Plasma Source Mass Spectrometric Analysis of Biological and Environmental Samples: Dealing with Potential Interferences

Introduction

Effectiveness of a plasma to dissociate the sample into ions has been the basis of the development of plasma source optical emission spectrometer (OES) and mass spectrometer (MS) for elemental and isotope analysis. Among the available ways of inducing and sustaining a plasma, only inductively coupled plasma (ICP) has gained commercial application. The ICP is an electrodeless discharge in a gas at atmospheric pressure, maintained by energy coupled to it from a radio frequency generator. This is done by a coupling coil, which functions as the primary of radio frequency transformer, the secondary of which is created by the discharge itself (Jarvis et al., 1992). An ICP-MS system consists of a plasma source (ICP) interfaced with a quadrupole MS. The plasma ionizes the elements of the sample and the MS serves as a detector that measures the mass to charge (m/z) ratio of the element(s) or isotope(s) of interest. Generally an argon (Ar) plasma is used, but other plasma sources have also been proposed (Brown et al., 1988; Satzger et al., 1987).