nal standard. Urine samples (10 ml) were acidified to
pH 1 with concentrated HCl and then run through a
Waters C,8-Sep Pak. The SepPak cartridge was preeluted
with 2 ml MeOH and 5 ml H2O. The cartridge
was washed with 10 ml 0-01 M HCl and 1 ml
benzene. Air was drawn through the cartridge to
dryness and the sample eluted with 2-5 ml of CHC13
(1% HAc). The CHC1, fraction was evaporated to
dryness, redissolved in 1 ml MeOH, and esterified
with 1 ml of CHCl,/SOCl2 (90:10) for 30 minutes.
After evaporation the ester was redissolved in 2 ml of
ethyl acetate and analysed by GC-MS.