Extraction discharge source for enhancing analyte line intensities in inductively coupled plasma atomic emission spectrometry

A supplementary electrical discharge is generated by extraction of the axial channel of an Ar inductively coupled plasma (ICP) into a small vacuum chamber. The spectral background levels and background noise emitted by this discharge are similar to those from the ICP alone. The discharge enhances the intensities of ion lines by factors of up to 13 relative to intensities observed from the ICP alone. Neutral atom lines from elements with high ionization energies (approx. >9 eV) are also enhanced but by less than ion lines: neutral atom lines from easily ionized elements are suppressed by the discharge. Metal oxides in the ICP can be seen to dissociate into atomic species as they enter the discharge. These effects are attributed to more efficient atomization, excitation, and ionization in the discharge and to the tendency of analyte species to be constricted or concentrated closer to the central axis of the ICP as they flow into the discharge. Under the same operating conditions a 40-MHz plasma generates a more intense discharge and yields higher intensity enhancements than does a 27-MHz plasma