Ben Fairman

Determination of natural uranium and thorium in environmental samples by ETV-ICP-MS after matrix removal by on-line solid phase extraction

An on-line solid phase extraction method has been developed for the determination of 238 U and 232 Th biological certified reference material using inductively coupled plasma mass spectrometry (ICP-MS). Absolute detection limits were 2.7 pg and 3.1 pg for the determination of 238 U and 232 Th respectively, both being blank limited. The result for the determination of 238 U in NASS-4 Open Ocean Sea Water was 2.13±0.28 ng ml –1 compared with a certified value of 2.68±0.12 ng ml –1 . The results for the determination of 238 U in SLRS-3 River Water was 0.043±0.002 ng ml –1 compared with an indicative value of 0.045 ng ml –1 . Results for the determination of 238 U and 232 Th in NIST 1575 Pine Needles were 14.6±3.4 ng g –1 and 28.3±4.5 ng g –1 respectively compared with certified values of 20±4 ng g –1 and 37±3 ng g –1 , using a dry and wet ashing sample preparation method. Results for the determination of 238 U and 232 Th in NIST 1566a oyster tissue were 121±21 ng g –1 and 29±8 ng g –1 for 238 U and 232 Th compared to certified and indicative values of 132±12 ng g –1 and 40 ng g –1 , using the same method. When a lithium metaborate fusion method was used, results for 238 U and 232 Th were 23.3±2.0 ng g –1 and 36.2±5.6 ng g –1 respectively in NIST 1575 Pine Needles. The application of electrothermal vaporisation ICP-MS (ETV-ICP-MS) to NASS-4 Open Ocean Sea Water gave 2.81±0.54 ng ml –1 and SLRS-3 River Water 0.045±0.004 ng ml –1 for 238 U. When the fused NIST 1575 samples were analysed using ETV-ICP-MS, results for 238 U and 232 Th were 19.5±1.7 ng g –1 and 38.8±2.2 ng g –1 respectively. Absolute detection limits for ETV-ICP-MS were 30 fg and 9 fg for 238 U and 232 Th respectively, both being blank limited.

Speciation of organo-tin compounds using liquid chromatography–atmospheric pressure ionisation mass spectrometry and liquid chromatography–inductively coupled plasma mass spectrometry as complementary techniques

Abstract A liquid chromatographic method for the determination of dibutyltin (DBT), tributyltin (TBT), diphenyltin (DPhT) and triphenyltin (TPhT) in sediments has been developed, which is compatible with both atmospheric pressure ionisation (API) mass spectrometry and inductively coupled plasma (ICP) mass spectrometry. As a result of this development both techniques may be used for the complementary speciation of organo-tin compounds. The chromatographic system comprises of a Kromasil-100 5 μm C18 (150×2.1 mm) column and a mobile phase of 0.05% triethylamine in acetonitrile–acetic acid–water (65:10:25), at a flow-rate of 0.2 ml min−1. The optimisation of the LC–API-MS conditions is discussed, together with the analysis of a real sediment sample for DBT and TBT using selected ion monitoring (SIM).

Development of a Multi-element Hydride Generation–Inductively Coupled Plasma Mass Spectrometry Procedure for the Simultaneous Determination of Arsenic, Antimony and Selenium in Waters

A multi-element hydride generation–inductively coupled plasma mass spectrometry (HG–ICP-MS) method for the simultaneous determination of arsenic, antimony and selenium in water matrices has been developed. The method involves an off-line pre-reduction procedure for the reduction of Se VI to Se IV by HCl, combined with an on-line reduction of As V and Sb V to the trivalent state with thiourea and generation of the hydrides. Analytical characteristics include detection limits of 0.08 ng g -1 As, 0.06 ng g -1 Sb and 0.10 ng g -1 Se, linearity of four orders of magnitude and short and long term reproducibility of between 8 and 12%. Results from four reference water samples for As, Sb and Se showed data which were all within 10% of the target values. Interferences were minimal for As and Sb, whereas Cu 2+ , and to a lesser extent Ni 2+ and Cd 2+ , caused signal suppression effects on Se. Advantages over an alternative, single element, HG–AFS technique include speed of analysis (by a factor of two) and elimination of the conflicting chemistry requirements, traditionally found with sequential single element hydride generation methods.

Method comparison for the determination of labile aluminium species in natural waters

Abstract An inter-laboratory comparison project to evaluate the portability of a standard method for the determination of aluminium species in waters and to investigate the probability of producing reference waters for aluminium speciation analysis is described. High-density polyethylene containers were found to be appropriate for the storage of water samples, intended for speciation analysis, after leaching with 10% (v/v) nitric acid for 48 h. A quality control programme for total aluminium in water samples was completed by all participating laboratories, showing the value of such a parallel programme, especially for aluminium with its inherent problems with contamination. Water samples (lake and tap) proved to be stable for up to 30 days, after which increasing pH caused aluminium hydroxy species to precipitate. A defined Driscoll-Pyrocatechol Violet fractionation method was found to be robust enough to be fully portable, the participating laboratories achieving relative standard deviations of 15% for the toxic “labile monomeric” aluminium fraction in the more stable water samples.

Structured approach to achieving high accuracy measurements with isotope dilution inductively coupled plasma mass spectrometry

This study investigated a method for simplifying the implementation of ID-ICP-MS, to achieve high accuracy measurements. The method developed is an adaptation of an earlier methodology that utilised an iterative ‘matching’ procedure. While retaining the many advantages of this approach, we have removed the iterative component and simplified the ‘matching’ step between the spiked mass bias calibrant and the spiked sample. Based on a conventional analysis, an approximate ‘match’ (usually within 5%), was made between the spiked reference standard and the spiked sample. This provides the basis for calculating the final result using the normal IDMS equation, while retaining many of the benefits of the full ‘matching’ procedure. These benefits negate many sources of error, such as mass bias, detector dead time and characterisation of the spike material. Many common errors and necessary corrections are negated or eliminated when using the new procedure. Examples are given of the method as applied to the analysis of certified reference materials, such as waters and plastics as well as blind trial data. The accuracy achieved using this procedure, on blind trial solutions, is typically to within 1% (relative to concentration) at the 95% level of confidence.

