E. Hywel Evans

Effect of organic solvents and molecular gases on polyatomic ion interferences in inductively coupled plasma mass spectrometry

The introduction of an organic solvent (ca. 10% propan-2-ol in water) or a molecular gas (<5% O2 or N2) into the central channel of the inductively coupled plasma has been shown to cause dramatic reductions in signals due to the polyatomic ions ArCl+, ArAr+ and ClCl+, with corresponding increases in the In+ : XY+ ratios using inductively coupled plasma mass spectrometry (ICP-MS). Some evidence for the competitive formation of species such as ArC+, ArN+ and ArO+, or CCl+, NCl+ and OCl+ in preference to the other interfering ions, was observed, depending on the method employed. The use of N2 at a flow-rate of 0.03 l min–1 doped into the central channel is recommended for the minimisation of ArCl+ interference in analysis by ICP-MS.

Simple approach to reducing polyatomic ion interferences on arsenic and selenium in inductively coupled plasma mass spectrometry

The addition of small amounts of an organic solvent (e.g., propanol) or a molecular gas (e.g., nitrogen or oxygen) is shown to reduce the interferences on arsenic and selenium of polyatomic ions (ArCl+, Ar2+) at masses 75, 77 and 78 in inductively coupled plasma mass spectrometry.

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.

Dissolved silver in European estuarine and coastal waters

Silver is one of the most toxic elements for the marine microbial and invertebrate community. However, little is known about the distribution and behaviour of dissolved silver in marine systems. This paper reports data on dissolved and sediment-associated silver in European estuaries and coastal waters which have been impacted to different extents by past and present anthropogenic inputs. This is the first extended dataset for dissolved silver in European marine waters. Lowest dissolved silver concentrations were observed in the Gullmar Fjord, Sweden (8.9 +/- 2.9 pM; x +/- 1sigma), the Tamar Estuary, UK (9.7 +/- 6.2 pM), the Fal Estuary, UK (20.6 +/- 8.3 pM), and the Adriatic Sea (21.2 +/- 6.8 pM). Enhanced silver concentrations were observed in Atlantic coastal waters receiving untreated sewage effluent from the city of A Corũna, Spain (243 +/- 195 pM), and in the mine-impacted Restronguet Creek, UK (91 +/- 71 pM). Anthropogenic wastewater inputs were a source of dissolved silver in the regions studied, with the exception of the Gullmar Fjord. Remobilisation of dissolved silver from historically contaminated sediments, resulting from acid mine drainage or sewage inputs, provided an additional source of dissolved silver to the estuaries. The ranges in the log particle-water partition coefficient (K(d)) values of 5-6 were similar for the Tamar and Mero estuaries and agreed with reported values for other estuaries. These high K(d) values indicate the particle reactive nature of silver with oxic sediments. In contrast, low K(d) values (1.4-2.7) were observed in the Fal system, which may have been due to enhanced benthic inputs of dissolved silver coupled to limited scavenging of silver on to sediments rich in Fe oxide.

Feasibility study of low pressure inductively coupled plasma mass spectrometry for qualitative and quantitative speciation

Low-pressure ICPs (LP–ICPs) formed with helium have been utilized as ion sources for MS. In the first part of the paper a description is given of a plasma operated at 90 W forward power, used to ionize organotin and organolead compounds introduced by GC, with detection limits of 11, 2 and 14 pg obtained for tetraethyltin (TEtSn), tetrabutyltin (TBuSn) and tetraethyllead (TEtPb), respectively. The same plasma operated at 45 W forward power yielded fragment ions of TEtSn and TBuSn. In the second part, a customized mass spectrometer for use with an LP–ICP is described. The optimum power for the generation of fragment ions of perfluorotributylamine (PFTBA) was found to lie between 5 and 8 W. Two optima for skimming distance were observed, at 6 and 8 mm downstream of the sampler orifice. Mean ion kinetic energies for fragment ions of PFTBA at 69,219 and 502 m/z were 1.2, 1.7, and 2.1 eV, respectively, at 6 W forward power, but increased when the power was increased to 8 W. Molecular and other fragment ions were observed for chloro-, iodo- and dibromobenzenes introduced using GC.

