and the second solution contains the ascorbic acid. Furthermore, the final concentrations of acid and molybdate are decreased from 0.2 to 0.1 mmol/L and from 0.78 to 0.39 mmol/L,respectively. A lower final acidity is also used by Strickland and Parsons (1968). Two separate reagent solutions are more stable and the compensation for turbidity is easier.