the aqueous phase acidified with 40 mL of 6M
HCl and the resulting free fatty acids extracted with
2 500 mL diethyl ether. Pentafluorobenzyl esters were
then prepared from one-third of the sample using acetonitrile/
diisopropylamine/pentafluorobenzyl bromide
(1000:10:1, v/v) at 608C for 30 min under nitrogen as
described by Pawlosky et al., (Pawlosky et al., 1992).
Excess reagent and solvent were removed under
oxygen-free nitrogen; samples were dissolved in isohexane
and stored at 2208C under argon until analysis.