Collision and Reaction Cells

Interference removal using I le mode and Kinelie Knergy Diseriminalion (KHD) 

At cell entrance, analyte and polyatomic ion energies overlap. Energy spread is narrow, due to ShieldTorch System. 

Energy loss from each collision with a He atom is the same for analyte and polyatomic ion, but polyatomics are bigger and so collide more often. 

By cell exit, ion energies no longer overlap polyatomics are rejected using a bias voltage step (energy discrimination) 

For ultratrace analysis, reaction mode may provide better interference removal than collision mode. There are some disadvantages to this approach. Each reaction gas will only remove interferences that react with that cell gas, so some interferences may remain. The analyst mnst know what interferences to remove in order to choose the reaction gas. This is not always possible with nnknown samples. Reaction gases can react with the sample matrix and analytes to create new interferences. These cell-formed interferences are often unpredictable and may lead to erratic resnlts. Reaction gases may react with analytes and reduce their sensitivity severe loss of sensitivity for Cu and Ni has been reported when using Hj and ammonia. 

Gregory K Koyanagi, Diethard K Bohme and Dmitry R Bandura 

The use of collision and reaction cells for differentiation or elimination of isoharic interferences in plasma mass spectrometry has become commonplace. The ability to rapidly select and advance a chemical reaction scheme for a single-element or multi-element analysis is therefore cmcial for expeditious result generation. Implicit in determining an effective chemical reaction scheme is an understanding of the physics and physical chemistry underlying ion-molecule reactions. 

Selection of the neutral species for use in a reaction/collision cell mass spectrometer is a balancing act between many competing factors. First, the neutral must be amenable to introduction into the cell in a convenient, controlled and reproducible manner. Also, the neutral must have a relatively low atomic or molecular mass so as to reduce the effects of collisional scattering. Lastly, the neutral must react with the interference ion with a high efficiency per collision to effect rapid and quantitative conversion (preferably to a single product). 

The choice of reagent gas admitted to the reaction/collision cell is influenced by the reactivity of that gas towards both the interference ion and the analyte ion. Furthermore chemical resolution of an isoharic overlap can be effected either by removal of the interference ion (by chemical reaction) or by addition of a known mass to the analyte ion to move it to a cleaner area further up in the mass spectmm. Although metal ions exhibit a diverse range of ion-molecule chemistries, it 

Inductively Coupled Plasma Mass Spectrometry Handbook Edited by Simon M. Nelms 2005 Blackwell Publishing Ltd. ISBN 978-1-405-10916-1 

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Instrumental developments (e.g., of sector field instruments with multiple ion collection, introduced in 1992, or the insertion of collision and reaction cells in order to reduce disturbing isobaric interferences), the progress in applications for ultratrace analysis, also in combination with on line hyphenated separation techniques (HPLC, CE), especially routine capability as well as decreasing price and user friendly maintenance mean that sales are increasing by 10 % every year. To improve the analytical performance of ICP mass spectrometers for precise isotope ratio measurements (e.g., for geochronology or for the study of fine isotope variation in nature) powerful instrumentation with high mass dispersion and multiple ion collector systems instead of single ion collection are commercially available on the analytical market. 

I. Feldmann, N. Jakubowski, D. Stueuer, Application of a hexapole collision and reaction cell in ICP-MS. Part 1 instrumental aspects and operational optimisation, Fresenius J. Anal. Chem., 365 (1999), 415-421. 

D. W. Roppenall, G. C. Eiden, C. J. Barinaga, Collision and reaction cells in atomic mass spectrometry development status and applications, J. Anal. Atom. Spectrom., 19 (2004), 561-570. 

J. Marchante-Gayon, C. Thomas, I. Feldmann, N. Jakubowski, Comparison of different nebulisers and chromatographic techniques for the speciation of selenium in nutritional commercial supplements by hexapole collision and reaction cell ICP-MS. J. Anal. Atom. Spectrom., 15 (2000), 1093-1102. 

Commercial yeast-based supplements Hot water extraction IP HPLC-ICP-MS with hexapole collision and reaction cell, hydraulic high pressure nebulizer... 

Collision and reaction cell techniques have been used for many years in the study of organic and biological mass spectrometry, but only in the last few years in ICP-MS. The development of collision and reaction cells extended the capability of the technique by allowing the selective attenuation or removal of problematic spectral interferences. Today a variety of collision/reaction cells using various gasses (H2, He, CH4, NH3...) are available, virtually able to eliminate the problems associated with polyatomic interferences for most elements in food and beverage matrices. However, the simultaneous multi-element capability and maximum productivity of ICP-MS is partially reduced by the different CRC tuning conditions required to eliminate a specific interference in a specific matrix. 

Marchante-Gay6n, J. M., Feldmann, I., Thomas, C., Jakubowski, N. Speciation of selenium in human urine by HPLC-ICP-MS with a collision and reaction cell. J Anal At Spectrom 2001, 16, 457 463. 

Koppenaal, D.W. Eiden, G.C. Bari-naga, C.J. Collision and Reaction Cells in Atomic MS Development, Status, and Applications. J. Anal. Atom. Spectrom. 2004,19,561-570. 

F. Keenan and W. Spence, Theory and Applications of Collision/Reaction Cells How Collision and Reaction Cells Work for Interference Removal in ICP-MS, Thermo Fisher Scientific Web-based Presentation, 2007, http //breeze.thermo.com/crcs. 

When assessing the capabilities of collision and reaction cells, it is important to understand the level of interference rejection that is achievable, which will be reflected in the instrument s DL and BEC values for the particular analytes being determined. This has been described in greater detail in Chapter 10, but depending on the nature of interference being reduced, there will be differences between the collision/reaction cell methods as well as with the collision/reaction interface approach. It is therefore critical to evaluate the capabilities of commercial instrumentation on the basis of your sample matrices and particular analytes of interest. 

However, it should be emphasized that when you are comparing systems, it should be done with your particular analytical problem in mind. In other words, evaluate the interference suppression capabilities of the different collision and reaction cell interface approaches by measuring BEC and DL performance for the suite of elements and sample matrices you are interested in. In other words, make sure it works for your application problem. This is even more important with the collision/ reaction interface because it works on a slightly different principle, and as it does not use a traditional cell, it is unclear how it discriminates between all the generated by-product interfering ions from the analyte ions. 

Finally, recent trends and developments in speciation analysis using collision and reaction cell ICP-MS and multicollector-ICP-MS (MC-ICP-MS) will be discussed. This new instrumentation opens up more possibilities in speciation analysis, be it for the measurement of elements traditionally not attempted with ICP-MS or for element isotopes traditionally ruled out due to molecular interference, like Fe or °Se, as well as opening up new opportunities in the determination of precise isotope ratios in species. 

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