Helium Microwave-induced Plasma Mass Research Articles

Evaluation of a Direct-Injection Nebulizer (DIN) for Liquid Sample Introduction in Helium Microwave-Induced Plasma Mass Spectrometry (MIP-MS)

A direct-injection nebulizer (DIN) has been evaluated for liquid sample introduction in helium microwave-induced plasma mass spectrometry (MIP-MS). A short-term stability test with the direct-injection nebulizer was found to give less than 0.5% RSD for twenty minutes. Isotope abundances for K, Ca, Cr, and Se were determined with less than 10% error on all isotopes. All elements have linear dynamic ranges of two to three orders of magnitude. Detection limits are low to sub-ppb for all elements. Ion lens tuning plays an important role in multielement determinations. Oxide, hydroxide, and doubly charged ions are determined for Cr, As, Sr, Cs, Ba, and Pb. The effect of 10% methanol and high-dissolved salts is investigated.

Trace analysis in high matrix aqueous solutions using helium microwave induced plasma mass spectrometry

The practical aspects of a He microwave induced plasma (MIP) mass spectrometry system for the determination of As, Se, Br and I in biological samples were investigated. A prototype instrument with a toroidal helium MIP coupled to a quadrupole mass spectrometer was used. Liquid samples were analysed by pneumatic nebulization with a Meinhard nebulizer without desolvation. The plasma was operated at 380 W with 3.6 l min–1 cooling gas, 0.8 l min–1 nebulizer gas, 0.6 l min–1 intermediate gas and 0.5 ml min–1 sample uptake rate. Arsenic, Se, Br and I showed linearity of more than 4 orders of magnitude. The detection limits (3s) were determined for 75As, 78Se, 79Br and 127I, and were 0.05, 0.25, 0.30 and 0.07 µg l–1, respectively. The influence of Na and K on the response of As was less than 20% up to concentrations of 1000 mg l–1. Analysis of 3% HCl causes an interference at a concentration of 1 µg l–1 of As, analysis of 1000 mg l–1 of Ca causes an interference at a concentration of 2 µg l–1 of As. Both of these elements in the solution cause significant interference in the determination of 75As, due to the formation of the 40Ca35Cl polyatomic ion. Biological reference materials (liver, muscle, milk, flour, diet and fish) and different fish samples were analysed for As and Se after high-pressure ashing with HNO3. Bromine was found to be a good internal standard for these elements. The results obtained with the He-MIP showed good agreement with the certified values for most of the materials investigated. Bromine and I were determined after alkaline digestion with tetramethylam-monium hydroxide. The determination of Br was complicated by severe memory effects. The results obtained for the few available reference materials showed acceptable agreement with the certified values.

The helium microwave-induced plasma: an alternative ion source for plasma mass spectrometry

Helium microwave-induced plasmas are a useful alternative ion source for plasma mass spectrometry in certain applications including nonmetal detection. A review of investigations concerning helium microwave-induced plasma mass spectrometry is presented. The advantages of helium plasmas are discussed and initial MIP-MS work is reviewed. Both gaseous and aqueous sample introduction techniques are discussed including chromatographic techniques, electrothermal vaporization and solution nebulization. In addition, other studies including fragmentation and fundamentals are reviewed.

Gas chromatographic determination of phosphorus, sulfur and halogens using a water-cooled torch with reduced-pressure helium microwave-induced plasma mass spectrometry

A system is described that utilizes a reduced-pressure water cooled microwave-induced plasma torch to interface a gas chromatograph with a plasma mass spectrometer. The detection limits vary with the compound used. For phosphorus in triethyl phosphate the detection limit is 86 pg and for chlorine in chlorotoluene, it is 22 pg. A seven component mixture was analysed simultaneously for compounds containing chlorine (m/z 35 and m/z 37), phosphorus (m/z 31), sulfur (m/z 32), bromine (m/z 79 and m/z 81) and iodine (m/z 127). A Supelco pesticide mixture was also analysed with simultaneous detection of chlorine and sulfur. Sub-nanogram detection limits were obtained for all elements studied.

Isotope Ratio Measurements of Iron, Bromine and Selenium in Aqueous Solutions by Helium Microwave-Induced Plasma Mass Spectrometry

A helium microwave-induced plasma (MIP) at atmospheric pressure has been generated in a modified TM010 Beenakker cavity. The MIP was coupled with a laboratory-built mass spectrometer used to measure the isotope ratios of Fe, Br and Se, which are not easily measured by an Argon inductively coupled plasma (ICP) source, due to spectral interference. In helium MIP, the analyte signal intensities are maximum when a torch edge is sampled; unidentified molecular ions appear across the entire mass range when the torch center is sampled. The measured isotope ratios agree quite well with the accepted values, and the detection limits are in the low-ppb range.

