I am going to analyze the assay of vitamin E ( α-Tocopherol) and sitosterol in plan sterols capsule (vegetable oils, nutsoil, Tocopherol, Phytosterol..) by GC with FID detector. The peak areas of standard (Tocopherol) are 10% lower than the peak of sample but the result of sitosterol is good. Is there a possible explanation for such a behavior?
Following more details:
Column: SE 54; Carrier gas: helium; Injector: 320°c; Detector:320°c; oven:300°isotherm (50min)
Internal standard (IS): 0,5 % Octacosan
Standardsolution: 60mg tocopherol/5ml (THF) and 1ml of standard+1ml IS/5ml THF.
Sample preparation: 10 capsules +10 ml IS/50 ml THF.