Abstract
The chromotropic acid method for formaldehyde is widely used in air pollution studies. During an investigation of incinerator performance, long-term samples frequently produced yellow-brown colors with the reagent rather than the red-purple given with formaldehyde alone. The major interferences have been shown to be oxides of nitrogen found in solution from the air samples as nitrate or nitrite ions. Attempts were made to reduce interference by various procedures. The final method employs absorption in bisulfite solution to form the aldehyde-bisulfite complex and prevent formation of nitrates, followed by heating to remove the volatile components. The sample is then reacted with chromotropic acid and determined according to the usual procedure. The effect of various concentrations of oxides of nitrogen is shown.