Skimmer Cone Research Articles

Measurement of I-129 in environmental samples by ICP-CRI-QMS: possibilities and limitations

129I is preconcentrated from environmental samples and its accessibility is addressed for inductively coupled plasma quadrupole mass spectrometer with collision/reaction interface (ICP-CRI-QMS). By applying oxygen as CRI gas through skimmer cone, the signal of the interfering 129Xe from the impurity of plasma gas can be eliminated while the formation of 127I1H1H+ can be partially removed. The improved ICP-QMS can be employed for investigation of 129I in environmental samples with a 129I/127I ratio down to 10-7. The detection capability was demonstrated by measuring 129I in seaweed samples collected around the nuclear fuel reprocessing plant at La Hague. The abundant 127I in the sample matrix causes a serious problem and degrades the detection capability of the instrument when the concentration of 127I is larger than 105 ng/g. Even combined with a sufficient pre-concentration procedure, ICP-QMS is not considered as a suitable technique for the analysis of 129I in uncontaminated environmental samples with 129I/127I ratio of less than 10-7. Results are presented for seaweed samples collected around La Hague. In addition, time dependant I concentrations and ratios are given for colloids and water sampled from Lake Thun.

Plasma Gas-Switching Method for Gas Chromatography/ Inductively Coupled Plasma Mass Spectrometry and Determination of Polybrominated Diphenylethers with High Precision and Sensitivity

The drift in sensitivity due to carbon deposition on the sampling cone, skimmer cone and ion lenses has been a serious problem in gas chromatography/inductively coupled plasma mass spectrometry (GC/ICP-MS). To overcome this problem, a high-speed switching method between a mixed-gas plasma and a pure-argon plasma (named plasma gas-switching method) using an oxygen permeation tube and a switching valve was developed. This enabled both the cleaning of deposited carbon and an enhancement of the sensitivity; as a consequence, both the repeatability and the sensitivity of polybrominated diphenylether (PBDE) were improved by more than 3 and 4 times, respectively. The drifts of sensitivity over a period of 8 h were less than 5% in most cases. Concerning the analytical performance of thermally labile congeners from octa- to deca-BDE, the detection limits, dynamic ranges of the calibration graphs and unequivalent sensitivities were remarkably improved by using a metal capillary separation column coated with a very thin (0.05 micromm) film of immobilized-polydimethylsiloxane. The detection limits ranged from 0.014 pg (BDE-154) to 0.093 pg (BDE-209), which were equal or superior to the lowest values reported hitherto by GC/MS (high resolution). A remarkable loss of sensitivity for highly-brominated congeners, such as nona- and deca-BDE, was observed in an analysis of PBDE technical mixtures when the solvent was methanol. The loss of sensitivity turned out to be due to an activation of the retention gap used for on-column injection; this problem was solved by changing methanol to isooctane in the sample-preparation step before analysis.

Influence of Fragmentor Voltage and Solvent on Negative Ionization Behaviors of Uvinul 3039 Using LC/APCI-MS

