You’re nervous. They’re nervous. You could easily spend all night chatting to the same person simply because it’s easier than moving on and starting again with a new contact. By the same token, someone might want to monopolise you, but you’re dying to get away and chat to more people. How to you escape politely, with charm and grace, rather than causing offence? It helps if you have a get-away plan ready.
You might say you’re off to the bathroom, or the bar, or to get some food. But most experts think it’s better to be honest than make excuses. You could simply thank the person for their time and say you enjoyed meeting them, then move on. Or say you’ve just spotted a colleague or friend you’d like to catch up with, or ask for the person’s contact information and make plans to carry on the conversation another time. A handshake always helps seal things politely and professionally, as does a smile, and it also helps enormously to say how much you’ve enjoyed meeting them, leaving them with a positive message.