A routine tool for the analysis of solid samples
Meike Hamester, Lothar Rottmann und Joachim Hinrichs
Thermo Fisher Scientific
Hanna-Kunath Strasse 11
28199 Bremen, Germany
meike.hamester@thermo.com
=> Thermo Scientific ELEMENT GD Product Webpages
The glow discharge mass spectrometry has been commercially available since the mid eighties and is the method of the choice for the direct quantitative analysis of trace elements, e.g. impurities in conductive solids. The solids analyzed are typically high purity metals.
| Glow Discharge Mass Spectrometry |
| A glow discharge is produced when a voltage is applied between two electrodes in an argon gas filled cell. The target sample is used as the cathode. The diameter of the anode determines the diameter of the ablated sample surface (8 mm). The sample surface is impacted by ions that are accelerated towards the sample. The atoms sputtered from the sample surface are subsequently ionized in the plasma formed in the glow discharge cell. Since the processes of sampling and ionization are separated, GD-MS is subject to minimal levels of matrix effects - an important advantage for quantification. The ions are then accelerated with a voltage of - 8000 V into the mass spectrometer, passing through the magnetic field and separated according to their mass and energy. In the electrostatic analyzer (ESA), ions of different energies are focused, so that a high precision mass separation is produced. This so-called double focusing arrangement permits an accurate mass identification, guaranteeing unambiguous element identification. In the detection system, ions are detected over a linear range of 12 orders of magnitude. |
Glow discharge mass spectrometry (GD-MS) is established as the high performance tool for the solid analysis of high purity metals down to single digit ppb levels. However, there were several drawbacks of the technique mainly due to the sector field analyzer currently used for this technology. Older generations of sector field analyzer suffer from slow scan speed, poor mass stability and complex GD sources that result in difficult operation and very low sample throughput. Consequently, GD-MS did not succeed in conquering many routine laboratories. The analytical performance was never in doubt, but both its operation and sample throughput were not sufficient to meet the demands of modern routine laboratories.
Since Spark Source Mass Spectrometers (SSMS) and DC-Arc Spectrometers are no longer commercially available and optical glow discharge spectroscopy (GD-OES) cannot offer the desired analytical performance, especially in terms of detection limits, ICP-MS interfaced with laser ablation systems has become more and more of interest for the analysis of elements in solid samples. The trend towards shorter wavelengths in modern laser systems has offered definite improvements in quantification but a µm scale focused laser beam is not ideal for bulk analysis since reproducibility suffers due to sample inhomogeneities. The advantage of glow discharge is the sampling area of 8mm, ideal for the representative analysis of bulk materials. In order to convey GD-MS to a wider audience it was necessary to develop an instrument that was convincing not just in its analytical performance but also addressed concerns regarding ease of use, sample throughput and data management.
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Thermo Fisher Scientific has taken the task and introduced a new GD-MS, the Thermo Scientific ELEMENT GD, which was launched early 2005. The foundation for the ELEMENT GD is the sector field mass spectrometer ELEMENT2 - a high resolution ICP-MS. The ELEMENT2 features innovative scan techniques and mature magnet field control that directly translates into short analysis times and high sample throughput. When using older generation sector field mass spectrometers, it was necessary to "search" for the isotope on the mass scale as they suffered from poor mass accuracy and stability. The ELEMENT sector field analyzer impresses with the highest mass accuracy and stability that allows sharp determination of the mass of interest ? a huge benefit for the analysis time. While older types of GD-MS instruments used to analyze about 4 samples per day, the ELEMENT GD analysis up to 6 samples per hour - complete quantification from ultra-trace to matrix
- One Element GD for the entire periodic system
- Complete analysis of solid materials or powders from ultra trace to matrix in a single analysis.
- ca. six samples per hour
- Metals, Powders, Alloys, Carbon, Silicon etc.
- Bulk analysis or depth profile
|
Special emphasis was taken on the development of the glow discharge source in the ELEMENT GD. In order to utilize fully the scan speed of the mass analyzer, a so-called "fast flow GD source" was implemented. This is a high power source (similar to "Grimm type source") that uses voltages between 700V and 2000V, currents up to 150mA and Argon flows up to 400ml/min. The combination of high power with high Argon flow results in high sputter rates and sensitivity.
The new detection system introduced in the ELEMENT GD represents another groundbreaking innovation. The basic principle for all quantification in GD-MS is the measurement of Ion Beam Ratios (IBR). All matrix elements are measured and the traces normalized to the total ion beam. The matrix can therefore be considered as a type of internal standard. The ELEMENT GD incorporates a detection system capable of measuring 12 orders of magnitude linear dynamic range that allows the precise quantification of matrix and ultra-traces in a single analysis ? all in about 10 minutes.
