Michael Foulkes

Methods for the determination and speciation of mercury in natural waters—A review

This review summarises current knowledge on Hg species and their distribution in the hydrosphere and gives typical concentration ranges in open ocean, coastal and estuarine waters, as well as in rivers, lakes, rain and ground waters. The importance of reliable methods for the determination of Hg species in natural waters and the analytical challenges associated with them are discussed. Approaches for sample collection and storage, pre-concentration, separation, and detection are critically compared. The review covers well established methods for total mercury determination and identifies new approaches that offer advantages such as ease of use and reduced risk of contamination. Pre-concentration and separation techniques for Hg speciation are divided into chromatographic and non-chromatographic methods. Derivatisation methods and the coupling of pre-concentration and/or separation methods to suitable detection techniques are also discussed. Techniques for sample pre-treatment, pre-concentration, separation, and quantification of Hg species, together with examples of total Hg determination and Hg speciation analysis in different natural (non-spiked) waters are summarised in tables, with a focus on applications from the last decade.

Slurry Nebulization in Plasmas

SUMMARY OF CONTENTS Introduction Plasma Techniques Used in Slurry Analysis Importance of Slurry Particle Size on Analytical Performance Slurry Preparation Grinding Methods Dispersion of Slurries Magnetic Stirring and Vortex Mixing Ultrasonic Agitation Solid Particle Size Distribution Measurements Influence of Slurry Concentration Modifications to the Sample Introduction System Nebulizers Spray Chambers Torches Use of a Sheathing Gas Use of a Tandem Source Use of Flow Injection Use of an Inverted Geometry Plasma Calibration Techniques Aqueous Calibration Use of Internal Standards Use of Standard Additions Use of Empirical Correction Factors Use of Intrinsic Internal Standardization Use of Standard Slurries Optimization Use of Mixed Gas Plasmas Matrix Effects Fundamental Studies Aerosol Formation, Transportation and Loss Temperature Measurements Applications of Slurry Sample Nebulization into Plasmas References

Gold-Coated Silica as a Preconcentration Phase for the Determination of Total Dissolved Mercury in Natural Waters Using Atomic Fluorescence Spectrometry

A novel solid-phase preconcentration method is reported, using in-house gold-coated silica adsorbent packed in a microcolumn, for the determination of dissolved mercury in natural waters by atomic fluorescence spectrometry (AFS). The adsorbent was prepared by chemical reduction of a Au(III) solution with hydroxylamine in the presence of suspended silica particles. The resulting Au nanoparticles on the silica surface were highly efficient for adsorbing different mercury species from acidified waters without additional reagents. The acidified aqueous samples were passed over the microcolumn, either incorporated in a fully automated flow injection (FI) system directly coupled to the AFS or as part of a portable FI system for in situ preconcentration. After rinsing and drying of the column, Hg(0) was released by heating and directed to the AFS cell for quantification. The method offers significant advantages because no reagents are needed for species conversion, preconcentration, sample storage, or desorption and therefore the risk of contamination is minimized and blank values are lowered. This results in a low detection limit of 180 pg L(-1) using a sample volume of only 7 mL and good reproducibility, with relative standard deviations <3.2% (n = 10, [Hg] = 5 ng L(-1)). Recoveries were all >90% in spiked river waters (spiked [Hg] = 0, 1, 5, 10 ng L(-1)), and the experimental value for the certified reference material ORMS-4 (elevated mercury in river water) was 22.3 +/- 2.6 ng Hg L(-1) which was in good agreement with the certified value of 22.0 +/- 1.6 ng Hg L(-1) (recovery = 101%). The method was successfully applied to seven different natural waters and wastewaters ([Hg] 0.5-4.6 ng L(-1)) from south west England.

Detection of genotoxins in the marine environment: adoption and evaluation of an integrated approach using the embryo-larval stages of the marine mussel, Mytilus edulis.

