D. Conrad Grégoire

The effect of easily ionizable concomitant elements on non-spectroscopic interferences in inductively coupled plasma-mass spectrometry

Abstract Reported are the effects of easily ionizable concomitant elements on non-spectroscopic interferences in ICP-MS. Analyte ion suppression was studied for 7 Li, 11 B, 58 Ni, 45 Sc, 89 Y and 205 Tl in the presence of concomitant elements spanning a mass range from 23 (Na) to 207 (Pb) dallons. For the analytes studied, it was found that the greater the atomic mass of the concomitant element, the greater was the analyte ion count rate suppression. For a given set of experimental conditions, the greater the atomic mass of the analyte, the lower was its susceptibility to ion count rate suppression by any concomitant element. The severity of non-spectroscopic interferences decreased as the sampler orifice was positioned further away from the center of the plasma and also as the sampling depth was increased. Dilution of a solution containing a given molar ratio of concomitant to analyte reduced the extent of analyte ion suppression. Non-spectroscopic interferences in ICP-MS can be attributed to ambipolar diffusion effects in the plasma that result from the presence of easily ionizable concomitant elements.

Saline ground waters and brines in the Canadian Shield: Geochemical and isotopic evidence for a residual evaporite brine component

Abstract Saline Ca-Na/Cl type groundwaters and brines sampled in deep mines over an extensive area of the Canadian Precambrian Shield have elevated Br Cl ratios which may indicate that the chlorinity of these waters was derived from the infiltration of residual evaporitic brines, remnants of the great marine incursions of the Paleozoic era. Boron concentrations in these waters are generally low (i.e., 11 B 10 B ratios of these waters are significantly greater than the average value for continental crustal rocks with the highest values (~4.19) approaching that of present-day seawater (4.20). Moreover, the boron isotopic ratios generally trend to higher values with increasing chlorinity which supports the conclusion from the Br-Cl relationship that most of the chloride in shield brines is of marine origin, rather than a product of water/rock interactions. If this is correct, crystalline rocks must then be sufficiently permeable on a regional scale to have allowed the brine to infiltrate to depths of several kilometers where it now resides.

Background spectral features in electrothermal vaporization inductively coupled plasma mass spectrometry: molecular ions resulting from the use of chemical modifiers

Abstract The formation of background polyatomic ions in electrothermal vaporization inductively coupled plasma mass spectrometry is reported. Vaporization temperatures ranging from 800 to 2500°C were studied. Carbon-containing polyatomic ions interfere with the determination of Mg, Si, Ti, Ca and Cr. Polyatomic ions resulting from the vaporization of ascorbic acid, sodium chloride, magnesium nitrate, nickel nitrate and palladium nitrate chemical modifiers were studied. Microgram quantities of chemical modifier resulted in oxide and argide polyatomic ion intensities equivalent to picogram background equivalent masses for interfered analyte isotopes. In most cases alternative analyte isotopes free of interference were available. The formation of carbide of nitride modifier molecular ions was not observed. The argon dimer could be used as a diagnostic tool to indicate plasma loading effects and matrix suppression effects resulting from the use of chemical modifiers.

Direct analysis of solids by ultrasonic slurry electrothermal vaporization inductively coupled plasma mass spectrometry

The direct analysis of solids using ultrasonic slurry electrothermal vaporization inductively coupled plasma mass spectrometry is reported. National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1632a Trace Elements in Coal (Bituminous), Total Diet SRM 1548 and National Research Council of Canada LUTS-1 Lobster Hepatopancreas RM were analysed for a number of elements including Ni, Cu, Cr, Pb, Mn and Co. As a consequence of matrix effects, most analytes were determined using the method of standard additions, although Ni, Cu, Pb and Mn in NIST coal and Pb in LUTS-1 were successfully determined by external calibration using aqueous standards. With the exception of Cr in the coal sample, excellent agreement was obtained between the concentration determined and the certified range. Monitoring of the argon dimer during the high temperature vaporization cycle was shown to be an effective means of assessing matrix effects and selecting calibration strategies for individual analytes. Calculated limits of detection range from 0.07 ng g–1 for Co to 3.2 ng g–1 for Cr in 2 mg samples.

Electrothermal vaporization for inductively coupled plasma mass spectrometry and atomic absorption spectrometry: symbiotic analytical techniques. Invited lecture

New techniques have been developed for investigating fundamental phenomena occurring during electrothermal vaporization (ETV) as applied to atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). The different nature of electrothermal AAS (ETAAS) and ETV-ICP-MS data make possible the melding of information from both techniques in order to differentiate solid-phase and gas-phase chemical reactions leading to vaporization and atomization and elucidate the mechanism of matrix interferences and the chemistry involved in chemical modification. The significance of chemical modification for ETV-ICP-MS is demonstrated and the use of ETV-ICP-MS in assisting ETAAS for rapid method development is shown. The importance of mass transport effects in ETV-ICP-MS is demonstrated, which indicates that knowledge of the physical and chemical form of the analyte and matrix components is important to the practical application of ETV-ICP-MS to chemical analysis. Non-spectroscopic or matrix interferences in ETV-ICP-MS are more severe than in solution nebulization ICP-MS.

