ASTM D5770 Test Method for Semiquantitative Micro Determination of Acid Number of Lubricating Oils During Oxidation Testing
6. Apparatus
6.1 Glass Beakers, 10 mL capacity, or glass vials, 4 dram or 6 dram.
6.2 Glass Syringe, 2 mL to 5 mL capacity. A 5 mL inter-changeable syringe with a 20 gage, 12 cm needle is satisfactory.
6.3 Dropping Pipet, glass with rubber bulb, capable of delivering 35 drops to 40 drops of oil.
7. Reagents
7.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless indicated otherwise, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades can be used provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
7.2 Acid Number Reference Solution - Any stable, oil-soluble acid which will produce an acid number of approximately 0.5 mg/g KOH is acceptable. This solution shall be standardized using Test Method D974 or D664. A solution of 0.20 % by mass dodecenylsuccinic anhydride in HVI 250 base oil or in an ISO 10-22 (60-100 SUS) oil has proven satisfactory.
7.3 Alcoholic Potassium Hydroxide Standard Solution (0.1 M) - Prepare approximately 0.1 M solution by dissolving KOH in propanol-2-ol. Standardize against pure potassium acid phthalate in about 100 mL of water, using phenolphthalein to detect the end point. (Commercial grades of this reagent have been found to be satisfactory.) (Warning - Corrosive.) (Warning - Poisonous if ingested, alkaline, causes irritation producing dermatitis.)
7.4 Dodecylsuccinic Anhydride - (Warning - Irritating to eyes and skin.)
7.5 p-Naphtholbenzein Indicator Solution - The p-naphtholbenzein must meet the specifications in Appendix X1 of Test Method D974. Prepare a solution containing 10 g of p-naphtholbenzein/L in a 50:50 mixture of toluene:propanol-2-ol. (Warning - Flammable. Vapor harmful.)
NOTE 2 - In a 1992 study, only Kodak, Fisher, and Baker (Mallinkrot) were found to meet the specifications. However, the Kodak brand is no longer available. The Fisher Reagent Solution was the only commercially available solution to meet the specifications.
7.6 Propanol-2-ol (Isopropyl Alcohol) - (Warning - Flammable.)(Warning - It has been reported that, unless inhibited against it, peroxides can form in propanol-2-ol and, as the storage vessel or equipment such as a dispensing bottle become empty and approach dryness, an explosive mixture can occur.)
7.7 Titration Solution - Mix 350 mL of toluene, 350 mL of propanol-2-ol, and 7 mL of the p-naphtholbenzein solution in a 1 L plastic bottle. Add 15 mL of 0.1 M potassium hydroxide alcoholic solution and mix well. (Warning - Flammable. Vapor harmful. Corrosive.)
NOTE 3 - The strength of the titration solution depletes with time and should be periodically replaced. Up to one month has been found to be satisfactory.
7.8 Toluene - (Warning - Flammable. Vapor harmful.)