Engineering plastics undergo degradation when exposed to the ultraviolet radiation in sunlight. This degradation process results in appearance changes such as discoloration, chalking, and crazing as well as reduction of physical properties. UV absorbers slow down the degradation process by absorbing harmful ultraviolet radiation and dissipating it as thermal energy. Analysis of UV absorbers is very important to understand polymer degradation studies and qualityassurance testing. 2-Ethylhexyl-2-cyano-3,3-diphenylacrylate (Uvinul 3039) is one of popular cyanoacrylate UV absorbers since it is aprotic and stable UV absorber. Uvinul 3039 has a single absorption band with a maximum at 305 nm. Analysis of UV absorbers is difficult because of requirement of a sensitive method for identification, high molecular weight, and high polarity. Thus, gas chromatography (GC) is not suitable for analysis of UV absorbers. Although high performance liquid chromatography (HPLC) with UV detection has been successfully used, this method is only applicable to compounds having UV-absorbable groups. These problems can be solved by the use of liquid chromatography/mass spectrometry (LC/MS), 1,2 especially LC/MS with atmospheric pressure chemical ionization (LC/APCIMS) 3 . Block and coworkers 3 analyzed antioxidants and UV stabilizers for polymeric materials using LC/APCI-MS. In APCI, a corona discharge makes solvent reactant ions that are used to ionize the sample by chemical ionization. Solute and sample are vaporized by pneumatic nebulization. APCI relies upon gas-phase ion-molecule reactions to place a charge on neutral analytes, so it is especially important to understand these reactions. Kostiainen and Bruins reported that a judicious selection of solvent can be made to promote ionization of the compound of interest. 4-7 When mobile phase transports analyte molecules, APCI can deliver a proton to the analyte. The solvent-derived ions serve as reagents for proton transfer ionization. Mass spectrometry with APCI gives a great deal of structural information in a short analysis time. In APCI-MS, fragmentation pattern can be obtained by varying the fragmentor voltage (or accelerating voltage) and some fragment ions are produced to identify the structure of an analyte. 8 A key parameter in tuning the instrument’s sensitivity is the fragmentor voltage (similar to cone voltage in other instruments). At higher fragmentor voltage settings, collisioninduced dissociation (CID) can be initiated in the region between the end of the transfer capillary and the first skimmer cone, so that fragmentation increases. 9 In this study, we analyzed Uvinul 3039 using LC/APCI-MS with negative ion mode and investigated the ionization behaviors such as formation of solvent-adducted ion and fragmentation by varying the fragmentor voltage and kind of solvent. Methanol, ethanol, and acetone were employed as the solvent and eluent. These solvents have been used for extraction of organic additives including UV absorbers from plastic polymers such as polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET), and poly(vinyl

δ30Si and δ29Si Determinations on USGS BHVO‐1 and BHVO‐2 Reference Materials with a New Configuration on a Nu Plasma Multi‐Collector ICP‐MS

We report silicon isotopic determinations for USGS rock reference materials BHVO‐1 and BHVO‐2 using a Nu Plasma multi‐collector (MC)‐ICP‐MS, upgraded with a new adjustable entrance slit, to obtain medium resolution, as well as a stronger primary pump and newly designed sampler and skimmer cones (“B” cones). These settings, combined with the use of collector slits, allowed a resolution to be reached that was sufficient to overcome the 14N16O and 14N2 interferences overlying the 30Si and the 28Si peaks, respectively, in an earlier set‐up. This enabled accurate measurement of both δ30Si and δ29Si. The δ value is expressed in per mil variation relative to the NBS 28 quartz reference material. Based on data acquired from numerous sessions spread over a period of six months, we propose a recommended average δ30Si of −0.33 ± 0.05‰ and −0.29 ± 0.11‰ (2se) for BHVO‐1 and BHVO‐2, respectively. Our BHVO grand mean silicon isotope composition (δ30Si =−0.31 ± 0.06‰) is significantly more negative than the only published value for BHVO‐2, but is in very good agreement with the recently established average value of ocean island basalts (OIB), confirming the conclusion that the OIB reservoir has a distinct isotopic composition from the solar reservoir as sampled by chondrites.

Speciation of iodate and iodide in seawater by non-suppressed ion chromatography with inductively coupled plasma mass spectrometry

A non-suppressed ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP-MS) has been developed for simultaneous determination of trace iodate and iodide in seawater. An anion-exchange column (G3154A/101, provided by Agilent) was used for the separation of iodate and iodide with an eluent containing 20 mM NH 4NO 3 at pH 5.6, which reduced the build-up of salts on the sampler and skimmer cones. The influences of competing ion (NO 3 −) in the eluent on the retention time and detection sensitivity were investigated to give reasonable resolution and detection limits. Linear plots were obtained in a concentration range of 5.0–500 μg/L and the detection limit was 1.5 μg/L for iodate and 2.0 μg/L for iodide. The proposed method was used to determinate iodate and iodide in seawaters without sample pre-treatment with exception of dilution.

