Desolvation Device Research Articles

Precise measurement of 226Ra/230Th disequilibria in deep-sea sediments by high-sensitivity ICP-MS

We describe a new method suitable for the precise and accurate determination of 226Ra in porewater and sediment samples using a single-collector sector field ICP-MS (ThermoFisher Element XR) equipped with an Apex-Q desolvation device and a high-sensitivity Jet-X interface. In combination with 230Th measurements in parallel sediment samples, this method allows precise and accurate quantification of the 226Ra/230Th disequilibria in surface sediment cores, thereby enabling the use of this isotope pair as a tracer of solute transfer across the sediment-water interface in the deep ocean. The method integrates a step of isotope dilution with 228Ra as an internal spike, a pre-concentration of Ra and Ba by MnO2 precipitation, and an efficient separation of Ra from other undesirable elements using a cation exchange resin and a Triskem Sr-spec resin. With the inclusion of one or two additional cation resin columns and the use of up to 16 bed-volumes of a lower molarity (1.7 M) HCl eluent, our procedure eliminates the complicated matrix effects persistently encountered in previous studies, and provides a highly purified solution suitable for 226Ra measurement using an Element XR ICP-MS apparatus. Consequently, we are able to determine the activity of 226Ra in ∼20–50 ml of porewater or 100 mg of sediment with an internal precision of ∼1.0% and an accuracy of ∼99.2%. The precise measurements of porewater and solid phase 226Ra in a sediment core from the North Pacific Ocean allowed the distribution coefficient (Kd) of 226Ra to be constrained tightly within a range of 4700–11,600 ml g−1. Moreover, with the aid of a one-dimensional exchange model, the combination of the 226Ra and 230Th measurements allowed us to estimate a 226Ra flux of 1140 ± 20 dpm m−2 y−1 from the sediment core.

Mass-spectrometric determination of iodine-129 using O2-CO2 mixed-gas reaction in inductively coupled plasma tandem quadrupole mass spectrometry.

This paper presents a mass-spectrometric method for determining the radionuclide iodine-129 (129I) from the significant amount of interference in inductively coupled plasma tandem quadrupole mass spectrometry (ICP-MS/MS) using a dynamic reaction cell passing a mixture gas of O2 and CO2. Thus far, mass spectrometry analysis of trace amounts of 129I has been hampered by the presence of xenon-129 (129Xe) and the formation of polyatomic ions from excess amounts of stable isotope 127I. In this study, flowing a mixture gas of O2 and CO2 into the dynamic reaction cell (Q2) successfully removed both 129Xe interference and polyatomic interference (127IH2) in the analysis of 129I in ICP-MS/MS. The resulting ratio of (background noise of m/z 129)/127I was 4.6 × 10-10 ± 3.3 × 10-10, which enables the analysis of 10mBq/L of 129I in the presence of 100mg/L of stable 127I without chemical separation. The detection limit of this method was 0.73mBq/L (= 0.11ng/L) with an APEX-Q sample inlet desolvation device. For demonstration purposes, spike and recovery analysis of rainwater was performed, and good agreement between the spiked and recovered amounts was achieved.

New Orientation: A Downward-pointing Vertical Inductively Coupled Plasma Mass Spectrometer for the Analysis of Microsamples

We present a prototype of a vertical-downward configuration of an inductively coupled plasma mass spectrometer (ICPMS) allowing the sample introduction from the top. With this novel approach to orient the ICP downward, we aim to expand the sample transport capabilities in ICPMS especially for the transport of droplets or particles with a final goal to analyze individual cells. Because of this gravity-assisted sampling approach, the transport of larger sized droplets, that is, droplets that would be difficult to transport into a horizontally oriented ICPMS, becomes possible and, furthermore, becomes independent of the droplets' size or size distribution. We demonstrate that droplets of an initial size of 70 μm can be successfully transported into the plasma at dispensing frequencies up to 1 kHz without the need for a desolvation device. In addition, we observed that the implementation of a desolvation device, that is, a gas-exchange device (GED), can improve the detection efficiencies (DEs). Compared to operating conditions that are commonly reported for ICPMS experiments, significantly different optimization parameters (radio frequency power and gas flow rates) were tested in the presented experiments here while instrument type-specific DEs were obtained.

