Study of a pulsed glow discharge ion source for time-of-flight mass spectrometry

This paper describes a new type of glow discharge (GD) ion source coupled to a time-of-flight mass spectrometer (TOFMS). The GD is operated in the microsecond pulse (μs-pulse) mode. The operational parameters of the μs-pulse GD were optimized against the ion signals, giving 180 Pa for the discharge pressure, 3 A for the transient discharge current, 1.75 kHz for the discharge frequency and 2 μs for the discharge pulse duration. Experimental results show that the discharge current in the μs-pulse mode can be one order of magnitude higher than that obtained in the d.c. mode. The structure of the interface between the μs-pulse GD and the mass spectrometer was found to be critical, and a Macor disc must be applied in front of the sampling orifice in order to shield the sampling plate from the anode of the GD to achieve both a good vacuum and the best sputtering. A transient sputtering rate of 24.4 μs s⁻¹ mm⁻² was reached in the μs-pulse mode and was significantly higher than that for the d.c.-GD. Typical mass spectra of brass and nickel samples were studied and are discussed. © 1997 Elsevier Science B.V.     

RF-pulsed glow discharge time-of-flight mass spectrometry for glass analysis: Investigation of the ion source design

Radiofrequency (RF) millisecond pulsed glow discharge (PGD) coupled to time-of-flight mass spectrometry (TOFMS) was investigated for direct elemental analysis of glass samples. Aiming at achieving highest elemental sensitivity, appropriate discrimination from polyatomics, and good crater shapes on glasses, a new Grimm-type GD chamber (termed from now “UNIOVI GD”, designed and constructed in our laboratory) was coupled to TOFMS, and the results compared with those obtained with the former GD design (here denominated as “GD.1”) of the initial RF-PGD-TOFMS prototype. The critical differences distinguishing the two GDs under scrutiny are the GD chamber thickness (15.5 mm for the GD.1 and 7 mm for the UNIOVI GD) and the “flow tube” which is inserted in the GD.1 and inexistent in UNIOVI GD.     

Organic mass spectrometry and control of fragmentation using a fast flow glow discharge ion source

Representative organic vapors have been introduced into the flowing afterglow of a low power (<5 W) dc-glow discharge, coupled to a quadrupole mass spectrometer. When a positive bias was applied to the ion sampling orifice, the very surprising result was that molecular mass spectra were obtained with a high sensitivity. When a negative bias was applied to the ion sampling orifice, fragmentation of the analyte was observed with an increase in the extent of ion dissociation as the voltage was increased. The breakdown pattern is compound-specific and would be useful in confirming the identity of an unknown sample. When combined with chromatographic separation, the FFGD-MS technique could be used for chemical speciation studies at the sub-picogram level.     

Analytical glow discharge mass spectrometry

Various types of glow discharge mass spectrometric systems as well as their applications are considered. Special attention is paid to radiofrequency and pulsed glow discharges combined with time-of-flight mass spectrometers. Along with typical application fields of glow discharge mass spectrometry, analysis of semiconductors, polymers, and dielectrics, as well as isotope analysis and depth profiling are also reviewed. Some methods of standard-free mass spectrometric analysis of solids are considered. Prospects for combining glow discharge mass spectrometry with preliminary chromatographic separation are discussed.     

Modeling the effect of the cathode geometry in a DC glow discharge ion source for mass spectrometry

A self-consistent, two-dimensional hybrid fluid-particle model is used to study the effect of cathode geometry on the plasma produced in an argon glow discharge for conditions typically of the commercially available glow discharge mass spectrometer system (VG9000 spectrometer and Megacell source). For a given power supply voltage and gas pressure, we show that the spatial distribution of the plasma in the discharge volume is strongly dependent on the cathode geometry. The plasma created in a discharge with a pin cathode tends to form a ring around the cathode, while the plasma in a discharge with a larger diameter, disk cathode is centered on-axis between the cathode face and the anode. The ion current arriving at the entry plane of the mass spectrometer thus depends strongly on the cathode geometry. This suggests that analytical performance can be enhanced by optimization of the cathode (sample) geometry.     

Chemical ionization mass spectrometry using a glow discharge ion source combined with a nebulizer sampling system

A glow discharge chemical ionization (CI) source equipped with a pneumatic nebulizer for sample introduction has been constructed. A comparative study of the discharge CI and conventional CI by electron impact from a hot filament is made for various polar compounds using oxygen-containing reagents such as water and methanol. The potential utility of the discharge ion source to liquid chromatography/mass spectrometry is also discussed.     

辉光放电质谱技术应用进展

对辉光放电质谱(GDMS)在金属与半导体、非导体、薄层与深度分析、分子信息分析方面的应用和一些新装置、新方法进行了综述.着重介绍了近20年来我国学者在辉光放电质谱方面的成就,并结合国际上的报道对该领域的发展现状进行了总结.     

