Bonded stationary phases fatty acid ester separation

Alternative procedures for reverse-phase HPLC of fatty acids have been developed, in which fatty acid esters containing strongly UV-absorbing substituents in the alcohol moiety are prepared, so that components emerging from the columns can be detected by means of UV spectrophotometry. Borch [119] was one of the first to exploit this technique and obtained some remarkable separations of fatty acids, in the form of the phenacyl esters, by means of HPLC with a Cis-bonded stationary phase and... 

As fatty alcohols are comparable in structure and molecular weight to fatty acid methyl esters, they are usually subjected to GC on the same stationary phases and under near-identical conditions. It is certainly possible to separate alcohols in the free form by GC, especially on modem WCOT columns of fused silica, but sharper peaks are obtained if less polar derivatives such as the acetates, trifluoroacetates or TMS ethers are prepared. Suitable preparation procedures are described in detail in Chapter 4. Jamieson and Reid [438] studied the relative retention times of many different saturated and unsaturated fatty alcohols in the free form and as the acetates on packed GC columns containing polar polyester phases, and concluded that very similar separation factors applied as with the equivalent fatty acid methyl esters. The order of elution was - methyl ester < alcohol acetate < free alcohol. A TMS ether derivative would be expected to have a lower retention time than an acetate, but the separation factors for double bonds in the alkyl chain in this instance were found to be lower than with the acetates and resolution in general was poorer some changes in retention sequence for specific isomers was noted, depending on the type of derivative [439]. In contrast, the free alcohol eluted before derivatized forms on non-polar phases [944]. It is therefore possible to use equivalent chain-length data for the provisional identification of fatty alcohols in the same way as with methyl ester derivatives of fatty acids (see Chapter 5). 

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