Application of the Different Analytical Methods for Non-chromophoric Pharmaceutical Compounds

The physicochemical properties of non-chromophoric compounds that lack a group to absorb UV-visible radiation make them difficult to analyze with a simple detector. Pharmaceutical formulations and their unknown impurities, which show weak or no response with a UV detector, remain undetected and pose a challenge to the analysis of these compounds. Direct measurement of a chromophore complex formed between the compound and the colored ions present in the electrolyte solution with UV detection is one of the validated methods to analyze non-chromophoric compounds. The derivatization with either chromophore or fluorescent group for the detection of the non-chromophoric compounds with HPLC-UV-Vis or fluorescence detector is also commonly used to study the physicochemical properties of the pharmaceutical formulations. The other techniques to analyze such non-chromophoric compounds include conductivity (ionic molecules), amperometry (molecules oxidized or reduced), mass spectrometry, evaporative light scattering detector (ELSD), condensation nucleation light scattering detector (CNLSD), capillary electrophoresis (CE), gas chromatography (GC), etc. This review covers various separation and detection techniques developed for the analysis of non-chromophoric compounds.