I need to analyse red blood samples for fatty acids on GC-FID but want to repeat some of the samples later on GC-MS/MS. I was wondering about the stability of the fatty acid methyl esters (FAME) after extraction. After transmethylation with 5% H2SO4 a hexane/FAME supernatant is formed. The supernatant is then evaporated under nitrogen to remove the hexane, which then forms a FAME residue. Normally we redissolve this FAME residue in hexane to be able to inject the sample for GC analysis directly thereafter. I was wondering how stable this FAME residue will be for later analysis if stored under nitrogen at -80°C? Should I BHT and if so, at which stage? When the GC-MS/MS becomes available I can just redissolve with hexane to inject the samples.