Then 10 ml of 1 M NaOH solution was added to the absorber tube. Diluted with distilled water about 50 g of lead carbonate powder was added into the absorber tube to precipitate sulfide which can interfere with ISE-CN− reading.
The absorber tube was attached to the vacuum and connected it to the condenser. The vacuum was turned on and the air flow adjusted to approximately 1–2 bubble/s entering the boiling flask through the air inlet tube.