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All the main detection techniques commonly used with capillary electrophoresis (CE) can only detect analytes with specific properties. Fluorescence detectors can only detect analytes that fluoresce, UV detectors can only detect analytes that absorb UV light and amperometric detectors can only detect analytes that can be oxidized or reduced at an electrode. Even mass spectrometry, which is generally considered a universal detection technique, can only detect analytes separated by CE that can be efficiently converted into ions by electrospray ionization.
The one detection technique that can work with CE and is truly universal is refractive index (RI) detection, in which analytes are detected by changes they cause in the extent to which light is bent, or refracted, as it passes through the CE buffer. The problem is that RI detection isn’t particularly sensitive, especially at the small scales of CE.