AH Chemistry Investigation help needed!

I am having to write my method and things for my chemistry investigation, and I'm a bit stuck.. I am wanting to find a) the concentration and b) the purity of the vitamin C found in differently processed orange juices. I'm a bit stuck about how to do both these things together. I was going to do a titration with potassium iodate solution (giving me a colour change), but then to find the purity I'd need a solid of the vitamin C for melting point apparatus, so then I couldn't do the titration :( bit of a problem going on there, and none of the chemistry teachers in my school are being very helpful :P

Does anyone have any suggestions as to what I could do instead of either a titration or melting point apparatus, so that I could find BOTH the concentration and purity. Remember I do only have access to school supplies- nothing too complex!

Thanks :)