Langmuir probe measurements of the ion extraction process in inductively coupled plasma-mass spectrometry. Part 2. Measurements of floating voltage and radiofrequency voltage

摘要

A single Langmuir probe is thrust axially through the skimmer into the supersonic jet of a typical interface for inductively coupled plasma-mass spectrometry (ICP-MS) Floating voltage V_f is measured from current-voyage curves at various axial positions and is generally in the range +2 to +7 V in tb supersonic jet A disturbance at the skimmer, when present, induces a sharp increase in V_f in the vicnhy of the skimmer tip Floating voltage generally decreases as the probe is retracted farther behind the skimmer. The measured d c voltages are attributed primarily to plasma rectification and to the calore-lectric effect between two metal surfaces at different temperatures in a plasma. An r.f voltage of up to 25 V (peak-to-peak) at the frequency of the plasma generator can also be measured behind the sampler.