Fundamental studies of the extraction process in inductively coupled plasma mass spectrometry

A reduced pressure jet extracted from an inductively coupled plasma (ICP) was studied for information about conditions during the extraction process in inductively coupled plasma mass spectrometry (ICP-MS). The background spectrum and intensity ratio of ion lines to atom lines were similar to those from the ICP, except the lines from the jet were much weaker. Gas kinetic temperatures in the Mach disk region of the extracted plasma were of the order of 2200 K. Fluorescence studies indicated there was little neutral sodium inside the zone of silence of the free jet, which showed that little ion-electron recombination occurred during the initial extraction and supersonic expansion;The potential measured inside the supersonic jet was of positive polarity and varied with sampling position, plasma power, and aerosol gas flow rate in much the same way as both the potential outside in the plasma and the ion kinetic energy. The potential of the probe was affected by both the mass and the concentration of alkali metals in the sample solution. A high potential in the jet also tended to be noisy and would be detrimental to the stability of an ICP-MS device. Electron temperature ( T[subscript]e), electron density ( n[subscript]e) and floating potential ( V[subscript]f) were measured with a single Langmuir probe inside the supersonic jet. Electron temperature in the range 7000 to 15000 K increased when nebulized water was introduced into the plasma, and n[subscript]e was of the order of 10[superscript]13 cm[superscript]-3. The addition of easily ionized concomitant elements (K or Cs) caused a substantial decrease in T[subscript]e. Electron density was not greatly affected by the presence of either nebulized water or concomitant elements. The trends of T[subscript]e and n[subscript]e as plasma operating conditions were changed indicated that T[subscript]e was strongly affected by a secondary discharge between the plasma and the sampling orifice, whereas n[subscript]e was not. Floating potential was in the range 2 to 5 volts and varied with plasma conditions in essentially the same way as did previous measurements with a floating probe. These observations substantiated previous theoretical descriptions of the various properties of supersonic jets extracted from inductively coupled plasmas;The feasibility of a secondary discharge as an atomic emission source was evaluated by studying rinse-out time, memory, and matrix effects. ftn*This work was performed at the Ames Laboratory under contract No. W-7405-eng-82 with the U.S. Department of Energy. The United States government has assigned the DOE report no. IS-T-1414 to this dissertation