N. Kasthurikrishnan et al., THIN PERVAPORATION MEMBRANES FOR IMPROVED PERFORMANCE IN ONLINE FLOW-INJECTION ANALYSIS MEMBRANE INTRODUCTION MASS-SPECTROMETRY, Rapid communications in mass spectrometry, 10(7), 1996, pp. 751-756
Characterization of some thin (10-50 mu m) and selective (zeolite fill
ed) sheet pervaporation membrane materials for the on-line analysis of
volatile compounds in solution by membrane introduction mass spectrom
etry and dow injection analysis is reported, A comparison of the membr
ane performance, both in aqueous (normal) and organic (reverse) phase,
is made using a seven-component test mixture and a triple quadrupole
mass spectrometer, While no significant difference is observed in the
normal phase experiments, reverse phase experiments with the thin memb
ranes showed an improvement in rise times and analysis times by a fact
or of two, Thus, the thin membranes are more suitable for chemical and
petrochemical on-line process monitoring where the frequency of sampl
ing is of great importance, The thin hydrophobic membranes allow enoug
h water to permeate the membrane for chemical ionization to be perform
ed as an alternative to electron impact provided an ion trap mass spec
trometer is used. The detection limits observed for the compounds stud
ied using water as a chemical ionization reagent are similar to those
achieved by a two-stage enrichment microporous membrane/jet separator
device interfaced to an ion trap mass spectrometer and are in the lowe
r parts-per-billion range for some of the compounds studied (5 ppb for
methyl ethyl ketone, 5 ppb for acetone), Thus the thinner hydrophobic
membranes offer the unique combination of rapid permeation and low de
tection limits in chemical ionization experiments with an ion trap.