Double-focusing Sector Field ICP-MS Research Articles

Postmortem reference concentrations of 68 elements in blood and urine.

Fatal intoxications, both accidental and intentional, are a global issue. In the Western world, intoxications with pharmaceuticals dominate, but in other parts of the world, other substances are more common. In a forensic setting, elemental intoxications are of great importance when investigating both accidental, suicidal, and homicidal deaths. The current study presents normal postmortem reference concentrations of 68 elements in femoral blood and urine. In addition, possible sources of error such as contamination from sample tubes, preservative potassium fluoride (KF) solution, and storage time are evaluated. Paired femoral blood and urine samples from 120 cases of death by suicidal hanging in Sweden were collected. Additionally, multiple batches of sample tubes and multiple batches of KF solution were also analyzed. Concentrations of elements were determined by double focusing sector field ICP-MS. Key descriptive statistics for 68 elements are provided in blood and urine. Contamination from sample tubes was minor compared to the overall mean elemental concentrations in both blood and urine. KF solution contained a large assortment of elements, but the overall contribution is relatively minor for most elements given the small amounts of solution added to samples. There were significant differences for 22 elements in blood and 17 elements in urine between samples with short and long storage time. The present study provides an important tool when evaluating postmortem elemental concentrations. It fills a needed gap between large antemortem population studies and postmortem case reports or small case series of elemental intoxications.

Postmortem reference concentrations of elements in blood and urine

To establish postmortem reference concentrations of elements. Fatal intoxications, both accidental and intentional, are a global issue. In the western world intoxications with pharmaceuticals dominate, but in other parts of the world other substances are more common. Intoxication with elemental compounds is generally considered to be uncommon. In a forensic setting, elemental intoxications are of great importance when investigating both accidental, suicidal, and homicidal deaths. Arsenic, for example, is a classical poison which also has relevance in the modern era. Unlike for pharmaceuticals, postmortem reference concentrations for elements are scarce. For many elements it is therefore unknown if, and to what extent, they are affected by postmortem redistribution. The current study presents normal postmortem reference concentrations of 68 elements in femoral blood and urine. In addition, possible sources of error such as contamination from collection tubes, preservative potassium fluoride solution and storage time are evaluated. Paired blood and urine samples from 120 cases of death by suicidal hanging in Sweden were collected. 20 cases from each of the six local units of forensic medicine were used to account for possible regional differences. Additionally, the included cases reflected both short and long storage times. To account for possible elemental contamination from collection tubes and the added potassium fluoride solution, multiple batches of tubes and multiple samples of potassium fluoride solution were also analysed. Concentrations of elements were determined by double focusing sector field ICP-MS. Key descriptive statistics for all 68 elements are provided (including mean, median and percentiles) in blood and urine. Forensic highlights include blood concentrations of total arsenic (mean: 4.25 μg/g), thallium (mean: 0.14 μg/g) and antimony (mean: 14.82 μg/g). For several elements in blood and urine ( n = 24 and n = 25, respectively) a majority of elemental concentrations were below the limit of detection. The contribution of contamination from collection tubes were minor compared to the overall mean elemental concentrations in both blood and urine. Though the added solution of potassium fluoride contained a large assortment of elements, given the small amounts of this solution added to samples, the overall contribution is minor for most elements relative to the overall mean. However, there was a significant difference between samples with short and long storage time for 22 elements in blood and 17 elements in urine. These differences reflected both increases and decreases in concentration. Relative to antemortem elemental concentrations the postmortem concentrations show both increases and decreases. Of special note are markedly higher concentrations for several elements in blood (such as cadmium, chromium, manganese and antimony) compared to several antemortem populations. In general, it can be assumed the phenomenon of postmortem redistribution is as large for elements as it is for drugs and other substances. When evaluating individual concentrations, it is important to be aware of potential sources of contamination and the potential influence of storage time. Concentrations indicating overexposure must be evaluated together with autopsy findings and case circumstances to form a holistic view of the case as a whole. The present study provides an important tool when evaluating postmortem elemental concentrations. It fills a needed gap between large antemortem population studies and postmortem case reports or small case series of elemental intoxications. Together with the forensic autopsy and circumstantial information the present references will aid in diagnosing cases of potential elemental overexposure.

