In vitro experiments designed to examine low metHb yields in vivo. MetHb formation, determined by EPR spectroscopy or absorption spectroscopy, was due to infusion of AS (50 μM) added to: (A) oxyHb (1mM) diluted in phosphate buffered saline, oxyHb (1mM) diluted in plasma, oxyHb (1 mM) diluted in plasma that was incubated with NEM (10 mM) for 1 hour at 37°C prior to mixing with oxyHb, oxyHb (1mM) + GSH (10 mM), and oxyHb (1 mM) + bovine serum albumin (5g/dL, ~750 μM). Error bars represent one standard deviation, n=3. (B) AS (50 μM) added to: oxyHb (1 mM), red blood cells (1mM) diluted in phosphate buffered saline, and whole blood (1mM) diluted in plasma. Concentrations were determined by EPR spectroscopy after incubation for 2 hours at 37°C. Error bars report the standard error of the mean, n=3.