The kinetics of the formation of the phosphomolybdenum complex was monitored at different temperatures with a-tocopherol as the reducing agent (Fig. 2). A reaction time of around 90 min seemed to be enough to achieve a maximum in the production of phosphomolybdenum complex. Though the formation of the green complex could proceed at room temperature, this reaction showed a positive dependence on temperature, so that a significant yield increase was observed at higher temperatures. Stability of the green complex at room temperature (25°C) was also monitored. No changes in the spectrum of the complex were seen, and only a negligible increase of absorbance at 695 nm occurred after several days (not shown).