Yes, you can. Cologne and perfume are cheaper duty-free, especially for larger bottles. It's a good opportunity to replace your favorite if it's running out! A note on this: if you have connecting flights, don't buy your duty-free cologne before the first flight. Instead, wait to buy it just before your last flight. You can carry duty-free items onto your first flight, but they'd have to be checked in again on your next flight, and any liquid over 100ml will be thrown out.