ASTM D664 for acid number of petroleum products
ASTM D664 for acid number of petroleum products by potentiometric titration
9. Standardization of Apparatus
9.1 Determination of Meter Readings for the Aqueous Buffer Solutions - To ensure comparable selection of end points when definite inflection points are not obtained in the titration curve, determine daily, for each electrode pair, the meter readings obtained with aqueous acidic and basic buffer solutions.
NOTE 9 - The response of different glass electrodes to hydrogen ion activity is not the same. Therefore, it is necessary to establish regularly for each electrode system the meter readings corresponding to the buffer solutions arbitrarily selected to represent acidic or basic end points.
9.2 Immerse the electrodes in the pH 4 and the pH 11 aqueous buffers and stir each of them for approximately 5 min, maintaining the temperature of the buffer solution at a temperature within 2°C of that at which the titrations are to be made. Read the cell voltage for each of them. The readings so obtained are taken as the end points in titration curves having no inflection points.
10. Preparation of Sample of Used Oil
10.1 Strict observance of the sampling procedure is necessary since the sediment itself is acidic or basic or has absorbed acidic or basic material from the sample. Failure to obtain a representative sample causes serious errors.
10.1.1 When applicable, refer to Practice D4057 (Manual Sampling) or Practice D 4177 (Automatic Sampling) for proper sampling techniques.
10.1.2 When sampling used lubricants, the specimen shall be representative of the system sampled and shall be free of contamination from external sources.
NOTE 10 - As used oil can change appreciably in storage, test samples as soon as possible after removal from the lubricating system and note the dates of sampling and testing.
10.2 Heat the sample (see Note 11) of used oil to 60 more or less 5°C in the original container and agitate until all of the sediment is homogeneously suspended in the oil. If the original container is a can or if it is glass and more than three-fourths full, transfer the entire sample to a clear-glass bottle having a capacity at least one third greater than the volume of the sample. Transfer all traces of sediment from the original container to the bottle by vigorous agitation of portions of the sample in the original container.
NOTE 11 - When samples are visibly free of sediment, the heating procedure described can be omitted.
10.3 After complete suspension of all sediment, strain the sample or a convenient aliquot through a 100-mesh screen for removal of large contaminating particles.
NOTE 12 - When samples are visibly free of sediment, the straining procedure described can be omitted.
