Eric J. Singh
Determining the Carbon Number of
and Leon 1. Gershbein Northwest Institute for Medical Research Chicago, Illinois
n-Fatty Acids by TLC
In the course of an investigation of thinlayer chromatographic separation and analysis of human sebum components, a method was devised to determine the carbon numbers of straight chain fatty acids. It may prove interesting for adaptation by professors desiring a unique demonstration of the effectiveness of TLC as an analytical tool. Glass plates, 20 X 5 X 0.4 cm, were coated with silica gel G to a thickness of 0.25 mm. They were airdried at 25" for 16 hr, then heated in an oven at 110'' for 30 min, cooled, and stored over silica gel. Samples of about 1 fig were dissolved in ether and delivered by micro-syringe a t a point 2.0 cm from the edge of the plate. The system was dried by air blower, and introduced into a chamber containing l-butanol which had been saturated with water and equilibrated for 12 hr a t 20". The solvent was allowed to ascend 15 cm from the starting line. At the conclusion of the run, a straight line solvent front was observed. This was marked and the plates dried. The staining of spots was effected with concentrated sulfuric acid containing 0.1% potassium dichromate. The average Rt values for the acids were: caproic caprylic caprlc lauric myristic palmitic stearie
1.00 0.85 0.72 0.59 0.45 0.33 0.19
The mean deviation from the average was *0.01 in This investigation was supported by public ~ ~ ~ service l t h Grant, CA 06487, from the National Cancer Institute.
each instance. The data are plotted in the figure. This relationship holds well for these acids, but does not apply to unsaturated members occurring simultaneously in various test mixtures. The Rr values for acids below Cgor above CIScould not be evaluated since they tended toward 1.00 and 0.00 respectively.
u
6
8
10
12
14
16
18
CARBON ATOMS Relation between carbon number of n-fany acids and Rr value.
This method can be carried out quickly, requires minute amounts of sample, and has definite advantages Over other procedures which require the preparation of esters.
Volume 43, Number I , January 1966
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