Noise power spectra of the inductively coupled plasma

Noise power spectra for the ICP were determined under various conditions, by Fast Fourier Transform (FFT) digital techniques. The major noise types observed were white noise, low frequency noise, and high frequency proportional noise. The high frequency proportional noise increased with concentration of analyte and radio frequency input power. The high frequency proportional noise decreased with increasing nebulizer flow rate and coolant gas flow rate.. The low frequency noise components extended to higher frequencies as the resonance wavelengths of the measured transitions increased. Changing the observation height in the plasma determined which noise types were present in the noise power spectrum. At observation heights near the power coils, all three noise types were present, whereas, low frequency noise predominated at significantly greater heights. Changing the torch design changed the relative amplitudes of the different high frequency proportional noise components, but did not greatly change their respective peak frequencies.