The chemistry of the chromotropic acid method for the analysis of formaldehyde

Abstract

Formaldehyde is present in the indoor air of many industrial and non-industrial environments. The procedure most commonly employed in North America for its analysis is one that uses chromotropic acid and concentrated sulphuric acid. The nature of the purple chromogen that is produced in the analytical procedure has not been fully understood until now. Evidence will be presented to support the hypothesis that the chromogen has a mono-cationic dibenzoxanthylium structure and not a para.para-quinoidal one that is commonly cited.