Potential of methyl fluoride as a universal reaction gas to overcome spectral interference in the determination of ultratrace concentrations of metals in biofluids using inductively coupled plasma-tandem mass spectrometry.

Methyl fluoride (a mixture of 10% CH3F and 90% of He) was evaluated as a reaction gas in inductively coupled plasma-tandem mass spectrometry (ICPMS/MS) in the context of the determination of ultratrace concentrations of medically relevant metals (Al, Co, Cr, Mn, Ni, Ti, and V) in blood serum and urine. Via product ion scanning, whereby only ions of the mass-to-charge ratio of the target nuclide were admitted into the octopole reaction cell, the various reaction product ions formed for each of the target elements were identified at different CH3F gas flow rates. Limits of detection (LODs) and of quantification (LOQs) and linearity of the calibration curve were documented under (i) optimized ICPMS/MS conditions for single-element monitoring and (ii) compromise conditions, allowing for multielement determination. Even under compromise settings, instrumental LODs were below 10 ng/L for all target elements, while the use of CH3F provided interference-free conditions for their determination in the biofluids of interest. Quantitative data obtained for Seronorm blood serum and urine reference materials were in excellent agreement with the corresponding reference values and/or results obtained using double-focusing sector-field ICPMS (for those elements for which no certified values were available or that were affected during reconstitution), proving the potential of this reaction gas for multielement ultratrace analysis via ICPMS/MS.

Concentrations of toxic and essential elements in Lebanese bread

Concentrations of 20 minor, trace, and ultratrace elements relevant to human health (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Hg, Li, Mn, Mo, Ni, Pb, Sb, Se, Si, Sn, V, and Zn) were determined in three varieties of Lebanese bread (white and brown double loaf bread, Saj bread) sampled at five geographical regions (Grand Beirut, South of Lebanon, North of Lebanon, Mount of Lebanon, and Beka’a) during the wet and dry seasons. The analyses were carried out by double-focusing sector-field inductively coupled plasma-mass spectrometry (DF-SF-ICP-MS). The data were discussed in terms of nutritional elements supplied by type of bread, the risk of contamination by toxic elements (As, Cd, Pb) owing to the manufacturing process, and variations related to geographic distribution and seasonal sampling.

Polyatomic interferences in plutonium determination in the femtogram range by double-focusing sector-field ICP-MS

The determination of very low concentrations of plutonium, in the femtogram per millilitre range, in environmental samples using ICP-MS can be interfered by polyatomic species containing heavy elements, from hafnium to bismuth. Mass-to-charge ratios of these polyatomic species are very close to the ones of the plutonium isotopes and cannot be separated from them in the low resolution mode currently used for trace analysis. In this paper, we present an evaluation of the extent and impact of these interferences on the background at masses of plutonium isotopes 239Pu and 240Pu, based on measurement of environmental samples for three years using a double-focusing sector-field ICP-MS. We demonstrate that these molecular interferences, especially the ones involving lead, mercury, and iridium through species PbO2+, ArHg+, IrO3+, must be considered as the additional background induced by these interferences (on average for all interferences respectively ∼1.2 and ∼1.9 counts s−1 at 239 and 240 atomic mass units) is often higher than the instrumental background measured with deionised water acidified at 2% by ultra-pure grade HNO3 (∼0.4 counts s−1), and are generally of the same order as other usual sources of background for low-level plutonium analysis by ICP-MS, i.e.242Pu tracer isotopic impurities, 238U hydrides and peak tail. Thus, if not corrected, these polyatomic interferences may lead to false detection of femtogram amounts of plutonium or overestimation of results. The extents of formation of the main polyatomic species are highly variable from one analysis to the other, over one or two orders of magnitude, depending on instrumental settings. Chemical purification procedures are very efficient in eliminating the greater part of heavy elements present in the initial samples. However, these procedures also bring heavy elements into the final sample solutions through contamination by the atmosphere, glassware and reagents.

