Suppression of analyte signals by various concomitant elements was investigated. In addition to the ionization interference by easily ionizable elements reported previously, signal suppression by heavy matrix elements was found to be significant. The interference trend followed the order of atomic weight of the matrix elements, i.e., the larger the atomic weight, the severer the suppression effect. Ion scattering by collision with matrix atoms or ions in the course of ion traveling from the sampling orifice is proposed as the mechanism of the matrix effect.