Chromatographic method for the analysis of both in process and finished sevoflurane

A process for preparing fluoromethyl 2,2,2-trifluoro-1-(trifluoromethyl)ethyl ether(sevoflurane), said process comprising:

• a) reacting a reacting mixture comprising 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), hydrogen fluoride (HF) and a formaldehyde equivalent to form a first crude sevoflurane;
• b) isolating a second crude sevoflurane by extraction of the first crude sevoflurane, by cooling said first crude sevoflurane to generate two layers, one of which two layers is enriched in sevoflurane, or by distilling said first crude sevoflurane;
• c) optionally isolating a third crude sevoflurane by purifying said second crude sevoflurane;
• and
• d) isolating a finished sevoflurane by distilling the second crude sevoflurane or the third crude sevoflurane;
• wherein at least one of steps a)–d) further comprises monitoring by gas chromatography using a capillary column, whereby at least one impurity of the process is isolated and quantitatively analyzed, and the capillary column is packed with at least one material selected from the group consisting of a polyethylene glycol and an alkyl polysiloxane.