It was a pleasure meeting with you yesterday and having the opportunity to discuss your education and your career goals.
I appreciate your candidness and feel that since your objectives are to work in the field of [specify area] you should attempt to obtain a position with a firm that would enable you to gain experience in your preferred area. Unfortunately, our business does not afford you this opportunity.
I am certain that you will find a position which suits you soon and I believe that you have a great deal to contribute.
Please accept my best wishes for your future.