| 摘要 |
A method of analyzing an analyte contained in a plasma, in inductively coupled plasma mass spectrometry (ICP-MS). A sample of the plasma is drawn through an orifice in a sampler, then skimmed in a skimmer orifice, and the skimmed sample is directed at supersonic velocity onto a blunt reducer having a small orifice therein, forming a shock wave on the reducer. Gas in the shock wave is sampled through an offset aperture in the reducer into a vacuum chamber containing ion optics and a mass spectrometer. This reduces space charge effects, thus reducing mass bias and also reducing the mass dependency of matrix effects. Since the region between the skimmer and the reducer can operate at about 0.1 Torr, which is the same pressure as that produced by the roughing pump which backs the high vacuum pump for the vacuum chamber, a single common pump can be used for both purposes, thus reducing the hardware needed. In a simplified version, the skimmer can be replaced by a small beam blocking finger which extends across a line of sight between the sampler and reducer orifices and occludes the reducer orifice from the sampler orifice. |
