- Method ASTM D3231/ASTM D4951
- Repeatability variable, see method
- Reproducibility variable, see method
- Blending linear
- Additive Correction No
This test method covers the determination of phosphorus generally present as pentavalent phosphate esters or salts, or both, in gasoline.
The limitation of phosphorus was introduced due to its damaging effects on steel, catalytic converters, and its toxicity to the environment.
The method is run by burning the sample in a crucible filled with zinc oxide. It is then baked in the oven until the carbon has been removed and only the metals remain. That sample is then reduced using sulfuric acid and reacted ammonium molybdate and hydrazine sulfate. This solution will turn a blue hue depending upon the amount of phosphorus the solution contained. It is then quantified by using a spectrophotometer.