In regional reconnaisance geochemical prospecting, it is desirable to determine as many elements as possible, in order to provide a comprehensive cover for the detection of most types of ore mineralization. Multi-element simultaneous instruments are ideally suited to this task, but the maximum number of wavelength dispersive channels (monochromators) which may be fitted to any one of the commercially available X-ray spectrometers is approximately thirty. Because some of these channels are required for the measurement of background, the practical limit for spectral lines is about twenty-five. Additional elements may be determined by inclusion of a scanning channel, but its sequential operation increases the analysis time per sample.