Application of internal standardization in ICP-QMS through discrete sample introduction methodologies

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Non-spectral matrix effects in ICP-MS are often corrected by the method of internal standardisation. In the case of discrete sampling a common algorithm refers to the ratio of either maxima or areas of both analyte and internal standard peaks. The current work describes a protocol for internal standardisation across the transient peak based on the calculation of analyte-to-internal standard ratio for every scan sweep. Thus, a new converted function, Every Sweep Internal Standardisation (ESIS) ratio versus time, is obtained. One required merit is a dynamic estimation of variable matrix influence. Three discrete sampling systems coupled to an ICP-QMS instrument have been studied (i.e., flow injection, air segmented discrete introduction and injection into an air carrier). Two internal standard introduction modes (i.e., continuous and pulse) have been evaluated. For continuous mode, the ESIS function has a profile similar to the sample injection peak while for the pulse mode it has approximately constant values only within a limited time interval. The ESIS zone of stability for the tested sampling systems has been critically evaluated. By ESIS protocol lower RSDs have been found than the common internal standardisation. The matrix correction efficiency achieved with ESIS ranged between 96%–105%, 94%–106% and 93%–110% for an alcoholic beverage (alcohol content up to 40%), high salt content solution (NaCl up to 3%) and moss sample, respectively.