High Efficiency Nebulizer Research Articles

Axial inductively coupled plasma time-of-flight mass spectrometry using direct liquid sample introduction

This report is concerned with the first investigation of a direct injection high efficiency nebulizer (DIHEN) as a microliter-solution introduction system for axial inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS). The effect of rf generator frequency on analytical performance indices is investigated at both 27 and 40 MHz at operating conditions suitable for the DIHEN: a solution uptake rate of 100 µL min−1, nebulizer gas flow rate of 0.2 L min−1, and rf power from 800 to 1700 W. Four observations indicate an increased secondary discharge at 27 MHz compared to 40 MHz for the DIHEN compared to conventional solution introduction: (1) higher background count rates, (2) faster and wider ion deflection pulse times, (3) increased doubly-to-singly charged ion ratios (Ba2+/Ba+ = 0.03 vs. 0.02), and (4) reduced oxide-to-metal ion ratios (CeO+/Ce+ = 8.5 vs. 51) at 27 MHz in comparison with 40 MHz. Analytical figures of merit achieved, including detection limits, sensitivity, and precision using DIHEN-ICP-TOFMS are superior in both normal and cool plasma conditions to those obtained with a conventional nebulizer-spray chamber arrangement operated at a solution uptake rate of 1 mL min−1. For example, typical precision (percent relative standard deviation, %RSD) for the DIHEN at 27 MHz is less than 0.6% for an integration time of 10 s. The signal intensity is nearly a factor of 2 higher with the DIHEN compared to the conventional nebulizer-spray chamber arrangement. Isotope ratio precision acquired by the DIHEN-ICP-TOFMS system closely approximates values predicted by Poisson counting statistics for both steady-state and transient signals. Finally, fast transient analysis (ca. 12.75 ms) is demonstrated for Sn and Cr isotopes in human lung fibroblast cells.

Determination of 236U/238U isotope ratio in contaminated environmental samples using different ICP-MS instruments

This paper considers use of the 236U isotope to monitor the spent uranium from nuclear fallout using inductively coupled plasma mass spectrometry (ICP-MS) in soil samples collected in the vicinity of the Chernobyl Nuclear Power Plant (NPP). Sector field ICP-MS (ICP-SFMS) and quadrupole based ICP-MS without and with hexapole collision cell (ICP-CC-MS) were used for uranium isotope analysis. In addition, a multiple ion collector ICP-MS (MC-ICP-MS) was used for high-precision isotope ratio measurements. A 238U+ ion sensitivity of 18 GHz ppm−1, 12.4 GHz ppm−1 and 16 GHz ppm−1, respectively, was observed in ICP-SFMS, ICP-CC-MS and MC-ICP-MS with ultrasonic nebulizer. An absolute sensitivity of 3600 counts fg−1 was achieved for uranium by using a direct injection high efficiency nebulizer for solution introduction in ICP-SFMS. The detection limit for 236U was in the fg g−1 range and abundance ratio sensitivity for 236U/238U was 5 × 10−6, 3 × 10−7, 6 × 10−7, and less than 3 × 10−7 in ICP-SFMS, MC-ICP-MS, quadrupole ICP-MS and ICP-CC-MS at mass resolution m/Δm = 300, respectively. Interlaboratory comparison yielded a good accuracy (0.4–1.6%) of 236U/238U isotope ratios ranging from 1.5 × 10−3 to 3.2 × 10−4 measured in samples containing 100 ng of uranium. The 236U/238U isotope ratios and spent uranium fraction were determined in Chernobyl soil samples using single ion detector ICP-MS and multiple ion collector ICP-MS (MC-ICP-MS). In comparison to 235U/238U isotope ratio, the 236U/238U isotope ratio provided more sensitive and accurate determination of the portion of spent uranium from Chernobyl NPP in spent/natural uranium mixture in soil samples down to 0.1%. The concentration of Chernobyl spent uranium in upper 0–10 cm soil layers in investigated areas in the vicinity of Chernobyl NPP amounts to 2.4 × 10−9 g g−1 to 8.1 × 10−7 g g−1 depending mainly on the distance to the Chernobyl reactor.

