Abstract
Lubricating grease is a mixture with complex properties that poses far more difficult analytical challenges than do its individual components. At many petroleum testing laboratories, Inductively Coupled Plasma Atomic Emission Spectroscopy, or ICP-AES, is used for the analysis of additive elements and wear metals in oil. However, it may also be used to measure the concentration of both additive metals and contaminants in lubricating grease. However, unlike some of the other matrices that are routinely analyzed, grease cannot be simply diluted for direct sample introduction into the instrument without some form of acid digestion. This paper will discuss how ICP-AES is used as a grease analysis tool. Several sample preparation schemes will be covered, including classical sulfated ash on a hot plate, microwave assisted dry ash, and microwave assisted acid digestion. Comparison data from different digestion techniques will illustrate potential problems that may be encountered by the analyst in each of these methods. The advantages of closed-vessel microwave digestion for the analysis of elements that are often volatilized under normal digestion conditions will be discussed.
