Determination of low-molecular-weight aldehydes in stack gas and automobile exhaust gas by liquid chromatography

Improved procedures for sample collection and derivatization are proposed for detecting low-molecular-weight aldehydes, which are performed directly in a bubbler containing a methanol or acetonitrile solution of 2,4-dinitrophenylhydrazine (2,4-DNPH) and an acidic catalyst. An aliquot is then injected into a liquid chromatograph. This method avoids extraction and condensation as in usual formaldehyde analysis by liquid chromatography and hence it is simple and fast. The optimum molar ratio of 2,4-DNPH to aldehydes is 23:1. The recoveries achieved for formaldehyde, acetaldehyde, propionaldehyde and butyraldehyde all exceed 85%, with detection limits of 51, 57, 12 and 14 ppb (v/v), respectively. The 2,4-DNPH derivatives were investigated further by ultraviolet and mass spectrometry. 2,4-Dinitrophenylhydrazones are identified as the reaction product of aldehydes with an acidic solution of 2,4-DNPH. This method was used to evaluate the amounts of aldehydes emitted from an oil-fuelled boiler and a gasoline engine under different operating conditions.