Precise selenium isotope measurement in seawater by carbon-containing hydride generation-Desolvation-MC-ICP-MS after thiol resin preconcentration

The isotopic compositions of Se in natural materials can be measured by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in combination with hydride generation and desolvation device. Although oceans are important targets for research, precise isotopic analysis of Se in seawater is generally difficult owing to its low concentrations and the much higher concentrations of other elements. We developed a robust, accurate method for the precise determination of Se isotopic composition in seawater. A hydride generator combined with a desolvation device with methane addition was coupled to MC-ICP-MS to measure Se isotopes precisely. Two new thiol resins were used to preconcentrate and separate Se from the seawater matrix efficiently, and Se was quickly eluted by small amounts of concentrated HNO3. No detectable Se isotope fractionation was observed during the preconcentration and separation procedure. The carbon-containing plasma increased Se sensitivity, suppressed the spectral interference signal, and improved precision by >3 times. The precisions (2sd, n=24) of Merck Se standard solutions for δ82/78Se, δ82/77Se, and δ82/76Se were 0.07‰, 0.10‰, and 0.16‰, respectively. The δ82/76Se values of standard solutions agreed well with results obtained by other research groups. The method was used to obtain a depth profile for dissolved inorganic Se (DISe) isotopes in seawater from the Northwestern Pacific Ocean. The range of δ82/76DISe was 0.41‰ to 1.59‰, indicating that Se isotopes fractionate sufficiently to clarify the biogeochemical cycling of this element in the ocean.

The influence of the sample introduction system on signals of different tin compounds in inductively coupled plasma-based techniques

The influence of the sample introduction system on the signals obtained with different tin compounds in inductively coupled plasma (ICP) based techniques, i.e., ICP atomic emission spectrometry (ICP–AES) and ICP mass spectrometry (ICP–MS) has been studied. Signals for test solutions prepared from four different tin compounds (i.e., tin tetrachloride, monobutyltin, dibutyltin and di-tert-butyltin) in different solvents (methanol 0.8% (w/w), i-propanol 0.8% (w/w) and various acid matrices) have been measured by ICP–AES and ICP–MS. The results demonstrate a noticeable influence of the volatility of the tin compounds on their signals measured with both techniques. Thus, in agreement with the compound volatility, the highest signals are obtained for tin tetrachloride followed by di-tert-butyltin/monobutyltin and dibutyltin.The sample introduction system exerts an important effect on the amount of solution loading the plasma and, hence, on the relative signals afforded by the tin compounds in ICP–based techniques. Thus, when working with a pneumatic concentric nebulizer, the use of spray chambers affording high solvent transport efficiency to the plasma (such as cyclonic and single pass) or high spray chamber temperatures is recommended to minimize the influence of the tin chemical compound. Nevertheless, even when using the conventional pneumatic nebulizer coupled to the best spray chamber design (i.e., a single pass spray chamber), signals obtained for di-tert-butyltin/monobutyltin and dibutyltin are still around 10% and 30% lower than the corresponding signal for tin tetrachloride, respectively. When operating with a pneumatic microconcentric nebulizer coupled to a 50°C-thermostated cinnabar spray chamber, all studied organotin compounds provided similar emission signals although about 60% lower than those obtained for tin tetrachloride. The use of an ultrasonic nebulizer coupled to a desolvation device provides the largest differences in the emission signals, among all tested systems.

