Ralph E. Sturgeon

Pre-concentration of trace metals from sea-water for determination by graphite-furnace atomic-absorption spectrometry☆

Determination of Cd, Zn, Pb, Cu, Fe, Mn, Co, Cr and Ni in coastal sea-water by graphite-furnace atomic-absorption spectrometry after preconcentration by solvent extraction and use of a chelating ion-exchange resin is described. Following the extraction of the pyrrolidine-N-carbodithioate and oxinate complexes into methyl isobutyl ketone, the trace metals are further preconcentrated by back-extraction into 1.5M nitric acid. Preconcentration on the chelating resin is effected by a combined column and batch technique, allowing greater preconcentration factors to be obtained. Provided samples are appropriately treated to release non-labile metal species prior to preconcentration, both methods yield comparable analytical results with respect to the mean concentrations determined as well as to mean relative standard deviations. Control and treatment of the analytical blank is also described.

Atomic spectrometric detection of hydride forming elements following in situ trapping within a graphite furnace

The historical development of in situ techniques in the graphite furnace based on chemical generation of hydride forming elements and mercury coupled with batch and flow injection sampling formats is presented. Detection via AAS, MIP-AES, ICP-MS and FANES is considered. The current state-of-the-art, including advantages and limitations of this approach, is discussed.

Solid phase microextraction as a tool for trace element speciation

Abstract Applications of solid phase microextraction (SPME) for trace element speciation are reviewed. Because of the relative novelty of the technique in the inorganic analytical field, the first part of this review provides a short overview of the principles of SPME operation; the second part describes typical SPME applications to elemental speciation. Volatile organometallic compounds can be collected by SPME from the sample headspace or liquid phase, directly or after derivatization. The usual separation method for the collected volatile species is gas chromatography. Non-volatile analyte species can be collected from the sample liquid phase and separated by liquid chromatography or capillary electrophoresis. Currently, most SPME applications in the inorganic field comprise analyte ethylation and headspace extraction followed by gas chromatographic separation of tin, lead and mercury species. The use of SPME for the study of equilibria in complex systems is also discussed and future roles of solid phase microextraction in the inorganic analytical field are raised.

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.

Applications of chemical vapor generation in non-tetrahydroborate media to analytical atomic spectrometry

Chemical vapor generation (CVG) using tetrahydroborate(III) remains the most popular and successful derivatization procedure enabling gaseous sample introduction into analytical atomic spectrometers that are routinely used for the determination of trace and ultratrace amounts of hydride-forming elements as well as Cd and Hg. The number of elements amenable to tetrahydroborate(III)-derivatization has recently been extensively enlarged. Despite its many obvious advantages, drawbacks remain, such as significant interferences from transition metals. Consequently, many alternative approaches have been developed to overcome these shortcomings and to further expand the suite of elements amenable to CVG for sample introduction. This article reviews these non-tetrahydroborate-based approaches, including photochemical vapor generation (photo-CVG), borane complexes CVG, alkylation based on Grignard reactions and derivatization with NaBEt4, cold vapor generation with SnCl2, halide generation, electrochemical hydride generation, oxide generation, and generation of volatile chelates. Special attention is given to two newly developed CVG approaches: photo-CVG and reduction in the presence of cyanoborohydrides.

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).

Headspace single-drop microextration for the detection of organotin compounds

The performance of single-drop microextraction (SDME), coupled with gas chromatography/mass spectrometry, was assessed for the determination of tributyltin compounds in water and solid samples. Experimental parameters impacting the performance of SDME, such as microextraction solvent and sampling and stirring time, were investigated. Analytical results obtained by SDME were compared with those generated by conventional solid phase microextraction (SPME) and liquid-liquid extraction (LLE) for the determination of TBT in PACS-2 sediment certified reference material (CRM).

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.

Determination of copper in environmental matrices following vapor generation.

Copper was determined in environmental matrices following generation, separation, and atomization of a volatile species formed by the merging of an acidified sample solution with an aqueous sodium tetrahydroborate solution at room temperature. The copper species, as yet unidentified, was phase separated in a conventional gas-liquid separator and directed via a stream of Ar carrier gas to an inductively coupled plasma atomic emission detection system. Optimum conditions for generation were investigated. The efficiency of generation/transfer was estimated to be 50%, and no interference from the presence of 1000 mg/L concentration of As, Cd, Co, Ni, Fe, Cr, Mn, Pb, Se, and Zn concomitants was evident. Simple aqueous standards were used for calibration purposes, and good agreement was obtained with certified values in the analysis of National Research Council of Canada marine sediment BCSS-1 and lobster hepatopancreas tissue TORT-1.

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.