High resolution imaging of barium ions and atoms near the sampling cone of an inductively coupled plasma mass spectrometer

Planar laser-induced fluorescence was used to map density distributions of ground state barium atoms, ground state barium ions, and excited-state barium ions in the region between the load coil and the sampling cone of an inductively coupled plasma mass spectrometer. The effects of power, nebulizer gas flow rate, and the addition of lithium to the sample on the distributions were studied. The maps reveal that the radial distributions of atomic species across the diameter of the plasma are compressed as the plasma is drawn into the sampling orifice, and that as a result of that compression, the distribution of ions across the 1-mm diameter of the sampling orifice is non-uniform. The distribution changes as conditions in the plasma change. The skimmer cone that separates the first and second stages of the differentially-pumped vacuum interface transmits ions exclusively from the center of the distribution that exists at the sampling cone. As a result, the overall efficiency with which ions are transmitted through the vacuum interface varies as conditions in the plasma change.

High resolution studies of the origins of polyatomic ions in inductively coupled plasma-mass spectrometry, Part I. Identification methods and effects of neutral gas density assumptions, extraction voltage, and cone material

Common polyatomic ions (ArO +, NO +, H 2O +, H 3O +, Ar 2 +, ArN +, OH +, ArH +, O 2 +) in inductively coupled plasma-mass spectrometry (ICP-MS) are identified using high mass resolution and studied using kinetic gas temperatures ( T gas) determined from a dissociation reaction approach. Methods for making accurate mass measurements, confirming ion identifications, and correcting for mass bias are discussed. The effects of sampler and skimmer cone composition and extraction voltage on polyatomic ion formation are also explored. Neutral species densities at several locations in the extraction interface are estimated and the corresponding effects of the T gas value are calculated. The results provide information about the origins of background ions and indicate possible locations for their formation or removal.

Development of Rapid Plutonium Analysis for Environmental Samples by Isotope Dilution/Inductively Coupled Plasma Mass Spectrometry with On-line Column

This paper describes our development of a rapid on-line column/ID-ICP-MS technique for the analysis of plutonium (Pu) in environmental samples using an UTEVA extraction chromatograph resin (UTEVA resin) column. It took only 40 min to separate and measure Pu in the sample solution, including the time for conditioning the resin column for the next analysis. In our method, Pu in a 3 M nitric acid solution was fed to the UTEVA resin, and then eluted from the resin by reducing Pu to Pu(III) with 3 M nitric acid mixed with 0.01 M ascorbic acid after washing the resin. The outflow from the resin column was directly introduced to an ICP-MS system. The low concentration of ascorbic acid and the small volume of the eluting solution (0.6 mL) made successive stable analysis possible without any skimmer cone clogging. The chemical recovery of Pu during column operation was 70%, and typical lower detection limits for 239Pu, 240Pu and 242Pu were 9.2, 4.3 and 7.5 fg (21, 36 and 1.1 microBq), respectively. We analyzed five international standard materials for Pu, and obtained good results.

Characterization of a focal plane camera fitted to a Mattauch-Herzog geometry mass spectrograph. 2. Use with an inductively coupled plasma.

A novel charge-sensitive detector array, termed the focal plane camera (FPC), has been coupled to a Mattauch-Herzog mass spectrograph (MHMS) with an inductively coupled plasma ionization source. The FPC employs an array of gold Faraday cups, each with its own charge-integrating circuit that allows the simultaneous detection of several m/z ratios. The ion-sampling interface of the MHMS has been redesigned to provide better heat transfer away from the sampler and skimmer cones and to reduce the negative effects of turbulent gas flows around the plasma. The instrument has produced limits of detection in the tens to hundreds of parts per quadrillion regime and isotope ratio accuracy and precision of 5% error and 0.007% RSD, respectively. Limits of detection with the FPC are comparable to those obtained with a single-channel secondary electron multiplier (SEM). However, the isotope ratio accuracy and precision are better with the FPC than when the SEM is employed. The dynamic range has been shown to be linear over 7 orders of magnitude.

