Comparison of ionic line-based internal standardization with axially and radially viewed inductively coupled plasma atomic emission spectrometry to compensate for sodium effects on accuracy

A comparison was conducted to verify the efficiency of internal standardization as a function of the observation mode in ICP-AES to compensate for the matrix effects on accuracy due to the presence of Na. An ICP system that allowed the use of either the radial or axial viewing mode was used. Operating conditions, i.e., power and carrier gas flow rate, were selected so as to obtain so-called robust and non-robust conditions. Robust conditions corresponded to a residual depressive effect due to the aerosol transport and filtering. The concentrations of test elements were determined based on the use of calibration graphs constructed with solutions that did not contain Na, while the elements were in solutions containing 10 g l(-1) of Na. Because only ionic lines exhibited a similar behavior, different ionic lines were used in order to cover a large range of ionization and excitation energies. A single internal standard was used, based on the Ni II 231 nm line. The results confirmed that efficient infernal standardization was obtained when robust conditions and radial viewing mode were used. A slight degradation of the internal standardization efficiency was observed when the axial viewing mode was used. Conclusions about possible matrix mismatches are given and exemplified.