Solution A-Dissolve 2 g of NaK tartrate and 100 g of Na2CO3 anhydrous in 500 mL of 1 N NaOH (20 g in 500 mL of reagent-grade water); the solution, uncolored and transparent, is diluted to 1000 mL with reagent-grade water. Solution A should be stored at 4°C, and it will remain stable for 2-3 months, after which the Na2CO3 tends to precipitate. In this case, the solution cannot be further utilized.