New torch design with an in-built chamber for liquid sample analysis by ICP-AES

The analytical performance of the torch integrated sample introduction system (TISIS) for the analysis of very low sample volumes by ICP-AES is described. The TISIS consists of a commercially available torch with a low inner volume cavity (i.e., 5–9 cm3) placed at its base, which is attached to the shortened plasma injector tube through a special PTFE adapter. The nebulizer is vertically fitted to the torch base by means of a home-made Teflon adapter that has an exit for the drain solution. The aerosol is thus generated at the base of the TISIS cavity. The nebulization conditions corresponded to very low liquid flow rates (i.e., from 5 to 200 µl min−1) and conventional gas flow rates (i.e., 0.7 l min−1). Based on previously published work, these nebulization conditions favored aerosol solvent evaporation. At ambient temperature and below 40 µl min−1, almost all the solvent was evaporated and no drain was needed. Therefore, the main purpose of the TISIS cavity was to promote efficient solvent evaporation (instead of selecting the maximum drop size introduced into the plasma) and to simplify the transport path. In order to enhance solvent evaporation, the primary aerosols must be as fine as possible. In the present work, two pneumatic micronebulizers were employed: a so-called high efficiency nebulizer (HEN) and a MicroMist. For the sake of comparison, the HEN was coupled to a double-pass spray chamber and the MicroMist to a cyclonic type spray chamber. The results indicated that the TISIS exhibited promising behavior in ICP-AES, giving rise to emission intensities similar to or higher than both conventional reference systems. No further deterioration of the plasma thermal characteristics was observed when using the TISIS with respect to conventional chambers. The signal stability and limits of detection were similar for the different systems employed.

Noise characteristics and analytical precision of a direct injection high efficiency and micro concentric nebuliser for sample introduction in inductively coupled plasma mass spectrometry

Noise power spectra and analytical precision data were generated and compared for a direct injection high efficiency nebuliser, DIHEN, and a micro concentric nebuliser, MCN, combined with a double pass or cyclone spray chamber for sample introduction in inductively coupled plasma mass spectrometry, ICP-MS. The different systems were compared using liquid flow rates of 85 or 100 µL min−1. Steady-state signals for 115In+ and steady-state isotope ratio measurements for 107Ag+/109Ag+ were chosen for the investigation. For background and shot noise limited precision the DIHEN was found to give better precision than the double pass spray chamber system due to higher sensitivity. For flicker noise limited precision it was found that white noise and pump interference noise were higher, and 1/f noise and mains power interference noise were lower, for the DIHEN compared to the spray chamber systems. As a result of this, for 115In+ measurements, the DIHEN gave 2–9 times higher relative standard deviation, RSD, at measurement frequencies above 1 Hz but slightly lower RSD (not statistically significant) at frequencies below 0.1 Hz compared to the conventional systems. For the isotope ratio measurements, due to the high white noise level, the DIHEN generally gave poorer precision compared to the double pass spray chamber system. To convincingly explain the rationale for the observed flicker noise limited precision data, the effect of different noise components on analytical precision was evaluated. This study made obvious the relationship between precision and different noise components visualised in noise power spectra. Such information is useful for rational optimisation of operating conditions and technical developments of instrumentation. The mathematical simulation procedure used for this study was also applied to experimental data to predict analytical precision at typical measurement frequencies.

Influence of the spray chamber design for vapor-based liquid sample introduction at room temperature in ICP-AES

This paper describes a new concept for the introduction of very low liquid sample volumes in ICP-AES. Three single pass low inner volume spray chambers have been designed and characterized: two cylindrical ones of different inner volumes, 4 and 8 cm3, and a spherical type one, with 11 cm3. In every case a high efficiency nebulizer (HEN) has been used to generate the aerosol, and comparison with a conventional cyclonic spray chamber has been performed. The chambers were designed to enhance solvent evaporation within the spray chamber at liquid flow rates below 100 µl min−1, and to obtain a simple aerosol path. The aim was to combine the advantages of a spray chamber and those of a so-called direct injection nebulizer (DIN). The best analytical results, viz., repeatability, signal-to-background ratio and limits of detection, were obtained with the 8 cm3 single pass chamber. Results were usually improved when compared with the conventional cyclonic spray chamber. It has also been found that the interferences due to organic solvents (ethanol, formic and acetic acid), aqueous solutions and mixtures thereof (water–ethanol solutions) were less severe for the single pass spray chamber than for the cyclonic one.

