a mixture of 2.5 mmol L#1 2,20-azobis(2- amidinopropane) hydrochloride (ABAP) and 20 mmol L#1 2,20- azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS2#) stock solu- tion in 100 mL of phosphate buffer (100 mmol L#1 phosphate and 150 mmol L#1 NaCl, pH 7.4).