ASTM D2896 for base number of petroleum products
ASTM D2896 for base number of petroleum products by potentiometric perchloric acid titration
9. Preparation of Sample
9.1 It is essential to ensure that the sample is representative since any sediment can be acidic or basic or have adsorbed acidic or basic material from the sample. When necessary, samples are warmed to aid mixing. Used oils should be vigorously shaken to ensure homogeneity before sampling.
NOTE 8 - As used oils can change appreciably in storage, samples should be tested as soon as possible after removal from the lubricating system and the dates of sampling and testing, if known, should be noted.
10. Preparation of Electrode System
10.1 Preparation of Electrodes - When the reference electrode is to be changed from aqueous bridge to nonaqueous, drain out the aqueous solution, wash out all crystals of KCl with water, then rinse the outer jacket (salt bridge) several times with NaClO4 electrolyte solution. Finally fill the outer jacket with NaClO4 electrolyte solution up to the filling hole. When using the sleeve-type electrode, carefully remove the ground-glass sleeve and thoroughly wipe both ground surfaces. Replace the sleeve loosely and allow a few drops of electrolyte to drain through to flush the ground-glass joint and to wet the ground surfaces thoroughly with electrolyte. Set the sleeve firmly in place, refill the outer jacket with the NaClO4 electrolyte solution, and rinse the electrode with chlorobenzene. When in use, the electrolyte level in the reference electrode should be kept above that of the liquid in the titration beaker to prevent entry of contaminants into the salt bridge. When not in use, fill the reference electrode with the NaClO4 electrolyte solution, leave the bung in the filling orifice, and immerse both electrodes in distilled water, keeping the level of the electrolyte above that of the distilled water.
10.2 Testing of Electrodes - Test the meter-electrode combination when first put into use or when new electrodes are installed and retest at intervals thereafter as follows:
10.2.1 Procedure A - Dip the electrodes into a well-stirred mixture of 100 mL of glacial acetic acid plus 0.2 g of KHC8H4O4 and record the reading given by the meter. Rinse the electrodes with chlorobenzene and immerse in 100 mL of glacial acetic acid plus 1.5 mL of 0.1 N HClO4 solution. The difference between readings is to be at least 0.3 V.
10.2.2 Procedure B - Dip the electrodes into a well-stirred mixture of 60 mL of glacial acetic acid plus 0.1 g of KHC8H4O4 and record the reading vein by the meter. Rinse the electrodes with chlorobenzene and immerse in 50 mL of glacial acetic acid plus 0.75 mL of 0.1 N HClO4 solution. The difference between readings is to be at least 0.3 V.
NOTE 9 - See Appendix X4 for a possible procedure to check the electrode performance.
10.3 Cleaning of Electrodes - Following a titration, first wash the electrodes with titration solvent to remove any adhering oily material from the previous titration. Then wash the electrodes with water to dissolve any NaClO4 that may have formed around the sleeve of the reference electrode and to restore the aqueous gel layer of the glass electrode. Rinse again with the titration solvent. Before starting a series of sample titrations, follow this rinsing procedure, then run one or two blank titrations on the solvent to condition the electrodes. Repeat the blank titrations if necessary.
10.4 Maintenance of Electrodes - When there is reason to believe that the glass electrode has become contaminated, it can be cleaned by immersion in cold chromic acid (Warning - Corrosive and carcinogenic) or an alternative non-chromium-containing strongly-oxidizing acid cleaning solution for 5 min, followed by thorough water washing. After this cleaning treatment, test the electrode as described in 10.2. The reference electrode can be cleaned by draining and refilling with fresh NaClO4 solution. Maintain the electrolyte level in the reference electrode above that of the liquid in the titration beaker at all times. Do not allow the electrodes to remain immersed in titration solvent for any appreciable period of time between titrations. While the electrodes are not extremely fragile, handle them carefully at all times and particularly avoid scratching the glass electrode.
