Cool NMR with Olive Oil

Like everyone else, I am thrilled to be in Italy, and Siena is amazing. Since this is my first time in Europe, I didn’t know what to expect. The tourist time in Rome was very good for me. I started to trust my map reading skill and the power of a smile and a “per favore". Now in Siena, I am ready to learn some Chemistry.

The poster that interested me the most was presented by Daniela Valensin and discussed the use of Nuclear Magnetic Resonance Spectroscopy (NMR) in analysis of olive oil. NMR uses strong magnetic fields to identify nuclei with magnetic spins; primarily ¹H and ¹³C. On the graph of the NMR, different nuclei appear as peaks along a horizontal scale. The integration, or area under the peak indicates how many nuclei are the same. All this information can be used to determine the chemical structure of the molecule. On a wide scale spectrum, olive oil can be easily differentiated from other vegetable oils. On a much smaller scale, individual olive oils can be identified. Differences in soil and climate affect the chemical make-up of the oil, so an oil can be identified by where and when it was made.

There were two kinds of spectra presented on the poster that I had never seen before. They were both 2 dimensional. In a standard 1H NMR, the signal from a hydrogen nuclus is affected both by its location in the molecule and the hydrogens on neighbouring carbons. This neighbouring affect is called splitting, and can be seen on the spectrum. The peak appears to be divided into n+1 sub peaks, were n is the number of neighbouring hydrogens. In complex molecules these splitting patterns can overlap and get very confusing. This is were 2 dimensional spectra are useful. The first one is Correlation Spectroscopy (COSY). In COSY, magnetic field are generated from both the x and y axis, and the nuclei appear as dots along a diagonal. Neighbouring hydrogens appear as dots on coordinates off the diagonal. The coordinates of the split signal can make it easier to determine which hydrogens are neighbours. The second type is Total Correlation Spectroscopy (TOCSY). Like COSY, TOCSY produces a 2D plot, but it shows correlation from hydrogens 3 or 4 carbons away in addition to the neighbouring ones.

http://www2.hmc.edu/www_common/chemistry/nmr/page8.htm

http://u-of-o-nmr-facility.blogspot.com/2008/01/1-h-tocsy.html