Investigation of non-spectroscopic interference and internal standardization method in axially and radially viewed inductively coupled plasma optical emission spectrometry using cross-flow and ultrasonic nebulization

The matrix effects on radially and axially viewed inductively coupled plasma optical emission spectrometry (ICP-OES) equipped with cross-flow (CFN) and ultrasonic nebulizer (USN) were evaluated for the determination of multi-elements in various sample matrices. Na, Ca, Mg, Al, Mn, Cu, Si and Fe were used as matrix elements and the change in light intensities of selected analyte elements with a wide range of spectral lines differing in energy sum ( summation of excitation energy and first ionization energy) were compared. From the correlation of the change in line intensity and energy sum of analyte elements and the second ionization energy of matrix elements, a novel observation on non-spectroscopic interference is described. Based on our experimental results, two types of non-spectroscopic interferences resulting from different matrix elements were observed, regardless of the sample introduction systems or observation modes. Moreover, besides the fact that the second ionization energy of matrix elements shows unique effect on the change in the analyte spectral lines, bigger matrix effect was found for analytical lines possessing energy sum larger than 14.03 eV in the presence of matrix elements with second ionization energy lower than 15.64 eV. The applicability of RF power adjustment and internal standardization were investigated for the compensation for matrix interferences. It was found that satisfactory corrected results can be achieved by the use of single internal standard as the second ionization energy of matrix element is higher than 15.75 eV. However, in view of the different depressive effect occurring in the analyte spectral lines, the the similarity in energy sum of analytical lines and internal standard has been confirmed by using two internal standards for compensating the matrix interferences caused by matrix elements with second ionization energy lower than 15.64 eV.