Determination of Phosphorus-Containing Compounds by Spectrophotometry

Abstract

No single method has been applicable for the determination of total phosphorus in the large spectrum of naturally-occurring and synthetic phosphorus-containing compounds, especially for those of extreme stability; e.g., ionic 0,O-dialkyl phosphates and 0-alkyl alkylphosphonates; the available phosphorus assay procedures determine only certain classes of phosphorus compounds. Phosphate esters from cells and tissues have been assayed routinely for total phosphorus after acid hydrolysis (e.g., 1). Nonesterified alkylphosphonates have been determined after alkaline persulfate oxidation (2); however, 0-alkyl alkylphosphonates are not hydrolyzed quantitatively (3), and the detection limit and the sensitivity in these determinations are poor (30-1600 nmol/assay). We have found (Cook and Daughton, unpublished data) that dry ashing with 5 M HNO3 (4) results in incomplete and erratic recovery of dihydrogen 2-aminoethylphosphonate as orthophosphate. Subsequently, we found that a published method for wet ashing of aminoalkylphosphonates (5) could be extended and modified to give a simple, safe, general procedure for nongaseous phosphorus compounds in the 1-50 nmol range: this new procedure is described here. The orthophosphate resulting from the ashing was assayed by the highly sensitive method of Bartlett ( I ).