Detectors corona-charged aerosol

A promising detection principle utilizes similar nebulization procedure as applied in ELS, namely the corona-charged aerosol detectors, CAD. In CAD, the aerosol particles interact with an ionized gas (usually nitrogen). The particles become charged and electrically detected [294]. It has been shown that the response of CAD does not depend on the nature of analyte. On the other hand, the size of the aerosol depends on the mobile phase composition and it has to be calibrated. 

Figure 9.11 Corona charged aerosol detector (CAD). (Courtesy of ESA)...

Figure 8.69 Schematic of a Corona charged aerosol detector.

This, in turn, is dependent upon the volume of the particle being formed. The relationship between particle surface area and volume is not linear. This is observed experimentally as the response curves for the Corona charged aerosol detector are typically expressed as the second-order polynomial function over a range of up to four orders of magnitude. However, over a narrow concentration range, good linearity of the CAD response is observed with sufficient accuracy. The application of power function can now correct for this physical characteristic and deliver a more linear response over a larger dynamic... 

Additional detection techniques that can be employed to help solve mass balance issues with RP-HPLC are MS [30], chemiluminescent nitrogen-specihc detector [31], evaporative light-scattering detector, ELSD [32], and corona charged aerosol detection [CAD] [33],... 

For analytes with no UV chromophore or weak UV chromophore, detection methods such as Corona charged aerosol detection (CAD), evaporative light scattering detection (ELSD), or MS can be used. These detectors require that analytes be nonvolatile and mobile phase be compatible with detectors. 

In addition to ELS, charged aerosol (CA) or corona detector has more recently been introduced as a very promising HPLC detection system [105] while the sensitivity of the two systems is quite close, CA detector offers the advantage of a nearly linear response factor, particularly crucial for the assessment of enantiomeric purities, whereas ELS provides a nonlinear response at very low or high levels of analytes, resulting from several light scattering mechanisms and particle size distribution. 

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