In genetic ecotoxicology or eco-genotoxicology, there is lack of well-validated systems which could demonstrate the utility of multiple endpoints in environmental quality assessment. For an evaluation of genotoxic potential of heterogeneous marine sediment samples collected from a small fishing harbour in the UK, an in vivo test system using embryo-larval stages of the common mussel, Mytilus edulis was validated against direct and indirect acting reference mutagens. The system appeared to be sensitive and reproducible for cytogenetic endpoints analysed (sister chromatid exchanges (SCEs) and chromosomal aberrations (CAbs)). Following validation and chemical characterisation of the environmental samples, multiple endpoints were measured. Determination of the maximum tolerated dose (MTD) was carried out as a measure to determine cytotoxic effects as a confounding factor for genotoxicity, based on developmental and cytotoxic (in terms of proliferative rate index or PRI) effects. Evaluation of the genotoxic potential of the samples gave a positive response for all the endpoints tested, linking different levels of biological organisation (i.e., chromosomal, cellular and organismal) for the observed effects. The study also emphasises the need for the assessment of the short and long-term impacts of dredge disposal on marine biota by including laboratory-based bioassays and incorporating an integrated approach which could yield as much useful information as possible in overall hazard and risk assessment for aquatic genotoxicity.

Slurry nebulization inductively coupled plasma spectrometry-the fundamental parameters discussed

Abstract Slurry nebulization inductively coupled plasma atomic emission spectrometry (ICP-AES) has been investigated to examine how the particle size distribution of the slurry affects analytical accuracy and precision. An empirical upper diameter for the particle size distribution of a slurry of 2–2.5 μm was derived from the analysis of a range of slurries possessing different particle size distributions. A model for slurry particle transport is suggested that gives good agreement with experimental data. The model assumes that for an arbitrarily defined but realistic standard slurry, the maximum allowable particle size is that which allows the occupation of every aerosol droplet by one solid particle. Theoretical considerations and empirical data suggest that for accurate analyses by slurry nebulization, the particle size distribution of the slurry should not exceed a value, determined by density, of 2.9 μm for a material of density 1 g cm−3 falling to 1.5 μm for a material of density 7 g cm−3. Certain carbonaceous materials were shown to be susceptible to micro-flocculation, resulting in 5–10 member assemblies formed from fine primary particles. This led to transport behaviour and analytical recoveries that would normally be associated with slurries of much coarser particle size. With the required conditions of complete dispersion and the correct particle size distribution, slurry nebulization ICP-AES was applied successfully to a range of certified reference materials using simple aqueous standards for calibration.

Determination of the growth promoter, 4-hydroxy-3-nitrophenyl-arsonic acid in chicken tissue by coupled high-performance liquid chromatography–inductively coupled plasma mass spectrometry

A method has been developed to measure the levels of the growth promoter 4-hydroxy-3-nitrophenylarsonic acid (roxarsone) in samples of tissue from chickens fed on a diet supplemented with this compound. Extracts of the tissue were prepared for analysis by a trypsin enzymolysis digestion technique and bulk matrix separation was performed by anion-exchange column chromatography. Further separation of the roxarsone from other species was achieved using reversed-phase high-performance liquid chromatography. Detection of the arsenical compound was by inductively coupled plasma mass spectrometry. No roxarsone was detected in chickens fed on the supplemented diet with or without a withdrawal period (7 d on base feed after the administration period) at a quantification limit of 25 ng g–1. Recoveries for roxarsone from spiked (standard additions) samples of chicken tissue varied between 85 and 103%.

Speciation and preconcentration of CrIII and CrVI in waters by retention on ion exchange media and determination by EDXRF

The preconcentration, separation and determination of Cr III and Cr VI have been achieved by using a combination of ion exchange media and energy dispersive X-ray fluorescence (EDXRF) spectrometry. The species in aqueous solution have been retained sequentially on activated alumina and Dowex 1-X8 for Cr VI and three different cation exchangers, Dowex 50W-X8, Zerolite and activated alumina, for Cr III and then determined directly on the adsorption media. The results obtained show that the Dowex resins are the best for the speciation of chromium in waters. The use of these resins allows linear ranges of over three orders of magnitude and a reduction of those matrix effects so often observed in EDXRF. The method was tested using a 100-fold diluted Ground Water and Waste Water Pollution Control Check Standard WP-15 which contains Cr III and was spiked with Cr VI . Full recoveries were achieved from this standard with precision values of 4% or less. The detection limits obtained for a preconcentration factor of 50 were 0.3 mg l –1 for Cr VI on Dowex 1-X8 and 0.4 mg l –1 for Cr III on Dowex 50W-X8. These limits were reduced to 0.03 and 0.04 mg l –1 , respectively, if a 500-times preconcentration factor was employed. The scope of the method was investigated further by analysing spiked samples of local natural waters (river and sea) for both Cr III and Cr VI species directly. While the advantages of using this methodology are clearly seen, some limitations are noted for samples of high saline content.

