Method development for determination of airborne carbonyls using cartridge-based approaches
by So Chun In
90 p. : ill. ; 30 cm
Airborne carbonyls play an important role in chemical and physical processes in the atmosphere. Accurate quantification of their concentration levels is a necessary initial step to assessing their role in atmospheric chemistry. In this thesis work, method development work is focused on two cartridge-based approaches for determination of airborne carbonyls....[ Read more ]
Airborne carbonyls play an important role in chemical and physical processes in the atmosphere. Accurate quantification of their concentration levels is a necessary initial step to assessing their role in atmospheric chemistry. In this thesis work, method development work is focused on two cartridge-based approaches for determination of airborne carbonyls.
The first part of work addresses low collection efficiency issue for 24-hr sampling when using 2,4-dinitrophenyl hydrazine (DNPH)-coated solid sorbent cartridges. Sampling time of as long as 24-hr is often used in ambient monitoring programs, however, collection efficiencies of the DNPH cartridges for 24-h sampling have not been characterized for carbonyls other than formaldehyde and acetaldehyde. Poor CEs for acetaldehyde with 24-h sampling has been reported in one study and other carbonyls were found in this work to suffer similar poor collection efficiency (<58%) problem with 24-h sampling. The reason for the low collection efficiencies was postulated to be related to the change of acidity on the sorbent as sampling proceeds, which leads to reduction in the reaction rate of DPNH-carbonyl reactions. The low collection efficiency issue has been solved by increasing the amount of DNPH coating to 2.5 mg per cartridge.
In the second part of work, a cartridge-based sampling method coupled with GC/MS quantification is developed for the determination of airborne carbonyls. The coating agent on the cartridge is pentafluorophenylhydrazine (PFPH). Carbonyls are trapped as PFPH derivative during sampling, which have sufficient thermal stability and adequate volatility to be amicable for GC/MS analysis. Previous efforts taking this approach failed to obtain satisfactory collection efficiencies for C1 – C3 carbonyls. In this work, we have successfully resolved the issue of low collection efficiencies by increasing the coating amount from 0.15 mg to 2.95 mg PHPF per cartridge. We have established the optimum sampling conditions for 18 carbonyls with good collection efficiencies, that is, a sampling flow rate of up to ~ 1 L/min for 4-h sampling duration or a sampling flow rate of up to ~0.3 L/min for 24-h sampling duration. The newly developed method was applied to determine carbonyls in ambient environment, in a roadside environment, in a kitchen, and in a room influenced by incense burning.