Multi-element analysis of bread, cheese, fruit and vegetables by double-focusing sector-field inductively coupled plasma mass spectrometry

An analytical method using double-focusing sector-field ICP MS was developed for the routine simultaneous multi-element analysis for essential and toxic elements (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Hg, In, Li, Ni, Mn, Mo, Pb, Si, Sb, Se, Sn, V and Zn) in different food samples (bread, cheese, fruit and vegetables). Samples were hot-plate digested with a mixture of concentrated HNO3 and H2O2. Interfering ions involving matrix constituents were detected for several elements at the resolution of 300 (typical for a quadrupole analyzer) and could be separated at the 4000 and 10 000 resolution. The method was validated by the analysis of certified reference materials: wheat flour (NIST 1567a), non-fat milk powder (NIST 1549) and brown bread (BCR-IRMM 191). The method used in our laboratory over the period of one year for the analysis of over 300 samples showed a typical interday precision of 3–5% and intraday precision of 5–10% for virtually all the elements and investigated matrices.

P, S and Cl trace detection by laser ablation double-focusing sector field ICP-MS to identify local defects in coated glasses

Glass defects are always undesired because of their significant costs to manufacturing industries. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a versatile technique for local trace element analysis in a wide variety of solid samples. Furthermore, the coupling of laser systems to double-focusing sector field mass analyzers provides low limits of detection with a high mass resolving power, allowing the accurate analysis of P, S and Cl traces in local defects of coated glasses. Three different types of defects, depending on the impurities identified at the LA-ICP-MS profiles, were found in the selected coated glasses (with metallic and oxide films in the low nanometre range), enabling the unambiguous identification of the contamination source that produces the local defects.

Direct multi-element analysis of crude oils and gas condensates by double-focusing sector field inductively coupled plasma mass spectrometry (ICP MS)

A double-focusing sector field ICP MS was optimized for the direct simultaneous determination of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sn, Ti, V in organic solutions. Polyatomic interferences originating from the carbon-rich matrix were completely eliminated at a resolution of 4000 allowing the detection limits at the low pg g−1 level to be obtained (typically one order of magnitude lower than using a quadrupole ICP MS). A method for the routine comprehensive trace element analysis of xylene solutions of oil samples using external calibration was developed. It was validated by the analysis of three certified reference materials and applied to the analysis of 2 gas condensate samples and 4 oil samples of different origins.

Quantitative Imaging of Selenium, Copper, and Zinc in Thin Sections of Biological Tissues (Slugs−Genus Arion) Measured by Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Quantitative imaging analysis of endogenous an exogenous elements throughout entire organisms is required for studies of bioavailability, transport processes, distribution, contamination and to monitor environmental risks using indicator organisms. An imaging mass spectrometric technique using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was developed to analyze selenium and metal distributions in longitudinal sections (thickness, 100 microm) of entire slugs (genus arion). Slugs were fed with either a placebo or solutions containing 1000 microg mL(-1) Se. Samples (raster area, 25 mmx45 mm) were scanned together with synthetic matrix-matched standards with a focused beam of a Nd:YAG laser (wavelength, 266 nm; diameter of laser crater, 50 microm; laser power density, 3x10(9) W cm(-2)) in a large laser ablation chamber. The ablated material was transported with argon as carrier gas to the ICP ion source at a double focusing sector field ICPMS. Ion intensities of selenium (78Se+, 82Se+) were measured together with 13C+, 63Cu+, and 64Zn+ within the entire tissue section. The regression coefficient of the calibration curve was 0.998. Inhomogeneous distributions for Se but also for C, Cu, and Zn were found. Selenium was enriched in the kidney (150 microg g(-1) in Se-treated animals versus 15 microg g(-1) in the placebo-treated animal, respectively) and in the digestive gland (200 microg g(-1) versus 25 microg g(-1)). Highest Se concentrations were detected in the gut of Se-treated slugs (250 microg g(-1)), and additional Se occurred in the skin of these animals. Cu was enriched in the heart and the mucous ventral skin. Interestingly, in addition to the localization in the digestive gland, Zn was detected only in the dorsal skin but not the ventral skin. The developed analytical technique allows the quantitative imaging of selenium together with selected metals in thin sections of biological tissue with limits of detection at the submicrogram per gram range.

