As has been mentioned previously [268], methylation in the presence of water or in the water phase presents a problem for the analyst [247,323–325]. Successful methylation with diazomethane, acetyl chloride–methanol and boron trifluoride–methanol requires an organic reaction medium. Leibich and Gesele [326] proposed trimethyloxonium tetrafluoroborate (TMO) for the methylation of carboxylic acids in a water phase. Bannon et al. [327] have outlined some possible errors concerning the preparation of FAMEs.