Converting a String to HEX in SQL

I'm looking for a way to transform a genuine string into it's hexadecimal value in SQL. I'm looking something that is Informix-friendly but I would obviously prefer something database-neutral

Here is the select I am using now:

SELECT SomeStringColumn from SomeTable

Here is the select I would like to use: SELECT hex( SomeStringColumn ) from SomeTable

Unfortunately nothing is that simple... Informix gives me that message: Character to numeric conversion error

Any idea?