ASTM D3340 Test Method for Lithium and Sodium in Lubricating Greases by Flame Photometer
8. Procedure
8.1 Weigh to the nearest 1 mg approximately 1 g of the grease into a platinum dish or crucible. Heat the dish until the sample can be ignited with a flame. Maintain at such a temperature that the sample burns at a uniform and moderate rate, leaving only ash and carbon when the burning ceases.
8.2 Cool the dish and completely moisten the residue by the dropwise addition of concentrated sulfuric acid. Heat the dish at a low temperature, taking care to avoid spattering of the contents, and continue heating until fumes are no longer evolved. Place the dish in a furnace at 550 +/- 25°C (1022 +/- 45°F) and continue heating until the oxidation of the carbon is practically complete.
8.3 Cool and repeat 8.2 to complete the sulfation.
8.4 Extract the sulfated ash with hot distilled water and transfer the aqueous extract, filtering if necessary, to a 100-mL volumetric flask. Allow to cool and make up to the mark with distilled water.
8.5 Prepare the following fresh calibration standards by appropriate dilution of the stock solutions:
8.5.1 Lithium Sulfate - Solutions containing 0, 3, 6, 9, 12 and 15 mg/L lithium.
8.5.2 Sodium Sulfate - Solutions containing 0, 1, 2, 3, 4, and 5 mg/L sodium.
8.6 Obtain the flame photometer readings for each calibration standard and prepare curves relating concentration to photometer reading.
8.7 Obtain readings for the extract derived from 8.4 and determine the lithium and sodium contents from the calibration curves.
NOTE 1 - Further dilution may be necessary.
