ABSTRACT
There are a small number of elements that are recognized as having poor detection limits by ICP-MS. These are predominantly elements that suffer from major spectral interferences generated by ions derived from the plasma gas, the matrix components, or the solvent/acid used in sample preparation. Examples of these interferences include the following:
• 40Ar16O+ in the determination of 56Fe+
• 38ArH+ in the determination of 39K+
• 40Ar+ in the determination of 40Ca+
• 40Ar40Ar+ in the determination of 80Se+
• 40Ar35Cl+ in the determination of 75As+
• 40Ar12C+ in the determination of 52Cr+
• 35Cl16O+ in the determination of 51V+
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.1 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 and collision/reaction interfaces. Designs for collision/reaction cells and collision/ reaction interfaces 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.2 This research was investigated further by Koppenaal and coworkers in 1994, who
carried out studies using an ion trap for the determination of iron, vanadium, arsenic, and selenium in a 2% hydrochloric acid matrix.3 However, it was not until 1996 that studies describing the coupling of a collision/reaction cell with a traditional quadrupole ICP mass spectrometer were published. Eiden and coworkers experimented using hydrogen as a collision gas,4 whereas Turner and coworkers based their investigations on using helium gas.5 These studies and the work of other groups at the time6,7 proved to be the basis for modern collision and reaction cells and interfaces that are commercially available today. Let us take a look at the fundamental principles of collision/reaction cells and interfaces.