A glow discharge ion source with fourier transform ion cyclotron resonance mass spectrometric detection

A glow discharge (CD) ion source has been coupled to a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer using a four-element electrostatic lens to accelerate and focus ions generated external to the instrument’s high magnetic field into its analyzer cell. Like other CD mass spectrometers, GD-FT-ICR can provide a quantitative measure of bulk analyte concentration with good precision and accuracy. Although detection limits currently attainable are several orders of magnitude higher than the commercially available magnetic sector-based instrument, CD-FT-ICR holds promise for ultrahigh resolving power elemental mass analysis. Several schemes are proposed to lower the detection limits of the technique while still providing high enough resolution to resolve isobaric interferences.     

Comparison of the efficiency of spark source, laser, glow discharge and secondary ion mass spectrometry for bulk analysis

Summary After describing the design and properties of the ion sources, the analytical performances of spark source, laser, glow discharge and secondary ion mass spectrometry are compared. The criteria are the sample requirements, the detectable elements, the detection limits, element sensitivity factors and the achievable accuracy. Typical areas of use for these methods are derived from these properties.

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Vergleich der Leistungsfähigkeit von Funkenquellen, Laser, Glimmentladungs- und Sekundärionen-Massenspektrometrie für die Bulk-Analyse

     

Development of a dielectric barrier discharge ion source for ambient mass spectrometry

A new ion source based on dielectric barrier discharge was developed as an alternative ionization source for ambient mass spectrometry. The dielectric barrier discharge ionization source, termed as DBDI herein, was composed of a copper sheet electrode, a discharge electrode, and a piece of glass slide in between as dielectric barrier as well as sample plate. Stable low-temperature plasma was formed between the tip of the discharge electrode and the surface of glass slide when an alternating voltage was applied between the electrodes. Analytes deposited on the surface of the glass slide were desorbed and ionized by the plasma and the ions were introduced to the mass spectrometer for mass analysis. The capability of this new ambient ion source was demonstrated with the analysis of 20 amino acids, which were deposited on the glass slide separately. Protonated molecular ions of [M + H](+) were observed for all the amino acids except for L-arginine. This ion source was also used for a rapid discrimination of L-valine, L-proline, L-serine and L-alanine from their mixture. The limit of detection was 3.5 pmol for L-alanine using single-ion-monitoring (SIM). Relative standard deviation (RSD) was 5.78% for 17.5 nmol of L-alanine (n = 5). With the advantages of small size, simple configuration and ease operation at ambient conditions, the dielectric barrier discharge ion source would potentially be coupled to portable mass spectrometers.     

Characterization of a glow discharge ion source for the mass spectrometric analysis of organic compounds

A glow discharge ion source has been constructed for the mass spectrometric analysis of organic compounds. Characterization of the source has been made by studying the effect of pressure and discharge current on ionic distributions by anodic ion sampling along the discharge axis. Ion and electron densities and electronic temperatures have been calculated by using the single Langmuir probe technique to correlate the extraction efficiency with measured ion distributions and gain some insight into the ionization of organic molecules. The spectra obtained for several classes of organic compounds show that formation of parent-molecular ions by proton transfer, resulting partly from the background water molecules, is a major low energy process while charge transfer, Penning ionization, and electron ionization ace probably responsible for the fragmentation observed. The spectra result from the simultaneous occurrence of high and low energy reactions, and their structural information content is very high, yielding both molecular and extensive fragment ion information. The glow discharge ion source has proved to be essentially maintenance-free, easy to operate, stable, and can be used at reasonable mass resolution (up to 70001. The source also provides picogram range detection limits and has a linear response range of about six orders of magnitude, which makes it an interesting ion source for routine analysis. Preliminary work conducted with chromatographic interfaces indicates that its use can be easily extended to both gas and liquid chromatography.     

辉光放电离子源质子转移反应质谱对水中苯的分析方法研究

报告了自行研制的质子转移反应质谱(Proton Transfer Reaction Mass Spectrometry, PTR-MS)装置结合动态气体提取技术直接测量水中苯浓度的新方法. N2连续地将水溶液中的苯提取出来, 用质子转移反应质谱测量其在液面顶空中的分压强P随时间的变化关系, 从而得到苯的亨利常数H 利用亨利定律就可以给出苯在水溶液中的浓度. 考察了苯在提取气体及水溶液中达到平衡需要的液面高度, 测量了28 ℃时苯的亨利常数. 以此为基础测试了水中苯的浓度, 测量结果与配制的溶液浓度相一致. PTR-MS结合动态气体提取技术测量水中苯的浓度, 检出限为1 μg/L. 方法可以拓展到水中其它挥发性有机物浓度的测量.     

