A Reliable Method for Quantification of Phosphonates and Their Impurities by 31P NMR

A report of a phosphorus-31 nuclear magnetic resonance (31P-NMR) method to determine four alkylpolyphosphonates, aminotris(methylene phosphonic acid) (ATMP), 1-hydroxyethylidene diphosphonic acid (HEDP), ethylene diamine tetra (methylene phosphonic) acid (EDTMP), and diethylenetriamine penta(methylene phosphonic) acid (DTPMP), as well as impurities (orthophosphoric acid and phosphorous acid) is described. Initially, the purity of phosphonate standards was verified. Next, calibration curves using methylphosphonic acid were built and validated. The results were compared using single point calibration. Subsequently, 24 commercial samples of phosphonates were analyzed using the two NMR methods. Concentrations determined by the two techniques were statistically equivalent. Limits of detection of 1.7, 2.4, 3.4, 2.4, 0.9, and 0.8 mg mL−1 were obtained for ATMP, HEDP, EDTMP, DTPMP, orthophosphoric acid, and phosphorous acid, respectively. 31P NMR with a single point calibration is a rapid and accurate method to a...