Effect of matrices with low second ionization potentials on analytical signals in inductively coupled plasma mass spectrometry

A low second ionization potential element matrix reduces the mass spectrometric analytical signals at matrix concentrations as low as milimoles. The matrix effects on different analytes and argon are similar and can be accounted for by application of a single internal standard at an accuracy of about 20%. For a higher accuracy, the analyte specific internal standards have to be selected and/or proper matrix reference materials and dilution of samples should be used. Typically, the degree of the double to single ionization is also suppressed in the presence of the matrix while a small increase in the ionization temperature is observed. The increase of the temperature can be caused by the lower energy losses to ionization in the presence of a matrix. We discuss secondary effects such as an increase of the temperature gradients, the ionization degree and ambipolar diffusion. We point out the possibility of charge transfer from argon to the doubly ionized ions in lanthanides and in some transition group elements and discuss the role of this phenomenon to the matrix effect.