectrometry (ETV-ICP-MS). The results suggest that live of these elements (Ru, Rh, Pd, Ir and Pt) are reduced to their metallic state in the graphite furnace and then vaporized by direct sublimation of the metal. For Os, the vaporization mechanism is different. In the presence of HNO3, two distinct vaporization processes are observed. Volatile oxides of Os are released at low temperatures, but some of this oxide is reduced to relatively involatile Os metal which is then vaporized when the temperature is increased above 2000°C. The addition of TeCl2 chemical modifier was found to have minimal effect on the vaporization mechanism and sensitivity for determination for five of the PGEs. For Os, however, the analytical sensitivity and limit of detection was improved when Te modifier was used in conjunction with a lower vaporization temperature of 1400°C. Optimum conditions for the determination of the PGEs by ETV-ICP-MS are reported, along with their absolute limits of detection; these range from 0.015 pg for Ir to 0.25 pg for Os.

The spectral interference on 31P+ from the 14N16O1H+ polyatomic ion was essentially eliminated using electrothermal vaporization sample introduction for ICP mass spectrometry (ETV-ICP-MS). Vaporization of P from an electrographite surface stabilized P to higher vaporization temperatures when compared to pyrolytic graphite but resulted in high background signals due to memory effects. The thermal vaporization characteristics of (NH4)2HPO4, H3PO4, Na2HPO4, K2HPO4 and Ca(H2PO4)2.H20 were investigated. Most P compounds undergo thermal decomposition as the graphite tube is heated and are vaporized as metaphosphates. Iron is a common matrix element in geological materials and many finished products such as steels. The presence of 1 μg of Fe can cause suppression of the P signal. This interference is most pronounced at high graphite tube heating rates. Nickel, La and Zr were used as chemical modifiers in order to stabilize P to higher vaporization temperatures through compound formation allowing for the removal of matrix components prior to the volatilization of P. Lanthanum and P when vaporized together results in the formation of a thermally stable P species, most likely LaP. As a modifier, however La is not suitable due to the high background signal (memory effect) produced when vaporized especially on an electrographite surface. Although Ni is effective in thermally stabilizing P, large quantities of the metal are co-vaporized with P resulting in analyte signal suppression. Zirconium was found to be the best modifier for removing the interference produced from the presence of an iron matrix and could be added in large amounts without itself causing P signal suppression. An absolute detection limit of 4 pg was obtained for P vaporized in the presence of 2 μg of zirconium.

Reported are the mechanism of vaporization and optimum experimental conditions for the determination of Ra and other alkaline earth elements (Be, Mg, Ca, Sr and Ba) by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). Calculated and published data along with new experimental results suggest that these elements are vaporized from the surface of the graphite tube as oxides. These oxides are then transported to the argon plasma where dissociation and ionization take place. Appearance temperatures and maximum pyrolysis temperatures obtained experimentally generally agree with values obtained using graphite furnace atomic absorption spectrometry (GFAAS). For Ra, the optimum pyrolysis and vaporization temperatures were 1400 and 2500 °C, respectively. Diluted (1:500) seawater, used as a physical carrier, was effective in improving sensitivity when used in small quantities, but caused significant suppression of the Ra signal when the analyte was co-vaporized with quantities of salt in excess of 40 µg. An absolute limit of detection of 1.7 fg was obtained corresponding to 34 fg ml -1 in a 50 µl sample.

An improved experimental method for the chemical speciation and study of metal ion reactions with soils and soil components is reported. The method that combines on-line HPLC micro extraction with off-line microfiltration can avoid the hysteresis problem, identify relevant free and bound chemical species, and produce mechanisms constants. The method is demonstrated with Zn(II) and Cd(II) reactions with a soil from a St. Lawrence River watershed.

