Commercial systems for in situ quantification can be categorized as monochromatic slit scanning densitometers, diode-array scanners, and image analyzers (charged-coupled device cameras and flatbed scanners) [9,12,53–55]. Specific detectors for radioisotopes and interfaces for direct evaluation by spectrosocopic instruments (mass spectrometry and infrared and Raman spectroscopy) are also available. In recent years there has been a growing interest in biological detection using, among others, various luminescence reactions and conditions that facilitate instrumental detection [62,63]. This approach complements a long history of the use of in situ chemical reactions for selective and sensitivedetection or visualization of thin-layer chromatograms (see Section 4).