ASTM D2896 for base number of petroleum products
ASTM D2896 for base number of petroleum products by potentiometric perchloric acid titration
6. Apparatus
6.1 Potentiometric Titrimeters, either automatic recording or manual.
6.2 Glass Electrode, pH 0 to 11, general-purpose type.
6.3 Reference Electrode, silver/silver chloride (Ag/AgCl) reference electrode with a nonaqueous bridge as described in Section 10. (See also 19.1.)
NOTE 3 - Some reference electrodes with fritted or fiber diaphragms and some combined glass plus reference electrodes systems are commercially available, such as the single-rod glass plus silver/silver chloride electrode assembly. During the development of this test method, the use of electrodes of these types gave problems in some laboratories, but not in others. Accordingly, these electrodes are permitted in this test method, provided that the sodium perchlorate bridge is used; however, when stability or other problems arise with their use, the sleeve-type electrode should be used.
6.4 Stirrer, either mechanical or electrical, with variable speeds and with propeller or paddle of chemically inert material. When an electrical stirrer is used, it must be grounded so that disconnecting or connecting the power to the motor will not produce a permanent change in meter reading during the course of a titration. A magnetic stirrer with stirring bar can be used provided it meets these conditions.
6.5 Buret, 10 or 20-mL, graduated in 0.05-mL divisions and calibrated with an accuracy of more or less 0.02 mL, or an automatic buret of similar accuracy.
6.6 Titration Beaker, made of borosilicate glass or other suitable titration beaker, tall form recommended.
6.6.1 For Procedure A, use a beaker of 250 or 300 mL capacity. For Procedure B, use a beaker of about 150 mL capacity such that 60 mL of titration solvent will cover the electrodes.
NOTE 4 - Other beakers of suitable size capacity may be used.
6.7 Titration Stand, suitable to support the beaker, electrodes, stirrer, and buret. An arrangement that allows for the removal of the beaker without disturbing the electrodes, buret, and stirrer is desirable.
NOTE 5 - Some apparatus may be sensitive to interference by static electricity, shown by erratic movements of recorder pen or meter indicator, when the titration assembly (beaker and electrodes) is approached by the operator. In this case surround the beaker closely with a cylinder of copper gauze that is electrically grounded.
7. Reagents and Materials
7.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, 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 may 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 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean reagent water that meets the requirement of either Type I, II, or III of Specifcation D1193.
7.3 Acetic Acid, glacial (Warning - Toxic and irritant).
7.4 Acetic Anhydride (Warning - Toxic and irritant).
7.5 Chlorobenzene (Warning - Toxic and irritant).
7.6 Perchloric Acid, Standard Solution in Acetic Acid (0.1 N) (Warning - Powerful oxidant when dry or heated. Great care should be taken to avoid contact with organic matter under conditions that may result in subsequent drying or heating, and spills should be washed immediately and thoroughly with water) - Mix 8.5 mL of 70 to 72 % perchloric acid (HClO4, 70 to 72 %) (or 10.2 mL of 60 to 62 % HClO4 solution) with 500 mL of glacial acetic and 30 mL (or 35 mL if the 60 to 62 % HClO4 solution is used) of acetic anhydride. Dilute to 1 L with glacial acetic acid. Allow the solution to stand for 24 h.
NOTE 6 - Excess acetic anhydride should be avoided to prevent acetylation of any primary or secondary amines that may be present.
7.7 Potassium Hydrogen Phthalate - (KHC8H4O4).
7.8 Sodium Perchlorate Electrolyte - (Warning - Sodium perchlorate is toxic and an irritant. It is also a powerful oxidizing agent when heated. Great care should be taken to avoid contact with organic matter under conditions that may result in subsequent drying or heating, and spills should be washed immediately and thoroughly with water.) Prepare a saturated solution of sodium perchlorate (NaClO4) in glacial acetic acid. An excess of undissolved NaClO4 shall always be present at the bottom of the solution.
7.9 Titration Solvent - Add one volume of glacial acetic acid to two volumes of chlorobenzene.
7.10 Sodium Carbonate, anhydrous (Na2CO3).
7.11 Sodium Acetate Solution, 0.1 N in acetic acid (for back titration, see Sections 16 and 17) - Dissolve 5.3 g of anhydrous Na2CO3 in 300 mL of glacial acetic acid. Dilute to 1 L with acetic acid after solution is complete.
