Silver ion HPLC of p-methoxyphenacyl derivatives of unsaturated fatty acids. I. Mobile phase effects

The effect of the mobile phase composition on the retention and resolution of positionally isomeric octadecamonoenoic (18:1), eicosamonoenoic (20:1), octadecatrienoic (18:3), and eicosatrienoic (20:3) fatty acids in silver io n high performance liquid chromatography was studied on model fatty acid mi xtures. Prior to chromatography, the fatty acids were converted into p-meth oxyphenacyl derivatives. Hexane-based and dichloro-methane-based mobile pha ses that contained acetonitrile, methanol, and iso-propanol as modifiers we re examined. All three modifiers ensured reliable resolution of the respect ive isomeric fatty acids and are of practical interest. In contrast to acet onitrile and methanol, iso-propanol was found to reverse the elution order of difficult to resolve components that gave adjacent chromatographic peaks . This finding indicates the active role of mobile phase in the chromatogra phic process.