Argon-based interferences

Darrouzes, J., Bueno, M., Lespes, G., Holeman, M., Potin-Gautier, M. Optimisation of ICPMS collision/reaction cell conditions for the simultaneous removal of argon based interferences of arsenic and selenium in water samples. Talanta 71, 2080-2084 (2007)... 

The cold/cool plasma approach, which uses a lower temperature to reduce the formation of the argon-based interferences, has been a very effective way to get around some of these problems. However, this approach can sometimes be difficult to optimize, is only suitable for a few of the interferences, is susceptible to more severe matrix effects, and it can be time consuming to change back and forth between normal and cool plasma conditions. These limitations and the desire to improve performance have led to the commercialization of collision/reaction cells (CRC) and collision/reaction interfaces (CRl). Designs for CRC and CRl were based on the early work of Rowan and Houk, who used Xe and CH4 in the late 1980s to reduce the formation of ArO+ and Ar2 species in the determination of Fe and Se with a modified tandem mass spectrometer. This research was investigated further by... 

Under normal hot plasma conditions (typically, RF power of 1200-1600 W and a nebulizer gas flow of 0.8-1.0 L/min), these isotopes would not be available for quantitation because of the argon-based interferences. Under cool plasma conditions (typically, RF power of 600-800 W and a nebulizer gas flow of 1.2-1.6 L/min), the most sensitive isotopes can be used, offering low ppt detection in aqueous matrices. However, not all instruments offer the same level of cool plasma performance, so if... 

S. J. Hill, M. J. Ford, L. Ebdon, Simplex optimisation of nitrogen-argon plasmas in inductively coupled plasma mass spectrometry for the removal of chloride based interferences, J. Anal. Atom. Spectrom., 7 (1992), 719-727. 

Sanz-Medel and co-workers reported on selenium determination in biological samples by isotope dilution analysis in ICP-QMS with an octopole collision cell." The argon based isobaric interference arising during measurements of °Se was eliminated by using a hydrogen flow of 4 ml min in the octopole cell, so that it is possible to determine Se with a detection limit of 14pgg. ... 

The collision/reaction interface, which will be discussed later in this chapter, uses a slightly different principle to remove the interfering ions. It does not use a pressurized cell before the mass analyzer, but instead, injects a reaction/collision gas directly into the interface between the sampler and skimmer cones. The injection of the collision/reaction into this region of the ion beam produces collisions between the argon gas and the injected gas molecules, and as a result, argon-based polyatomic interferences are destroyed or removed before they are extracted into the ion optics. 

Using cool plasma conditions Although not utilized so much since the development of collision/reaction cells and interfaces, all instruments today have the ability to use cool plasma conditions. By reducing RF power to 500-700 W and increasing nebulizer gas flow to 1.0-1.3 L/min, the plasma temperature is lowered, which reduces argon-based polyatomic interferences such as °Ar 0+, " °Ar+, and ArH+ in the determination of difficult elements such as Fe, Ca+, and Such dramatic deviations from normal operating conditions (-1000 W, 0.8 L/min) wiU affect the electrical characteristics of the plasma. 

The argon ICP is by far the most common type of plasma to be coupled with mass spectrometric detection. As discussed above, alternative gas and mixed gas plasmas have been used, but several other types of plasma have also been employed one such plasma is the microwave-induced plasma (MIP). The MIP usually utilises helium and is therefore very highly ionising. It suffers far fewer interference problems than argon-based plasmas, although traditionally it has had the reputation of not being a very robust plasma, i.e. it is easily extinguished by the... 

Two colorimetric methods are recommended for boron analysis. One is the curcumin method, where the sample is acidified and evaporated after addition of curcumin reagent. A red product called rosocyanine remains it is dissolved in 95 wt % ethanol and measured photometrically. Nitrate concentrations >20 mg/L interfere with this method. Another colorimetric method is based upon the reaction between boron and carminic acid in concentrated sulfuric acid to form a bluish-red or blue product. Boron concentrations can also be deterrnined by atomic absorption spectroscopy with a nitrous oxide—acetjiene flame or graphite furnace. Atomic emission with an argon plasma source can also be used for boron measurement. 

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