TEMPERATURE-PROGRAMMED DESORPTION FOR MEMBRANE INLET MASS-SPECTROMETRY

We present a novel technique for analyzing volatile organic compounds in air samples using a solid adsorbent together with temperature-progr ammed desorption and subsequent detection by membrane inlet mass spect rometry (TPD-MIMS). The new system has the advantage of a fast separat ion of compounds prior to the detection by MIMS. The gaseous sample is simply adsorbed on the adsorbent, which is then rapidly heated from 3 0 degrees C to 250 degrees C at a rate of 50 degrees C/min, Trapped or ganic compounds are released from the adsorbent into a helium stream a t different temperatures depending on the strength of the interaction between the individual compound and the adsorbent. The helium stream c arries the desorbed compounds to a membrane inlet (90 degrees C) equip ped with a thin (25 pm) silicone membrane. The thin membrane and the h igh temperature of the membrane inlet allows most volatile compounds t o diffuse through the membrane into the mass spectrometer in a few sec onds. In this fashion we could completely separate many similar volati le compounds, for example toluene from xylene and trichloroethene from tetrachloroethene. Typical detection limits were at low or sub-nanogr am levels, the dynamic range was 3 orders of magnitude, and the analys is time for a mixture was about 3-4 minutes. (C) 1998 John Wiley & Son s, Ltd.