d-alpha is natural and dl-alpha is synthetic… You definately want d-alpha as it’s the purest form. Think of the dl as ‘dis-like’… I had the same question as you and did some research and that is what I found out without getting into all of the details…here is some brief info…not sure it will help.
d-alpha tocopherol: By far the most extensively studied form of vitamin E, this natural antioxidant is what you find in most E products.
dl-alpha tocopherol: The synthetic form of d-alpha tocopherol. Although less expensive, it’s also less biologically active than its natural counterpart. If you notice “dl” rather than “d” at the beginning of the name, you know it’s synthetic.