Correcting sensitivity drift during long-term multi-element signal measurements by solid sampling-ETV-ICP-MS

Solid sampling-electrothermal vaporisation-inductively coupled plasma-mass spectrometry (SS-ETV-ICP-MS) is an attractive technique for the direct simultaneous determination of trace elements in solid samples and especially in long-term studies (i.e. assessment of the homogeneity of reference materials). However, during these studies a downward drift in the instrument sensitivity has been observed due likely to deposits on the sampling and skimmer cones and on the ion lens of the mass spectrometer. Accordingly, in this paper, several means of correcting and/or suppressing sensitivity drift are proposed and evaluated for the monitoring of Cd, Cu, Hg, Mn, Pb, Sb, Se, Sn, Tl, U and V in different reference materials of inorganic and organic (biological) origin. From that studies, the combination of the use of the argon dimer as internal standard together with a modification in the ETV-ICP connection tube seems to be the best mean of getting stable sensitivity during at least 60 consecutive ETV runs.

High-precision Cu and Zn isotope analysis by plasma source mass spectrometry

Spectral interferences originating from instrumental and sample-matrix components continue to present a major analytical challenge to high-precision isotope ratio measurements by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). This is particularly true when measuring stable isotopic variability of Cu and Zn, where instrumental and sample-matrix related spectral components may obscure the very small isotopic anomalies that typify these metals in terrestrial materials. We present a systematic characterisation and quantification of spectral interferences across the mass range 63Cu to 70Zn using two MC-ICP-MS instruments: a Micromass IsoProbe and a VG Axiom. Significant instrumental Ni backgrounds of up to 40 mV total Ni occur on the IsoProbe, reflecting streaming off the Ni-sampler and/or skimmer cones. This Ni contribution, however, is insufficient to account for the excess peak contribution at 64amu, suggestive of an as yet unidentified interference contribution at this mass. By contrast, Ni backgrounds on the Axiom are roughly one order of magnitude lower, and no comparable interference occurs at 64amu. High-resolution mass scans on the Axiom have identified 40Ar12C16O+ and 40Ar14N14N+ species at 68amu and 40Ar14N16O+ at 70amu. Also, HNO3-related 1H1H14N16O16O16O+ and 1H1H14N16O16O18O+ species at 64amu and 66amu respectively were observed on the Axiom using solution nebulisation. None of these species were observed on the IsoProbe, possibly reflecting the effect of an Ar-bled hexapole collision cell that reduces molecular interferences through ion-molecule reactions. Instrumental backgrounds have been successfully corrected using an on-peak acid blank subtraction procedure. Zinc hydride adducts occur on the Axiom using solution nebulisation. These interferences are eliminated using a desolvated plasma, and have been corrected by monitoring the 64Zn1H+/64Zn ratio on a pure Zn solution and applying an offline peak subtraction. No Zn hydride interferences were observed on the IsoProbe, suggesting differences in instrument design influence the formation and/or persistence of these species. Matrix-induced interference contributions on the Axiom and IsoProbe show increasing significance from argides (NaAr+, MgAr+, AlAr+) to oxide/hydroxide (TiO+, TiOH+, VO+, VOH+, CrO+, CrOH+) to double-charged species (Ba2+, Ce2+). Switching from solution nebulisation to a desolvated plasma enhances argide and double-charge species, and concurrently depresses oxides and hydroxides, reflecting changing conditions within the ICP-source. These results highlight the importance of removing problematic matrix components prior to Cu and Zn MC-ICP-MS isotope ratio measurements.

Sources of mass bias and isotope ratio variation in multi-collector ICP-MS: optimization of instrumental parameters based on experimental observations

