I tried different ways and also looked around but can\'t get this running. I need to concat the following:
\"concat(
\'this is; \\\"a sample\',
//XM
In XML/XSLT you do not escape characters with a backslash.
The problem with the apostrophe inside of your concat strings is that the XML parser loading the XSLT will expand it before the concat gets evaluated by the XSLT engine; so you can't use an entity reference for the apostrophe character unless it is wrapped in double quotes (or entity references for double quotes, as Dimitre Novatchev's answer demonstrates).
" for the double quote ".Applied in the context of an XSLT:
'
If you need a 100% XPath solution that avoids the use of XSLT variables, then Dimitre's answer would be best.
If you are concerned with how easy it is to read, understand, and maintain, then Michael Kay's suggestion to use XSLT variables for the quote and apostrophe might be best.