Items in "quotes" that need to be italics

[Iasonas]

I am writing formulae and applications for engineers. I need to state "in" for inches in the superscript, but then I get into a different type of function! So I can use the quotes "" to write "in" for inches. The problem is that all the rest of the things that are there, such as "lbf", or "psi", etc, that I do not need to set in quotes come in italics. Is there a way I can have the "in" as it is set in the formula to come out in italics too? E.g. I may want to say that d=18^"in" and I want that "in" to be in italics.
Thanks

[acknak]

d=18^{italic "in"}