Authentication of Kalix (N.E. Sweden) vendace caviar using inductively coupled plasma-based analytical techniques: Evaluation of different approaches

Different analytical approaches for origin differentiation between vendace and whitefish caviars from brackish- and freshwaters were tested using inductively coupled plasma double focusing sector field mass spectrometry (ICP-SFMS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP–MS). These approaches involve identifying differences in elemental concentrations or sample-specific isotopic composition (Sr and Os) variations. Concentrations of 72 elements were determined by ICP-SFMS following microwave-assisted digestion in vendace and whitefish caviar samples from Sweden (from both brackish and freshwater), Finland and USA, as well as in unprocessed vendace roe and salt used in caviar production. This data set allows identification of elements whose contents in caviar can be affected by salt addition as well as by contamination during production and packaging. Long-term method reproducibility was assessed for all analytes based on replicate caviar preparations/analyses and variations in element concentrations in caviar from different harvests were evaluated. The greatest utility for differentiation was demonstrated for elements with varying concentrations between brackish and freshwaters (e.g. As, Br, Sr). Elemental ratios, specifically Sr/Ca, Sr/Mg and Sr/Ba, are especially useful for authentication of vendace caviar processed from brackish water roe, due to the significant differences between caviar from different sources, limited between-harvest variations and relatively high concentrations in samples, allowing precise determination by modern analytical instrumentation. Variations in the 87Sr/ 86Sr ratio for vendace caviar from different harvests (on the order of 0.05–0.1%) is at least 10-fold less than differences between caviar processed from brackish and freshwater roe. Hence, Sr isotope ratio measurements (either by ICP-SFMS or by MC-ICP–MS) have great potential for origin differentiation. On the contrary, it was impossible to differentiate between Swedish caviar processed from brackish water roe and Finnish freshwater caviar based solely on 187Os/ 188Os ratios.

Ultratrace determination of uranium and plutonium by nano-volume flow injection double-focusing sector field inductively coupled plasma mass spectrometry (nFI–ICP-SFMS)

A sensitive analytical procedure based on nano-volume flow injection (FI) and inductively coupled plasma double-focusing sector field mass spectrometry (ICP-SFMS) was developed for the ultratrace determination of uranium and plutonium. A 54-nl sample was injected by means of a nanovolume injector into a continuous flow of carrier liquid at 7 μl min−1 prior to ICP-SFMS. The absolute detection limits were 9.1 × 10−17 g (3.8 × 10−19 mol, ∼230000 238U atoms) and 1.5 × 10−17 g (6 × 10−20 mol, ∼38000 242Pu atoms) for uranium and plutonium, respectively. The method was validated for the determination of the uranium isotope ratios by the analysis of a certified isotope reference material (NIST U350). The analysis of a contaminated urine sample showed the enriched uranium to be the origin of contamination. Another application concerned the determination of plutonium at the subfemtomolar level in water with a detection limit down to the ag ml−1 range (6 × 10−18 g ml−1).

Precise determination of sulfur isotopic ratio in aqueous solutions by inductively coupled plasma mass spectrometry

Analytical procedures for complete separation of SO42− in aqueous solutions and precise sulfur isotopic ratio determination using inductively coupled plasma double focusing sector field mass spectrometry (ICP-SMS) operated at low resolution (m/Δm = 300) were developed. A platinum guard electrode and an Aridus sample delivering apparatus were combined to reduce 16O16O+ interferences at m/z 32 and to enhance analytical sensitivity. A precision of better than 0.1% for successive measurements of seawater and IAPSO was achieved with 2–5 μl aqueous solutions in less than a minute of measurement time. The sulfate concentrations measured in rains, seawater and pore waters agree well with those obtained by ion chromatography. The downcore δ34S variations in porewater at Site 1202 are greater than 50‰, highlighting the effects of sulfate reduction. The sulfur isotopic compositions in rains and seawater samples reflect sensitively the source and oxidation/reduction conditions.