Iodine Determination by Microwave Plasma Torch Atomic Emission Spectrometer Coupled with Online Preconcentration Vapor Generation Technique

This article focuses on iodine determination by microwave plasma torch atomic emission spectrometry (MPT-AES) coupled with online preconcentration vapor generation method. A new desolvation device, multistrand Nafion dryer, was used as the substitute for condenser desolvation system. Some experimental conditions, such as preconcentration time, acidity of sample solution, rinsing solution acidity and dynamic linear range were investigated and optimized. The new desolvation system eliminates the problem of decreasing emission intensity of I(I) 206.238 nm line with the increase of working time on a conventional condenser desolvation system, thus greatly improving the reproducibility.

A direct ultratrace determination of platinum in environmental, food and biological samples by ICP-SFMS using a desolvation system

The purpose of this study was to develop a robust, reliable and accurate method that allows measurements of platinum in the sub-ppt range in environmental, food and biological samples. The quantification of platinum was performed with digested samples, exploiting the high sensitivity of inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in low resolution mode. The hafnium oxide interference affecting the determination of platinum was investigated. A desolvation device in combination with a membrane unit was used as the sample introduction system, in order to minimize the oxide formation. A HfO+/Hf+ ratio of 0.01% was obtained (50 times lower than with a standard inlet system), thus interferences were strongly reduced and no mathematical corrections were necessary in most samples. The platinum value found in the reference material road dust BCR 723 agreed with the certified value (within the 95% confidence limit). Additionally, recovery tests in spiked peat and hay samples confirmed the accuracy of this technique at an acceptable precision from 3.5% to 15.5% (RSD). The method was applied to the measurement of environmental and food samples from two locations, one near a well-frequented motorway, one from an alpine site. The higher platinum concentrations measured at the first site confirmed the polluting effect of the traffic. Swiss diet samples, urine samples and corresponding reference materials, SRM 1548 and SRM 2670 for total diet and urine, respectively, were measured as well. The method was successfully applied to the determination of trace and ultratrace levels of platinum in the samples, with very low limits of detection of 4.5 ng kg−1 in dry environmental and food samples, corresponding to 0.2–1.8 ng kg−1 in fresh weight samples and of 0.5 ng L−1 in urine samples.

Design and development of a highly sensitive, field portable plasma source instrument for on-line liquid stream monitoring and real-time sample analysis

The development of a highly sensitive, field portable, low-powered instrument for on-site, real-time liquid waste stream monitoring is described in this article. A series of factors such as system sensitivity and portability, plasma source, sample introduction, desolvation system, power supply, and the instrument configuration, were carefully considered in the design of the portable instrument. A newly designed, miniature, modified microwave plasma source was selected as the emission source for spectroscopy measurement, and an integrated small spectrometer with a charge-coupled device detector was installed for signal processing and detection. An innovative beam collection system with optical fibers was designed and used for emission signal collection. Microwave plasma can be sustained with various gases at relatively low power, and it possesses high detection capabilities for both metal and nonmetal pollutants, making it desirable to use for on-site, real-time, liquid waste stream monitoring. An effective in situ sampling system was coupled with a high efficiency desolvation device for direct-sampling liquid samples into the plasma. A portable computer control system is used for data processing. The new, integrated instrument can be easily used for on-site, real-time monitoring in the field. The system possesses a series of advantages, including high sensitivity for metal and nonmetal elements; in situ sampling; compact structure; low cost; and ease of operation and handling. These advantages will significantly overcome the limitations of previous monitoring techniques and make great contributions to environmental restoration and monitoring.

Study of using a Nafion dryer as a desolvation device for MPT-AES

In this paper a novel desolvation device, Nafion dryer has been introduced into an MPT-AES, and its operating parameters, such as heating temperature, purge gas flow rate and peristaltic pump rotation speed, have been optimized. A comparison between a condensation system and the Nafion dryer system was carried out and the results indicated that the Nafion dryer system has good performance for desolvation.

