2.1. Reagents
All chemicals were of analytical grade and used as received
without any further purification. Solutions were prepared with
MilliQ water (Millipore, Inc.; O = 18 MO/cm). L-ascorbic acid
(99%) was purchased from Merck (Germany); stock solutions of
AA were prepared daily in acetate buffer (AB) (Merck-Germany)
at pH 3.7 and in phosphate buffer (PBS) at pH 6.3. The phosphate
buffer saline solution was made using NaCl (137 mM), KCl
(2.7 mM), Na2HPO4 (8.1 mM) and KH2PO4 (1.47 mM) from Sigma
and then adjusted to pH 6.3.
For titrimetric measurements, oxalic acid dihydrate and 2,6-
dichlorophenol-indophenol sodium salt dihydrate, sodium hydrogen
carbonate (NaHCO3-powder P 99.5%) were purchased from
Merck (Germany).
Catalase from bovin liver (EC 1.11.1.6) were purchased from
Sigma–Aldrich. Meta-phosphoric acid (HPO3) was purchased from
Merck. Hydrogen peroxide (30% solution from Merck-Germany)
was diluted and used as 10% solution.