Determination of 226Ra at ultratrace level in mineral water samples by sector field inductively coupled plasma mass spectrometry

An analytical procedure has been proposed for the determination of (226)Ra at the low femtogram per ml concentration level in mineral water samples using double focusing sector field ICP-MS (ICP-SFMS). For the pre-concentration and separation of radium from the matrix elements in water a tandem of a laboratory-prepared filter, based on MnO(2), and Eichrom "Sr-specific" resin was used. The recovery of the method was determined to be 70.5%. The limit of detection for (226)Ra determination was 0.02 fg ml(-1), including a pre-concentration factor of 10. In addition, uranium concentration and uranium isotope ratios were measured by ICP-SFMS. In several mineral water samples with a relatively high uranium content, (226)Ra concentrations were found between 0.7-15 fg ml(-1). The effective dose of the contribution was calculated using the radionuclide concentration and dose conversion factors from the World Health Organization, WHO (1993). Assuming a mineral water consumption of 2 l d(-1), a slightly higher calculated dose than the suggested limit for drinking water (0.1 mSv y(-1)) was found in some samples.

Evaluation of a single collector, double focusing sector field inductively coupled plasma mass spectrometer for the determination of U and Pu concentrations and isotopic compositions at trace level

This work explores the performance of the “Axiom”, a double focusing sector field ICP-MS (ICP-SFMS) in the determination of actinide concentration and isotopic ratio at trace level. On the actinide mass range the performances observed are characterized by high sensitivity, around 2.8·106 cps·µg−1·l, and low background, below 0.3 cps. Therefore, the absolute instrumental detection limit is approximately 0.05 fg for Pu isotopes. Furthermore, the 235U/238U ratio for a 0.5 µg·l−1 U500 isotopic standard could now be measured using the ICP-SFMS with a relative standard deviation less than 0.1%. Moreover, the accuracy of the measured ratio was demonstrated at low concentration with the target value remaining within experimental uncertainty limits.

Reduction of UH+ formation for 236U/238U isotope ratio measurements at ultratrace level in double focusing sector field ICP-MS using D2O as solvent

The main factors affecting the accurate and precise determination of 236U using ICP-MS are instrumental background, the isobaric interference of 235UH+ molecular ion on 236U+ analyte ions, and the presence of 238U+ and 235U+ peak tails. An optimized analytical method for attenuating the influence of these factors on uranium isotope ratio measurements at ultratrace level of environmental samples has been developed. In order to reduce 235UH+ formation, D2O (heavy water) is used as a solvent for the dissolution and dilution of uranium samples. Abundance sensitivity was improved by use of medium mass resolution (m/Δm = 4450) in comparison with low mass resolution in double-focusing sector field ICP-MS (ICP-SFMS). For solution introduction the performances of several different sample introduction systems (Meinhard, Aridus and ultrasonic nebulizer) were studied. It has been shown, that for all nebulization systems, a diminution in UH+/U+ is observed in D2O as compared with H2O as solvent. Optimum results were obtained in ICP-SFMS for a desolvating microconcentric nebulizer system (Aridus) with a minimum hydride formation rate of 9 × 10−7 and a limit for 236U/238U isotopic ratio measurements of 3 – 5 × 10−7. A comparison was performed of three commercially available sector field ICP-MS devices, with good agreement found between single collector and multiple collector ICP-MS (MC-ICP-MS).

Determination of rhenium and osmium concentrations in molybdenite using laser ablation double focusing sector field ICP-MS

A technique for the in situ determination of Re and Os in molybdenite samples using direct solid sampling by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is described. The sample preparation is limited to molybdenite separation followed by grinding and pressing to pellets. For Re determination, the best results were obtained using external calibration in conjunction with internal standardization. Isotopes of both molybdenum and sulphur could be used as internal standards. This quantification approach provides precision levels generally better than 10% the relative standard deviation (RSD) with similar levels of accuracy. Os concentrations were derived from Re concentrations and measured isotopic ratios of intensities measured at masses 187 and 185, using W isotopes for on-line mass bias correction. As a rule, LA-ICP-MS results for Os agree with corresponding isotope dilution ICP-MS data to within 30%. Reproducibility is strongly dependent on the age of the molybdenite as well as on the precision of isotope ratio measurements, which in turn depend on Re and W concentrations. The proposed technique provides a rapid estimation of Re and Os concentrations for subsequent precise analysis by isotope dilution ICP-MS.

