Specific Advantages of MC-ICP-MS

The high ionization efficiency that characterizes plasma source mass spectrometers also has drawbacks, however. In particular, isotopic analysis by MC-ICP-MS is more susceptible than TIMS measurements to spectral interferences from isobars, molecular ions, and doubly charged species. Such interferences are furthermore much more problematic for isotope ratio than for element concentration measurements, as isotopic compositions typically need to be measured with an accuracy and precision of better than 100 ppm. In order to reduce spectral interferences to tolerable levels, isotopic analyses of complex natural samples in geo- and cosmochemistry are generally carried out following separation of the 

The technique of internal normalization is commonly apphed in both MC-ICP-MS and TIMS for the precise correction of the instrumental mass bias (see also Chapter 5) that is encountered during the analysis of radiogenic isotopic compositions [33, 34]. The ICP ion source of MC-ICP-MS, however, also features two characteristics that play an important role for isotopic analysis, where internal normalization cannot be applied. First, an ICP source operates at steady state and therefore mass fractionation is not primarily a time-dependent process, as in TIMS where the measured isotopic compositions change with time due to the progressive evaporation of a sample from the filament. The steady-state operation of an ICP ion source is beneficial for the correction of instrumental mass bias by external standardization, where the isotope ratio data obtained for a sample are referenced to the values obtained for bracketing analyses of an isotopic standard [27, 35]. Hence, this procedure is commonly termed standard-sample bracketing. 

In addition to these analytical advantages, the technique of MC-ICP-MS features further general benefits, particularly ease of operation, high sample throughput, and reasonable capital and operating costs, which have made such instruments very popular for isotopic research in many geo- and cosmochemical laboratories. 

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