analyte
/ AN-uh-lyte /
Picture a detective at a crime scene full of clutter — furniture, dust, a hundred fingerprints — but the detective only cares about one thing: a single suspect's print. In a chemical analysis there is also one thing you actually want to find or measure, surrounded by everything else. That one thing is the analyte. It is the specific substance whose presence or amount you are trying to determine.
Formally, the analyte is the chemical species being identified or measured in a sample. A single sample can hold thousands of different substances, but in any given measurement you usually point your method at one analyte (or a defined set of them). Everything in the sample that is not the analyte is, from your point of view, just background — often called the matrix.
Naming the analyte clearly matters because methods are tuned to specific targets, not to 'whatever is in there'. A glucose test is built to respond to glucose; it is not designed to tell you about cholesterol. The caveat is that the same molecule can be the analyte in one study and an unwanted interferent in another — analyte is a role a substance plays in a particular analysis, not a permanent label.
In a test for caffeine in a cup of coffee, caffeine is the analyte. The water, oils, sugars, and acids that make up the rest of the coffee are not the analyte — they are the matrix the analyte sits in.
The analyte is the one substance the measurement is aimed at.
Do not confuse the analyte (what you measure) with the sample (the material you took to measure it in). A sample contains the analyte; it is not the analyte.