Study of ionic-to-atomic line intensity ratios for two axial viewing-based inductively coupled plasma atomic emission spectrometers

Using two axially-viewed inductively coupled plasma (ICP) systems that exhibited different behaviors to matrix effects, the sensitivity of the Mg II 280.270 nm/ Mg I 285.213 nm line intensity ratio to the ICP operating conditions and to matrix effects was compared to that observed for alternative ionic-to-atomic line intensity ratios such as the Cd II 226.502 nm/Cd I 228.802 nm, Cr II 267.716 nm/Cr I 357.868 nm, Ni II 231.604 nm/Ni I 232.138 nm, Pb II 220.353 nm/Pb I 217.000 nm, and Zn II 206.200 nm/Zn I 213.857 nm ratios. Both robust and non-robust conditions were used. Some lines behaved differently, in particular the Mg I and Cr I lines, not only as a function of the matrix, but also as a function of the ICP system. The Mg II/Mg I ratio was found to remain a good compromise to follow changes in plasma conditions. The use of several ionic-to-atomic line ratios confirmed that axial viewing leads to matrix effects that are particularly sensitive for atomic lines. The effects cannot be totally suppressed, even under robust conditions, and regardless of the ICP system. An alternative to minimize matrix effects was the use of a buffer such as Cs at 10 g l⁻¹.