Determination of Available Phosphorous in Alkyl Phosphate

The available phosphorous compound of alkyl phosphates was determined by ascorbic acid-molybdenum blue spectrophotometry.This compound was total phosphorus minus inorganic phosphorus.The effect of definite wavelength,amount of color reagent,amount of sulfuric acid,color times on definite conditions were as follows:Definite wavelength was 820 nm,amounts of sulfuric acid,ammonium molybdate and ascorbic acid were 2.0,2.0,1.0 mL respectively;the reaction mixture was heated for 20 min in water bath at 70 ℃.Beer′s law was obtained in the range of 0.2 to 10 mg·L-1 between the values of absorbance and concentration of phosphorous.Corresponding to the linear regression equation,the total phosphorus:A=0.1924ρ+0.0134(r=0.999 5);Inorganic phosphorus:A=0.1846ρ+0.0094(r=0.999 1).The average recovery rate was 91% to 97%,RSD3.40% in the above-mentioned conditions.This method was simple to operate and easy for calculation,which was satisfactory for the determination of effective phosphorus in the alkyl phosphate.