Direct atomic spectrometric analysis by slurry atomisation. Part 9. Fundamental studies of refractory samples

Fundamental studies of the analysis of refractory slurries by inductively coupled plasma atomic emission spectrometry have identified transport and atomisation effects which may lead to reduced recoveries of analyte elements. When refractory ores containing different minerals are ground, apparently narrow particle size ranges may disguise subtle variations in particle size for different minerals of different hardness. Such samples may then segregate during nebulisation leading to low recoveries for some elements. Experiments using slurries of uniform particle size, cascade impactors and laser diffraction have confirmed the critical importance of particle size. Fine slurries show comparable mass transfer efficiencies to solutions and atomisation efficiency increases as particle size decreases. For difficult samples, e.g., refractory minerals, a particle size of less than 5 µm, with the bulk of the sample below 3 µm would seem to be optimal. It is also shown that a longer travel time in the plasma aids atomisation.

Direct atomic spectrometric analysis by slurry atomisation. Part 7. Analysis of coal using inductively coupled plasma mass spectrometry

The application of slurry atomisation-inductively coupled plasma mass spectrometry (ICP-MS) to major, minor and trace element determination in coals has been investigated. Eight certified reference material (CRM) coals have been ground by the bottle and bead method and analysed using both rapid scan semi-quantitative analysis, employing a single rhodium internal standard, and full quantitative analysis using simple aqueous standards for calibration. The semi-quantitative mode, which determines the concentration using the mass-response curve for 68 elements against the single internal standard, produced values which were within a factor of two of the certified reference value, in most instances. The full quantitative determination gave excellent agreement with the certified reference material coals for a large number of elemental constituents. The results from the determination of 16 elements of interest are discussed including the effects of polyatomic interferents and isotope sensitivity. Low recoveries were observed for aluminium and the factors which influence its response are discussed with respect to internal standards. When coal slurries of up to 1%m/V were analysed no effect from cone blockage was observed.

Effect of easily ionizable elements on solutions and slurries in an axially viewed inductively coupled plasma

A Perkin-Elmer Optima 3000 axially viewed ICP spectrometer was used to study the effects of EIEs on the spatially dependent ion and atom emission intensities from Mg containing solutions and slurries. Using the Mg 279.553 nm ion and 285.213 nm atom line emission profiles, ion:atom emission intensity ratios were measured, with and without EIEs, across the plasma to visualize the changes in energy transfer processes when an EIE is present. Transport effects are negated when this ion:atom/ion:atom ratio is employed. In the presence of an EIE, both atom line ratios and ion line ratios are enhanced for solutions and slurries and this enhancement increases in the order Li < Na ⩽ K < Cs. Profiles of ionEIE:ion and atomEIE:atom ratios show greater enhancement for the excited ion population that the excited atom population. This indicates an increased departure from simple ‘Saha’ LTE conditions for both solutions and slurries with EIEs. While similar energy transfer processes are seen for solutions and slurries, under these matrix conditions, the magnitude of the enhancement in slurries is less than that of solutions when Li and Na are present. A reduced atomization efficiency for slurries relative to the matrix-matched solutions is implied. This relative atomization efficiency is seen to change for different systems. A refractory MgO slurry, which contained particles up to 4 µm in diameter, gave a relative atomization efficiency of 80–85% in the absence of an EIE. In the presence of an EIE, the relative efficiency increased up to 100% in the order Li < Na ≈ K ≈ Cs. This effect may be attributed to (i) a ‘real’ increase in atomization efficiency, (ii) subtle changes in the rejection of a larger solid particle fraction or (iii) a combination of both. Atom line ratio profiles show spatially dependent structure, similar to a ‘caldera’, when EIEs are present. The rim of this atom caldera is the interface between the central analyte channel and the plasma body. These profiles allow the energy transfer processes that occur in this region to be visualized. The presence of EIEs causes this region to be enhanced and increase in the order, Li < Na ⩽ K < Cs. Ion line profiles are relatively flatter. Ion:atom ratio profiles show that an energy transfer process involving ion population enhancement occurs at the centre of the analyte channel when an EIE is present.