Applications of a charge-coupled device (CCD) imaging spectrometer as a detection system for the determination of two-dimensional images of transient atomization events in a furnace atomization plasma emission spectrometric (FAPES) source are reviewed. Spectrally, spatially and temporally resolved images of the emission from analyte species (Ag(I), Ca(I) and Ca(II)) and plasma support gas (He(I)) in a 50 W He rf plasma are presented and the advantages of using a CCD camera system for fundamental characterization of vaporization, atomization, and ionization processes in the FAPES source are discussed. The limitations associated with the current system — insensitivity and limited spectral resolution — are highlighted and means of overcoming them are suggested.

Rotating disk electrode (RDE) voltammetry with a mercury thin-film electrode on a glassy carbon substrate combined with anodic stripping voltammetry (ASV) using square-wave, differential-pulse, and staircase waveforms was applied to direct determination of Cu(II) and Pb(II) speciation in model solutions of Cu(II)−nitrilotriacetic acid and Pb(II)−nitrilotriacetic acid complexes and in snow samples. The dissociation rate constants of Cu(II) and Pb(II) complexes measured by square-wave voltammetry, differential-pulse voltammetry, and staircase voltammetry were found to be similar. Of the above three waveforms examined for their suitability for the study of Cu(II) and Pb(II) complexes in the above model solutions and in snow samples, staircase voltammetry gave the most satisfactory estimates of dissociation rate constants and diffusion coefficients of the metal complexes. However, the analytical sensitivity of square-wave voltammetry is 2 orders of magnitude higher than that of staircase voltammetry. Such hig...

Direct determination of selenium on or in atmospheric particulate matter (APM) has been achieved using an integrated filtration and analysis system developed in our laboratories. The filtration (sampling) and analysis system consists of a porous electrographite plate which is used initially for the purpose of collecting APM and subsequently as a probe in graphite probe furnace atomic absorption spectrometry. Selenium produced a double peak when it was atomized from such an electrographite probe. Palladium nitrate+magnesium nitrate, as a mixed chemical modifier or ascorbic acid as a chemical modifier, eliminated the double peak. The addition of the chemical modifier(s) also removed the unpredictable changes in the peak-height and the peak-area absorbance which occurred from one atomization cycle to the next if the chemical modifier was not used. Precision of 5% RSD (peak-area absorbance) was obtained for an aqueous solution of selenium standard containing 1.25 ng of selenium with palladium nitrate+magnesium nitrate mixed chemical modifier, or ascorbic acid chemical modifer. The characteristic masses and the limits of detection for the aqueous solution of selenium standard with palladium nitrate+magnesium nitrate mixed chemical modifier are 27 and 41 pg (peak-area absorbance), respectively, and with ascorbic acid chemial modifier are 29 and 36 pg, respectively (peak-area absorbance). The results of analysis of the NIST (formerly National Bureau of Standards) Standard Reference Material No. 1648, Urban Particulate Matter, for selenium with palladium nitrate+magnesium nitrate mixed chemical modifier gave a recovery of 92%, and a precision of 10% RSD, and characteristic mass and the limit of detection of 20 and 37 pg, respectively.

The mechanism of aluminium spike formation and dissipation of aluminium atoms in electrothermal atomization absorption spectrometry has been investigated using two different approaches. The first approach employs a graphite electrothermal atomizer coupled to an inductively coupled plasma mass spectrometer (ICP-MS) in a configuration that allows simultaneous measurement of atomic, or molecular, absorption signals and mass spectrometric signals. Aluminium sub-oxide (AlO and Al 2 O) and CO(g) spikes in ICP-MS are correlated with the appearance of both Al atom spikes and Al-containing molecule spikes in absorption spectrometry. The aluminium carbide (AlC 2 ) signal in ICP-MS is not coincident with the appearance of either Al atom spikes or Al-containing molecule spikes in absorption spectrometry. The second approach uses two different imaging systems, i.e. shadow spectral filming (SSF) and shadow spectral digital imaging (SSDI), to provide temporally and spatially resolved absorption profiles of Al atoms and Al-containing molecules during Al spike formation and dissipation. The transverse cross-sectional distribution of Al atoms and of Al-containing molecules in the graphite furnace are complementary to one another for both wall and platform atomization. The highest concentration of Al atoms is near the graphite surface, whereas the highest concentration of Al-containing molecular species is at the centre of the graphite tube. The Al-containing molecules observed in both wall and platform atomization consist of both gaseous Al-molecules and a non-uniformly distributed cloud of finely dispersed Al 2 O 3 (s,1) particles. A mechanism of formation that is consistent with the above experimental observations is presented. It is proposed that Al atom spikes are formed from gaseous Al 2 O precursors and that this reaction is triggered by the formation of a molten, condensed-phase Al 4 C 3 melt.

