Scott N. Willie

Sequestration of volatile element hydrides by platinum group elements for graphite furnace atomic absorption

Abstract Efficient trapping of the volatile hydrides of As, Sb, Se, Bi and Sn on μg masses of Pd and other platinum group metals (PGM) reduced in the graphite furnace occurs at a relatively low temperature (200°C). Analytical figures of merit are improved over hydride trapping on the bare tube wall. Conditions are established for multielement sequestration. Absolute limits of detection (3σ) range between 8 pg (Se) and 43 pg (As). The catalytic reactivity of PGMs promotes low temperature deposition of the hydrides by dissociative chemisorption. Thermal desorption of all analytes from the PGMs is first order. Arrhenius energies were used to characterize all analyte-substrate interactions.

Acid digestion of marine samples for trace element analysis using microwave heating.

A commercial laboratory microwave-acid digestion system employing two types of closed vessel, (A) completely closed and (B) pressure-relief type, was evaluated for use in sample decomposition prior to the determination of trace elements in marine biological tissue and sediment samples. The decomposition procedure consists in acid digestion in Teflon PFA vessels (with an HNO3-HClO4 mixture for marine biological tissues and an HNO3-HF-HClO4 mixture for marine sediments) using microwave heating. Subsequent evaporation on a hot-plate was undertaken with the sediment material. The resulting solutions are analysed by flame and graphite furnace atomic absorption spectrometry and by inductively coupled plasma atomic emission spectrometry. Both vessels provide rapid and almost equally satisfactory results for sample dissolution and analysis. Vessel A was judged to be more convenient whereas vessel B is likely to be safer. The sample preparation time was approximately 30 min for the marine biological tissue and 3–4 h for the marine sediment samples (including subsequent evaporation time on a hot-plate following a 30-min microwave digestion).

Determination of transition and rare earth elements in seawater by flow injection inductively coupled plasma time-of-flight mass spectrometry ☆

Abstract A method is presented for the quantitation of trace elements and rare earth elements (REE) in seawater by inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry. On-line separation and preconcentration was achieved using a timed flow-injection (FI) system incorporating a column containing iminodiacetate-based resin. The procedure was validated for selected transition elements by analysis of certified seawater reference materials NASS-5 and CASS-4. Recoveries of the rare earth elements (REE) from seawater were between 96 and 101%. Limits of detection (3s) were generally in the 20–50-pg l−1 range with nominal precision of 5–6% R.S.D. (n=5) when processing 50-ml sample aliquots of seawater. Sample throughput was 5 h−1 for the REE determinations and 15 h−1 for the transition elements of interest.

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.

Concentration of trace metals from sea-water by complexation with 8-hydroxyquinoline and adsorption on C18-bonded silica gel

A reversed-phase liquid chromatographic technique based on a combination of multielement chelation by 8-hydroxyquinoline with subsequent adsorption on C(18)-bonded silica gel is described for the concentration of Cd, Zn, Cu, Ni, Co, Mn and Fe from sea-water. Enrichment factors of 50-100 are readily obtained following elution of the absorbate with methanol to provide a matrix-free concentrate suitable for graphite-furnace atomic-absorption analysis. Quantitative recovery of these elements from near-shore samples of sea-water is demonstrated and the accuracy and precision of the technique are discussed.

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.

Comparison of 8-quinolinol-bonded polymer supports for the preconcentration of trace metals from sea water

Abstract 8-Quinolinol, immobilized on cross-linked polyvinyl pyrrolidone, a macroreticular styrene—divinylbenzene (XE-305) or methylated polystyrene (Merrifield resin) substrates, was used for the preconcentration of ions of Cd, Zn, Pb, Cu, Fe, Mn, Ni, Co, and Cr from sea water prior to their measurement by electrothermal atomic absorption spectrometry. Optimal results were obtained when the XE-305 substrate was used. Except for chromium, recoveries of the above elements from sea water with this material averaged 100% (range 88–109%) with absolute blanks ranging between 0.1 ng (Cd) and 7 ng (Zn). Performance is demonstrated by quantitation of metal ions in open ocean water.

Determination of total mercury in biological tissues by flow injection cold vapour generation atomic absorption spectrometry following tetramethylammonium hydroxide digestion

A simple, rapid and reliable method was developed for the determination of total mercury in biological samples. Samples were solubilized using tetramethylammonium hydroxide (TMAH). The organically bound mercury was cleaved and converted to inorganic mercury by on-line addition of KMnO4. The decomposed mercury together with inorganic mercury originally present in samples was determined by flow injection cold vapour atomic absorption spectrometry after reduction to elemental mercury vapour using NaBH4. A sample throughput of 100 measurements per hour was achieved after a 30 min dissolution with TMAH. The relative standard deviation for 20 micrograms l-1 Hg was 1.3% (n = 11) and the limit of detection was 0.1 microgram l-1 (3 sigma). The proposed method was validated by the analysis of a suite of certified marine biological reference materials, DORM-2 (dogfish muscle), DOLT-2 (dogfish liver) and TORT-2 (lobster hepatopancreas), with calibration against simple HgII standards.

UV/spray chamber for generation of volatile photo-induced products having enhanced sample introduction efficiency

A combined spray chamber/UV photolysis unit is described which is shown to substantially enhance sample introduction efficiency for several elements in the presence of 1–5% concentrations of formic, acetic and propionic acids. Enhancement factors of 2–40-fold were achieved for Ag, As, Se, Sb, Hg, I, Bi, Pb and Sn when the aerosol field within the cyclonic chamber produced during conventional concentric nebulizer sample introduction was illuminated by an axially placed 6 W mercury pen lamp. UV photolysis of the organic acids likely initiates radical reactions, generating volatile analyte species.

Determination of trace elements in sea water by graphite-furnace atomic absorption spectrometry after preconcentration by tetrahydroborate reductive precipitation

A method is described for the preconcentration of 16 elements from coastal and deep ocean sea water based on their reductive precipitation by sodium tetrahydroborate. The enrichment factors obtained were sufficient to permit the analysis of a near-shore sea-water reference material (11 elements) and an open ocean sea-water reference material (9 elements). Recoveries from 900 ml of sea water ranged from 80 to 107% (100-ml sample for Mn) with absolute blanks between <1.0 ng (Se) and 20 ng (Cu). Estimated detection limits varied from 0.3 ng l −1 (Pb) to 19 ng l−1 (As) based on a 36-fold concentration of a 900-ml sample.