Investigations of the Determination of Phosphorus in Organic Media by Atomic Absorption Heated Graphite Atomizer

Abstract

The analysis of phosphorus in organic compounds used as product additives has been investigated. It has been found necessary to change the organic phosphorus to inorganic phosphorus before measuring it by atomic absorption spectrophotometry. In the determination of tricresyl phosphate in gasoline the gasoline is ashed on magnesium sulfonate. The tricresyl phosphate is converted to Mg₂P₂O₇ and subsequently dissolved in nitric acid, diluted to desired concentration, and then injected into the heated graphite furnace. A calibration curve is made from gasoline containing a known phosphorus content to give a range of 1 to 10 ppm. Twenty-five microliters of the knowns and unknown are injected on 10 µl of a 1% solution of lanthanum nitrate on the graphite tube. An alkyl phenyl phosphite additive is diluted in dimethylformamide to bring it into solution in the range of 1 to 10 ppm phosphorus. A portion is ashed on magnesium oxide with the addition of 1 ml of 30% hydrogen peroxide. The Mg₂P₂O₇ is dissolved in nitric acid, then diluted to the calibration curve range. It is injected into the heated graphite furnace in the presence of 10 µl of a 1% lanthanum nitrate solution.