Ra. Ketola et al., TEMPERATURE-PROGRAMMED DESORPTION FOR MEMBRANE INLET MASS-SPECTROMETRY, Rapid communications in mass spectrometry, 12(12), 1998, pp. 773-778
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.