Would I be right to guess that your background is not in chemistry, more on the biological side ? If so, welcome to the club. From experience, my advice is to find good analytical chemists who can help you - modern instruments are seductively simple to operate and deceptively good at generating what looks like useful data but is in fact nearly useless, but for anything except the most straightforward problems and for routine analyses by standard methods you really need to have a pretty good understanding of what is going on in order to ask the right questions and design methods to answer them.
The first step is to clearly work out what question it is about the mushrooms that you want a chemical analysis to answer, because that will determine what (kind of) compounds you need to analyse for, and that determines which techniques are most appropriate.
Peter