A technique using Summa® canisters with cryogenic
preconcentration and gas chromatographic–mass spectrometric (GC-MS)
detection was developed to determine 143 C3–C12
volatile organic compounds (VOCs) including alkanes, alkenes, aromatics and
halohydrocarbons in ambient and indoor air. The method detection limits and
practical quantification limits were sensitive at 0.02 and 0.10 ppbv, respectively,
and the method precision and accuracy were also satisfactory. The stability
of C3–C12 VOC standards at ppbv levels under elevated
pressure in canisters was assessed over various time intervals (from 1 week
to 4 months after preparation) and most of the compounds were found to be
acceptably stable with a mean recovery of 85.6 ± 9.9% during the course
of a 4-month study. However, a small fraction (approximately 6%) of the compounds,
including two halohydrocarbons (bromotrichloromethane and benzyl chloride)
and six alkenes (2-methylbuta-1,3-diene (isoprene), cis-4-methylpent-2-ene, cis-3-methylpent-2-ene,
hept-1-ene, oct-1-ene and styrene) displayed relatively low recoveries in
the range 34.6–67.9%. The loss of these compounds is most probably caused
by their physical adherence to the active sites of the canister surface, chemical
decomposition and/or reactions with other species. The results indicated that
one must be cautious in attempting to measure these compounds owing to their
instability in canisters. Overall, this analytical technique, which has been
used for the determination of the VOCs under study in the toxic air pollutant
monitoring network administered by the HKSAR Government, was amenable to the
measurement of airborne VOCs collected both outside and inside a semi-confined
car park in the present study.
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