When teaching paper or thin-layer chromatography for the current Options A or B many teachers include the technique of rotating the paper or glass slide 90^o and performing the chromatography again with a different eluent. This is useful for separating out two components which have very similar R_­f values with the first eluent.  A similar process occurs in two-dimensional gas-liquid chromatography (2D GC). This can be achieved either by injecting the emerging components through a second column packed with a different stationary phase or by running two columns at different temperatures. One particular use of two-dimensional gas chromatography is in analysing oil spills. Around coastal waters oil slicks sometimes occur when oil-tankers clean their ‘empty’ tanks. 2D GC can be used to show whether the composition of the oil in the slick is the same as the oil from the tanker.

Recently there has been interest in oil sheens surrounding the Deep Water Horizon site. British Petroleum plc. are currently meeting huge compensation claims for the disaster that occurred in April 2010 (see my earlier blog on Chemistry and Politics). There is concern that the well, which was capped in 2010, may have started to leak. Another possible source of the leakage is the 80 tonne cofferdam which was abandoned during the operation to cap the well in 2010. A team from the Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Massachusetts and the Department of Earth Science and Marine Science Institute, University of California, Santa Barbara have recently published their findings on the analysis and likely source of the sheens. They used 2D GC to show conclusively that the sheens do not come either from the well or the cofferdam. The sheens contain alkenes which are absent in both the well and cofferdam oil. In fact the sheens’ composition is similar to those found in oil-covered debris immediately after the Deepwater disaster. This suggests that the likely source is oil from the wreckage of the Deepwater platform and that the amount of leakage will be finite. BP can breathe a sigh of relief.