辉光放电质谱法测定高纯铟中痕量元素

采用辉光放电质谱法(GDMS)对高纯铟中铁、铜、铅、锌、铊、镉、锡等14种元素进行了测定,对仪器工作参数进行了优化,对预溅射过程时间的确定和质谱干扰的排除进行了讨论,结果表明,GDMS是目前具有足够灵敏度对高纯导电材料进行直接分析的有效手段。     

The pulsed glow discharge as an elemental ion source

A pulsed glow discharge, rather than a conventional constant dc voltage discharge, is used as an ion source for a quadrupole mass spectrometer. Both sputter yield and ion signal are enhanced by using the pulsed system because of an increase in the voltage necessary to maintain a constant average current at the cathode over the pulse period. Irregularities are seen in the pulse spectrum that appear as rapid surges in the ion signal for both sputtered and contaminant gas species. These peaks appear at the beginning of the pulse for gaseous species but are limited to the postpulse period for sputtered species. Differences in the signal forms allow for the discrimination against selected types of ion signals by using narrow data collection gates placed over different portions of the pulse period.     

Polymer screening by radiofrequency glow discharge time-of-flight mass spectrometry

The aim of this work is to optimise and evaluate radiofrequency glow discharge (RF GD) time-of-flight mass spectrometry (TOFMS) for identification of organic polymers. For this purpose, different polymers including poly[methylmethacrylate], poly[styrene], polyethylene terephthalate-co-isophthalate and poly[alpha-methylstyrene] have been deposited on silicon wafers and the RF GD-TOFMS capabilities for qualitative identification of these polymeric layers by molecular depth profiling have been investigated. Although some molecular information using the RF continuous mode is available, the pulsed mode offers a greater analytical potential to characterise such organic coatings. Some formed polyatomic ions have proved to be useful to identify the different polymer layers, confirming that layers having similar elemental composition but different polymer structure could be also differentiated and identified.     

Analysis of solution residues by glow discharge mass spectrometry

A technique for the analysis of microliter volumes of solution by glow discharge mass spectrometry (GDMS) has been successfully demonstrated. Cathode preparation involves mixing an aliquot of the sample solution with a pure conducting powder, followed by drying and pressing before conventional GDMS analysis. The analyte signal at the 100-ppm level was observed to be stable to better than 5% for the duration of the analysis (30–45 min). Internal and external reproducibilities were better than 5%, and the ion signal intensity was linear with concentration over at least four orders of magnitude. Quantification was demonstrated by means of user-defined relative sensitivity factors. Relative standard deviations were better than 15% for the elements investigated, with no preconcentration of the analyte.     

Internal glow discharge-fourier transform ion cyclotron resonance mass spectrometry

A glow discharge (GD) ion source has been developed to work within the high magnetic field of a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Characterization of this source revealed that the optimum operating voltage, pressure, and current are significantly lower than those for normal glow discharges. The sputter rate was lowered to 1/30th of that found with a normal glow discharge source operated external to the high magnetic field region. Operation of the GD source closer to the FTICR analyzer cell than with previous experimental designs resulted in improved ion transport efficiency. Preliminary results from this internal GD source have established detection limits in the low parts per million range for selected elemental species.     

A novel isotope analysis of oxygen in uranium oxides: comparison of secondary ion mass spectrometry,glow discharge mass spectrometry and thermal ionization mass spectrometry

The natural variation of the oxygen isotopic composition is used among geologists to determine paleotemperatures and the origin of minerals. In recent studies, oxygen isotopic composition has been recognized as a possible tool for identification of the origin of seized uranium oxides in nuclear forensic science. In the last 10 years, great effort has been made to develop new direct and accurate n(¹⁸O)/n(¹⁶O) measurements methods. Traditionally, n(¹⁸O)/n(¹⁶O) analyses are performed by gas mass spectrometry. In this work, a novel oxygen isotope analysis by thermal ionization mass spectrometry (TIMS), using metal oxide ion species (UO⁺), is compared to the direct methods: glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS). Because of the possible application of the n(¹⁸O)/n(¹⁶O) ratio in nuclear forensics science, the samples were solid, pure UO₂ or U₃O₈ particles. The precision achieved using TIMS analysis was 0.04%, which is similar or even better than the one obtained using the SIMS technique (0.05%), and clearly better if compared to that of GDMS (0.5%). The samples used by TIMS are micrograms in size. The suitability of TIMS as a n(¹⁸O)/n(¹⁶O) measurement method is verified by SIMS measurements. In addition, TIMS results have been confirmed by characterizing the n(¹⁸O)/n(¹⁶O) ratio of UO₂ sample also by the traditional method of static vacuum mass spectrometry at the University of Chicago.