A general method is presented for the determination of DPPD in a variety of biological materials such as feeds, chicken fat and organs, serum and egg yolk, based on extraction with light petroleum, purification of the extract and measurement of the red colour formed with 72% sulphuric acid containing a little nitric acid.
A study has also been made of some relevant properties of DPPD and its quinoid oxidation product, NN′‐diphenyl‐p‐quinonediimine (“quinone‐dianil”, QDA).