What is the inlet method for sampling on the MS-200?
The MS-200 uses a dual membrane inlet system. Thus, the appropriate acronym for the MS-200 is MIMS; Membrane Inlet Mass Spectrometry. The basis of this method is the selective transport of analyte molecules across a semi-permeable membrane. The permeation of the host gas (typically air) is smaller than the flow of organic analytes of interest and thus an enrichment factor of 10-100 is obtained with each membrane. The membranes serve a second function: to create two pressure reducing steps to the high vacuum environment of the mass spectrometer. Gas introduction is via a standard1/8″ Swagelock fitting. Sample is drawn at ~100ml per minute (simply to guarantee a fresh and representative sample on the membrane). From there the sample permeates into the intermediated vacuum space at around 1/1000 atmospheric pressure, and then permeates through the second membrane into the mass spectrometer where it is mass analysed.
