. "e double bond and having from about 16 to about 22 carbon atoms, and R is a polar group selected from the group consisting of oxy radicals of choline, ethanolamine, inositol, serine, glycerol, and alkanols having from 1 to 4 carbons; (b) adding an enzyme quenching reagent to said enzyme/substrate solution; c) adding to thiol-sensitive reagent to said solution to produce a chromophore; and d) meas" . . . .