how to add #states property to a field element in drupal 7?
Fields always have have nested names like field_something[und][value] or something like that. I guess your query (:input[name="field_ctype"]) is wrong.

I find the easiest way to get it right is using the Firebug/Developer tools Console. Play around with jQuery(':input[...]') until it matches what you're expecting. Also check the name of the form element.