9. Tilt the digestion flask and CAREFULLY add a sufficient amount of sodium hydroxide - thiosulfate reagent to form an alkaline layer (pink zone) in the bottom of the flask. Usually 50 mL of reagent is needed for every 50 mL of digestion reagent used.
10. Connect the flask to the distillation apparatus, mix thoroughly and distill 200 mL of distillate into a boric acid absorbing solution. (See Section 11 for the distillation procedure.)
11. Determine Total Kjeldahl Nitrogen as ammonia using one of the methods outlined in Sections 12, 13, and 14.