Shīpéi yíhuìr.  

失陪一会儿。

Excuse me for a moment.

Notes:

失陪(shīpéi): to leave

一会儿(yíhuìr): for a while

*This expression is very polite. So Chinese people usually say it in a formal meeting and dinner.

Example:

A：失陪一会儿。

     Shīpéi yíhuìr.  

     Excuse me for a moment.

B：好的。

     Hǎo de.

     Ok.