Division 3.9.2 Internal standard solution, 50 μg/ml

Transfer 5,0 ml of the internal stock standard solution (3.9.1) into a 50 ml graduated flask, make up to the mark with DMF (3.6) and mix. Wrap the flask with aluminium foil or use amber flask and store in the refrigerator. At a temperature of ≤ 4 ^oC the solution is stable for 1 month.