ASTM D2764 Standard Test Method for Dimethylformamide-Insoluble (DMF-I) Content of Tar and Pitch
12. Procedure
12.1 Make and record all weighings to the nearest 0.5 mg.
12.2 Transfer 0.45 g to 0.55 g of Celite to a clean, filtering crucible. Distribute the Celite evenly over the bottom. Dry in an oven at 221 °F to 230 °F (105 °C to 110 °C) for 30 min. Cool in a desiccator and weigh. Record the mass of crucible plus Celite.
12.3 Transfer 0.45 g to 0.55 g of previously dried Celite to a clean, dry, and tared 100 mL beaker and weigh. Record the mass of Celite. Place 0.5 g of working sample in the same beaker and reweigh. Calculate and record the mass of the sample.
12.4 Add 25 mL of dry dimethylformamide (DMF) to the beaker while stirring the mixture with a stirring rod or thermometer to break up lumps, then cover the beaker with a small watch glass. Place the beaker and a wash bottle containing DMF in a water bath maintained at 203 °F to 212 °F (95 °C to 100 °C). (A suitable mass can be used to keep the beaker from being upset in the water bath.) Digest for at least 30 min. Occasionally stir the contents of the beaker to promote digestion. Check for completeness of digestion by inspecting the bottom of the beaker for undigested pitch or tar.
12.5 Insert the filter tube with adapter into the filter flask and place the previously prepared and tared crucible in the adapter. Carefully add sufficient DMF to the crucible to wet the Celite thoroughly. Apply suction, and form a mat of evenly distributed Celite. Maintain suction until filtration and subsequent washing with DMF are completed.
12.6 Pour the hot DMF-pitch mixture into the crucible, while the Celite in the crucible is still wet without disturbing the mat. Stir the mixture in the beaker immediately before pouring successive portions into the crucible. Allow the contents to drain completely, but not to the extent that the insoluble material on the filter appears substantially dry.
12.7 Wash the beaker, thermometer or stirring rod, and crucible with small portions (2 mL to 3 mL each) of DMF at 203 °F to 212 °F (95 °C to 100 °C) from the wash bottle. Pass all the washes through the filter. Allow each wash to pass almost completely through the filter before the next is added. Use a suitable policeman to sweep the insoluble particles into the crucible. Repeat the DMF washes until the filtrate is the same color as the DMF used for washing. Twelve washings are usually enough.
12.8 Discontinue the suction. Fill the crucible with acetone; reapply suction until the solvent has passed through the filter, then discontinue suction and repeat the operation with fresh acetone three more times. Maintain full suction for a minimum of 5 min after the last acetone wash. Remove the crucible and wipe the outside with a clean, soft cloth or tissue moistened with acetone.
12.9 Place the filtering crucible in the drying oven at 222 °F to 230 °F (105 °C to 110 °C) and dry to constant mass (+/- 0.5 mg). When the hot crucible is removed from the drying oven, it should have no odor of DMF (Note 1). Transfer the crucible to the desiccator and cool for 25 min, then weigh and record the mass of the filtering crucible and its contents.
NOTE 2 - Insoluble matter on the filter, after washing with acetone, should have no odor of DMF, which is evidence of insufficient washing. If odor of DMF is detectable, repeat the entire determination.
13. Calculation
13.1 Calculate the DMF-insoluble (DMF-I) content as follows:
DMF - I, % = [(A - B - C)/D] x 100
where:
A = total mass of the filtering crucible, Celite (added to the crucible and to the sample), plus DMF insoluble matter.
B = initial mass of the filtering crucible containing dried Celite,
C = mass of dry Celite added to the sample, and
D = mass of working sample used for the determination.
