I'm still struggling with these damn things!

What I am trying to do with regex is cleanup strings by deleting unwanted characters (replace with "<nothing>"). The previous expressions were good at specifiying what IS allowed but I now essentially need to do the opposite and express what IS NOT allowed in order to match and replace those characters.

I'm now stuck again with replacing single occurrences of ' while preserving double occurrences. The following (simplified) expression correctly matches % and & but also matches every ' which is unwanted:

([%&]|('){1})

Any suggestions please?

To be truthful, I'd far sooner express everything that IS allowed and then somehow flip the expression's meaning.