Addition of molecular gases to argon gas flows for the reduction of polyatomic-ion interferences in inductively coupled plasma mass spectrometry

Addition of 1% N2 to the coolant Ar gas flow at a nebulizer gas flow rate of 0.95 dm3 min–1 can eliminate 40Ar35Cl+ and dramatically reduce 35Cl16O+ and 37Cl16O+, without losing sensitivity for a representative analyte, In. Addition of 3% N2 to the central channel gas flow, at a nebulizer gas flow rate of 0.70 dm3 min–1, has the same effects on polyatomic-ion interferences but also results in a loss in sensitivity to some extent. No significant effects on oxides (48Ti16O+, 140Ce16O+, 238U16O+) and doubly charged (138Ba2+) species were observed with or without N2 addition. Addition of CH4 to the Ar gas flows has a similar effect to that of N2 addition, but results in carbon deposition on the sampling cone and a more complicated spectrum. Results of analyte determination for a reference material confirmed that addition of N2 could be applied to real samples.

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.

Analysis of geoporphyrins by high-temperature gas chromatography inductively coupled plasma mass spectrometry and high-performance liquid chromatography inductively coupled plasma mass spectrometry. Plenary lecture

High-temperature gas chromatography (HTGC) and high-performance liquid chromatography (HPLC) have been coupled to inductively coupled plasma mass spectrometry (ICP-MS) for the determination of geopophyrins from oils shales. A New, directly heated stainless-steel capillary interface was used to introduce the eluent into the ICP torch. The interface was robust, simple to install, programmable and introduced minimal loss (5–10%) in chromatographic efficiency. The HTGC–ICP-MS was used for rapid metal fingerprinting of the geoporphyrin fractions. Cobalt, Chromium, iron, nickel, titanium, vanadium and zinc metalloporphyrins were fingerprinted. For quantitative analysis HPLC–ICP-MS was preferred. Quantitative data obtained by HPLC–ICP-MS and HPLC with UV absorption detection of nickel geoporphyrins from Julia Creek and Serpiano oil shales showed good agreement. Levels of nickel porphyrins were in the range 15–120 µg g–1 in the samples analysed. The potential for multi-element, multi-isotopic detection is clearly illustrated using up to ten elements/isotopes virtually simultaneously.

An evaluation of reversed-phase and ion-exchange chromatography for use with inductively coupled plasma-mass spectrometry for the determination of organotin compounds

An evaluation of reversed-phase high-performance liquid chromatography (HPLC) employing mobile phases compatible with direct coupling to inductively coupled plasma-mass spectrometry (ICP-MS) is described for the selective and sensitive detection of organotin species. The findings of this study are compared with established methods, employing ion-exchange chromatography. In order to achieve optimum performance, both the HPLC and ICP-MS were optimized for speciation work. The results from studies using various mobile phases for the separation of a range of tin compounds (inorganic tin, tributyltin, dibutyltin and monobutyltin) are discussed both in terms of resolution and compatibility with ICP-MS instrumentation. Tropolone, a commonly used complexing agent for organotin species, is also discussed with reference to the chromatographic separation of tin species. Finally, the role of isotope dilution analysis in conjunction with HPLC-ICP-MS for organotin speciation is described with respect to the European Community Standards, Measurements and Testing (BCR) certified material programme.

Low pressure inductively coupled plasma source for mass spectrometry

The generation of a low pressure Ar inductively coupled plasma has been successfully performed without any modification to the torch box of a commercial inductively coupled plasma mass spectrometer. A water-cooled, low pressure torch and interface, designed to allow sampling for mass spectrometry, are described. Using gas chromatography sample introduction, it was possible to measure the analytical signal for a sample of 1-bromononane. The background spectrum contained many of the polyatomic ions seen for atomospheric plasmas, thought to be due to small leaks in the vacuum seals.