A computer model has been developed that allows the calculation of the three-dimensional distributions of free atoms and condensed particles inside tube-type electrothermal atomizers. This model is a numerical solution of the three-dimensional diffusion equation written with the appropriate boundary conditions. The proposed model takes the following geometrical and physical factors into account: real tube geometry of an atomizer provided with a dosing hole, analyte vaporization, the size of the region occupied by the sample prior to atomization, three-dimensional analyte diffusion in a non-isothermal furnace environment, and its gas phase (homogeneous) condensation at the cooler parts of the atomizer. The physical processes that take place in electrothermal atomizers are common to all analytes and are the background against which chemical processes take place. Silver was used as the test element for modelling because Ag is a relatively inert element in electrothermal atomization, for which physical processes can be expected to dominate over chemical processes. Imaged representations of the calculated three-dimensional distributions of free Ag atoms and condensed Ag micro-droplets within Perkin-Elmer HGA-type atomizers are given. The imaged representations show that, even for a relatively inert element such as silver, the distribution of atoms in electrothermal atomizers is quite non-homogeneous.

The mechanism of vaporization of yttrium and the rare earth elements (REEs) has been studied using graphite furnace atomic absorption spectrometry (GFAAS) and inductively-coupled plasma mass spectrometry (ICP-MS). The appearance temperatures for Y and the REEs obtained by GFAAS were generally identical to the appearance temperatures obtained using ETV-ICP-MS. At lower temperatures, Y and the REEs are predominantly vaporized in atomic form or as oxides, while at temperatures above 2500°C, the elements are vaporized as oxides and/or carbides. This accounts for the very high sensitivity of ETV-ICP-MS compared to GFAAS for the determination of these elements. Absolute limits of detection for Y and all of the REEs using ETV-ICP-MS ranged from 0.002 pg for Tm to 0.2 pg for Ce. The use of freon as a chemical modifier was effective in controlling analyte carbide formation and reducing memory effects.

In an attempt to understand the implications of using glow discharge atomizers in atomic absorption spectrometry (AAS), line profiles and kinetic (Doppler) temperatures were measured in commercial hollow cathode lamps and a laboratory-constructed, jet-assisted dc glow discharge atomizer using a high-resolution Bomem Fourier transform spectrometer. Line profiles were measured in the hollow cathode lamps as current was increased from 1 to 30 mA for three resonance atomic lines (Mg 285.21 nm, Al 308.22 nm, and Pb 283.31 nm) having distinctly different hyperfine structure. Although the Al 308.22-nm line was largely unaffected by self-absorption as the lamp current was increased, the Pb 283.31-nm and Mg 285.21-nm lines exhibited pronounced self-absorption broadening at relatively low lamp currents. Kinetic temperatures in the hollow cathode lamps ranged from 320 ± 20 K at low lamp currents to 840 ± 20 K at high currents. With the use of the Ar(I) 415.86-nm line from the argon discharge gas as a thermometric species, kinetic temperatures of 460 ± 20 K to 620 ± 20 K were measured in the glow discharge atomizer under typical analytical operating conditions. These low atomizer gas temperatures imply that the sensitivity and linear dynamic range of analytical calibration curves will be more strongly affected by the lamp current of the primary radiation source and the spectral properties of the analysis line in glow discharge AAS than in flame or furnace AAS, and that operation at low lamp current is essential for optimal analytical performance. The degrees to which the linear dynamic range and the slope of the analytical calibration curve would be affected by the hyperfine structure of the analysis line, the extent of self-absorption in the hollow cathode lamp, the hollow cathode kinetic temperature, and the glow discharge kinetic temperature are considered separately for each atomic line investigated. The kinetic temperatures in the hollow cathode lamps and the glow discharge atomizer were so close that it was possible to obtain absorption line profiles for the three resonance atomic lines in the glow discharge atomizer with the use of hollow cathode lamps as primary radiation sources, i.e., without the necessity of using a continuum source of radiation.

