Spectral line broadening and radiative electron-ion recombination processes may make significant contributions to the total spectral background level when inductively coupled plasma excitation sources are observed with spectrometers having low stray light levels. These background contributions are more easily identified in inductively coupled plasma discharges because of their stable background level and by the fact that net analyte line intensities are affected to such a small degree by changes in the concentration of concomitants. The wings of collisionally broadened lines may produce significant background changes at wavelengths removed 10 nm from the parent line center. For some elements such as Mg, linear Stark-broadened lines produced spectral background at unexpectedly large displacements from the line center. The radiative Al ion-electron recombination continuum produces a greater than tenfold increase in the background from ~210 down to 193 nm at Al solution concentration of 2500 μg/ml. Thus, a solution containing only 250 μg/ml of Al will cause an ~100% increase in the background level below 210 nm over that measured when deionized water is nebulized into the plasma.
G. F. Larson and V. A. Fassel, "Line Broadening and Radiative Recombination Background Interferences in Inductively Coupled Plasma-Atomic Emission Spectroscopy," Appl. Spectrosc. 33, 592-599 (1979)