The first thing to do is separate your question into its component concepts. Say you're interested in a procedure to determine Bisphenol-A in water using chromatography. That's three distinct concepts:
(In analytical chemistry, questions often parse into related analyte, matrix, and method concepts that are easy for a human to understand, but hard for a computer to relate intelligently. So you'll often get false hits that contain these terms, but the terms turn out not to be related to each other in the way you'd like.)
