*2.4. Sample Collection and Processing*

*Plasma.* Peripheral blood was collected into 4 mL K3-EDTA vacutainer tubes, which were kept on ice at all times. Samples were centrifuged at 4 °C to pellet cells and the plasma was collected and kept on ice for extraction of ascorbate. Plasma samples were treated with an equal volume of ice-cold 0.54 M perchloric acid containing the metal chelator DTPA (100 μmol/L) to precipitate protein [21]. The de-proteinated supernatants were stored at −80 °C until HPLC analysis.

*Urine.* Urine was collected into pre-weighed 50 mL sample containers and an aliquot was removed for urinary creatinine determinations. Urine samples were treated with an equal volume of ice-cold 0.54 M perchloric acid containing the metal chelator DTPA (100 μmol/L) to precipitate protein [21]. The de-proteinated supernatants were stored at −80 °C until HPLC analysis.
