CHEMILUMINESCENCE CHEMICAL SENSING 485 imprinted polymer are expected to develop not only with the molecule recognition function but also as a special CL reaction medium. By injection of appropriate elements, the immobilized reagents can be released quantitatively from the immobilized column to perform CL reaction mixing; after mixing, the chemiluminescence signal can be detected through the detectors. Photomultiplier tubes (PMTs) are almost universally used as detectors in luminescence instrumen- tation (Figure 7.5). The most important photomultiplier characteristic is the quantum effi ciency as a function of wavelength, which depends on the composition of the photocathode. Another important photomultiplier characteristic is gain, which determines sensitivity. Also, the dark-current level of a PMT is very important because under conditions where intensities reaching the detector are low, the dark current is likely to be the primary source of background signal. Also, by cooling the tube, the signal/noise ratio can be improved.