Analysis of the starting materials methyl esters of palm kernel and sunflower oils and the products of the hydrogenation reaction. During the hydrogenation reaction an amount of the starting material containing cis-olefinic bonds undergoes positional and geometric isomerizations reactions to form several different positional and trans-isomers especially under the conditions were the selectivity to methyl stearate was below 50 mol%. These various cis/trans- and positional FAME isomers obtained as products in the mixture after the reaction and also the various FAME compounds in the starting materials of methyl esters of palm kernel and sunflower oils were identified by comparison of GC and GC/MS analytic data with data for authentic samples. GC/MS was measured on a Varian Star 3400CX GC coupled with a Varian Saturn 2000 ion trap MS and equipped with a flame ionization detector (FID) and a SP-2560 capillary column (100 m × 0.25 mm i.d. × 0.2 µm film thickness) which was purchased from Supelco (Athens, Greece). The SP-2560 capillary column is one of the two columns applied in the approved American Oil Chemists’ Society (AOCS) official method Ce 1 h-05for the determination of cis-, trans-, saturated, monounsaturated and polyunsaturated fatty acids in vegetable or non-ruminant animal oils and fats by capillary GLC method [49]. Carrier gas was He at230 kPa. The oven temperature was initially set at 170◦C for 0 min and then increased to 220◦C with a rate of 1◦C/min. The injector and detector temperatures were set both at 220◦C. GC analyses were performed on a Shimadzu GC-14B equipped with a FID detector and with both columns a SP-2560 and an HP-Innowax capillary column. The GC conditions using the SP-2560 capillary column are the same as described above in GC/MS analyses. When using the HP-Innowax capillary column (30 m × 0.251 mm i.d. × 0.50 µm film thickness) which was purchased from Agilent Technologies the carrier gas was He at 150 kPa, the initial oven temperature was 170◦C followed by an increase to 240◦C with a rate of 3◦C/min. The injector and detector temperatures were 240◦C.