There's no duty free before domestic departure security at Terminal B at ORTIA. You do have to clear immigration, retrieve your bag and pass through customs on international arrival at Terminal A before turning left out the arrival door and proceeding to Terminal B for domestic check in. The safest gamble might be to have some bubble wrap in a checked bag and transfer the duty free to a check in bag.
There is, as you perhaps surmise, no definitive answer until you get there and find out at bag check what the drill is.