escape sequence inside xpath function

[Richard]

I am trying to use the concat expression where one of the arguments is a
string of text that must include a double quote.
I tried to use \" , but it does not work..
I need my output string to look like this:
doc( "text" )
so I have this :
concat("doc( \"",textbox,"\")")

I also tried "" instead of \" and that did not work either..