Determination of halogenated compounds with supercritical fluid chromatography–microwave-induced plasma mass spectrometry

Helium microwave-induced plasma mass spectrometry (MIP-MS) has been evaluated as an element selective detector for supercritical fluid chromatography (SFC). In this study the determination of halogenated hydrocarbons at trace levels is demonstrated by using two test compounds, 1-chloronaphthalene and 1-bromo-2-methylnaphthalene. The SFC–MIP-MS interface was developed and optimized. Chromatograms obtained for the two halogenated compounds show detection levels in the low picogram range with absolute minimum detectable quantities of 100 and 25 pg for Cl and Br, respectively. Absolute detection limits were found to be 15 pg for Cl and 0.75 pg for Br. The linear ranges are over 3 orders of magnitude (50 pg–50 ng) and reproducibilities for the sample injections are of the order of 5% relative standard deviation. A preliminary chromatogram for a standard pesticide mixture is also presented.

Helium Microwave-Induced Plasma Mass Spectrometric Detection for Reversed-Phase High-Performance Liquid Chromatography

Reversed-phase high-performance liquid chromatography (HPLC) is directly coupled to helium microwave-induced plasma mass spectrometry (He MIP-MS) for the element-selective detection of halogenated organic compounds. Absolute detection limits are approximately 50 pg Br for brominated compounds, 1 pg I for iodinated compounds, and 10 ng Cl for chlorinated compounds. The linear dynamic range for Br- and I-containing compounds is 3-4 orders of magnitude. However, the linear range for chlorinated species is severely limited by high background at m/z = 35. The relative standard deviation for repetitive injections is less than 10%. The helium microwave-induced plasma is operated at moderate powers (300-350 W) and with a total helium consumption of 6-8 L/min. The effect of organic solvents on the background mass spectrum is investigated.

Low-pressure helium microwave-induced plasma mass spectrometry for the detection of halogenated gas chromatographic effluents

A low-pressure helium microwave-induced plasma was interfaced to a mass spectrometer and the system was utilised as a detector for gas chromatography. The over-all system was optimised with respect to microwave power and the first-stage pressure of the mass spectrometer. The linear dynamic range for iodobenzene extended over three orders of magnitude starting at 1 pg. The absolute 3σ detection limit for iodine was 0.1 pg. The evaluation of the interface for the detection of bromine indicated an interference at mass 79 due to the formation of a polyatomic nickel species. A preliminary detection limit of 3.5 pg was calculated for bromine. A second interface design was used in a preliminary investigation of the backgrounds at masses 35 and 37. The background 35/37 ratio was correct, indicating a source of chlorine within the system. The detection limit for chlorine was 24 pg.

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.

Preliminary investigation of a tangential flow torch with coupling probe injector for helium microwave induced plasma mass spectrometry

A stable, low gas-flow torch has been developed for use with a helium microwave induced plasma (MIP). A toroidal plasma with central analyte introduction is obtained by the addition of a tantalum coupling probe injector tube. This injector penetrates through 100% of the total cavity depth and aids in the efficiency of power transfer to the cavity, in plasma initiation, and in circumventing the effects of a lack of homogeneity in the microwave field on analyte distribution in the plasma. The tangential helium flow was 41/min and the microwave power was 60 W.

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

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.

Helium microwave-induced plasma mass spectrometry for capillary gas chromatographic detection: speciation of organotin compounds

Helium microwave-induced plasma mass spectrometry has been utilised as an element selective detector for capillary gas chromatography. Several trialkyltin and tetraalkyltin compounds were separated via capillary gas chromatography using a DB-1701 stationary phase. Two different tangential flow torches were evaluated. The major difference between the two torches is the use of a tantalum injector which extends through the microwave cavity and provides a means of introducing the effluent from the capillary column directly into the helium plasma. The optimum signal to noise ratio for the tantalum injector torch was obtained at a microwave power of 70 W with a plasma gas flow-rate of about 3 l min–1. Detection limits obtained with the tantalum injector torch ranged from 0.09 to 0.35 pg of Sn, while those achieved using the standard tangential flow torch ranged from 1 to 4 pg of Sn for the organotin species investigated. The relative standard deviation (RSD) of peak-height reproducibilities ranged from 2.4 to 4.3% for manual injection using the tantalum injector torch for 50 pg of Sn. The manual injection of 1 ng of compound resulted in an RSD of ca. 7% for peak height using the standard tangential flow torch. Linear dynamic ranges were over at least three orders of magnitude.

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.