Timothy M. Davidson

Detection of Halogenated Compounds by Capillary Gas Chromatography with Helium Plasma Mass Spectrometry Detection

A gas Chromatograph was coupled to a helium microwave-induced plasma mass spectrometer for the detection of halogenated hydrocarbons. The absolute detection limits for the chlorinated compounds investigated ranged from 9.2 to 21 picograms, while the detection limits for brominated and iodinated compounds ranged from 0.92 to 1.05 picograms. The linear dynamic ranges were found to be 2.5–3 orders of magnitude. The results obtained are compared with optical emission from this and other laboratories.

Helium microwave induced plasma mass spectrometry for detection of metals and nonmetals in aqueous solutions

Abstract A helium microwave induced plasma is evaluated as an ion source for plasma mass spectrometry. Analyte position studies were performed to assess background interferences and the distribution of analyte ions within the helium plasma as a function of nebulizer flow rates. Helium microwave induced plasma mass spectrometry provides detection of the halides in aqueous samples as positive ions at the low to sub-ppb levels. Detection limits for metals are in the sub-ppb range. Determination of selenium and bromide isotope ratios are possible down to the low ppb level. Flow injection was used in a preliminary matrix study. A sodium concentration of 2000 ppm was found to suppress the analyte signals by 15 to 50%. This suppression can be partially corrected for by using internal standards.

Feasibility of the direct analysis of urine by inductively coupled argon plasma mass spectrometry for biological monitoring of exposure to metals

Urine samples have been analysed for metals using inductively coupled plasma mass spectrometry (ICP-MS). The samples were simply diluted (1 + 9) with 2% v/v nitric acid and introduced into the ICP-MS system. Data for multi-element determinations were obtained by scanning the mass range from 2 to 256 u at a rate of 0.5 scans s–1 for 4 min. Under these conditions, the detection limits are less than 1 ng ml–1 for the original urine sample with linear ranges in excess of 1 × 104. The quantitative performance of the technique applied to real samples was comparable to that obtained from established methods for antimony, mercury and cadmium. The application of this approach to certain metals is restricted by the presence of a number of interferences in the range m/z= 10–80. The system was operated for an entire working day with no evidence of deterioration in the mass spectrometer interface and with a system stability of the order of 5% relative standard deviation. Within the limits described, this method provides a useful tool for monitoring a variety of metals in urine at the levels which might be of interest in a programme of biological monitoring of human exposure.

A Moderate-Power Nitrogen Microwave-Induced Plasma as an Alternative Ion Source for Mass Spectrometry

The moderate-power nitrogen plasma is evaluated as an alternative ion source for plasma mass spectrometry. The nitrogen MIP-MS exhibits linear dynamic ranges of about 3–4 orders of magnitude and low ppb to sub-ppb detection limits for most elements under multielement scanning conditions. Nitrogen MIP-MS is capable of determining K, Ca, Cr, As, and Se at their major isotopes. In addition, nitrogen MIP-MS provides lower detection limits than argon ICP-MS for K (0.48 ppb) and Ca (0.24 ppb). The nitrogen MIP-MS system allows the determination of isotope ratios for 10 ppm of Ca (40/44) and 100 ppb of K (39/41), Cr (52/53), and Se (80/78) with less than 5% error.

Minimisation of sample matrix effects and signal enhancement for trace analytes using anodic stripping voltammetry with detection by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry

An on-line flow system for anodic stripping voltammetry has been investigated for the pre-concentration of cadmium and copper and the separation of copper from a sodium matrix for detection by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry (ICP-MS). Good signal enhancement was obtained with pre-concentration of moderate sample volumes. Matrix elimination of more than 99% was possible for reasonably high concentrations of undesired matrix elements, namely Na and U. Isotope ratio data for ICP-MS indicated that the interference of ArNa+ on Cu+ at m/z 63 could be minimised.

