ASTM D3235 Standard Test Method for Solvent Extractables in Petroleum Waxes
8. Procedure
8.1 Melt a representative portion of the sample, using a water bath or oven maintained at 70 °C to 100 °C (158 °F to 212 °F). As soon as the wax is completely melted, thoroughly mix. Preheat the pipet or equivalent measuring device in order to prevent the solidification of wax in the tip, and withdraw a portion of the sample as soon as possible after the wax has melted. The mass of wax transferred to the test tube must be 1.00 g +/- 0.05 g. Allow the test tube to cool, and determine the mass to at least the nearest 1 mg.
NOTE 3 - The mass of a test tube which is cleaned by means of solvent will not vary to a significant extent. Therefore, a tare mass may be obtained and used repeatedly.
8.2 Pipet 15 mL of the solvent mixture into the test tube and place the latter just up to the level of its contents in a hot water or steam bath. Heat the solvent-wax mixture, stirring up and down with the wire stirrer, until a homogeneous solution is obtained. Exercise care to avoid loss of solvent by prolonged boiling.
NOTE 4 - Very high-melting wax samples may not form clear solutions. Stir until the undissolved material is well dispersed as a fine cloud.
8.2.1 Plunge the test tube into an 800 mL beaker of ice water and continue to stir until the contents are cold. Remove the stirrer. Remove the test tube from the ice bath, wipe dry on the outside with a cloth, and determine the mass to at least the nearest 0.1 g.
NOTE 5 - During this operation the loss of solvent through vaporization should be less than 1 %. The mass of the solvent is, therefore, practically a constant, and after the masses of a few samples are determined, this mass can be used as a constant factor.
8.3 Place the test tube containing the wax-solvent slurry in the cooling bath, which is maintained at -34.5 °C +/- 1.0 °C (-30.0 °F +/- 2.0 °F). During this chilling operation, stir the contents of the tube by means of a temperature measurement device placed in the tube. It is important that stirring by means of the temperature measurement device be almost continuous, in order to maintain a slurry of uniform consistency as the wax precipitates. Do not allow the wax to set up on the walls of the cooling vessel nor permit any lumps of wax crystals to form. Continue stirring until the temperature reaches -31.7 °C +/- 0.3 °C (-25.0 °F +/- 0.5 °F).
8.4 Remove the temperature measurement device from the tube and allow it to drain momentarily into the tube, then immediately immerse in the mixture the clean, dry filter stick, which has previously been cooled by placing it in a test tube and holding at -34.5 °C +/- 1.0 °C (-30.0 °F +/- 2.0 °F) in the cooling bath for a minimum of 10 min. Seat the ground-glass joint of the filter so as to make an airtight seal. Place an unstoppered weighing bottle, the mass of which was previously determined, together with the glass stopper to the nearest 0.1 mg, under the delivery nozzle of the filtration assembly.
NOTE 6 - Take every precaution to ensure the accuracy of the mass of the stoppered weighing bottle. Prior to determining this mass, rinse the clean, dry weighing bottle and stopper with the solvent mixture described in 6.3, wipe dry on the outside with a cloth, and place in the evaporation assembly to dry for about 5 min. Then remove the weighing bottle and stopper, place near the balance, and allow to stand for 10 min prior to determining the mass. Stopper the bottle during this cooling period. Once the weighing bottle and stopper have been dried in the evaporation assembly, lift only with forceps. Take care to remove and replace the glass stopper with a light touch.
8.5 Apply air pressure to the filtration assembly and immediately collect about 4 mL of filtrate in the weighing bottle. Release the air pressure to permit the liquid to drain back slowly from the delivery nozzle. Remove the weighing bottle immediately, and stopper and determine the mass to at least the nearest 10 mg without waiting for it to come to room temperature. Unstopper the weighing bottle and place it under one of the jets in the evaporation assembly maintained at 35 °C +/- 1 °C (95 °F +/- 2 °F), with the air jet centered inside the neck, and the tip 15 mm +/- 5 mm above the surface of the liquid. After the solvent has evaporated, which usually takes less than 30 min, remove the bottle, stopper, and place near the balance. Allow to stand for 10 min and determine the mass to the nearest 0.1 mg. Repeat the evaporation procedure, using 5 min evaporation periods, until the loss between successive determinations is not over 0.2 mg.
9. Calculation
9.1 Calculate the amount of extractables in the wax as follows:
Solvent extractables, percent by mass = 100 AC/BD
where:
A = mass of extractables residue, g,
B = mass of wax sample, g,
C = mass of solvent, g, obtained by subtracting mass of test tube plus wax sample (8.1) from mass of test tube and contents (8.2), and
D = mass of solvent evaporated, in g, obtained by subtracting mass of weighing bottle plus extractables residue from mass of weighing bottle plus filtrate (8.5).