Application of double focusing sector field ICP-MS for multielemental characterization of human hair and nails. Part III. Direct analysis by laser ablation

The capabilities of laser ablation double focusing sector field inductively coupled plasma mass spectrometry for the determination of 55 elements in nails and hair were studied. Quantification was performed by external calibration using in-house matrix-matched standards in tablet form following correction for variations in ablation efficiency by internal standardization using a matrix element (S). For nails, intra-individual long- and short-term chronological variations as well as depth distribution patterns were studied. For the majority of elements tested, significant enrichment was found in the surface of the nail. Element distributions along a hair strand were investigated with a spatial resolution of 2.5 mm.

Uncertainty calculation on the determination of calcium absorption in nutritional experiments with enriched stable isotopes and detection by double focusing sector field ICP-MS with a shielded torch

A new method for the measurement of calcium isotope ratios and total calcium, using a double focusing sector field inductively coupled plasma mass spectrometry (ICP-MS) instrument equipped with a shielded torch, is presented. The method was applied for the measurement of the 44Ca/43Ca, 42Ca/43Ca and 44Ca/42Ca ratios and total calcium by isotope dilution in urine samples from two different nutritional experiments set up to determine the calcium absorption from various foods. The isotope ratios were measured with a precision of 0.25%, 0.23% and 0.05% RSD for 44Ca/43Ca, 42Ca/43Ca and 44Ca/42Ca, respectively. The precision of the 44Ca/42Ca ratio is only limited by counting statistics, whereas the precision is limited by uncertainty from the needed background and interference corrections when the minor 43Ca isotope is used for analysis. Uncertainty calculations on the determination of calcium absorption in the nutritional experiments are presented. These calculations show that, for a double stable isotope procedure (administration of enriched stable 44Ca and 42Ca), the overall uncertainty is controlled by the precision of the ICP-MS measurement of the isotope ratios (44Ca/43Ca, 42Ca/43Ca), whereas, for a mixed radioisotope–stable isotope procedure (administration of enriched stable 44Ca and the 47Ca radioisotope), the overall uncertainty is mainly controlled by the uncertainty in the measurement of total calcium by isotope dilution ICP-MS. From these results, it was concluded that, when optimizing the performance of nutritional experiments, the emphasis should be placed on different parameters depending on the exact analysis involved. The results also show that uncertainty calculations are very useful in pinpointing the critical parameters of an experiment.

Multielemental analysis of Mn-Fe nodules by ICP-MS: optimisation of analytical method.

Two acid digestion procedures (microwave-assisted and room temperature) were developed for the quantitative analysis of ferromanganese nodules by inductively coupled plasma double focusing sector field mass spectrometry (ICP-SFMS). Different compositions of the acid mixture, dilution factors and corrections for spectral interferences were tested. A combination of nitric, hydrochloric and hydrofluoric acids is necessary for complete sample digestion, with lowest acid to sample ratios (v/m) of 15 and 1.5, respectively, for the last two acids. Sample dilution factors higher than 2 x 10(4) should be used in order to decrease matrix effects and provide robust long-term instrumental operation. In spite of high dilution, method detection limits in the sub-microg g(-1) range were obtained for 54 out of 71 elements tested, due to the high detection capability of ICP-SFMS, as well as the special care taken to ensure the purity of reagents, to clean the instrument sample introduction system and to minimise sample handling. Owing to the presence of unresolved (at the resolution available) spectral interferences, accurate determination of Au, Hg, Os, Pd, Re and Rh is impossible without matrix separation. The accuracy of the entire analytical method was tested by the analysis of two nodule reference materials. The results generated agreed to within +/-2% for about 10, within +/-10% for more than 40 and within +/-20% for about 50 of 53 elements for which certified, recommended or literature values are available. A precision better than 3%, expressed as the between-digestion relative standard deviation (n = 4), was obtained for the majority of elements, except in cases limited by low analyte concentrations.

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.