Determination of actinides in environmental and biological samples using high-performance chelation ion chromatography coupled to sector-field inductively coupled plasma mass spectrometry

High-performance chelation ion chromatography, using a neutral polystyrene substrate dynamically loaded with 0.1 mM dipicolinic acid, coupled with sector-field inductively coupled plasma mass spectrometry has been successfully used for the separation of the actinides thorium, uranium, americium, neptunium and plutonium. Using this column it was possible to separate the various actinides from each other and from a complex sample matrix. In particular, it was possible to separate plutonium and uranium to facilitate the detection of the former free of spectral interference. The column also exhibited some selectivity for different oxidation states of Np, Pu and U. Two oxidation states each for plutonium and neptunium were found, tentatively identified as Np(V) and Pu(III) eluting at the solvent front, and Np(IV) and Pu(IV) eluting much later. Detection limits were 12, 8, and 4 fg for 237Np, 239Pu, and 241Am, respectively, for a 0.5 ml injection. The system was successfully used for the determination of 239Pu in NIST 4251 Human Lung and 4353 Rocky Flats Soil, with results of 570+/-29 and 2939+/-226 fg g(-1), respectively, compared with a certified range of 227-951 fg g(-1) for the former and a value of 3307+/-248 fg g(-1) for the latter.

Comparison of fluorimetric and inductively coupled plasma mass spectrometry detection systems for the determination of aluminium species in waters by high-performance liquid chromatography

The comparison of element-specific detection using HPLC–ICP-MS with an established HPLC–fluorimetric method for aluminium speciation in waters is described. This comparison allowed the identification of some problems with a fluorimetric detection method based around 8-hydroxyquinoline-5-sulfonic acid, particularly its comparatively poor selectivity and Al-species dependent response factors. The power of ICP-MS as a detector for HPLC systems is demonstrated by the simultaneous detection of Al, Mg, Zn, and Fe. The increased selectivity of ICP-MS over molecular fluorescence is shown in the reliable quantification of Al3+ and AlF2+ in a range of tap and natural water samples. The fluorimetric technique exhibited varying response factors to different aluminium species while the specific detector gave constant signals. Both techniques provided similar values for the ‘free’ Al3+ fraction in a variety of natural waters but systematic differences were obtained in the quantification of the AlF2+ fraction. Problems with the ICP-MS detection method for Al-speciation analysis such as ion interferences and salt concentration of the mobile phase are commented upon.

Field sampling technique for the ‘fast reactive’ aluminium fraction in waters using a flow injection mini-column system with inductively coupled plasma atomic emission spectrometric and inductively coupled plasma mass spectrometric detection

A novel field sampling strategy for the ‘fast reactive’ Al fraction in natural waters is described. The method is based on the isolation of the Al fraction which reacts with 8-hydroxyquinoline in under 3 s at pH 5.0. The resulting Al–8-hydroxyquinoline complex is sorbent-extracted from the sample stream onto mini-columns containing Amberlite XAD-2 non-ionic resin. The retained ‘fast reactive’ Al is then eluted with 1.0 mol l–1 HCl for on-line element-specific detection by inductively coupled plasma atomic emission spectrometry or inductively coupled plasma mass spectrometry (ICP-MS). Data from field sampling trials show good agreement with those for the toxic Al fraction as measured by an established high-performance liquid chromatography technique. Between-column relative standard deviations of 8% at the 100 µg l–1 level, a limit of detection of 1.8 µg l–1(ICP-MS) and ease of use are the main advantages of the proposed method. The mini-column technique has the potential for solving many of the sample storage problems associated with Al-speciation studies, particularly for the determination of the more toxic (or ‘fast reactive’) fraction.

Orthodox uncertainty budgeting for high accuracy measurements by isotope dilution inductively coupled plasma-mass spectrometry

A full uncertainty budget for the analysis of copper in dilute nitric acid solution by isotope dilution ICP-MS has been formulated and described. The budget was dominated by the contribution of the standard uncertainty of the measured isotope amount ratios of the sample blend and the blend used for mass bias correction. The contribution from other components such as weighing, isotopic composition, standard solution concentration, and dilution factors were not very significant. The accuracy of the method was demonstrated by the analysis of NIST SRM 3114 copper solution.

Simultaneous determination of arsenic, antimony and selenium in aqueous matrices by electrothermal vaporization inductively coupled plasma mass spectrometry

A method for the simultaneous determination of As, Se and Sb in aqueous matrices by ETV–ICP-MS has been developed. Complex interactions between the analytes and various chemical modifiers are described. A mixed modifier of Pd(NO 3 ) 2 –Ni(NO 3 ) 2 was finally selected for quantitative multi-element analysis. Criteria of merit of the proposed method include a 0–100 ng g -1 linear range for As and Sb and 0.5–100 ng g -1 for Se. Internal standardisation using Te was used to help produce repeatability of 3.9% for As, 6.9% for Se and 2.1% for Sb at the 1 ng g -1 level. Detection limits of 0.03, 0.08 and 0.01 ng g -1 for As, Se and Sb, respectively, are routinely achievable. The accuracy of the proposed method was demonstrated with the analysis of several reference waters. A severe negative interference on Se by high HCl concentrations could be overcome with the use of a Pd(NO 3 ) 2 –Mg(NO 3 ) 2 –ascorbic acid chemical modifier.