ASTM D3227 Sulfur in Gasoline, Kerosine, Aviation Turbine, and Distillate Fuels
ASTM D3227 Standard Test Method for (Thiol Mercaptan) Sulfur in Gasoline, Kerosine, Aviation Turbine, and Distillate Fuels (Potentiometric Method)
8. Preparation of Apparatus
8.1 Glass Electrode - After each manual titration, or batch of titrations, in the case of automatic titration systems, wipe the electrode with a soft, clean tissue and rinse with water. Clean the electrode at frequent intervals (at least once a week) by stirring in cold chromic acid solution (Warning - Causes severe burns. A recognized carcinogen. Strong oxidizer - contact with other material may cause fire. Hygroscopic. An equivalent, chromium-free cleaning solution may be used) for a few seconds (10 s maximum). When not in use, keep lower half of the electrode immersed in water.
8.2 Silver/Silver-Sulfide Electrode - Each day prior to use, or as triggered by the analysis of a quality control (QC) sample (see Section 12), prepare a fresh silver sulfide coating on the electrode by the following method:
8.2.1 Burnish electrode with polishing paper or cloth until a clean, polished silver surface shows.
8.2.2 Place electrode in operating position and immerse it in 100 mL of titration solvent containing 8 mL of Na2S solution.
8.2.3 Add slowly from a buret, with stirring, 10 mL of 0.1 mol/L AgNO3 solution over a period from 10 to 15 min.
8.2.4 Remove electrode from solution, wash with water, and wipe with a soft, clean tissue.
8.2.5 Between manual titrations, or batches of titrations in the case of automatic titration systems, store the electrode a minimum of 5 min in 100 mL of titration solvent containing 0.5 mL of the 0.1 mol/L AgNO3 solution.
