Real and composite emission lines as internal standards in the determination of As, Se and Sb by inductively coupled plasma optical emission spectrometry

A method that enlarges the pool of potential internal standards for axially viewed inductively coupled plasma optical emission spectrometry has been developed and evaluated. This method is based upon the visualization of the similarity of matrix-induced behavior among emission lines by principal component analysis according to the procedure suggested by Grotti et al. (J. Anal. At. Spectrom., 2003, 18, 274). For a certain analytical line, more choices of internal standards are provided from composite spectral lines created by combining real spectral lines in such a way as to integrate their characteristic behaviors. The method was applied in the determination of As, Sb and Se in solutions that modelled plant and food sample digests, to compensate for the matrix effect due to the presence of nitric or hydrochloric acids as well as a variety of matrix elements including aluminium, calcium, iron, magnesium, manganese, phosphorus, potassium, sodium, sulfur, and zinc. Under robust plasma conditions, the matrix-induced errors, which averaged between 8 and 23%, were decreased to an average of between 2 and 5% by the composite internal standards procedure. The methodology was validated by the accurate analysis of two certificated reference materials (DORM-2 and DOLT-3).