Cochin laboratory

DOCTOR TEST (P 19, ASTM D-4952, IP 30, ISO 5275)

Mercaptan sulfur (R-SH) and hydrogen sulfide (H2S) are undesirable contaminants because, apart from their corrosive nature, they possess an extremely unpleasant odor. Such compounds should have been removed completely during refining but their presence and that of free sulfur are detected by application of the Doctor test. The Doctor test measures the amount of sulfur available to react with metallic surfaces at the temperature of the test. The rates of reaction are metal type-, temperature-, and time dependent. Sulfur present as mercaptans or as hydrogen sulfide in distillate fuels and solvents can attack many metallic and nonmetallic materials in fuel and other distribution systems. A negative result in the Doctor test ensures that the concentration of these compounds is insufficient to cause such problems in normal use.