Gene S. Hall

Determination of halogens in organic compounds by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS)

The feasibility of the determination of sub ppm to percentage levels of halogen elements (fluorine, chlorine, bromine, and iodine) in solid organic compounds and drug substances by double focusing sector field high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) was investigated. Samples were dissolved in appropriate solvents and then diluted in either deionized water or 5% (v/v) ammonium hydroxide. By applying medium or high resolution, the background counts can be lowered by up to five orders of magnitude compared to conventional quadrupole ICP-MS systems. The signal sensitivities and memory effects of all four elements in different solvents were compared and assessed. The methods were applied to the determination of sub ppm to percentage levels of F, Cl, Br and I in a series of organic compounds and Merck drug substances. The results were found to be in excellent-to-reasonable agreement with the known or theoretical values of these compounds or drug substances. The limit of detection in solution for F was estimated to be 5 µg ml−1 (medium resolution), and for Cl, Br and I was 3 (high resolution), 0.08 (high resolution) and 0.03 (high resolution) ng ml−1, respectively.

Isotopic and elemental composition of iron, nickel, and chromium in type I deep-sea spherules: implications for origin and composition of the parent micrometeoroids

We report elemental and isotopic analyses of Fe, Ni, and Cr in type I deep-sea spherules with masses ranging from 43 to 256 μg. We measured (1) the isotopic compositions of Fe and Cr by thermal ionization mass spectrometry; and (2) the elemental concentrations of Fe, Ni, and Cr and the isotopic compositions of Ni by inductively-coupled plasma mass spectrometry. Evaporation of Fe, Ni, and Cr during atmospheric entry led to large and similar average degrees of mass-dependent fractionation, Φ, in most spherules. The average value, ∼16‰/AMU, corresponds to mass losses of 80–85%, assuming open-system evaporation of the atoms. We find ΦCr ∼ ΦFe, in seven spherules. This observation implies similar evaporation rates for Cr and Fe and that the measured Cr/Fe ratios (mass/mass) are close to those of the progenitors. Four spherules have Cr/Fe ∼0.003; two others with low Cr/Fe, ∼8 × 10−4, high Fe/Ni, ∼2000, and ΦCr ∼ ΦFe ∼0, may belong to a different, possibly terrestrial, population. A seventh spherule with “chondritic” Cr/Fe, ∼17 × 10−3 and subaverage ΦCr and ΦFe, 8–10‰/AMU, may represent still another source of particles. Because the higher vapor pressure of pure Cr should lead to ΦCr > ΦFe we infer either that Cr has a low activity coefficient in liquid Fe or that it forms a relatively involatile species there. A best fit correlation between ΦCr and ΦFe can be expressed in the form ΦCr = 0.31 × ΦFe1.47, although the data also are adequately fit by a linear regression. Correlated variation of ΦNi and ΦFe can be fit by the empirical relationship ΦNi = 0.016 × ΦFe2.58. For low ΦFe, we find ΦNi ΦFe, which probably reflects the increase with temperature of the vapor pressure of pure Ni, changes in activity coefficients of Fe and Ni, and the formation of relatively involatile wustite and magnetite. Differences between ΦNi and ΦFe in many samples mean that measured Fe/Ni ratios may differ appreciably from pre-atmospheric values. After compensating for evaporation by using the Rayleigh law, we estimate an average pre-atmospheric Fe/Ni ratio (by mass) in type I spherules of 19 ± 4 (σmean). Similarly, by assuming Ir is involatile, we obtain a preatmospheric ratio of Ir/Ni = 3 × 10−5, which is about 10 times smaller than the average measured value, but similar to the cosmic (CI) abundance ratio of 4 × 10−5. Cosmogenic nuclides have been detected in some Type I spherules at levels indicating irradiation as metal in space. Among conventional meteorites, the best matches to both the Cr/Fe and Fe/Ni ratios inferred for type I progenitors are metal from CO, CV, and CR chondrites and from unequilibrated ordinary chondrites. The match with metal from CM chondrites is acceptable but somewhat poorer. Iron meteorites, because of their low Cr/Fe ratios and low flux to Earth, make unlikely progenitors for type I spherules. We propose that most type I spherules derive from metal grains in carbonaceous-chondrite-like objects that were freed by comminution in space, or, less likely, that collisions of large objects formed droplets rich in metal.

Multielemental analyses of tree rings by inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) was evaluated for major, minor, trace, and ultra-trace elemental analyses of individual tree rings. The samples were obtained from an old-growth Douglas fir (Pseudotsuga menziesii) growing 15 km northeast of Mount St. Helens volcano, Washington, USA and from trees at various other North American sites. Samples were brought into solution by microwave digestion in sealed Teflon vessels. Eightly percent of elements from Li to U had detection limits in the solid (wood) below 8.0 ng g−1 (parts per billion, ppb). When selected element concentrations in the Mount St. Helens samples are plotted against time, two anomalous peaks occur at A. D. 1478 and 1490 that closely correlate with past eruptions of the volcano. These preliminary results show that ICP-MS is a rapid and sensitive analytical method for multielemental analyses of individual tree rings.

High-energy mass spectrometry of 10Be using a tandem van de graaff accelerator

Abstract A method of measurement of specific 10Be contents of naturally occurring materials is described. The method is based on mass spectrometry of 10Be/9Be ratios, using the Rutgers-Bell tandem van de Graaff accelerator. The detection limit is currently approximately 107 atoms 10Be, and the precision, when not limited by counting statistics, is 13%. The linear proportionality of observed 10Be/9Be ratio to actual ratio in sample has been verified within uncertainty over more than two orders of magnitude in ratio. Results are presented for the application of the method to determination of 10Be contents of six samples from various locations in the Antarctic H-chondrite ALHA 78084. No significant variations among the samples due to differences in shielding from cosmic rays were observed.

