APPROACHES TO INTERFERENCE-FREE ELEMENTAL ANALYSIS WITH ICP-MS

A feasibility study of the prospect of performing elemental analysis in inductivity coupled plasma-mass spectrometry (ICP-MS) without isobaric or chemical interferences is presented. The approach uses the generalized standard addition method (GSAM), which is implemented using: (a) alternatives to the conventional multipoint calibration curves using training sets based on statistical experimental designs; (b) advanced analysis of the data set generated subsequent to the calibration; and (c) a rapid, on-line method for managing the preparation and measurement of training set standards using discontinuous flow analysis (DFA). The DFA system considerably reduces the time and labor involved in constructing training sets of standards. The GSAM is a calibration/data analysis procedure that intelligently utilizes the large quantities of data that are readily generated in ICP-MS. Conventional ICP-MS procedures do not always use the data available to its full advantage. The GSAM is capable of overcoming interferences due to isobaric overlaps and chemical effects within the plasma source. A limitation of the GSAM is that all analytes and all interferences must be known in advance. The GSAM will not correct for a completely unknown interference. A promising approach for overcoming the limitations of GSAM when second-order bilinear data are available (e.g., from simultaneous mass spectrometric-atomic emission data) is the generalized rank annihilation method (GRAM), which can be used to correct for unexpected interferences and extract the mass or emission spectra of the unknown interferent from the data set.