Highly selective detection of formaldehyde and its analogs in clams based on unique and specific conjugation reactions via ultraviolet-visible absorptions

•Oxalyldihydrazide is used as the reagent for the specific detection of HCHO.•Aldehyde and ketone groups can react with hydrazide to form hydrazone bonds.•Hydrazone bonds with different UV absorptions can be detected by UV spectroscopy.•HCHO and its analogs can be detected with good sensitivity and specificity.•This method can be used for detecting HCHO in clams and other foods.