Mixed-gas inductively coupled plasma atomic emission spectrometry using a direct injection high efficiency nebulizer.

Experimental studies and computer simulations were conducted to identify plasma operating conditions and to explore and contrast the excitation conditions of Ar, Ar-O2, and Ar-He inductively coupled plasmas (ICPs) for the introduction of microliter volumes of sample solutions with a direct injection high efficiency nebulizer (DIHEN). The best MgII 280.270 nm/MgI 285.213 nm ratio (6.6) measured with Ar ICP atomic emission spectrometry for the DIHEN (RF power = 1500 W; nebulizer gas flow rate = 0.12 L min(-1)) was less than the ratio (8.2) acquired on the same instrument for conventional nebulization (1500 W and 0.6 L min(-1)). Addition of small amounts of O2 or He (5%) to the outer gas flow improved excitation conditions in the ICP, that is, a more robust condition (a MgII/MgI ratio of up to 8.9) could be obtained by using the DIHEN with Ar-O2 and Ar-He mixed-gas plasmas, thereby minimizing some potential spectroscopic and matrix interferences, in comparison to Ar ICPAES.

Modified direct injection high efficiency nebulizer with minimized dead volume for the analysis of biological samples by micro- and nano-LC-ICP-MS

A direct injection high efficiency nebulizer (DIHEN) was modified for µLC-ICP-MS by inserting an additional internal capillary with od 90 µm and id 20 µm to minimize the interface dead volume. The modified DIHEN was compared with a conventional microflow nebulizer with a spray chamber interface with respect to sensitivity, signal stability and organic modifier dependency at flow rates ranging from 0.5 to 5 µl min−1. Although the modified DIHEN was slightly less sensitive, its signal stability was superior, its modifier dependency was less pronounced and its chromatographic resolution was much better due to its extremely small dead volume. These characteristics were demonstrated by the analysis of a mixture of synthetic phosphopeptides (31P detection) and synthetic thyroxine (127I detection). The influence of an organic modifier in the analyte solvent on the detection sensitivity was tested using the bioelements sulfur, phosphorus and iodine as examples. Phosphorus and iodine show an increased signal proportional to the amount of organic modifier with an intensity maximum of between 40% and 60% of modifier, which corresponds to a metal-like characteristic. For the detection of sulfur this characteristic is counteracted by a signal suppression effect proportional to the amount of organic modifier, which is caused by the formation of polyatomic species such as sulfur oxide.

Metallothionein isoforms separation and cadmium speciation by capillary electrophoresis with ultraviolet and quadrupole-inductively coupled plasma mass spectrometric detection

A complete characterisation of metallothioneins (MTs) in biological systems requires first an optimal separation of the different isoforms and sub-isoforms present. A method for the adequate separation of rabbit liver MT1 and MT2 mixtures by capillary zone electrophoresis (CZE) with UV detection is developed here. Different experimental conditions affecting both, peak shape and resolution achieved, are investigated in detail. Thus, the influence of the composition, ionic strength and pH of the buffer solution, and the separation voltage, have been studied. In order to improve the resolution between sub-isoforms, the electroosmotic flow has been also changed and its effect investigated by adding organic modifiers. Analytical performance characteristics are evaluated: calibration graphs were linear between 70 and 205 μg ml −1 for MT1 and between 83 and 242 μg ml −1 for MT2, while the detection limits were 4 and 3 μg ml −1, respectively. Speciation of the metal–MTs compounds has been accomplished by the coupling CZE–ICP–MS by means of different nebulisers: a conventional concentric Meinhard nebuliser, a Babington type one and a high efficiency nebuliser (HEN). Finally, real sample MTs analyses have been carried out in mussel hepatopancreas cytosols, previously exposed to a metal enriched environment.

A high-efficiency cross-flow micronebulizer interface for capillary electrophoresis and inductively coupled plasma mass spectrometry.

