Analysis of alpha‐linolenic acid geometrical isomers in deodorized oils by capillary gas‐liquid chromatography on cyanoalkyl polysiloxane stationary phases: A note of caution

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Abstract
Analysis of alpha‐linolenic acid geometrical isomers in deodorized or heated oils by capillary gas‐liquid chromatography (GLC) on polar cyanoalkyl polysiloxane stationary phases requires some care to avoid interferences with other fatty acids. Depending on the temperature of the column, thecis‐11 20∶1 acid may elute before, with or after thecis‐9,cis‐12,cis‐15 18∶3 acid during GLC. In some instances [temperature higher than 180°C with a CP Sil 88 column (Chrompack, Middelburg, The Netherlands)], the 20∶1 acid coelutes with thetrans‐9,cis‐12,cis‐15 18∶3 acid, leading to abnormally high levels of this last isomer. Consequently, the degree of isomerization of alpha‐linolenic acid will be over‐estimated under such conditions. It is recommended that the behavior ofcis‐11 20∶1 acid relative to temperature be checked carefully prior to the determination of alpha‐linolenic acid geometrical isomers by GLC. Temperatures lower than 160°C seem appropriate to separate all of these components from each other and fromcis‐11 20∶1 acid in a 50 m×0.25 mm i.d. CP Sil 88 capillary column.