The mechanism of vaporization and atomization of U in a graphite tube electrothermal vaporizer was studied using graphite furnace atomic absorption spectrometry (GFAAS) and electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). Graphite furnace AAS studies indicate U atoms are formed at temperatures above 2400°C. Using ETV-ICP-MS, an appearance temperature of 1100°C was obtained indicating that some U vaporizes as U oxide. Although U carbides form at temperatures above 2000°C, ETV-ICP-MS studies show that they do not vaporize until 2600°C. In the temperature range between 2200°C and 2600°C, U atoms in GFAAS are likely formed by thermal dissociation of U oxide, whereas at higher temperatures, U atoms are formed via thermal dissociation of U carbide. The origin of U signal suppression in ETV-ICP-MS by NaCl was also investigated. At temperatures above 2000°C, signal suppression may be caused by the accelerated rate of formation of carbide species while at temperatures below 2000°C, the presence of NaCl may cause intercalation of the U in the graphite layers resulting in partial retention of U during the vaporization step. The use of 0.3% freon-23 (CHF3) mixed with the argon carrier gas was effective in preventing the intercalation of U in graphite and U carbide formation at 2700°C.

A method is described for the trace analysis of single zircons for Y, La, Ce, Nd, Sm, Yb, Th and U by electrothermal vaporisation-inductively coupled plasma-mass spectrometry (ETV-ICP-MS). Zircons are cleaned by an abrasion process and dissolved in HNO 3 and HF in a pressure vessel. Following conversion to chlorides and evaporation to dryness, the dissolved zircon residue is re-dissolved in 500 μl of high-purity 2.5 M HNO 3 . Analyte concentrations were measured with a precision of ∼ ±6%. Agreement between found and reference values for BCS- 388 zircon reference material was excellent. Limits of detection for the analysis of a 10-μg zircon were 150 ng g −1 for Y, 90 ng g −1 for La, 115 ng g −1 for Ce, 65 ng g −1 for Nd,180 ng g −1 for Sm, 22 ng g −1 for Yb, 190 ng g −1 for Th and 80 ng g −1 for U. Absolute limits of detection for a 10-μl solution aliquot ranged from 4 to 36 fg (10 −15 g). Zircon solutions were analysed using external calibration by aqueous standards with the addition of a mixed component carrier (NASS-3 open ocean seawater). No matrix or spectroscopic interferences were observed from major-element matrix components. The analysis of a typical set of single zircons gave concentration levels well above the limit of detection for all elements except La.

Kinetic studies of uptake of metal ions by the Chelex batch technique were made to determine Cd, Cu and Pb speciation in model solutions, a snow sample and a river surface water sample. Inductively-coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS) were used for direct determination of these metals. ICP-MS with the solution nebulization technique minimized contamination and adsorption problems involved in the discrete sampling technique of GFAAS, and hence, gave more precise and accurate results. Also, ICP-MS allowed collection of many more data points than GFAAS and was able to resolve components with similar rates of dissociation, which could not always be resolved by GFAAS with its discrete sampling technique. ICP-MS was therefore preferable to GFAAS for kinetic studies of metal speciation. The kinetic data were analyzed by the iterative deconvolution method. The applicability of the Chelex batch technique to metal speciation was validated by analysis of model solutions containing these metal ions with or without EDTA, NTA and fulvic acid. Use of the Chelex batch technique for Cd, Cu and Pb speciation in snow and river surface water samples revealed a number of kinetically distinguishable components of these metals (as complexes) ranging from one to three, probably present as aquo ions or inorganic complexes in the snow sample, and bound to macromolecules/and or colloidal materials in the river surface water sample.

