Source: Laboratory of Jeff Salacup - University of Massachusetts Amherst

As mentioned in previous videos, the product of an organic solvent extraction, a total lipid extract (TLE), is often a complex mixture of hundreds, if not thousands, of different compounds. The researcher is often only interested in a handful of compounds. In the case of our two organic paleothermometers (U^k'₃₇ and MBT/CBT), the interest is in only 6 compounds (2 alkenones and 4 isoprenoidal glycerol dialkyl glycerol tetraethers). As discussed in the previous two videos in this series, purification techniques may be applied in order to pare down the number of compounds in an analyzed sample. These techniques may chemically alter the unwanted components (saponification), take advantage of the different compound chemistries (column chromatography), or use the different shapes and sizes of the molecules to include or exclude certain components from the analysis (urea adduction). The atomic structure of different chemicals leads some organic compounds to form long, narrow, straight chains (n-alkanes and alkenones), other organic compounds to form complex cyclic structures, others to form highly-branched structures, and yet others which form both cyclic and branched structures (GDGTs) (Figure 1). The different shapes and sizes of the compounds in a sample can be used to separate them from one another, in much the same way as a coin sorter separates coins of different denominations (sizes).

Figure 1. Comparison of different chemical structures. Decane, a straight-chained alkane (A; from from http://www.bpc.edu/mathscience/chemistry), cyclohexane, a cyclic alkane (B; from http://www.bpc.edu/mathscience/chemistry), a steroid, a poly-cyclic hydrocarbon (C; from www.wikiwand.com), and 2,2-dimethylbutane, a branched alkane (D; www.wikimedia.com). Please click here to view a larger version of this figure.