Paul J. Paulsen

Determination of trace elements in zinc by isotope dilution spark source mass spectrometry

Abstract The applicability of the isotope dilution technique in spark source mass spectrometry has been investigated for the determination of Pb, Cu, Cd, Ag, Tl, and Sn in zinc metal. In the procedure developed, a solution of the zinc is spiked with known amounts of stable isotopes of the elements to be determined, and the elements are electrodeposited onto gold wires that subsequently serve as electrodes for the mass spectrographic isotopic analysis. Chemical operations, including isothermal distillation of reagents, dissolution of the zinc, and the electro-deposition step are conducted in a closed system to minimize contamination. The results of the analysis of two NBS zinc standard reference materials include determinations ranging from 11 ppm (11 μg g ) for Pb to as low as 0.02 ppm (20 ng g ) for Sn. It is concluded that this method is of general utility for simultaneous multi-element trace analysis and is especially applicable in providing much needed standardization in spark source mass spectrometry.

A comparison of isotope dilution mass spectrometric methods for the assay of copper in copper ore reference materials

The trend toward lower assays in the repeated determination of copper in copper ore, Standard Reference Material 332, have resulted in the withdrawal of this reference material due to material instability. Recent analyses by both isotope dilution thermal ionisation mass spectrometry (TIMS) and isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) have confirmed this change in copper assay. In this study ICP-MS was shown to be an excellent method for the determination of the concentration of copper in copper ore and therefore may be capable of relatively high precision for a number of elements in inorganic matrices. Two experiments were designed to study the relationship between the high loss of volatile components on drying and the corresponding low copper assay. The slow oxidation of CuS to CuSO4 was confirmed. The accelerated moisture study indicated that exposure to changes in temperature and relative humidity did not cause this oxidation. Microwave drying provided additional information about moisture associated with the samples that had been oxidised.

Sample preparation approaches for isotope dilution inductively coupled plasma mass spectrometric certification of reference materials

Ratio measurements can be made by inductively coupled plasma mass spectrometry (ICP-MS) with precisions approaching 0.1–0.2% relative standard deviation, under carefully controlled conditions. This capability is well suited to isotope dilution quantification, since quantitative data are based solely on ratio measurements. Conversion of the precision of isotopic ratio measurements to accuracy requires attention to both the operation of the ICP mass spectrometer and to the sample preparation procedures. The concentration of Mg, Cd, Mo and Pb were determined in synthetic samples with average precision and accuracy of <0.15%. Although more extensive chemistry was required, analytical precision was better than 0.15% for Cu and Cd in zinc ore and for Cu and Mo in domestic sludge.

The use of isotope dilution mass spectrometry for the certification of standard reference materials

Abstract Isotope dilution mass spectrometry (IDMS) has been used extensively at the U.S. National Bureau of Standards as an accurate method to determine trace element concentrations in natural materials. Thermal ionization mass spectrometry is a single element technique capable of high accuracy and precision, and has been used for “definitive” measurements of trace elements in sera with 95% confidence limits less than 0.25%. Spark source mass spectrometry is a complementary multielement, high-sensitivity technique that has been used to determine up to 20 elements in a sample, with typical accuracies of 2%–5%. Together with appropriate chemical separations, such as anion and cation exchange, chelate resins, electrodeposition, and chemical extraction, IDMS has been applied to elemental concentration measurements ranging over eight orders of magnitude, from decigrams/gram to picograms/gram. Many of these applications have been used for the certification of a broad spectrum of biological and environmental Standard Reference Materials, including lead in Trace Elements in Water (SRM 1643), 15 elements in Coal Fly Ash (SRM 1633a), uranium in Bovine Liver (SRM 1577a), and mercury in water (SRM 1642).

Trace Element Determinations in a Low-Alloy Steel Standard Reference Material by Isotope Dilution, Spark Source Mass Spectrometry

A stable isotope dilution procedure using the spark source mass spectrograph was developed for the simultaneous determination of cerium, copper, neodymium, selenium, silver, tellurium, and zirconium in a low-alloy steel material. Except for copper, the elements were present at trace concentrations that are difficult to determine by most analytical methods. In the procedure, known amounts of the isotopically enriched elements were added to 100-mg samples, which were dissolved in perchloric and hydrofluoric acids. After evaporation of the solutions almost to dryness, dissolution of the residues, and addition of hydrofluoric acid to complex the iron, the resulting solutions were electrolyzed in polytetrafluoroethylene cells. The electrodeposit on high purity, gold cathode wires was sparked in the mass spectrograph and the isotope ratios of the isotopically equilibrated elements were measured. The concentrations, ranging from 0.041% for copper to 3.1 µ/g (ppm) for neodymium, were calculated from the general isotope dilution equation. The low-alloy steel is available from NBS as Standard Reference Material 1261.

