Capillary supercritical fluid chromatography--atmospheric pressure chemical ionization mass spectrometry of gamma- and alpha-linolenic acid containing triacylglycerols in berry oils.

The effect of the gamma-linolenic acid (18:3n-6) residue on the elution of triacylglycerols on a 25% cyanopropyl-25% phenyl-50% methylpolysiloxane stationary phase was confirmed by using capillary supercritical fluid chromatography-atmospheric pressure chemical ionization mass spectrometry [cSFC-(APCI)MS]. The general elution rule on this stationary phase is that triacylglycerols having the same ACN + 2n value coeluted (ACN = acyl carbon number and n = combined number of double bonds in the acyl chains). The different effect of gamma- and alpha-linolenic acid residues on the retention of triacylglycerols and the use of cSFC-(APCI)MS allowed the study of the number of different linolenic acid residue isomer combinations in triacylglycerols with an identical ACN and degree of unsaturation. Stearidonic acid (18:4n=3) residue was found to have a similar effect on the retention behavior of triacylglycerols as that of gamma-linolenic acid residue. The abundance of the [M - RCOO]+ ion, formed by the loss of one fatty acid moiety of a triacylglycerol, was found to be clearly higher in the case of gamma-isomer of the linolenic acid than that of alpha-isomer in the identical regiospecific position. This indicates that the distance of the double bonds from the glycerol backbone in the acyl chain affects the stability of a triacylglycerol molecule in the (APCI)MS system. The triacylglycerol composition and the fatty acid combinations of triacylglycerols were found to be almost identical in black currant (Ribes nigrum) and alpine currant (R. alpinum) seed oils.