Oil that has undergone biodegradation or photooxidation, contains oxygenated compounds. These compounds cannot be analysed by standard extraction and gas-chromatographic methods. Conventional methods do not analyse for polar compounds and would not count them in the analytical results.
Studies have shown that highly oxidized oil, including that undergoing biodegradation and photooxidation, is not properly analyzed by conventional techniques. Conventional analytical techniques may miss as much as 75% of the oil mass. Similarly for biodegradation analysis, conventional techniques may overstate biodegradation by as much as four times. Five possible analytical solutions to this problem are suggested and include; thin layer chromatography, derivitization and then GC analysis, FTIR, NMR and HPLC. The latter two techniques are typically applied to only the separated polar fractions of the oil. These techniques are in their infancy and much more work needs to be carried out. The biodegradation pathways of oil compounds are largely unknown. Biodegradation steps are known only for a few of the thousands of compounds in oils. Analytical methods for many of the biodegradation products are also absent or need development. The situation is very complex and only extensive research over dozens of years will improve the knowledge. The first step will be a generalized analysis step that includes most oxygenated compounds.