Stability of Oil Standards

Djaouida was curious about the stability of oil standards. First she wondered if water, as an impurity in the solvent, would be a problem. If so, she wanted to know how she could eliminate its effect upon the stability of organometallic standards. She also wanted to know what the best solvent for direct analysis of lubricating oils would be. Lastly, Djaouida asked how she might improve the stability of Silver for her applications.

	RE: Stability of Oil Standards Dear Djaouida,      The conventional problem with the stability of oil standards is a combination of trace water in the oil / solvent combined with a deficient quantity of organic acid needed to react with the metal forming a "soap". You might try adding some hexanoic anhydride. Otherwise, switch to xylene as the solvent. The xylene should be dried over three (3) Angstrom molecular sieves that themselves have been activated by heating to 300°C for three (3) hours. The xylene is a much better solvent for the lubricating oils and the drying will reduce the water content to insignificant levels, eliminating detectable hydrolysis.      The loss of Ag concerns me in that it may be that precipitation is occurring. Ag forms more insoluble precipitates than any other metal. It may continue to give you problems in spite of the changes I've recommended above. Thank you for your questions.     Paul R. Gaines, Ph.D. Serving you in chemistry