Kinetic studies of the rate of uptake of the metal ions Cd, Cu, and Pb by the Chelex batch technique have been made on model solutions containing the metal ions and the complexants EDTA, NTA, and fulvic acid. The metal ions were quantitated by inductively coupled plasma mass spectrometry, and the rates of uptake of the metal ions were analyzed by the iterative deconvolution method. In the presence of an excess of EDTA or NTA, all the metal ion was complexed with the chelating agent, forming a slowly dissociating complex. In the presence of fulvic acid, these metals formed strongly bound complexes with a range of slow dissociation rates. The results reveal the importance of [fulvic acid]/[metal ion] ratio and, hence, the extent of occupation of binding sites in fulvic acid (a polyfunctional complexes

Modifications to a commercial graphite furnace were made for its use as a sample introduction device with an inductively coupled plasma mass spectrometer (ICPMS) and to allow simultaneous measurement of the atomic absorption and mass spectrometric signals. The effect of the internal Ar carrier gas low, the total Ar carrier gas low, and the vaporization temperature on the integrated ion intensity for Ag was studied. An absolute limit of detection of 0.23 pg was obtained for Ag when vaporization took place from a graphite platform in the presence of sodium chloride chemical modifier. The utility of simultaneously measuring electrothermal atomization atomic absorption (ETAA) and ETV-ICP mass spectrometric signals was demonstrated by investigating the interference of MgCl 2 on the determination of Mn by ETAAS

The results of matrix interference studies using a commercially available cathodic sputtering atomizer for atomic absorption spectrometry are presented. Interferences have been found to result from disruption of the plasma chemistry, chemical reaction with the cathode substrate and changes in the spatial distribution of the solution residue on the cathode surface because of changes in the viscosity and the surface tension of the sample solution. The use of peak-area absorbance and the judicious choice of cathode material has been shown to eliminate some of the observed interferences.

Kinetic studies of chemical speciation by the Chelex-100 batch technique revealed aluminum is present both as an aquo ion and as simple complexes of inorganic ligands in snow, but probably bound to macromolecule complexants and/or colloidal substances in the Rideau River surface water. Two kinetically distinguishable components of aluminum having dissociation rate constants of 1.1 × 10−2, ≤ 5.4 × 10−4 s−1 and three kinetically distinguishable components of aluminum having dissociation rate constants of 5.5 × 10−3, 8.4 × 10−4, ≤6.3 × 10−5 s−1 were observed in snow and river surface water, respectively. One kinetically distinguishable component of zinc having a dissociation rate constant of 9.1 × 10−3 s−1, and three kinetically distinguishable components of zinc having dissociation rate constants of 8.5 × 10−3, 2.5 × 10−3, ≤ 6.0 × 10−5 s−1, were observed in snow and river surface water, respectively. Use of inductively-coupled plasma mass spectrometry (ICP-MS) with the solution nebulizer to follow the kinetics of the uptake of aluminum and zinc by the Chelex resin in the Chelex batch technique allowed collection of many more data points in the same time range than were obtainable by graphite platform furnace atomic absorption spectrometry (GFAAS) with an automatic sampler, with the result that ICP-MS had a greater ability to resolve labile complexes than GFAAS. ICP-MS is therefore preferable to GFAAS for kinetic studies of metal speciation in aqueous samples.