A pneumatic nebulizer interface for capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICPMS) is reported. The interface is constructed using a high-efficiency cross-flow micronebulizer (HECFMN) and has the following features. (1) Makeup solutions can be fed to the interface by nebulizer self-aspiration and liquid gravity pressurization. (2) The liquid dead volume of the interface is approximately 65 nL, much smaller than those (200-2500 nL) reported for other interfaces. (3) The interface can be stably operated at a liquid flow rate down to 5 microL/min with a high analyte transport efficiency up to 95% to the plasma and (4) does not induce noticeable laminar flow in the CE capillary at typical nebulizer gas flow rates of 0.8-1.2 L/min. Because of these features, baseline resolution of 10 lanthanides with a CE-ICPMS system using the HECFMN interface is achieved, and detection limits and peak asymmetry are 0.05-1 microg/L and 0.93-1.23, respectively, improved significantly over those reported previously for a CE-ICPMS system using a high-efficiency nebulizer interface. Peak precision for the 10 lanthanides is in the range of 6.2-12.3% RSD (N = 5). Peak widths are from 9.1 s for 139La to 17.9 s for 175Lu. The effects of nebulizer gas flow rate, makeup solution flow rate, and spray chamber volume on CE-ICPMS signal intensity and separation are also evaluated for the HECFMN interface by the separation of Cr3+ and Cr2O7(2-).

Ultratrace and isotopic analysis of long-lived radionuclides by double-focusing sector field inductively coupled plasma mass spectrometry using direct liquid sample introduction

This report is concerned with the investigation of double-focusing sector field inductively coupled plasma mass spectrometry (DF-ICPMS) for ultratrace and isotopic ratio analysis of long-lived radionuclides (226Ra, 230Th, 232Th, 233U, 237Np, 238U, and 241Am) using the direct injection high efficiency nebulizer (DIHEN). A new shielded torch arrangement, known as the guard electrode, improves relative sensitivity by a factor of six when the DIHEN is used. Absolute sensitivity with the DIHEN is on the order of 1300 (226Ra) to 1700 (238U) counts/fg at a solution consumption rate of 5 μL/min. This is a factor of from three to 20 better than the results obtained by a conventional nebulizer-spray chamber arrangement (e.g., ultrasonic and pneumatic nebulizers). The DIHEN-DF-ICPMS is successfully tested for isotope ratio measurements of 235U/238U standards and environmental radioactive waste solutions.

Simulation of droplet heating and desolvation in an inductively coupled plasma — Part I

The total desolvation rate of sample droplets in an argon inductively coupled plasma (Ar ICP) is investigated through the development of a two-phase continuum flow computer model. The desolvation model is supplemented by equations used to determine the trajectories of particles through the plasma. The model is used to calculate the behavior of aerosol droplets from a direct injection high efficiency nebulizer (DIHEN), a micronebulizer used to inject microliter quantities of samples that are toxic, expensive, or of limited volume. We use the combination of desolvation and transport models to present the first predicted spatial distribution of droplet concentrations and evaporation rates in an ICP flow. These data are compared with the behavior of a DIHEN spray in an environment with no net argon gas flow to determine the importance of gas flow rates to overall droplet concentration profiles in the ICP. In addition, two separate techniques (Stokes’ equation and the direct simulation Monte Carlo treatment) for determining droplet trajectories are contrasted.

Spatial aerosol characteristics of a direct injection high efficiency nebulizer via optical patternation

Optical patternation is used to study the aerosol produced by a direct injection high efficiency nebulizer (DIHEN), a micronebulizer used in inductively coupled plasma (ICP) spectrometries. The technique allows for the rapid and non-intrusive elucidation of the two-dimensional spray structure, planar mass distribution, spatial droplet size distributions, and spatial transient spray processes on the nanosecond-timescale. The aerosol cone diameter and the cone angle are reported at selected cumulative volume percent of the total aerosol and as a function of nebulizer gas flow and at three key axial locations from the DIHEN tip. Optical patternation reveals three major results for the DIHEN aerosol probed in the absence of the ICP torch: (1) the primary aerosol is spatially confined to a greater degree at a nebulizer gas flow rate of 1.0 l/min compared to 0.25 l/min, which is a flow rate commonly used by the DIHEN for maximal sensitivity in ICP mass spectrometry; (2) the aerosol rotates around the nebulizer axis, producing satellite droplets that are observed to a greater extent at lower nebulizer gas flow rates (0.25 l/min); and (3) satellite droplets are more prevalent at distances farther away from the nebulizer tip. The implication of these diagnostic results on the analytical performance of the DIHEN for ICP spectrometries is discussed, particularly, in relation to noise, imprecision, sample–plasma interactions, and the residence time of droplets in the plasma.

