Plasma torch interface

Sample introduction system Plasma torch Interface region Ion optics Roughing pumps Air/water filters... 

Cross-section of typical ICP ion source showing plasma torch and ion extraction interface. Extraction and skimmer sizes are slightly exaggerated for clarity. 

Diemer, J. and Heumann, K.G. (1997) Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography. Fresenius J. Anal. Chem., 357,74-79. Duan, YX., Wu, M., Jin, Q.H. and Hieftje, G.M. (1995) Vapour generation of nonmetals coupled to microwave plasma-torch mass-spectrometry. Spectrochim. Acta B, 50,355-368. Ebdon, L., Hill, S. and Jones, R (1987) Interface system for directly coupled high performance liquid chromatography-flame atomic absorption spectrometry for trace metal determination./. Anal. At. Spectrom., 2, 205-210. 

Many experimental parameters and components affect sensitivity, including the analyte transport efficiency of the sample introduction system and the mean size and size distribution of the aerosol entering the ICP. The plasma torch design, rf generator, load coil, interface between the atmospheric pressure ICP and mass spectrometer, ion optics, mass spectrometer itself, and detector also affect sensitivity. 

Figure 21 Supercritical fluid chromatography microwave induced plasma mass spectrometry (SFC-MIP-MS) torch interface. (From Ref. 113.)...

The combination of ICP torch and mass spectrometric resolution resulted in a much more powerful technique than ICP-AES in terms of sensitivity, selectivity and precision. Further, the coupling of MS to ICP results in the analysis of isotopes of various elements. In ICP-MS, the plasma torch is in a horizontal position and it works under normal pressure. An interface cone is placed between a plasma source and mass spectrometer. Ions produced in ICP are transferred to the mass spectrometer through a small hole (about 1 mm in diameter) in the cone. The mass spectrometer is usually a quadrapole analyser. 

MS is used in nuclear forensics to determine the isotopic composition of a sample. This information is used to establish how the material was produced. ICP-MS is an often used technique to determine isotopic compositions of the radioactive elements. ICP-MS consists of an argon plasma torch that atomizes a sample at atmospheric pressure. The sample is then transported to the mass analyzer (usually a quadrupole, TOP, or magnetic sector instrument), via a pressure interface region. ICP-MS is chosen for its good sensitivity, dynamic range, and quick sample throughput. ICP-MS can also simultaneously determine many isotopes in a single analysis. 

Before we take a look at the fundamental principles behind the creation of an ICP used in ICP-MS, let us take a look at the basic components used to generate the source—a plasma torch, radio-frequency (RF) coil, and power supply. Figure 4.1 shows their proximity compared to the rest of the instrument, and Figure 4.2 is a more detailed view of the plasma torch and RF coil relative to the MS interface. 

FIGURE 4.2 Detailed view of plasma torch and radio-frequency (RF) coil relative to the inductively coupled plasma mass spectrometry (ICP-MS) interface. 

FIGURE 6.1 Position of ion optics relative to the plasma torch and interface region. 

ICP-MS Besides the plasma torch and sample introduction supplies, ICP-MS requires consumables that are situated inside the mass spectrometer. The first area is the interface region between the plasma and the mass spectrometer, which contains the sampler and skimmer cones. These are traditionally made of nickel, which is recommended for most matrices, or platinum for highly corrosive samples and organic matrices. A set of nickel cones costs 700-1000, whereas a set of platinum cones costs about 3000-4000. Two sets of nickel cones and perhaps one set of platinum cones would be required per year. The other major consumable in ICP-MS is the detector, which has a lifetime of approximately 1 year, and costs about 1200-1800. Some systems also have a replaceable ion lens. It is suggested that five of these at 100 each are required for a routine laboratory. When all these are added together with the torch, the sample introduction components, and the vacuum pump consumables, investing in ICP-MS supplies represents an annual cost of 9,000-11,000. 

This is not to say that price is unimportant, but what might appear to be the most expensive instrument to purchase, might be the least expensive to run. Therefore, you must never forget the cost of ownership in the overall financial analysis of your purchase. So, by all means compare the price of the instrument, computer, and any accessories you buy, but also factor in the cost of consumables, gases, and electricity based on your usage. Maybe instrument consumables from one vendor are much less expensive than from another vendor. This is particularly the case with interface cones and plasma torches. Or maybe the purity of collision/reaction gases is more... 

Interfacing mass spectrometry with other analytical techniques (Section F) necessitates the use of specially designed interfaces and ionizing sources. These include thermospray, electrospray and ionspray for liquid chromatography-mass spectrometry (LC-MS), and an inductively coupled plasma torch (ICP) for ICP-MS (Topic E5). For gas chromatography-mass spectrometry (GC-MS), the carrier gas flows directly into the spectrometer where El ionization can then be used. 

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