Glow discharge - mass spectrometry

Glow-discharge methods need new developments or will go into decline. The greatest needs for GD methods are  

Several reviews deal with GD-MS [156,355,369,373, 375]. A recent monograph is available [166]. 

After compacting with a graphite or metal matrix. 

As a result of impurities in the filler gas and the complexity of the processes taking place, not only do analyte and filler gas ions occur in the mass spectra but also many other ions. Spectral interferences therefore can occur and for various 

The dependence of the ion current, ion intensity, and energy distribution on power, carrier gas pressure, and sampling distance in the case of a magnetron RF-GD for MS was investigated for a borosilicate glass cathode, and ion intensities were found to depend strongly on pressure and distance [762]. 

The possibility of separating the interfering signals depends on the instrument resolution. In the case of quadrupoles, the mass resolution is at best unity and these interferences can only be corrected for by mathematical procedures. However, even with high-resolution instruments having a resolution of 5000, many interferences remain, especially those with hydrides in the mass range 80-120 Da. 

Glow discharges operated at pressures in the 0.1-1 mbar range can be coupled to mass spectrometers by using an aperture between the two chambers with a size of about 1 mm. 

A special DC-GD for combination with a sector-field instrument has been designed for the analysis of high-purity Si [764]. The Si ion yield was found to increase with gas pressure, probably as a consequence of the enhancement in the Ar metastable population. The signals for the SiJ decrease perhaps as a result of an increase in dissociative collisions. Detection limits for elements such as Al, As, B, Cl, Fe, P, and U are at a level of 6 x 10 -6 x 10 atoms/cm.  

Due to its general setup, GD has the advantage that the atomization and ionization processes are separated in space and time, resulting in only minor variations in sensitivity and a low matrix dependence. This enables the quantification of elements without the need for standards tailored to the actual type of sample matrix [45,48]. 

On the downside, there are isobaric interferences such as pCAr] and [XH] ions that require R 5000 to avoid overlap with pure atomic ions [48]. Therefore, double-focusing magnetic sector instruments present the most successful mass analyzers in GD-MS [45]. Another disadvantage of GD-MS as compared to LA-ICP-MS or SIMS (Chaps. 15.4 and 15.5), for example, is the lack of spatial resolution. 

Example In the manufacture of aircraft engines and gas turbines superalloy is widely used due to its excellent performance, which to a great extent depends on the content of trace elements in the alloy. Critical control of the alloy s composition is therefore essential for the safe operation of such engines. The obvious method to avoid isobaric interferences is to select isotopes where no interferences exist. While H, Pb, and Bi meet this criterion, in case of Sn only the Sn ion is free of superimpositions, whereas Sn has serious interferences from Ars, Mo N2, and Te . To determine the correct content of elements in superalloy on a quadrupole GD instrument also when no suitable isotope exists, both matching the sample matrix by use of external standards and multivariable linear regression have extensively been used (Fig. 15.10) [61]. 

The atomic collision processes in the GD are sufficiently robust to break many tenaciously bonded species [54], Nonetheless, GC-GD-TOF-MS has even been demonstrated to be capable of delivering spectra of organic molecules and elemental information [63-65], 

Note The analytical problems of inorganic MS often require only certain selected isotopes or narrow m/z ranges to be measured. Multicollector systems, for example, are adjusted to simultaneously detect a few isotopes for the purpose of accurate isotope ratio determinations or to quantify a low-abundant isotope together with an isotopic standard for internal reference. Thus, the data is more often presented in tabular form or in plots of concentration versus variables such as depth of invasion, age of samples, or location on a surface. Mass spectra covering a wider range are only acquired for survey multi-element detection. 

Stage vacuum system is required. A cathodic extraction can be done at the cathode plume, by taking the sample as the cathode and drilling a hole in it. The aperture should reach the hot plasma center. In most cases the extraction of the ions, however, is done anodically. 

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The conventional method for quantitative analysis of galHum in aqueous media is atomic absorption spectroscopy (qv). High purity metallic galHum is characteri2ed by trace impurity analysis using spark source (15) or glow discharge mass spectrometry (qv) (16). 

GDQMS Glow Discharge Mass Spectrometry using a... 

Sputtered Neutral Mass Spectrometry, Glow-Discharge Mass Spectrometry... 

Elastic Recoil Detection Analysis Glow discharge mass spectrometry Glow discharge optical emission spectroscopy Ion (excited) Auger electron spectroscopy Ion beam spectrochemical analysis... 

Neutron Activation Analysis X-Ray Fluorescence Particle-Induced X-Ray Emission Particle-Induced Nuclear Reaction Analysis Rutherford Backscattering Spectrometry Spark Source Mass Spectrometry Glow Discharge Mass Spectrometry Electron Microprobe Analysis Laser Microprobe Analysis Secondary Ion Mass Analysis Micro-PIXE... 

FFF Field-flow fractionation GD-(MS) Glow-discharge (mass spectrometry)... 

There is a branch of MS specially designed for dealing with the analysis of inorganic materials.[21,22] Different specific ionization techniques, such as inductively coupled plasma mass spectrometry (ICP-MS),[23] glow discharge mass spectrometry (GD-MS)[24] and secondary ion mass spectrometry (SIMS),[25] are available and they are widely used in cultural heritage applications. Their description is beyond the scope of this chapter. 

F. L. King, J. Teng, and R. E. Steiner. Glow Discharge Mass Spectrometry Trace Element Determinations in Solid Samples. J. Mass Spectrom., 30(1995) 1061-1075. 

V. Hoffmann, M. Kasik, P. K. Robinson, and C. Venzago. Glow Discharge Mass Spectrometry. Anal. Bioanal. Chem., 381(2005) 173-188. 

S. DeGendt, R.E. Van Grieken, S.K. Ohorodnik and W.W. Harrison, Parameter evaluation for the analysis of oxide-based samples with radio frequency glow discharge mass spectrometry, Anal. Chem., 67 (1995) 1026-1033. 

The experiments were carried out on high purity aluminium from different producers (Table I) and Al-Ga alloys. The impurity concentration in the used materials was determined by glow discharge mass-spectrometry. The total impurity content in pure aluminium (0.4 - 7.7 ppm) was defined as the sum of the concentration of all found elements.The residual resistivity ratio RRR=p(273K)/p(4.2K) of the materials was measuredby the method prescribed by the U.S. National Bureau of Standards. 

Table 9.4 Result of trace analysis of high purity indium and zinc measured by spark source mass spectrometry (SSMS) and glow discharge mass spectrometry (GDMS), respectively.

Fourier transform infrared spectroscopy glow discharge mass spectrometry glow discharge optical spectrometry high energy electron diffraction high vacuum... 

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