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Modern Tools for More Effective Interference Removal in ICP-MS

Ana Rita Cristiano 1 ; Daniel Kutscher 2 ; Shona McSheehy Ducos 2
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Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is a widely recognized and powerful tool for the analysis of trace elements at trace or ultratrace levels. One of the main advantages is its robustness, as it can analyze a wide variety of sample matrices. The technique is frequently employed for the routine analysis of waters, soil and sludge samples, a wide variety of foodstuff, but also for clinical research with samples such as serum or urine. In addition, special accessories, such as Laser Ablation or Chromatography can be hyphenated to ICP-MS easily to directly analyze solid samples or quantify different chemical forms of an analyte. However, all of the above mentioned sample types and applications may lead to a special combination of interferences which interfere with the analyte of interest.

To recognize and overcome the resulting mostly polyatomic, but sometimes also isobaric interferences remains a challenge for ICP-MS users. The use of collision/reaction cell in quadrupole based ICP-MS is a well-established technique to remove or circumvent the extent of spectral interferences affecting the detection of certain isotopes. The use of different gases (inert such as helium or reactive gases such as hydrogen, oxygen or ammonia) may help to reduce the contribution of some interferences. Some examples are given in the following:

• The ultra-trace detection of Ti can be accomplished using NH3 cell gas with subsequent detection of ammonia cluster ions.
• As and Se can suffer from severe interferences caused by doubly charged ions of rare earth elements (e.g. Gd, Sm etc.). The use of O2 and a mass shift reaction (forming AsO and SeO respectively) can eliminate these interferences.
• Hydrogen is an effective way to eliminate Ar based polyatomic interferences (40Ar16O+ and 40Ar40Ar+) on the main isotopes of Fe and Se (56Fe and 80Se respectively).

These newly formed interferences can be eliminated through a more comprehensive control over ions entering and reacting in the collision/reaction cell system using a dedicated ion filter. Here, a new and easy-to-use technique to obtain the lowest possible detection limits for challenging samples by improved interference suppression is presented