Determination of uranium isotopic composition and 236U content of soil samples and hot particles using inductively coupled plasma mass spectrometry

As a result of the accident at the Chernobyl nuclear power plant (NPP) the environment was contaminated with spent nuclear fuel. The 236U isotope was used in this study to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP. Nuclear track radiography was applied for the identification and extraction of hot radioactive particles from soil samples. A rapid and sensitive analytical procedure was developed for uranium isotopic ratio measurement in environmental samples based on double-focusing inductively coupled plasma mass spectrometry (DF-ICP-MS) with a MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN). The performance of the DF-ICP-MS with a quartz DIHEN and plasma shielded torch was studied. Overall detection efficiencies of 4 x 10(-4) and 10(-3) counts per atom were achieved for 238U in DF-ICP-QMS with the MicroMist nebulizer and DIHEN, respectively. The rate of formation of uranium hydride ions UH+/U+ was 1.2 x 10(-4) and 1.4 x 10(-4), respectively. The precision of short-term measurements of uranium isotopic ratios (n = 5) in 1 microg L(-1) NBS U-020 standard solution was 0.11% (238U/235U) and 1.4% (236U/238U) using a MicroMist nebulizer and 0.25% (235U/238U) and 1.9% (236U/P38U) using a DIHEN. The isotopic composition of all investigated Chernobyl soil samples differed from those of natural uranium; i.e. in these samples the 236U/238U ratio ranged from 10(-5) to 10(-3). Results obtained with ICP-MS, alpha- and gamma-spectrometry showed differences in the migration properties of spent uranium, plutonium, and americium. The isotopic ratio of uranium was also measured in hot particles extracted from soil samples.

Evaluation of a direct injection high-efficiency nebulizer (DIHEN) by comparison with a high-efficiency nebulizer (HEN) coupled to a cyclonic spray chamber as a liquid sample introduction system for ICP-AES

In the present work the advantages and limitations of introducing the sample directly into the plasma through the use of a direct injection high-efficiency nebulizer (DIHEN) have been evaluated in ICP-AES. The reference system was a high-efficiency nebulizer (HEN), precursor of the DIHEN, coupled to a cyclonic spray chamber. It was found that the plasma can only be operated under non-robust conditions because of the high solvent loading. The issues considered in the present work were: (i) the aerosol characteristics; (ii) the ICP-AES analytical figures of merit; and (iii) the interferences induced by the presence of inorganic as well as organic matrices. The results indicated that the aerosols obtained by the DIHEN are coarser than those leaving the cyclonic spray chamber. Nonetheless, and due to the higher analyte transport efficiency, the DIHEN affords ICP-AES sensitivities and LODs up to 10–18 times better than the cyclonic spray chamber. Also, it was found that, under the plasma conditions tested, the optimum nebulizer gas and liquid flow rates in terms of sensitivity for the DIHEN were very different from those for the HEN with the cyclonic spray chamber. In the first case, the signal peaked at rather low liquid (Ql) and gas (Qg) flow rates, whereas for the cyclonic spray chamber moderate and/or high liquid and gas flow rates were advisable. Under a given set of plasma conditions, the DIHEN has been proven to produce problems due to deterioration in the plasma, derived from the higher solvent load with respect to the HEN coupled to the cyclonic spray chamber. Despite these findings and the fact that a non-robust plasma was used, the matrix effects for inorganic and organic species were significantly minimized, for a low Ql and for some lines, in the case of the DIHEN.

Interfacing capillary electrophoresis with inductively coupled plasma mass spectrometry by direct injection nebulization for selenium speciation

A demountable direct injection high efficiency nebulizer operating at low sample uptake rates was developed and used for coupling of capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICP-MS). When the nebulizer was used for continuous sample introduction, detection limits of 20 and 1 ng L−1 were obtained for 82Se and 103Rh, respectively, at sample uptake rates of 10–30 μL min−1, based on three times the standard deviation of blank solution (3σb, n = 10). The nebulizer was used as part of the interface for coupling of CE with ICP-MS and applied for speciation of aqueous selenium standards. The interface was operated in the self-aspirating mode with a sheath liquid uptake of 10 μL min−1. The CE-ICP-MS system resulted in baseline separation of selenate, selenite, selenocystine and selenomethionine within a total analysis time of 5.4 min. Detection limits were in the sub µg Se L−1 range, corresponding to absolute detection limits in the range 25–125 fg selenium. Repeatability (n = 6) expressed as relative standard deviations with respect to migration times, peak heights and peak areas were better than 1.6, 6.7 and 6.0%, respectively.

