An aliquot of 0.1 ml ofsample solution containing a reducing species (in water, methanol, ethanol, dimethyl sulfoxide,
or hexane) was combined in an Eppendorf tube with 1 ml of reagent solution (0.6 M sulfuric acid, 28mM sodium phosphate, and 4 mM ammonium molybdate).
The tubes were capped and incubated in a thermal block at 95°C for 90 min.