The vaporization and atomization of boron in the graphite furnace were investigated using both electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS). The results show that the majority of the boron is vaporized in molecular form and removed from the furnace at temperatures well below the appearance temperature of atomic boron. The effect of nickel nitrate chemical modifier on the vaporization of boron was also studied. The modifier is largely ineffective in preventing loss of boron from the graphite furnace prior to atomization. The extent of this preatomization loss, both in the presence and absence of the modifier, is reported. For the determination of boron by ETV-ICP-MS, the optimum sensitivity is obtained at a vaporization temperature of about 1800°C, i.e. well below the maximum possible vaporization temperature. This sensitivity is enhanced by the addition of the nickel modifier.

The graphical method and the iterative method for analysing kinetic data for metal speciation in waters are described. The graphical method involves successive subtractions of one component from the total concentration of the metal remaining, beginning with the slowest component. The iterative method uses nonlinear regression of the experimental data assuming different numbers of components to obtain the weighted residuals. The number of components which gives a minimum to the sum of squares of the weighted residuals represents the number of kinetically distinguishable components. The weighted residuals should also have a normal distribution throughout the course of the reaction. These methods were applied to simulated data for systems containing three components whose rate constants differed by a factor of two and for some cases by a factor of three. When the concentrations of each component were equal and the ratio of the rate constants equal to two, the values of the rate constants obtained by these analyses ranged from 2 to 19% of the assigned values, but the values for the initial concentrations were as much as 40% different from the assigned values. When the concentration of one component was altered the reliability of its recovered rate constant and initial concentration decreased. The advantage of the iterative method is that no prior knowledge of the number of components, rate constants and initial concentrations is required. It is demonstrated that both of these methods provide simple, reliable ways of analysing kinetic data for characterization of metal species in waters.

A scheme for metal speciation which combines physical characterization by size fractionation and chemical characterization by dissociation kinetics has been used to characterize trace metal species in a sample of rain water. The lability of the metal species in each size fraction of ultrafiltration was determined by differential pulse anodic stripping voltammetry and by ion-exchange with Chelex-100 resin, using both the column and the batch technique. Most of the Pb, Cd, Cu and Zn soluble species were ASV-labile and Chelex-labile, and fell in the small size fractions (

The vaporization properties of HCl and HNO3 under various furnace heating conditions were investigated. Drying-step temperatures of 140 °C (50 s) and pyrolysis-step temperatures of 400 °C (10 s) were effective in volatilizing most of the chloride from 10 µl of 1% v/v HCl, however, a small amount (40 ng) of acid was retained on the graphite even after pyrolysis at 400 °C. Under the same experimental conditions, HNO3 was completely volatilized from the graphite tube. The effect of a range of concentrations of HCl, HNO3, H2SO4 and H3PO4 on analyte signals was studied for Co, Cu, Ag, Cs, Pb, Bi and U. Analyte signals were enhanced by as much as a factor of two in the presence of 1% v/v HNO3 and H2SO4. Phosphoric acid suppressed analyte signals for Ag and Bi and the use of HCl resulted in relatively small changes in analyte sensitivity. The use of a pyrolysis step in the heating programme reduced the effects associated with acid matrices, but at the expense of signal intensity. A mixed modifier–carrier reduced the matrix effects associated with H2SO4 and H3PO4 and essentially eliminated them for HNO3 and HCl.

The mechanism of volatilization of tungsten from a graphite substrate has been investigated using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). Vaporization temperatures in the range 800–2700 °C were studied. In this temperature region two distinct vaporization processes occur, resulting in two separate ETV-ICP-MS peaks for tungsten. The earlier peak appears at temperatures as low as 850 °C and is attributed to the volatilization of tungsten oxide. At temperatures above 2500 °C a second peak appears when tungsten carbide is vaporized from the graphite surface. Results show that NaCl and NaF chemical modifiers are ineffective in preventing the formation of tungsten carbide. The signal-to-background ratio (S/N) for tungsten varies with vaporization temperature, with the optimum S/N and minimum limit of detection (0.51 pg) being obtained at vaporization temperatures around 1100 °C.