Analytical grade of amoxicillin (AMX) was purchased from Sigma
and cloxacillin (CLX) from Fluka, and was used to construct HPLC ana-
lytical curves for determination of antibiotic concentration. Potassium
dihydrogen phosphate (KH
2
PO
4
) was purchased from Fluka and aceto-
nitrile HPLC grade from Sigma. Hydrogen peroxide (30% w/w) and fer-
rous sulfate (FeSO
4
·7H
2
O) were purchased from R & M Marketing,
Essex, U.K.