8. Procedure
8.1 Using either Practice D4057 (manual sampling) or Practice D4177 (automatic sampling), obtain a representative sample of the material to be tested.
8.1.1 Preparation of Sample and Materials:
8.1.2 Warm the oil in the original container, if possible, to 60 +/- 5°C. Shake for a minimum of 30 min on the mechanical shaker to resuspend the insolubles uniformly.
NOTE 3 - Deviation from this sample preparation will normally result in poor precision. Correct sample size is particularly important.
8.1.3 Weigh 1 g of a representative sample of the oil into a 100-mL volumetric flask to the nearest 0.01 g. Certain oils can require smaller size samples to prevent plugging the membrane.
8.1.3.1 When the 100 mL of the mixture has not passed through the membrane after 2 min, discard the test and repeat with a smaller sample size (+/- 10 %) in the order listed:
8.1.4 Filter pentane through an 0.8-µm filter.
8.2 Preparation of Membrane:
8.2.1 Wash the membrane with 100 mL of filtered pentane (Warning - See Note 2) and place the membrane right side up (8.2.1.1) into individual aluminum weighing dish.
8.2.1.1 Important - The top side of the membrane as removed from the manufacturer's container shall be similarly orientated for the duration of the procedure. If the filter is reversed, the results are invalid.
8.2.2 Place the dish into the oven and dry for a minimum of 30 min at 90 +/- 5°C. At the end of the drying period, remove the dish from the oven and cool for a minimum of 30 min in a desiccator containing calcium chloride or some other material that will assure an atmosphere free of moisture and hydrocarbon vapors.
8.2.3 When the membranes have reached equilibrium (about 30 min), weigh the membrane to the nearest 0.1 mg.
8.2.4 Store the aluminum dish in the desiccator until ready for use.
8.3 Filtration:
8.3.1 Remove the membrane filter from the weighing dish with the flat forceps and center in the filtering apparatus. Assemble the funnel and clamp.
8.3.2 Fill the volumetric flask containing the sample to the 100-mL mark with filtered pentane. Stopper and shake well. Immediately, filter the mixture using a vacuum of 255 +/- 50 mm Hg (8.1.3.1). Rinse the flask and stopper twice with small amounts of filtered pentane, pouring the washings down the sides of the filter funnel. Rinse the walls of the filter funnel with a gentle stream of pentane dispensed from the wash bottle.
8.3.3 Carefully, remove the clamp and funnel. Wash any adhering insolubles from the funnel onto the membrane, using the wash bottle with pentane. Wash the membrane gently, particularly the edges, with pentane from the wash bottle. If any sample fails to remain on the membrane the test must be repeated.
8.3.4 Release the vacuum and carefully remove the membrane with the forceps. Place in the same aluminum weighing dish originally used and dry in the oven and cool in the desiccator as in 8.2.2. Weigh the membrane to the nearest 0.1 mg.
NOTE 4 - The use of a semimicro balance for particulates weighing less than 0.0010 g is strongly recommended.
9. Calculation
9.1 Calculate the pentane insolubles content of the oil by membrane filtration as follows:
Pentane insolubles, % = 100(M2 - M1)/S
where:
S = mass of sample, g,
M1 = initial mass of membrane, g, and
M2 = final mass of membrane and insolubles, g.