Charged Aerosol Detection: Factors for consideration in its use as a generic quantitative detector

Charged Aerosol Detection (CAD) is now established as a universal detector for High Performance Liquid Chromatography (HPLC) applications, and a complimentary technique or alternative to Evaporative Light Scattering or Ultraviolet detection.

CAD has already been used to quantify structurally diverse samples, providing that the sensitivity variation with changes in eluent composition was taken into consideration. Routine use of CAD in measuring solubilised drug standards resulted in a discrepancy in expected results and led to investigations into how mobile phase buffer could significantly affect quantification results. This study has shown the distinctive property of CAD in detecting the solution based ion pair of a drug substance and its adduct in a single analysis.

Introduction

Monitoring the concentration and quality of compounds in solution intended for physical or biological screening is of paramount importance within the pharmaceutical industry. Instrumentation that can produce quantifiable information, irrespective of the compound’s physical or chemical properties, and can be readily incorporated into on-line systems is the ideal solution. Several techniques have appeared over the last few years that showed promise as the elusive ‘universal’ detector. The need for universal detection methods for liquid chromatography led to the development of evaporative light scattering detection (ELSD) in the late 1970 and 1980s 1,2.

This detection method is useful both for detection of compounds without a chromaphore and detection of compounds separated with gradient elution, yielding advantages over ultraviolet absorption detection and refractive index detection respectively 3. Within similar compound classes a constant molar response can be measured.