ASTM D3339 Test Method for Acid Number of Petroleum Products
ASTM D3339 Standard Test Method for Acid Number of Petroleum Products by Semi-Micro Color Indicator Titration
6. Apparatus
6.1 Titration Buret - A micro scale, automatic buret with 0.01 mL subdivisions and at least a 2-mL buret capacity.

6.2 Titrant Reservoir - The preferred reservoir is one that is integral with the automatic buret, such as shown in Fig. 1. A titrant reservoir separate from the automatic buret may be used if the line connecting the reservoir with the buret is all glass. Exposure of the titrant to light should be minimized by use of amber glass for the reservoir, by wrapping the reservoir with foil such as aluminum foil, or by other suitable means. Also, the tube in the reservoir for titrant withdrawal is adjusted so that the end of the tube is about 20 mm (0.8 in.) from the bottom of the reservoir so that any precipitate that may collect on the bottom of the reservoir will not be disturbed. To further avoid disturbing any precipitate in the reservoir, movement of the reservoir must be minimized.
6.2.1 With either type of reservoir all entrances and exits to the buret and reservoir must be connected to absorption tubes to remove atmospheric carbon dioxide and water, for example, tubes containing 10 to 20-mesh anhydrous calcium sulfate as desiccant and soda-lime as carbon dioxide absorbent. Precautions must be taken to prevent introduction of any soda-lime into the titrant reservoir or buret.

6.3 Titration Beaker - 100-mL capacity tall-form Berzelius beaker without pouring spout. Approximate dimensions are 47 mm in inside diameter and 79 mm in height.

6.4 Titration Beaker Purging Stopper - A stopper to enclose the titration beaker. The stopper must be composed of an elastomeric material, such as neoprene, that is essentially unaffected by the titration solvent. Approximate stopper dimensions are 53 mm top diameter, 45 mm bottom diameter, and 25 mm height. The stopper is fitted with a 8-mm (0.3-in.) outside diameter glass inlet tube extending 15 ± 2 mm beyond the bottom of the stopper and with a 7 ± 1-mm inside diameter hole. The inlet tube and hole are placed on opposite sides of the stopper with a center-to-center separation distance of 30 ± 1 mm.

6.5 Purge Gas Rotameter, capable of indicating a flow rate of 10 L/h.

6.6 Stirrer Motor, variable speed, magnetically linked.

6.7 Stirring Bar, cylindrical, TFE-fluorocarbon encased, 25.4 mm long and 7.9 mm in diameter.

6.8 Pipet, capable of transferring 0.100 ± 0.002 mL of titration indicator solution.

6.9 Titration Solvent Buret - A 500-mL or larger capacity buret with 5-mL subdivisions. The top of the buret is stoppered and connected with an absorption tube, as in 6.2, to remove atmospheric carbon dioxide and water. An alternative means of dispensing the titration solvent may be used provided a dispensing repeatability within ± 1 mL for 40 mL is obtainable and the solvent in the dispenser is isolated from atmospheric carbon dioxide and water.

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 or to other such recognized standards for reagent chemicals. Other grades may be used, provided it is first ascertained that the reagent is of sufficient high purity to permit its use without lessening the accuracy of the determination.

7.2 Purity of Water - All references to water shall be understood to mean freshly distilled (carbon dioxide-free) water conforming to Specification D1193, Type II or III.

7.3 Ethyl Alcohol - (Warning - Flammable. Denatured - Cannot be made nontoxic.) USP 200 proof or denatured alcohol according to Formula 30 of the U. S. Bureau of Internal Revenue.

7.4 Propanol-2-ol, (Isopropyl Alcohol) Anhydrous, (Warning - Flammable, see also Note 3.) containing less than 0.9 % water.

NOTE 3 - It has been reported that, if not inhibited against it, propanol-2-ol can contain peroxides. When this occurs, an explosive mixture is possible when the storage vessel or other equipment such as a dispensing bottle, are near empty and approaching dryness.

7.5 p-Naphtholbenzein Indicator Solution - The p-naphtholbenzein must meet the specifications given in the Annex. Prepare a solution containing 10 g of p-naphtholbenzein per litre of titration solvent.

7.6 Nitrogen, dry and carbon dioxide-free.
7.6.1 In order to obtain repeatable results and a stable end point color change, it is especially important that the nitrogen purge gas be free of carbon dioxide. Prepurified grade nitrogen has been found to be satisfactory.

7.7 Phenolphthalein Indicator Solution - Dissolve 0.10 g of solid pure phenolphthalein in 50 mL of water and 50 mL of ethyl alcohol.

7.8 Titration Solvent - Consisting of 5.0 + 0.1 ml of water, 495 ± 1 ml of anhydrous propanol-2-ol and 500 ± 10 ml of Toluene.

7.9 Potassium Hydroxide Solution, Standard Alcoholic (0.01 M) (Warning - Corrosive.).

NOTE 4 - Commercially available reagents may be used in place of laboratory preparations.

7.9.1 Preparation - Add 3 g of solid KOH to approximately 1 L of anhydrous propanol-2-ol (isopropyl alcohol) (containing less than 0.9 % water) in a 2-L Erlenmeyer flask. Boil the mixture gently on a steam bath for 10 to 15 min while stirring to prevent caking of solids on the bottom of the flask. Add about 1 g of barium hydroxide and again boil gently for about 10 min. Cool to room temperature, stopper to prevent contact with the room atmosphere and allow to stand overnight (about 16 h). Filter the supernatant liquid through a 10-µm TFE-fluorocarbon membrane filter while avoiding unnecessary exposure to the atmosphere and then dilute the solution (approximately 0.05 M) with anhydrous isopropyl alcohol to a total volume of about 5 L (Note 5). Store the titrant in a chemically resistant dispensing bottle out of contact with cork, rubber, or saponifiable stopcock lubricant and protected by a guard tube containing soda-lime. Minimize exposure of the titrant to light by storing in the dark or in an amber bottle or by wrapping the bottle with aluminum foil.

NOTE 5 - Care should be taken to ensure a final normality of 0.011 ± 0.002.

NOTE 6 - Because of the relatively large coefficient of cubic expansion of organic liquids, such as propanol-2-ol, the standard alcoholic solutions should be standardized at temperatures close to those employed in the titrations of samples.

7.9.2 Standardization - The titrant is standardized (Note 6) against dried (at least 1 h at 110°C), pure potassium hydrogen phthalate using the method described in 9.1 for the acid number analysis, with the exception that water (40 ± 1 mL) is used as the solvent and 6 drops of phenolphthalein solution is used as the indicator. The blank is obtained in the same manner except that the potassium hydrogen phthalate is excluded. Standardize the titrant frequently enough to detect changes of 0.0003 M. The mean molarity determined by at least duplicate analyses is used as the titrant molarity for the acid number calculations.

7.10 Toluene (Warning - Flammable. Vapor harmful.), nitration-grade, or equivalent.