Time-of-flight mass spectrometric analysis of high-molecular-weight alkanes in crude oil by silver nitrate chemical ionization after laser desorption.

Time-of-flight mass spectrometry was used for the first time to analyze the hydrocarbons in crude oil. Alkanes in the saturated fraction of a crude oil sample were chemically ionized by the laser desorption of silver nitrate, and the silver-attached C24-C60 alkanes were resolved with mass accuracy below 7 ppm. This technique was used to evaluate the biodegradation of aliphatic hydrocarbons and cycloalkanes by oil-degrading microorganisms resident in seawater. It is shown that the aliphatic hydrocarbons were degraded in the range of 60-80%, while the mono-, di-, tri-, tetra-, and pentacycloalkanes were degraded in the range of 40-55, 20-30, 10-16, 5-9, and <5%, respectively. Its high sensitivity and speed of application could result in an analysis by laser desorption silver chemical ionization time-of-flight mass spectrometry being the method of choice for determining high-molecular-weight hydrocarbons in various petroleum products.