Avoidiing special characters on entry in Excel
 

Hello Everyone,
I use an Excel sheet as a backend for my Web service.I
want to prohibit user from entering special characters as ' in Excel sheet
I have used the FIND() function in the custom formula but this also fails
when I enter 'ketan (' as a 1st character).Then it aligns the word to the
left. and validation test fails

So is there any way out of this?