The typically strategy implemented to analyze the sample matrix with an additional technique such as XRF therefore becomes redundant. The high sensitivity and selectivity that delivers detection limits down to ppt levels makes the instrument the ideal tool for analysis of high purity metals from 3N to 7N quality. Table 1 shows the analytical results for 5N Copper (99.999% Purity) ? analysis time less than 5 minutes. The applications are broad and besides Copper, Aluminum, Gold and Iron include metals like Tantalum, Molybdenum and Niobium for high purity sputtering targets.
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Complete analysis in less than 10 minutes The new ELEMENT GD allows not just the analysis of impurities in a sample but also the complete analysis of a solid sample, e.g. aerospace alloys. Table 2 demonstrates the results for a Nickel-alloy that was analyzed from ppt (Thallium) to the matrix in a single analysis within 10 minutes. However, the ELEMENT GD is not limited to the analysis of metals. The glow discharge source is a direct current source but, due to the high power of the source, it is possible to analyze semiconductors, e.g. Silicon, which is used in solar cells. Powders, e.g. Carbon can be pressed as pellets and analyzed as well. Sample cooling is achieved by using Peltier devices, replacing the laborious use of cryogenic gases in older GD-MS instrumentation. Thus, metals like Gallium and Indium can be analyzed without problems.
| Isotope |
Concentration [ppb] |
Isotope |
Concentration [ppb] |
| 11B |
15 |
115In |
22 |
| 23Na |
45 |
119Sn |
65 |
| 24Mg |
13 |
123Sb |
666 |
| 27Al |
66 |
127I |
0.2 |
| 28Si |
385 |
130Te |
1 |
| 31P |
511 |
133Cs |
0.2 |
| 44Ca |
68 |
181Ta |
0.7 |
| 45Sc |
< 0.08 |
184W |
2 |
| 48Ti |
13 |
187Re |
0.1 |
| 51V |
3 |
189Os |
1 |
| 52Cr |
33 |
193Ir |
0.3 |
| 55Mn |
18 |
196Pt |
1 |
| 56Fe |
489 |
197Au |
0.4 |
| 59Co |
2 |
202Hg |
0.5 |
| 60Ni |
30 |
205Tl |
0.4 |
| 75As |
462 |
208Pb |
153 |
| 85Rb |
3 |
209Bi |
8 |
| 88Sr |
0.9 |
232Th |
< 0.07 |
| 89Y |
0.5 |
238U |
0.1 |
| 90Zr |
2 |
39K |
76 |
| 93Nb |
1 |
64Zn |
349 |
| 98Mo |
10 |
82Se |
108 |
| 109Ag |
225 |
102Ru |
15 |
| 114Cd |
4 |
106Pd |
42 |
| 65Cu |
99.9997% |
|
|
Table 1: Analysis of 5N Copper with ELEMENT GD
|
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| Isotope |
Unit |
Concentration
[ppb] |
Isotope |
Unit |
Concentration [ppb] |
| 107Ag |
ppm |
45.3 |
27Al |
% |
0.53 |
| 75As |
ppm |
5.8 |
28Si |
% |
0.11 |
| 11B |
ppm |
50.5 |
48Ti |
% |
1.05 |
| 209Bi |
ppm |
8.9 |
51V |
% |
0.044 |
| 31P |
ppm |
96.4 |
52Cr |
% |
17.5 |
| 206Pb |
ppm |
0.51 |
55Mn |
% |
0.11 |
| 207Pb |
ppm |
0.46 |
56Fe |
% |
18.2 |
| 208Pb |
ppm |
0.49 |
59Co |
% |
0.81 |
| 121Sb |
ppm |
1.65 |
60Ni |
% |
54.4 |
| 123Sb |
ppm |
1.67 |
63Cu |
% |
0.10 |
| 77Se |
ppm |
0.043 |
90Zr |
% |
0.002 |
| 119Sn |
ppm |
33.6 |
93Nb |
% |
4.42 |
| 120Sn |
ppm |
32.8 |
95Mo |
% |
2.50 |
| 130Te |
ppm |
0.010 |
181Ta |
% |
0.0095 |
| 205Tl |
ppm |
0.0006 |
184W |
% |
0.16 |
| Table 2: Complete characterization of a Nickel alloy in a single analysis. |
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Quantification, Depth profiling and software
The measurement of the matrix and Ion Beam Ratio quantification described above enables a semi-quantitative analysis of the sample without any calibration or standard. If higher accuracy results are required, standard materials (SRM) are required.
In particular, the ELEMENT GD distinguishes itself in terms of speed from older generation instruments. In consequence, the analysis time is significantly shorter but another benefit is the possibility to measure depth profiles. Depending on the element suites to be measured, depths profiles with resolutions of about 50 nm are achievable.
The software suite is the actual interface between the user and the instrument. The ELEMENT GD software package is based on its ICP-MS sibling (ELEMENT 2) and fulfils the highest demands. All instrument functions and the complete analysis procedure are software controlled. For remote use, control over LAN or through the Internet is possible. LIMS connectivity is also implemented.
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For further information please visit the product webpages.
1 Items Total 2,415.00 USD 