Application of helium microwave-induced plasma mass spectrometry to the detection of high ionisation potential gas phase species

The determination of fluorine, chlorine, bromine and iodine as positive ions is accomplished using a helium microwave-induced plasma (MIP) as an ion source for quadrupole mass spectrometry. A helium MIP sustained in an internally tuned TM010 cavity is interfaced to a commercially available mass spectrometer for the detection of the aforementioned halogens as positive ions. The mass spectral background of the helium MIP and the effect of plasma sampling parameters on the background are discussed. Detection limits for Cl+, Br+ and l+, from the methyl halogens, are estimated to be at picogram levels or lower.

Determination of copper and cadmium using an on-line anodic stripping voltammetry flow cell with detection by inductively coupled plasma mass spectrometry

An on-line anodic stripping voltammetry flow system was used to deposit copper and cadmium from National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 2670 Toxic Metals in Freeze-Dried Urine at a working electrode, with release of the analyte for detection by inductively coupled plasma mass spectrometry after the sample matrix was cleared from the cell. Recoveries determined against calibration graphs and by the method of standard additions were 94–115% for copper and 89–97% for cadmium. Spike recoveries for both analytes ranged from 92–106%. Elimination of the sodium-based polyatomic species at m/z= 62 and 63 remains highly efficient for up to 1 × 104µg cm–3 of sodium, whereas the use of dilute nitric acid as electrolyte gives far superior results for copper than those previously reported. Recent improvements in the system manifold design are discussed.

Helium source microwave-induced plasma mass spectrometric detection in the analysis of gas-chromatographic eluates

An atmospheric- and a low-pressure helium microwave-induced plasma have been coupled to a mass spectrometer for the detection of halogenated compounds. The atmospheric-pressure plasma system involved the use of a capillary gas chromatograph for the speciation of halogenated compounds and gave picogram sensitivities for both bromine and iodine. The atmospheric-pressure plasma was found to have elevated backgrounds at masses 35 and 37. These elevated backgrounds led to a low-pressure torch design which reduced these and other low-mass backgrounds. The analysis of halogenated compounds using the low-pressure torch was limited to the flow injection of methyl chloride and methyl bromide.

Hydrogen Isotope Analysis Using a Reduced-Pressure ICP Torch

Despite the apparent nonequilibrium conditions found in the plasma, this research has demonstrated that the flowing, reduced-pressure inductively coupled argon plasma can provide a rapid, sensitive, and effective new analytical method for hydrogen isotope analysis. The important characteristics which make this method useful include the following: no apparent molecular emission, the ability to correct the apparent isotope effect observed in static systems by flow regulation, the linearity of the response of atomic hydrogen and deuterium line intensities with concentration of H2 and D2 injected in the plasma gas mixture, and the minimal memory effects.

Background Spectral Features for Moderate-Power Nitrogen Microwave-Induced Plasma-Mass Spectrometry

The mass spectral background features of a moderate-power nitrogen microwave-induced plasma are presented. In general, the mass spectral background obtained from a nitrogen plasma is less congested at low mass than is the case with argon ICP-MS. In addition, there are no significant (less than 20 counts per second) background species above mass 60. At normal multiplier voltage, the major background species found in a dry nitrogen plasma include 14N+, 14NH+, 14N2+, 14N2H+, 14N16O+, 14N16OH+, 14N3+ and 14N4+. This background is unchanged by the nebulization of deionized water, 5% (v/v) acids (nitric, hydrochloric, and sulfuric acids), and 5% (v/v) methanol solutions. These background species do not interfere with the determination of K, Ca, and Se at their major isotopes, which commonly have interfering background species in Ar ICP-MS. On the basis of the nebulization of 5% HCl and methanol in the nitrogen plasma, As and Cr do not have isobaric interferences at their major isotope masses 75 and 52. In addition, preliminary studies on the effect of Na as a concomitant element on analyte signals indicate severe enhancement or suppression of analyte signals.