Seawater as a multi-component physical carrier for ETV-ICP-MS

Abstract The beneficence of NASS-3 sea water in enhancing analyte response in ETV-ICP-MS was investigated from a mechanistic viewpoint. Seawater serves as a multi-component physical carrier which acts primarily to increase the transport efficiency of analytes having wide ranging volatilities. A study of the major components of seawater revealed that HCl, released upon the hydrolysis of MgCl 2 , is most beneficial to very volatile elements (Cd, Rb, Cs and Tl), volatilization of NaCl affects elements of intermediate volatility (Pb, Ag, In, Ga and Bi), and MgO vaporization increases the transport efficiency of involatile elements (Co). Analyte signal enhancements were reduced or signal suppression occurred when NaCl or NASS-3 was added in amounts in excess of 0.07 μg. The carrier that caused the least signal suppression when used at high concentration was HCl. Decreasing the ETV heating rate enhances the effect of the physical carrier if the matrix element and analyte co-vaporize.

Ru/Ir ratios at the Cretaceous-Tertiary boundary: Implications for PGE source and fractionation within the ejecta cloud

Abstract Ruthenium and Ir are the least mobile platinum group elements (PGEs) within the Cretaceous-Tertiary (K-T) boundary clay. The Ru/Ir ratio is therefore the most useful PGE interelement parameter for distinguishing terrestrial and extraterrestrial contributions to the boundary clay. The Ru/Ir ratio of European marine K-T sections (1.67 ± 0.38) is statistically different from that of the North American continental sections (0.76 ± 0.26). It is unlikely that this difference is due to secondary PGE remobilization, PGE input to the boundary clay during multiple impacts, or volcanic emissions. The global difference in Ru/Ir ratios in the boundary clay may therefore be primary. The positive correlation between distance from the Chicxulub impact structure, Yucatan, Mexico, and Ru/Ir ratio and the more than 1000°C difference in the condensation temperatures of these elements lead us to propose that fractionation of Ru from Ir during condensation from the ejecta cloud may have occurred, resulting in the global difference in Ru/Ir ratios.

Determination of Inorganic and Total Mercury in Biological Tissues by Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry

A rapid method for the determination of total and inorganic mercury in biological tissues is presented using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV ICP–MS). Samples were solubilized using tetramethylammonium hydroxide. For the determination of total mercury sample aliquots (10 µl) are dried and vaporized into the plasma. For the determination of inorganic mercury, iodoacetic acid, sodium thiosulfate and acetic acid are added to the sample, cleaving the methylmercury from the tissue. Volatile methylmercury iodide is formed and removed from the ETV as the sample dries, leaving only inorganic mercury to be quantified. A limit of detection of 0.05 µg g -1 in solid samples was obtained. National Research Council of Canada reference materials DORM-2 (dogfish muscle), DOLT-2 (dogfish liver) and TORT-2 (lobster hepatopancreas) were used to assess the accuracy of the method.

Vaporization of acids and their effect on analyte signal in electrothermal vaporization inductively coupled plasma mass spectrometry

The vaporization properties of HCl and HNO3 under various furnace heating conditions were investigated. Drying-step temperatures of 140 °C (50 s) and pyrolysis-step temperatures of 400 °C (10 s) were effective in volatilizing most of the chloride from 10 µl of 1% v/v HCl, however, a small amount (40 ng) of acid was retained on the graphite even after pyrolysis at 400 °C. Under the same experimental conditions, HNO3 was completely volatilized from the graphite tube. The effect of a range of concentrations of HCl, HNO3, H2SO4 and H3PO4 on analyte signals was studied for Co, Cu, Ag, Cs, Pb, Bi and U. Analyte signals were enhanced by as much as a factor of two in the presence of 1% v/v HNO3 and H2SO4. Phosphoric acid suppressed analyte signals for Ag and Bi and the use of HCl resulted in relatively small changes in analyte sensitivity. The use of a pyrolysis step in the heating programme reduced the effects associated with acid matrices, but at the expense of signal intensity. A mixed modifier–carrier reduced the matrix effects associated with H2SO4 and H3PO4 and essentially eliminated them for HNO3 and HCl.

Determination of ultratrace levels of heavy metals in arctic snow by electrothermal vaporization inductively coupled plasma mass spectrometry

Application of electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) to the direct determination of trace heavy metals in surface samples of Arctic snow is described. Limits of detection by ETC-ICP-MS are in the fg range, viz., 29, 57, 86, 120, 140, 360, 420, 470, 870 and 3200 for Tl, Cs, Pb, Mn, Co, V, Cu, Ni, Cd and Cr, respectively. Direct quantification against simple aqueous standards is feasible using NaCl solution as a carrier. The latter was obtained in a high-purity form through dilution of the sea-water reference material National Research Council of Canada (NRCC) NASS-3. Assessment of accuracy was accomplished by analysis of the river water reference material SLRS-2 (NRCC) and by comparative analysis of the samples by electrothermal atomization atomic absorption spectrometry.