Optimization of the Wash-Off Method for Measuring Aerosol Concentrations

Using the fluorescence-washing technique, oleic acid particles tagged with uranine were extracted and analyzed fluorometrically. The possible sources of errors in the technique were evaluated in this study. First, the sensitivity of uranine fluorescence in different solutions was compared. The results indicated that uranine in distilled water with pH 10 buffer and in sodium hydroxide have high sensitivity. Second, the interference of oleic acid with uranine quantification in a variety of media was investigated. It was found that there is no interference from oleic acid in distilled water and sodium hydroxide solutions under our operating conditions. However, oleic acid did significantly quench the uranine fluorescence signal in ethanol. Third, the ability of different solutions to extract uranine from glass fiber and Teflon filters was tested. The results indicated that distilled water and sodium hydroxide solutions have the highest extraction ability of the media evaluated. Based on the results above, distilled water, 0.001 N sodium hydroxide, and 0.01 N sodium hydroxide solutions were the optimal washing solutions in the fluorescence-washing technique. It was also found that, for inlet washes, distilled water would not be reactive and have high extraction efficiency.