Emission peak position on the apparent energy scale is a function of the number of photons created in the radioactive decay process. The sample, which is the detector in liquid scintillation (LS) spectroscopy, may contain quenching substances. These inhibit creation of photons and, consequently, radionuclide emission peak shifts towards lower channels. Identification of the radionuclide by its peak position is therefore not straightforward under variable quench in LS spectroscopy. The end point of the Compton spectrum (or external standard quench parameter SQP(E)) gives a direct measure of the sample quench. It is normally used in LS spectroscopy for the measurement of counting efficiency. Because SQP(E) does not depend on the sample emission energy, it can be used in verification of the peak energy together with the peak position. Two known energy calibration lines are required as a function of quench to verify the peak energy.