Use of an ultrasonic nebulizer with membrane desolvation for analysis of volatile solvents by inductively coupled plasma atomic emission spectrometry

The petroleum and chemical industries need a rapid, and sensitive technique for the trace analysis of volatile feedstocks, intermediates and products, including high-purity solvents. Organic solvent loading of the inductively coupled plasma (ICP) adversely effects the application of ICP atomic emission spectrometry to analysis of volatile organic liquids when conventional sample introduction equipment is employed. The use was investigated of a membrane separator as a secondary desolvation device used with an ultrasonic nebulizer (USN) to further reduce organic vapour loading of the plasma and enable µg l–1 determinations to be performed on solvents and petroleum products boiling well below 100 °C. Two prototype membrane desolvator units and the final commercial unit were tested on a variety of materials including hexanes, methanol, tetrahydrofuran, acetone and dichloromethane. Organic vapour removal was efficient enough to permit the analysis of these materials at ‘normal’ sample introduction rates (1–4 ml min–1) and practical operating conditions. Detection limits similar to aqueous solution USN limits were achieved. Owing to the near complete solvent matrix removal provided by the USN-membrane sample introduction system, ‘universal calibration’ of the ICP should be possible at certain ICP operating conditions. Experiments were conducted with the goal of achieving a single calibration valid for a variety of volatile organic solvents. Accurate calibration was maintained for several diverse solvent types after applying corrections for solvent nebulization efficiencies relative to the calibration solvent.

Particle size measurements in the submicron range by the differential electromobility technique: comparison of aerosols from thermospray, ultrasonic, pneumatic and frit-type nebulizers

The differential electromobility technique was used for the comparison of droplet- and particle-size distributions in the 0.02–0.8 μm range for six nebulization systems often used in inductively coupled plasma (ICP) spectrometry: a thermospray nebulizer coupled to a membrane separator (TNMS); two ultrasonic nebulizers (USNs) used with desolvation; one pneumatic nebulizer (PN) used with and without desolvation; and a frit-type nebulizer. In general, volume concentration (volume of droplets or particles per cubic centimeter of injector gas) increased with NaCl concentration, and it was greater for TNMS followed by USNs compared to other nebulizers. For the desolvated aerosol produced by PN and USN, volume concentration was found to be independent of the temperature (140–180°C) of the heating tube for the desolvation device. As the nebulizer tip temperature in thermospray nebulization was varied from 160 to 240°C, a larger volume concentration of desolvated aerosol was produced. Size distributions shifted towards larger particles with increasing NaCl concentration. The implications of these observations in plasma spectrochemical measurements are discussed.

Calculations of the partial pressure of OH molecules in argon-plasma emission sources for spectrochemical analysis.

Calculations have been made for the partial pressure of OH molecules in argon plasmas into which a small amount of water vapor was introduced through a desolvation device. The Newton-Raphson method was applied to the calculation for a system consisting of O, H, OH, O2, H2, H2O, and argon. In the temperature range above 4000 K, where the system consisted mainly of O, H, OH, and argon, an approximate analytical calculation provided results in a good agreement with those obtained by the Newton-Raphson method. The partial pressures in the plasma jet light source and the high frequency plasma torch were determined by the methods proposed. Calculated ratios of the OH band emission intensities at two different temperatures are also given and are discussed.

Effects of potassium chloride on the analytical characteristics of the capillary arc excitation source.

In emission spectrometry using a capillary arc as an excitation source, the effects of potassium chloride in solutions on the spectrum and background intensities, analytical curves, precision, and sensitivity have been investigated. Sample solutions were sprayed with a pneumatic glass nebulizer, passed through a modified desolvation device, and the desolvated aerosols were introduced into the arc plasma to be excited. The capillary arc operated satisfactorily at a low argon flow rate of 1.15l/min. The spectrum intensity of iron increased and the background emission decreased with increasing potassium chloride concentration. When spraying solutions with more than 0.5 M potassium chloride, potassium chloride deposited on the inside of the capillary, reducing the emission stability. The use of 0.1 M potassium chloride solutions resulted in the improvement in detection limits for all the elements tested but tungsten and zirconium without marked decrease in the slope of analytical curves and reduction in the precision of measurements.