In order to determine impartiality you have to use your brain to think through what the themes of every article coming from the paper are. An impartial source of news will be critical of both sides, a biased source of news is only critical of one.

Bias doesn't necessarily make the news wrong but it does mean the news is framed in a way to benefit one particular group or another.

Check out the hill. They do a decent job of representing many different viewpoints without being alarmist. Opinion pieces are pretty clearly differentiated from reporting pieces.

apnews.com or reuters.com seem to be pretty impartial, since they are intended to be wire services.