Effect of acid concentrations on the excitation temperature for vanadium ionic lines in inductively coupled plasma-optical emission spectrometry

In routine analysis by inductively coupled plasma-optical emission spectrometry (ICP-OES), non-spectral interferences, which are classified into physical, chemical, ionization and excitation interferences, should be taken into consideration to obtain a more accurate analytical result. The excitation interference is principally due to a variation in the number of excited atoms resulted from a change in the excitation temperature of an ICP. It could be caused by variations not only in the discharge parameters, such as an radio frequency (rf) forward power but in physical parameters, such as the kind and concentration of acids in the sample solution. By using vanadium test solutions prepared at various acid concentrations, the excitation temperature was estimated from the Boltzmann plots. The excitation temperatures were slightly elevated with an increase in the acid concentration ranging from 0 to 50 ml in a 100 ml solution: increases of 33 and 16 K in a sulfuric acid system and a nitric acid-hydrochloric acid system, respectively were observed. The intensity ratios between vanadium ionic lines having almost the same excitation energy, and the intensity ratios having different excitation energies were also measured.