A sensitive and specific method for plasmalogens and other enol ethers

A spectrophotometric procedure for estimating plasmalogens and other enol ethers, based upon the specific reaction of the enol ether group with iodine, is presented. Optimum conditions for iodination with respect to methanol and KI concentration, pH, and time of incubation have been defined. After evaporating the solvent from the lipid extract containing 0.02 to 0.125 μmole plasmalogen, 0.9 ml methanol, 3.2 ml 0.094 m Na citrate (pH 5.5), 0.4 ml 3 m KI, and 0.5 ml 0.0005 m I2 in 3 m KI are added and mixed. After standing for 40 min at room temperature, the mixture is extracted with 5 ml n-butyl acetate. Absorbancy of the butyl acetate layer is read at 363 mμ. Lipid and reagent blanks and an I2 standard containing 0.25 μmole I2 are treated similarly except that 0.9 ml 3 m KI is added to both blanks in place of I2. Reproducibility is ±3.6% with 0.1 μmole levels of plasmalogen in lipid extracts. The range of enol ether estimated by this procedure is 0.02–0.125 μmole.