In this work, several contributing factors to the observed mass bias in inductively coupled plasma mass spectrometry (ICP-MS) have been identified. Analyses of the isotopic compositions of B deposited on sampler and skimmer cones demonstrate enrichment of 10B on the former and 11B on the latter. Grounding the capacitive discharge system to enhance sensitivity also magnified the level of 11B enrichment on the skimmer cone more than four-fold. This supersonic expansion of the ion beam behind the sampler is confirmed to be an important source of mass bias. Isotopic analyses of the Fe, Zn and Tl leached from used extraction lenses yielded a linear relationship between the levels of lighter isotope depletion and mass ratio. Although consistent with the space-charge effect, the fact that isotopically-heavy deposits were found demonstrates that the ion beam diverges into a relatively wide solid angle in the field-free region behind the skimmer. This severely impairs transmission of, in particular, the lighter isotopes. For a wide range of elements (Li, B, Fe, Ni, Cu, Sb, Ce, Hf and Re), the magnitude of the mass bias was found to be affected by the sample gas flow rate, as well as the distance between the sampler and the end of the torch, i.e., the sampling depth, employed in the Neptune multi-collector ICP-MS instrument. Mathematical analysis of the profiles of intensity variations as a function of these instrumental parameters revealed that the response peaks closer to the torch for the heavier isotopes of all studied elements. Owing to this spatial non-coincidence, tuning for maximum intensity on either isotope will result in sampling from a region where even slight plasma instabilities will be translated into substantial variations in mass bias. Therefore, in-plasma processes also contribute to the degree and temporal stability of mass bias. In light of these findings, recommendations for optimizing multi-collector ICP-MS with respect to obtaining the highest possible precision are presented.

Formation of polyatomic ions from the skimmer cone in the inductively coupled plasma mass spectrometry

The inductively-coupled plasma ion source for mass spectrometry is very sensitive for multielement analysis with detection limits down to sub part per trillion (ppt). Polyatomic ions which could be formed in the mass spectra may interfere in the analysis of some elements. Experimental conditions have great influences on the formation of polyatomic ions. The present work demonstrates that the skimmer materials (Au, Ag, Ni, Cu and Al) are participating in the formation of polyatomic ions. Heats of formation of polyatomic species formed from the skimmer materials such as: AuX, AgX, NiX, CuX and AlX, where X=Ar, O, N and H, are calculated by Gaussian program (G94W).

Ion stopping experiment to determine the origin of background ions in icp-ms

Ion stopping experiments have been performed using a triple grid placed between the ion extraction and collector lenses of a modified lens stack. Stopping voltages for ions extracted from the plasma were between 6.6 and 13.1 V (Be+), 9.8–13.1 V (Co+, In+, Ce+, Pb+), and 11.8–14.4 V (U+). Controlled contamination of the ion extraction interface was performed, and the stopping voltage for Be+ ions contributing to the subsequent background signal was determined to be between 1.5–5.9 V. This suggests that these ions originated downstream of the ion sampling interface, possibly due to deposition of Be on the skimmer cone, which was subsequently re-volatilised. The low stopping voltage of these ions meant that they would be prevented from entering the quadrupole by applying a small retarding potential on one of the lens elements (or possibly the quadrupole itself), while still admitting those ions with higher energies which were extracted from the plasma.

High-speed digital photographic study of an inductively coupled plasma during laser ablation: comparison of dried solution aerosols from a microconcentric nebulizer and solid particles from laser ablation

High-speed photographs and videos of an ICP are used to examine the fates of solid particles produced by laser ablation (LA) in an inductively coupled plasma (ICP). The trajectories, lifetimes, and emission behavior of particles traversing the plasma are studied under a variety of conditions. Desolvated particles from a nebulized yttrium solution and particles ablated from a Y2O3 pellet are mixed and introduced simultaneously into an ICP. High-resolution digital photographs and video sequences are captured using shutter speeds of approximately 65 µs. The plasma behavior of particles generated by a quadrupled Nd:YAG laser (266 nm) and an ArF excimer laser (193 nm) are compared, and either argon or helium is used as the transport gas through the ablation cell. No red emission clouds from YO are visible in the ICP when a 20 µL min−1 nebulizer is used to spray a 2000 ppm aqueous Y solution, suggesting that the wet droplets from this nebulizer desolvate almost completely before entering the ICP. These desolvated particles from the nebulized solution atomize and ionize like the small dry particulates from laser ablation. However, many large ablated particulates are observed to fly through the plasma intact, possibly contributing to signal noise, deposition on the sampler and skimmer cones, and elemental fractionation.

