This has come up before, a similar question asked just this way: A novice need to know if there are adulterants in diesel fuel. There are a number of analytical procedures that can be done by an analytical laboratory specializing in fuel analysis. But there's nothing a truck depot or home user can execute.
You really will have to be as specific as possible about your needs, your skills, your equipment and what you're looking for. Give us an example: how have you ever analyzed anything? I've worked for a number of QC laboratories, but I've never taken a small sample of automotive gasoline I was purchasing into my pharmaceutical lab and checked "Is the really octane 87? Because if I get 85 or less, I'm writing a letter."