ASTM D3340 Test Method for Lithium and Sodium in Lubricating Greases by Flame Photometer
3. Summary of Test Method
3.1 The sulfated ash of the grease is extracted with water and the lithium and sodium content of the resulting solution is determined by means of a suitable flame photometer.

4. Significance and Use
4.1 Lubricating greases can contain the lithium soap of hydroxy stearic acid or the sodium soap of various fatty acids as thickeners. The determination of total lithium or total sodium is a measure of the amount of thickener in the grease.