For glutathione determination, 300 L of whole blood was treated with metaphosphoric acid (5% final concentration; Sigma-Aldrich), centrifuged at 13 200 g for
15 min at 4 °C, and the supernatants were stored at –80 °C until analysis. The
heparinised tubes were subsequently centrifuged (2800 g) for 15 min at 4 °C
and plasma samples immediately subdivided into aliquots and stored at –20 °C until
analysis.