2,4-Dinitrophenylhydrazine(2,4-DNPH) is a selective reagent to carbonyl compounds. It readily reacts with high and low, saturated and unsaturated, aliphatic and aromatic carbonyl compounds, forming hydrazones. Therefore, 2,4-DNPH is widely used for colorimetric and chromatographic determination of various carbonyl compounds and their isomers in organic liquids and water. Until recently, 2,4-DNPH was not used to analyze air, where carbonyl compounds might be contained in microquantities. In analyzing atmospheric air, the entire sample (5-10 ml) should be used because of the low concentrations of the substances being studied. A limited amount (0.05 - 0.1 ml or less) can be taken for chromatographic analysis. Therefore, the sample must be concentrated. The results of our studies agree completely with the data of Lonhmon. Further chromatographic analysis showed that, along with hexane hydrazones, only a small part of 2,4-DNPH is eliminated from the acid solution, which appears on the chromatogram in the form of 1 spot at the start line and does not interfere with the analysis of microquantities of carbonyl compounds.