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DEVELOPMENT AND APPLICATION OF A SENSITIVE METHOD TO DETERMINE CONCENTRATIONS OF ACROLEIN AND OTHER CARBONYLS IN AMBIENT AIR
Impact/Purpose:
Acrolein is a reactive aldehyde that injures the airways in humans and other species, and the U.S. Environmental Protection Agency lists it among the mobile-source air toxics that pose the greatest health risk. Information on the acrolein concentrations to which people are exposed is an important prerequisite for assessing the risk to human health. Despite some technological improvements, it remains difficult to accurately measure acrolein at low levels because, upon collection, it rapidly forms unstable intermediates that are difficult to differentiate and quantify.
Dr. Judith Charles of the University of California–Davis proposed the develop a new method for measuring low levels of acrolein, crotonaldehyde, and other unstable aldehydes and apply the new method to assess exposure of tollbooth attendants in the San Francisco Bay area. During the middle of the second year, Dr. Charles became ill, and Dr. Thomas Cahill replaced her as the principal investigator and completed the study.
Description:
The sampler developed by Charles and Cahill, with Dr. Vincent Seaman, consists of a custom-built glass mist chamber in which air enters at a high flow rate and carbonyls are trapped in a solution of sodium bisulfite as carbonyl-bisulfite adducts. This reaction is rapid (on the order of seconds) for all the carbonyls tested, and its rate is dependent on the concentration of bisulfite. The optimal sampling time for acrolein and the other carbonyls is 10 to 30 minutes at a flow rate of approximately 20 L/min at 21C, and the optimal setup is two mist chambers in series. Longer sampling times, lower flow rates, and different temperatures were not evaluated. After collection, hydrogen peroxide is added to free the carbonyl from the adduct, and a derivatizing agent is added to form a carbonyl derivative suitable for gas chromatography with mass spectrometry. The calculated minimum detection limit for acrolein varied between experiments and ranged from 0.012 μg/m3 (0.005 ppb) to 0.035 μg/m3 (0.015 ppb), values well below the detection limits of other existing methods .
The collection efficiency of the mist chamber methodology was determined to be 80% in the laboratory and 71% in the field. Assuming that the collection efficiency is the same in the two chambers, it would be approximately 91% for the whole system in the field. This is only a relative measure of collection because it does not consider the initial amount of acrolein. Using the spike-recovery approach, the investigators found that 97% of the acrolein mass was recovered. For this test acrolein was dissolved in solvent and volatilized into a nitrogen stream. Although this approach was designed to simulate sampling in the field, it may not reflect entirely the actual conditions to which acrolein is exposed when sampled in ambient air. The test using the deuterated internal standard showed that, once the acrolein was trapped, 93% was retained throughout theanalytic process. Because the deuterated species was dissolved in the bisulfite solution in the mist chamber, rather than bubbled into the solution in an air stream (as it would be under ambient sampling conditions), the measure of internal standard retention does not evaluate the efficiency with which the carbonyl in the ambient air stream is trapped in the mist chamber solution. Overall, the Review Committee—in its independent evaluation of the study—thought that these analyses were useful and showed a high level of acrolein recovery under laboratory conditions. However, the dynamic processes that lead to absorption of acrolein in the field may vary.