Regex for comma separated strings

Hi all, I am trying to write a regex for a comma delimited strings, It should be accepting any string of format Name,Name and name should bealpha. One more thing is this validation should happen only if one particularlistitem of a radiobuttonlist is selected and should not do validation for other listitems, my concern is i should do itwithout javascript.Help me with this guys.

Thanks in advance.