(Equivalent Tests: IP 430 and ISO 13759)
EXPLANATION
Alkyl nitrate is added to diesel fuel to improve cetane number. This method can determine 0.03 to 0.30 volume percent of alkyl nitrate in diesel fuel and thus can serve as a basis for judging compliance with specifications covering any alkyl nitrate. The standards used for calibration must contain the same alkyl nitrate ester as the test specimen to be analyzed. Other nitrate esters, inorganic nitrate ions, and nitrogen oxides interfere.
TEST SUMMARY
Simultaneous hydrolysis of ester in 65 % sulfuric acid solution and nitration of m-xylenol by the nitric acid liberated is carried out. The resultant nitroxylenol is extracted from the reaction mixture and reacted with NaOH to form the yellow salt. The color is measured spectrophotometrically at 452 nm, and the concentration of alkyl nitrate is determined by reference to the slope of the calibration curve.
TEST PRECISION
The test method has no known bias.