Perspective. Impact of inductively coupled plasma mass spectrometry on certification programmes for geochemical reference materials

The National Institute of Standards and Technology (NIST) began using inductively coupled plasma mass spectrometry (ICP-MS) for the certification of its Standard Reference Materials (SRMs) in 1986, only a few years after instruments first became commercially available. The United States, Canadian and Ontario Geological Surveys (USGS, CGS, and OGS, respectively) also made early use of the method to provide new data for existing certified reference materials (CRMs) and other non-certified geochemical reference materials (GRMs). The application of ICP-MS extends to most elements in the periodic table. NISTs efforts have focused largely on environmentally important trace elements. However, the impact of ICP-MS analysis in geochemistry is greatest in providing certified values for the platinum group elements (PGEs) and the rare earth elements (REEs). This paper will review the growing impact of ICP-MS analyses on the certification of CRMs/GRMs. Examples include NIST SRMs 1646a Estuarine Sediment, 2709-2711 Soils, 113b Zinc Concentrate; Centre de Recherches Petrographiques et Geochemiques (CRPG) CRMs CHR-Pt+ and CHR-Bkgr; Canadian Certified Reference Materials Program (CCRMP) WGB-1 gabbro rock, TDB-1 diabase rock and three other CCRMP CRMs recently certified for the PGEs. NIST has used ICP-MS almost exclusively in conjunction with isotope dilution. This has not been the situation among other users, but is to be recommended in certification analysis for several reasons, which will be outlined.

High purity fluoropolymer materials: Trace element content and leaching

Abstract Many problems in analytical chemistry are shared by the high purity crystal growth community since both are greatly concerned with the effects of impurities either upon an analysis or upon a device. Fluoropolymers are widely used today in applications where inertness or high purity or both are needed. The behavior of these polymers in high purity solvent systems has been investigated by several analytical techniques. Both the resin from which finished parts are made as well as blow molded bottles have been evaluated to determine cationic impurities in both the resin and in leachates.

Approaches to the accurate characterization of high purity metal fluorides and fluoride glasses

Abstract The analytical challenges posed by the measurement of trace contaminants in high purity metal fluorides require that innovative chemical preparation procedures be used to enhance existing instrumental techniques. The instrumental techniques used to analyze these difficult matrices must be sensitive enough to detect extremely low levels of trace impurities, and the background interferences derived from the matrix (metal fluoride or glass) must be minimized. A survey of analytical techniques that have the necessary characteristics to analyze these materials will be given. In addition, means of controlling the chemical blank will be presented. Mass and atomic spectrometric techniques will be discussed, specifically graphite furnace atomic absorption spectrometry (GFAAS) and inductively coupled plasma-mass spectrometry (ICP-MS). Analytical procedures using GFAAS and ICP-MS have been developed to determine sub ppb (part per billion) levels of contaminants in high purity fluoride materials.

Isotope dilution spark-source mass spectrometric determination of total mercury in botanical and biological samples

A combustion technique for the isolation of mercury from organic matrices is described which minimises the chemical blank. The operating parameters for isotope dilution spark source mass spectrometry have been optimised for these samples. Concentrations of ca. 0.1 µg g–1 in solid samples, such as tuna, leaves and urine, have been determined with a precision of about 4%.

The Determination of Selenium and Tellurium in Stainless Steel, White Cast Iron, and Nickel Base Alloy Standard Reference Materials by Isotope Dilution Spark Source Mass Spectrometry

Procedures using stable isotope dilution spark source mass spectrometry were developed for the simultaneous determination of selenium and tellurium in stainless steels, white cast irons, and nickel based alloys. The selenium and tellurium were reduced using hypophosphorous acid except in the nickel based alloy where electrodeposition onto gold was also used for tellurium. A gold carrier was used to scavenge the selenium and tellurium efficiently during reduction. The samples were homogenized with gold and introduced into the mass spectrometer as electrodes. The concentrations calculated from the general isotope dilution equation ranged from 0.14 μg/g for selenium to 353 μg/g for tellurium. The materials tested were ten different Standard Reference Materials available from the NBS.