Interfacing sequential injection on-line preconcentration using a renewable micro-column incorporated in a ‘lab-on-valve’ system with direct injection nebulization inductively coupled plasma mass spectrometry

A sequential injection (SI) on-line ‘lab-on-valve’ separation/preconcentration system incorporating a renewable ion-exchange micro-column interfaced with inductively coupled plasma mass spectrometry (ICP-MS) via a home-made direct injection high efficiency nebulizer (DIHEN) is described. Aimed at eliminating spectroscopic and non-spectroscopic interferences, the renewable micro-column is first loaded by aspirating 15 µl of a SP Sephadex C-25 cation-exchanger bead suspension and then exposed to a defined volume of sample solution. Residuals of matrix components are pre-eluted with carrier solution (nitric acid,1∶80 v/v), and the measurands are subsequently eluted with a defined volume of nitric acid (1∶16 v/v). The leading volume of eluate (ca. 30 µl) is collected and introduced into the plasma via the DIHEN. The eluted beads are then discarded and a new column is aspirated for the next operation. Data acquisition is performed in parallel with the ensuing preconcentration process. With 2.0 ml sample loading, the enrichment factors are 35.2 (0.05–2.4 µg l−1) for Ni, and 9.1 (0.04–1.6 µg l−1) and 28.4 (1.6–3.2 µg l−1) for Bi. The detection limits (3σ) are 15 ng l−1 (Ni) and 4 ng l−1 (Bi), while the sampling frequency is 12 per hour. The precisions are 2.9% (0.8 µg l−1 Ni) and 1.7% (0.8 µg l−1 Bi). The procedure is validated by determination of nickel and bismuth in a certified reference material (CRM 320, River Sediment), and the recoveries are measured by spiking two human urine samples.

A direct injection high efficiency nebulizer interface for microbore high-performance liquid chromatography-inductively coupled plasma mass spectrometry

A simple, relatively low-cost interface is investigated for high-performance liquid chromatography using inductively coupled plasma mass spectrometry (ICP-MS) detection. The interface consists of a one-piece micronebulizer (direct injection high efficiency nebulizer, DIHEN), positioned in the ICP torch for the direct nebulization of solution into the base of the argon plasma. Microcolumn separations were performed in two modes: one, reverse-phase separation of three naturally occurring cobalamin species (hydroxocobalamin, cyanocobalamin, and adenosylcobalamin); and two, ion-pairing reverse-phase separation of five organolead and organomercury species [triethyllead (Et3Pb+), triphenyllead (Ph3Pb+), methylmercury (MeHg+), ethylmercury (EtHg+) and phenylmercury (PhHg+)]. For a 10 µL injection, absolute sensitivity in the ion pairing mode ranged from 2430 counts pg−1 (EtHg+) to 35880 counts pg−1 (Ph3Pb+) and peak area reproducibility (%RSD, n = 5) ranged from 0.7% (EtHg+) to 5.1% (PhHg+). Absolute detection limits were in the low- to sub-picogram range. Importantly, no plasma instability or carbon deposition on the nebulizer tip was observed using organic modifiers in the mobile phase of up to 20%.

Non-spectral interference effects in inductively coupled plasma mass spectrometry using direct injection high efficiency and microconcentric nebulisation