Determination of total toxic arsenic species in human urine using hydride generation inductively coupled plasma mass spectrometry

In order to evaluate people’s exposure to arsenic in drinking water, hydride generation inductively coupled plasma mass spectrometry (HG-ICP-MS), a simple and fast method, was developed to determine the total concentration of toxic arsenic species in the urine samples. Different factors affecting the hydride generation reactions were studied. It was found that under optimized conditions with 1% NaBH4, 0.2 M HCl and 0.05 M L-cysteine, the toxic arsenic species were effectively separated from non-toxic species. In addition, it was discovered that inorganic and monomethylarsenic species have similar sensitivities with HG-ICP-MS detection, while dimethylarsenic species have slightly lower sensitivity. With this method, good linearity, repeatability and recovery were achieved along with the low detection limit of 6 ng L−1 (3σ). This HG-ICP-MS method was employed to analyze a NIST standard reference material, SRM2670a, as well as urine samples from subjects under an arsenic exposure and remediation study; the concentration of all toxic species determined by this method was in good agreement with that measured by IC-ICP-MS speciation. The results suggested this HG-ICP-MS method is better than an ICP-MS total arsenic measurement in evaluating people’s exposure to inorganic arsenic in drinking water, because it can exclusively measure toxic arsenic species in urine, which come from inorganic arsenic exposure, with better sensitivity.

Element analysis of Pinus rigida intra-annual growth rings by photon-induced X-ray emission

A 3.7 MeV external proton beam was employed to produce X-rays in Pinus rigida Mill /pitch pine/ intra-annual growth rings and several elements were quantitatively determined. The PIXE experimental set-up, rapid sample preparation methods, and some interesting observations are discussed. In addition, statistical analysis of the tree-ring element concentrations revealed that Cl, K and Ca were slightly translocated whereas the other elements detected were not. The concentrations of several elements in the rings were negatively correlated with annual stream water pH which reflected precipitation pH.

Nickel isotope abundances of type I deep-sea spheres and of iron-nickel spherules from sediments in Alberta, Canada

Nickel isotope abundances were measured by ICP-MS in twenty-one whole, type I deep-sea spheres, in Ni-rich cores and oxide shells separated from three others, and in Fe-Ni alloy spherules from Alberta, Canada. The nickel isotopes in the whole deep-sea spheres are mass fractionated from 0.4 to 2.4%/ AMU. These: values correspond to open system vaporization losses of Ni as high as 94% (relative). The degree of mass fractionation correlates well with bulk nickel content in most cases. Taken together with published iron isotope data, the nickel isotope results indicate a pre-loss FeNi ratio of about 12 for many spheres. Similar ratios are observed in the following types of meteoritic material: EL-chondrite metal; IA, IIE, IIIA, and IVA iron meteorites; and metal from pallasites and mesosiderites. Metal cores separated from three deep-sea spheres contain between 40 and 52% Ni, with mass fractionations ranging from undetectable to a high of 0.8%/AMU. Within experimental error, the degree of Ni mass fractionation in each oxide shell was the same as that in the corresponding core. No mass-dependent isotopic fractionation of nickel was observed in Ni-rich spherules recovered from Alberta sands of Pleistocene age. In general, Ni-rich samples have low degrees of isotopic fractionation which suggests that the most rapid vaporization of Ni occurs when both Fe and Ni have been oxidized.

Sample preparation methods of tree-rings for PIXE-PIGE multielemental analysis

Abstract Tree-rings were collected from various sites within the United States to investigate the effects of atmospheric deposition on the growth of trees. Three different sample preparations were investigated to maximize detection limits and sample throughput, and to minimize element losses and sample contamination. The preparation methods included dry ashing at 450° C, cryogenic pulverization, and microwave wet digestion. Since PIXE-PIGE was used to determine the elements Li-U in the tree-rings at low concentrations, the method of cryogenic pulverization could not be used. Dry ashing was the preferred method and it was used to analyze the trace element concentrations in individual tree-rings. Detailed sample preparation methods are described along with applications for studying the affects of climate on the uptake of different elements in the rings.

High-performance liquid chromatographic determination of cocaine and its metabolites in serum microsamples with fluorimetric detection and its application to pharmacokinetics in rats.

A sensitive, selective and simple HPLC method with fluorimetric detection is described for quantitating cocaine and its three metabolites in rat serum microsamples (50 microl). Chromatographic separation is achieved on a Hypersil BDS C18 column (100X2.1 mm, 5 microm) with an isocratic mobile phase consisting of methanol-acetonitrile-25.8 mM sodium acetate buffer, pH 2.6, containing 1.0 x 10(-4) M tetrabutylammonium phosphate (14:10:76, v/v/v). The detection limit (0.5 ng/ml) for all the compounds, using direct fluorometric detection operated at excitation and emission wavelengths of 230 and 315 nm, respectively, was approximately five-times lower than that of using a UV detector operated at 235 nm. The effects of ratio of 2-propanol to chloroform in extraction solvents on the recovery and precision for cocaine and its metabolites were systematically examined. The method was used to study the pharmacokinetics of cocaine after administration of intravenous 2 mg/kg and oral 20 mg/kg doses.

Mass fractionation of nickel isotopes in metallic cosmic spheres

Abstract The isotopic abundances of stable Ni isotopes were measured by inductively coupled plasma mass spectrometry (ICP/MS) in seven cosmic, metallic (Type I) spheres collected from the deep sea. Mass-dependent enrichments of the heavier isotopes range from 0.5–2.8% / AMU, values larger than those reported previously for Ni in any solid, extraterrestrial sample. This mass fractionation most likely reflects the high-temperature vaporization and loss from some spheres of over 90% of the Ni initially present.