Performance evaluation of evaporative light scattering detection and charged aerosol detection in reversed phase liquid chromatography

In pharmaceutical industry ultraviolet (UV) detection is often used as the preferred detection technique in HPLC analysis since most pharmaceutical compounds possess a UV-absorbing chromophore. However, in case the active pharmaceutical ingredient (API) does not have a UV-absorbing chromophore, or if some of the impurities present lack a chromophore, they will not be detected in routine HPLC analysis employing only a UV detector and alternative detection schemes have to be used. Refractive index detection or mass spectroscopy (MS) can be used but these detectors have their intrinsic weaknesses, such as lack of sensitivity or high cost. With the appearance of semi-universal techniques such as evaporative light scattering detection (ELSD), and more recent, charged aerosol detection (CAD), detection of non-UV-absorbing compounds became feasible without having to resort to such complex or costly detection methods. This paper evaluates the different performance characteristics such as sensitivity, linearity, accuracy and precision of both the ELSD and CAD detector coupled to HPLC. One disadvantage of this type of detector is the non-linear response behaviour which makes direct linear regression for making calibration curves inaccurate.