Non-spectral interference effects in inductively coupled plasma mass spectrometry (ICP-MS) were investigated for the direct injection high efficiency nebuliser (DIHEN) the large bore DIHEN (LB-DIHEN) and a microconcentric nebuliser (MCN) with a cyclone spray chamber. Interference effects from nitric and sulfuric acid, methanol and sodium nitrate solutions were studied. Eight elements with different ionisation potentials (IP) and atomic masses were monitored at various nebuliser gas flow rates. The processes giving rise to interference effects observed with the DIHEN were investigated by monitoring relative analyte sensitivities at different radial plasma positions. It was found that the average magnitude of interference effects decreased in the order MCN ≈ DIHEN > LB-DIHEN, showing that analytical performance is improved by removing the spray chamber. It is suggested that remaining interference effects observed for the DIHEN are caused by a matrix induced spatial redistribution of the aerosol in the plasma due to differences in droplet size distribution and density between water and the matrix solutions. In addition, the high plasma solvent load with the DIHEN results in a pronounced negative correlation between relative analyte signal magnitude and IP. For the LB-DIHEN, these effects were smaller, and other element specific interference effects dominated. For the eight elements monitored, element specific interference effects increased in the order MCN < DIHEN < LB-DIHEN. Transient acid effects were also investigated and found to be virtually eliminated by the use of a DIHEN instead of the MCN system. For the latter, stabilisation times of 3–10 min were necessary when changing the nitric acid concentration between 0.22 and 2.2 mol l−1.

Oxide ion formation of long-lived radionuclides in double-focusing sector field inductively coupled plasma mass spectrometry and their analytical applications

The oxide ion formation of the long-lived radionuclides 226Ra, 230Th, 237Np, 238U, 239Pu, and 241Am was investigated in a mixed aqueous solution by double-focusing sector field inductively coupled plasma mass spectrometry (DF-ICP-MS) with a shielded torch under hot plasma conditions. The measurements of the relative oxide ion intensities by DF-ICP-MS were performed using different nebulizers [Meinhard nebulizer, microconcentric MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN)] for the solution introduction of aqueous standard solutions into the ICP. The highest oxide ion formation rate was observed for thorium in DF-ICP-MS under hot plasma conditions with a shielded torch (ThO +/Th + = 0.13, 0.26, and 0.41 for Meinhard nebulizer. MicroMist nebulizer and DIHEN, respectively). The application of the shielded torch in DF-ICP-MS yielded an increase in oxide ion formation for the Meinhard nebulizer by a factor of 2.7–7, for MicroMist nebulizer 1.6–13 and for DIHEN 1.7–2.8, compared to the original configuration without plasma shielding. The direct injection of sample solution by DIHEN-DF-ICP-MS results in a relatively high oxide ion formation rate (e.g. PuO +/Pu + of about 0.16 and 0.35 without and with a shielded torch, respectively). For the relative oxide ion intensities using the Meinhard and the microconcentric MicroMist nebulizers in DF-ICP-MS with shielded torch a decrease in the following sequence is observed: ThO +/Th + > UO +/U + > NpO +/Np + > PuO +/Pu + > AmO +/Am + ≫ RaO +/Ra +. The observed correlation of measured relative oxide ion intensities (ThO +/Th +, PuO +/Pu +, and UO +/U +) and bond energies of these oxides allows for the estimation of unknown bond energies for AmO and NpO (730 and 670 kJ/mol, respectively). High oxide ion intensity of long-lived radionuclides in DF-ICP-MS could be used in some cases for analytical purposes, e.g. the oxide ions are applied as analyte ions for interference-free isotope analysis and thus for checking the analytical results using the atomic ions of the analyte.

Direct Injection High Efficiency Nebulization in Inductively Coupled Plasma Mass Spectrometry under Cool and Normal Plasma Conditions

The direct injection high efficiency nebulizer (DIHEN) was investigated for application to inductively coupled plasma mass spectrometry (ICPMS) with a cool plasma. Elements are organized into three categories based on their performance in the cool and normal plasma. Sensitivity, precision, and detection limits are presented for elements (39K,40Ca, and56Fe) that suffer from mass spectral interferences (38ArH+,40Ar+, and40Ar16O+) derived from the plasma gas. Figures of merit are also reported for a group of elements that are suitable for analysis using either the cool or normal plasma condition. In a departure from previous published accounts, however, a group of elements is investigated that is suitable for analysis in the cool plasma only by measurement of the metal oxide ion because the sensitivity and precision of the atomic ion are inferior to those obtained for the metal oxide ion. The sensitivity and precision obtained for these molecular species are comparable to those obtained for the atomic ions of elements that are suitable for analysis using the cool plasma. Calibration curves for the metal oxide signal as a function of the metal concentration in the cool plasma are linear over six orders of magnitude, covering the concentration range from 1 ppt to 1 ppm. Nerve tonic tablets that contain Na, Mg, K, Ca, and Fe in unspecified amounts were analyzed under cool plasma conditions.