A modulated sample-introduction device for use in inductively coupled plasma emission spectrometry has been constructed and evaluated. With this device, the flow of aerosol to the excitation source is modulated by applying at a specific frequency a pressure pulse to the nebulizer chamber; the use of frequency-selective detection then permits efficient signal recovery. Unfortunately, background emission from the ICP was also found to be modulated at the sample-introduction frequency; the magnitude of background modulation depends on the depth of sample modulation and the types of spectral features present at the analytical line of interest. The sample-modulation device discriminated best between analyte emission and continuum background radiation, but performed most poorly when OH band emission was the dominant background interference. The construction and operation of the device are described and its performance for several elements is evaluated in terms of detection limits, S/B enhancement, and working-curve linearity.
A. W. Steele and G. M. Hieftje, "A Modulated Sample-Introduction System for ICP-Atomic Emission Spectrometry," Appl. Spectrosc. 40, 1127-1131 (1986)