Non-invasive characterization of stationary phases in capillary flow systems using scanning capacitively coupled contactless conductivity detection (sC4D)

Capacitively coupled contactless conductivity detection (C4D) has gained interest recently as an elegant new detection method for capillary electrophoresis and, to a lesser extent, liquid chromatography. However, in recent years, the versatility of this non-invasive detection system for research in materials and separation science has been demonstrated through non-traditional applications, mostly using scanning mode (sC4D). This involves the precise measurement of local differences in the conductive response of stationary phases housed within capillary columns. sC4D permits physical and chemical interrogation of stationary phases in capillary columns and microfluidic chips, with potential use in liquid and gas chromatography, capillary-zone electrophoresis or electrochromatography. sC4D also allows evaluation of chemically-modified surfaces to optimize procedures, coverage and chemical or biochemical activity. This review critically summarizes these developments and highlights the potential for widespread application of sC4D, beyond that of simple on-capillary detection.