Disclosed herein are methods for the chemiluminescent assay of a variety of analytes of interest. and a UV-absorber, hindered amine stabilizer, sterically hindered phenol, organophosphite, organophosphonite, organophosphine, or mixtures thereof. A light detector is positioned in the path of the emitted light and is scanned across the emitted light. The extension bar 3 is adjustably connected to a circular cylinder rod 4 by a coupling piece 6.