Mercury speciation analysis in soil samples by ion chromatography, post-column cold vapor generation and inductively coupled plasma mass spectrometry

A method of employing an ion chromatography (IC) column, an online post-column cold vapor (CV) generation system, coupled to an inductively coupled plasma mass spectrometer (ICP-MS), for the determination of inorganic mercury (Hg2+) and monomethylmercury (CH3Hg+) is described. The IC-CV-ICP-MS technique has generated a method with significant improvements in detection limits as well as shorter analysis time over previous methods. In addition, several major shortcomings associated with the conventional pneumatic nebulization system, e.g., high reflected power from organic solvent introduction into the plasma, deposition of carbon on the sampler and skimmer cones and significant memory effect, have been minimized. The analysis run was finished in as little as six minutes with a mobile phase of 65% methanol and 0.45 M hydrochloric acid. The detection limits (as Hg), based on three times the standard deviation of a standard solution, were found to be 35 pg mL−1 for Hg2+ and 73 pg mL−1 for CH3Hg+, with an injection volume of 400 µL. The proposed method was applied to mercury speciation analysis in two soil samples and compared with IC-ICP-MS using conventional pneumatic nebulization for sample introduction. Good agreement was obtained between the two methods. The analysis of extracts from soil samples spiked of Hg2+ and CH3Hg+ with this method showed recoveries of close to 100% for both species.

Further development of a simple glow discharge source for direct solid analysis by on-axis time of flight mass spectrometry

Different chamber design parameters have been investigated in order to improve the sensitivity of a simple glow discharge (GD) prototype constructed in our laboratory for the direct analysis of solid samples and designed to be easily and quickly exchanged with the inductively coupled plasma (ICP) source of a commercial ICP-time-of-flight mass spectrometer (TOFMS) instrument. Results showed that one of the most important parameters to be considered was the actual design of the channel(s) introducing the plasma gas into the GD. In fact, it was observed that the GD-MS sensitivity can be improved about one order of magnitude by using two opposite gas inlets in the chamber in order to obtain a better sampled plasma, as compared to the use of just one gas inlet. Further improvements on the GD-(TOF)MS sensitivity were achieved by reducing, from 12 mm to 5.5 mm, the distance between the skimmer cone of the (TOF)MS interface and the sample. Also, the use of a skimmer cone with an orifice of 0.7 mm instead of the 1 mm commercial one proved to be necessary to allow GD operation at pressures commonly used in analytical work. Advantages of this prototype include its capability of analysing directly solid samples with different shapes and sizes, the simplicity of the proposed GD design and its versatility because it can be easily “coupled to/removed from” the (TOF)MS commercial interface.

Ion chemistry of chloroethanes in air at atmospheric pressure

Ion chemistry at atmospheric pressure is of major relevance to novel methods for the abatement of volatile organic compounds (VOCs) that employ non-thermal plasmas. For this reason, positive and negative APCI (atmospheric pressure chemical ionization) mass spectra of all six di-, tri- and tetrachloroethanes diluted in air (500–1500 ppm) at atmospheric pressure were investigated at 30 °C and at 300 °C. Spectral changes due to collisional activation of the ions achieved by increasing ΔV, the potential difference between sampling and skimmer cones, are informative of structures and ion-molecule reactions. Positive ion chemistry of the chloroethanes (M) can, in general, be ascribed to C-C and C-Cl cleavages of the molecular ion, M+·, never detected but likely formed via exothermic charge exchange from primary ions of the APCI plasma. Exceptions to this characteristic pattern were observed for 1,1-dichloroethane and 1,1,2,2-tetrachloroethane, which give [M − H]+ and [M − HCl]+· species, respectively. It is suggested that both such species are due to ionization via hydride transfer. Upon increasing ΔV, the [M − HCl]+· ion formed from 1,1,2,2-tetrachloroethane undergoes the same fragmentation and ion-molecule reactions previously reported for trichloroethene. A nucleophilic reaction of water within the [C2H4Cl+](H2O)n ionic complexes to displace HCl is postulated to account for the [C2H5O+](H2O)m species observed in the positive APCI spectra of the dichloroethanes. Negative ion spectra are, for all investigated chloroethanes, dominated by Cl− and its ion-neutral complexes with one, two and, in some cases, three molecules of the neutral precursor and/or water. Another common feature is the formation of species (X−)(M)n where X− is a background ion of the APCI plasma, namely O2−,O3− and, in some cases, (NO)2−. Peculiar to 1,1,1-trichloroethane are species attributed to Cl− complexes with phosgene, (Cl−)(Cl2C=O)n(n = 1,2). Such complexes, which were not observed for either the isomeric 1,1,2-trichloroethane or for the tetrachloroethanes, are of interest as oxidation intermediates in the corona-induced decomposition process. No conclusions can be drawn in the case of the dichloroethanes, since, for these compounds, the ions (Cl−)(Cl2C=O)n and (Cl−)(M)n happen to be isobaric. Copyright © 2001 John Wiley & Sons, Ltd.

