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The next step consists in injecting a specimen of the mixture to be measured containing compounds 1, 2, and 3 . Labelling the elution peaks as and will give direct access to the percentage mass composition of the mixture represented by x₁, x₂, and x₃ via three equations of the following form:

The condition of normalization is that x₁ + x₂ + x₃ = 100

If the procedure is extrapolated to n components normalized to compound j (internal reference), a general expression for the response factor of a given compound i can be obtained:

(1.46)

It is also possible to determine K_i/j by plotting a concentration–response curve for each of the solutes.

In a mixture containing n solutes, if designates the area of the elution peak of compound i, and if the internal reference is j, then the content of compound i will obey the following equation:

(1.47)

This method is ideal to monitor rates of advancement of a chemical reaction and, at the same time, to follow the conversion kinetics.