Collections > Master's Papers > Gillings School of Public Health > The Efficiency of Aqueous Sodium Bisulfite as a Collection Medium for Formaldehyde, Using the Midget Impinger and Varying Sampling Conditions, and the Development of a Vapor Generation System for Use in the Study
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Currently, the most popular method for the collection of atmospheric samples of formaldehyde, known as the chromotropic acid method (and published by the National Institute for Occupational Safety and Health [NIOSH] as NIOSH Method 3500), includes the use of an impinger containing aqueous sodium bisulfite. A review of the literature indicated that the documentation of the collection efficiency for this method is limited to only a few combinations of air-flow rate, sampling time, and airborne formaldehyde concentration, and the consequent normal sampling time is about 1 hr. This study evaluated the collection efficiency across wide ranges of these factors for the purpose of extending the useful range of the method. A laboratory apparatus was developed that can precisely generate known airborne formaldehyde concentrations ranging from 0.4 to 6.4 ppm, and this generation apparatus was used to conduct the study. Very good collection efficiency, averaging 96%, was found across a wide range of each of the three factors varied in the study. Specifically, flow rates between 0.1 and 1 L/min, sampling times between 1 and 4 hr, and concentrations between 0.4 and 6.4 ppm were determined to provide good collection efficiency. An exception to this statement is that for the combination of long sampling times and high concentrations, a statistically significant trend of declining efficiency was detected; however, it was not determined what physical significance the latter finding held.