In capillary electrophoresis the background electrolyte must have a greater conductivity than the sample and, consequently, usually constitutes a suitable buffer. However, as well as maintaining a high conductivity the buffer must also control the pH of the electrophoretic system. The electrolyte type and concentration must also be chosen to be appropriate for the substances being separated. To allow versatility in detector choice, the buffers should be chosen to be UV transparent so that UV absorption or fluorescence can be used for detection. In some cases, the buffers must be volatile to permit mass spectrometry of inductively coupled plasma techniques to be used. For work at low pH values phosphate and citrate buffers can be employed but the phosphates do absorb UV radiation at about 260nm. Conversely, borate buffers are often used at high pH values.