Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: The challenge of techniques used for proteomic analyses is the difficulty in detecting small quantities of proteins. Although mass spectrometry is good for detecting small amounts of proteins, variations in protein expression in diseased states can be difficult to discern. Proteins are naturally unstable molecules, which makes proteomic analysis much more difficult than genomic analysis. Answer: proteins
Output:
The challenge of techniques used for proteomic analyses is the difficulty in detecting small quantities of what?