working standards were prepared daily on dilution with
ethanol. ABTS, 2,29-azinobis(3-ethylbenzothiazoline-6-
sulfonic acid) diammonium salt, and potassium persulfate
(di-potassium peroxdisulfate) were obtained from
Sigma-Aldrich (Poole, Dorset, UK) and HPLC grade
ethanol from Rathburn Chemicals Ltd. (Walkerburn,
Peebleshire, Scotland).