Ion chemistry of chloroethanes in air at atmospheric pressure

AbstractIon chemistry at atmospheric pressure is of major relevance to novel methods for the abatement of volatile organic compounds (VOCs) that employ non‐thermal plasmas. For this reason, positive and negative APCI (atmospheric pressure chemical ionization) mass spectra of all six di‐, tri‐ and tetrachloroethanes diluted in air (500–1500 ppm) at atmospheric pressure were investigated at 30 °C and at 300 °C. Spectral changes due to collisional activation of the ions achieved by increasing ΔV, the potential difference between sampling and skimmer cones, are informative of structures and ion‐molecule reactions. Positive ion chemistry of the chloroethanes (M) can, in general, be ascribed to C‐C and C‐Cl cleavages of the molecular ion, M+·, never detected but likely formed via exothermic charge exchange from primary ions of the APCI plasma. Exceptions to this characteristic pattern were observed for 1,1‐dichloroethane and 1,1,2,2‐tetrachloroethane, which give [M − H]+ and [M − HCl]+· species, respectively. It is suggested that both such species are due to ionization via hydride transfer. Upon increasing ΔV, the [M − HCl]+· ion formed from 1,1,2,2‐tetrachloroethane undergoes the same fragmentation and ion‐molecule reactions previously reported for trichloroethene. A nucleophilic reaction of water within the [C2H4Cl+](H2O)n ionic complexes to displace HCl is postulated to account for the [C2H5O+](H2O)m species observed in the positive APCI spectra of the dichloroethanes. Negative ion spectra are, for all investigated chloroethanes, dominated by Cl− and its ion‐neutral complexes with one, two and, in some cases, three molecules of the neutral precursor and/or water. Another common feature is the formation of species (X−)(M)n where X− is a background ion of the APCI plasma, namely O2−,O3− and, in some cases, (NO)2−. Peculiar to 1,1,1‐trichloroethane are species attributed to Cl− complexes with phosgene, (Cl−)(Cl2C=O)n(n = 1,2). Such complexes, which were not observed for either the isomeric 1,1,2‐trichloroethane or for the tetrachloroethanes, are of interest as oxidation intermediates in the corona‐induced decomposition process. No conclusions can be drawn in the case of the dichloroethanes, since, for these compounds, the ions (Cl−)(Cl2C=O)n and (Cl−)(M)n happen to be isobaric. Copyright © 2001 John Wiley & Sons, Ltd.

Ion trajectory simulation of inductively coupled plasma mass spectrometry based on plasma-interface behavior

An ion trajectory simulation study of inductively coupled plasma mass spectrometry (ICP-MS) was conducted based on a newly proposed plasma interface model. The model is based on the formation of a plasma boundary by interaction between plasma behind the skimmer cone and the electric field of the extraction lens system. An estimated plasma boundary position, or charge separation position is used to determine the initial conditions of the simulation study. Two regions of conditions, in terms of radio frequency (RF) power for the ICP and first extraction lens voltage showing characteristic sensitivity, were reasonably explained by this simulation. This paper suggests that the location and shape of the plasma boundary are key factors that affect the focusing properties and transmission of the ion lens.