ASTM D664 for acid number of petroleum products
ASTM D664 for acid number of petroleum products by potentiometric titration
6. Apparatus
6.1 Manual Titration Apparatus:
6.1.1 Meter, a voltmeter or a potentiometer that will operate with an accuracy of more or less 0.005 V and a sensitivity of more or less 0.002 V over a range of at least more or less 0.5 V when the meter is used with the electrodes specified in 6.1.2 and 6.1.3 and when the resistance between the electrodes falls within the range from 0.2 to 20 MΩ. The meter shall be protected from stray electrostatic fields so that no permanent change in the meter readings over the entire operating range is produced by touching, with a grounded lead, any part of the exposed surface of the glass electrode, the glass electrode lead, the titration stand, or the meter.
NOTE 4 - A suitable apparatus could consist of a continuous-reading electronic voltmeter designed to operate on an input of less than 5 x 10(-12) A, when an electrode system having 1000-MΩ resistance is connected across the meter terminals and provided with a metal shield connected to the ground, as well as a satisfactory terminal to connect the shielded connection wire from the glass electrode to the meter without interference from any external electrostatic field.
6.1.2 Sensing Electrode, Standard pH, suitable for nonaqueous titrations.
6.1.3 Reference Electrode, Silver/Silver Chloride (Ag/AgCl) Reference Electrode, filled with 1M–3M LiCl in ethanol.
6.1.3.1 Combination Electrodes - Sensing electrodes may have the Ag/AgCl reference electrode built into the same electrode body, which offers the convenience of working with and maintaining only one electrode. The combination electrode shall have a sleeve junction on the reference compartment and shall use an inert ethanol electrolyte, for example, 1M–3M LiCl in ethanol. These combination electrodes shall have the same response or better response than a dual electrode system. They shall have removable sleeves for easy rinsing and addition of electrolyte.
NOTE 5 - A third electrode, such as a platinum electrode, may be used to increase the electrode stability in certain systems.
6.1.4 Variable-Speed Mechanical Stirrer, a suitable type, equipped with a propeller-type stirring paddle. The rate of stirring shall be sufficient to produce vigorous agitation without spattering and without stirring air into the solution. A propeller with blades 6 mm in radius and set at a pitch of 30 to 45° is satisfactory. A magnetic stirrer is also satisfactory.
6.1.4.1 If an electrical stirring apparatus is used, it shall be electrically correct and grounded so that connecting or disconnecting the power to the motor will not produce a permanent change in the meter reading during the course of the titration.
6.1.5 Burette, 10-mL capacity, graduated in 0.05-mL divisions and calibrated with an accuracy of more or less 0.02 mL. The burette shall have a tip that extends 100 to 130 mm beyond the stopcock and shall be able to deliver titrant directly into the titration vessel without exposure to the surrounding air or vapors. The burette for KOH shall have a guard tube containing soda lime or other CO2-absorbing substance.
6.1.6 Titration Beaker, 250 mL capacity, made of borosilicate glass or other suitable material.
6.1.7 Titration Stand, suitable for supporting the electrodes, stirrer, and burette.
NOTE 6 - An arrangement that allows the removal of the beaker without disturbing the electrodes and stirrer is desirable.
6.2 Automatic Titration Apparatus:
6.2.1 Automatic titration systems shall be able to carry out the necessary analyses as prescribed in the method. As a minimum, the automatic titration system shall meet the performance and specification requirements listed in 6.1 as warranted.
6.2.2 A dynamic mode of titrant addition shall be used. During the titration, the speed and volume of the addition shall vary depending on the rate of change of the system. The recommended maximum volume increment is 0.5 mL and the recommended minimum volume increment is 0.05 mL.
