Nonanal 2,4-dinitrophenylhydrazone serves as a reference standard in analytical chemistry for the detection and quantification of nonanal, an aldehyde carbonyl compound. It is the stable hydrazone derivative formed by the reaction of nonanal with 2,4-dinitrophenylhydrazine (DNPH), a common derivatizing agent. This derivative enhances detection sensitivity and can be analyzed using techniques such as high-performance liquid chromatography (HPLC) or gas chromatography (GC). It is particularly useful in environmental and biological samples for measuring low concentrations of carbonyls, including in air quality monitoring to identify volatile aldehydes like nonanal from indoor air or industrial emissions.