Determination of phosphonic acid breakdown products by high-performance liquid chromatography after derivatization

A new HPLC method for the determination of oxidative breakdown products of aminopolyphosphonates is presented. The phosphonate nitrilotrismethylenephosphonic (NTMP) acid undergoes catalytic oxidation by molecular oxygen in the presence of manganese(II). The two diphosphonates iminodimethylenephosphonic acid (IDMP) and formyliminodimethylenephosphonic acid (FIDMP) are formed. The analytical method employs the derivatization of the aldehyde group in FIDMP by 2,4-dinitrophenylhydrazine and of the imine group in IDMP by 9-fluorenyl methylchloroformate. The two derivatives are quantified in separate runs using the same acidic phosphate–acetonitrile eluent with detection at 370 nm for FIDMP and 260 nm for IDMP. The detection limit for FIDMP is 0.01 μM, for IDMP 0.02 μM. The method is suitable for the determination of the breakdown products in wastewater.