quantitative analysis
Once you know your cupboard has sugar in it, the next natural question is: how much sugar — a teaspoon or a kilogram? Putting a number on the amount of something is quantitative analysis. It measures how much of a known substance is present, and reports the answer as a concentration or a mass: 5 milligrams, 12 parts per million, 0.3 percent.
Quantitative analysis is the determination of the amount or concentration of an analyte in a sample. It almost always rests on comparing the analyte's signal to that of known standards, often through a calibration curve, and it demands attention to errors, significant figures, and uncertainty, because the whole point is a trustworthy number.
It matters because most real decisions hinge on amounts, not mere presence: a drug at the right dose heals, at the wrong dose harms; a pollutant below a limit is safe, above it is illegal. The caveat is that every quantitative result is an estimate with a margin — a responsible report gives not just the number but how confident you can be in it.
After a qualitative test confirms a juice contains vitamin C, a quantitative analysis goes further and reports that the juice holds 45 milligrams of vitamin C per 100 milliliters.
Quantitative analysis puts a number on 'how much'.
A bare number is incomplete in quantitative work: a result such as '12.4' is meaningless without units and, ideally, an uncertainty, e.g. '12.4 plus or minus 0.3 milligrams per liter'.