trace analysis
Finding a single drop of dye in a swimming pool, and saying exactly how much dye it is — that is the flavor of trace analysis. It is the measurement of analytes that are present in tiny amounts, so small that they are easily lost, easily overwhelmed by the matrix, and easily faked by contamination.
Trace analysis is the determination of an analyte present at very low concentration, typically below about 0.01 percent of the sample, often reaching parts per million, parts per billion, or even lower. As a rough scale, major constituents are the bulk, minor constituents sit in between, and trace constituents are the faint whispers.
It matters because some of the most important questions in chemistry live at trace levels: toxic metals in drinking water, drug residues in food, pollutants in air. The caveat is that at these levels everything gets harder — a fingerprint, a dusty beaker, or a dirty reagent can add more analyte than the sample contains, so scrupulous blanks, clean glassware, and preconcentration become essential.
Detecting 2 micrograms of arsenic per liter of drinking water — well below one part per million — is trace analysis, where the cleanliness of the glassware can matter as much as the instrument.
Trace analysis measures analytes present in vanishingly small amounts.
The boundary between 'trace' and 'minor' is conventional, not a law of nature; different fields draw the line at slightly different concentrations. What is constant is that lower levels demand far stricter control of contamination.