The tracer-pulse method provides the real adsorption data points directly from simple, straightforward calculations and is therefore a superior method for multicomponent adsorption isotherm determination in HPLC. Only one important problem has restricted its use so far: the tracer peaks are invisible using any conventional detection principle. We present a solution to this problem with an approach with a firm base in analytical chemistry, utilizing stable isotopes and mass spectrometric detection. The new approach was used for the determination of binary adsorption isotherms, and a systematic investigation was made of its main sources of error. With this modification, the tracer method can be a prime choice for future characterizations of multicomponent separation systems and of competitive drug binding studies.