Detectors 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)...

The advent of the use of mass spectrometers as detectors and new mass detectors such as the charged aerosol detectors (CAD) and evaporative light scattering detectors (ELSD) should provide high-sensitivity detection of compounds that do not absorb UV light. The only problem with most of these is that they are expensive and, therefore, not readily available. When prices come down, they should finally eliminate the use of derivatives in HPLC analysis. 

Some compounds are transparent and undetected by UV and FL detectors. They may be present in tiny enough quantities to be undetected by RI detectors. Evaporative light scattering detectors (ELSD) and charged aerosol detectors (CAD) can see almost any compound with good sensitivity. Mass spectrometric detectors (MSD) also can see almost any compound at high sensitivity and can also determine its molecular weight. 

CAD (Charged Aerosol Detector)—A universal, mass detector that evaporates column effluent using a gas nebulizer in the presence of a caronal discharge needle that ionizes compound droplets so they can be detected on an electrometer. 

Figure 11.3 Normal-phase HPLC separation of tocopherols (Ts) and tocotrienols (T3s) from barley kernels. A. Detection via fluorescence, ex 294 nm, em 326 nm, B. Detection via a charged aerosol detector. For FIPLC parameters see Moreau et al. (2006).

Although tocopherols and tocotrienols can be detected by UV absorbance at 280 nm, fluorescence detection (excitation 294 nm and emission 326 nm), as shown in Figure 11.3, has proven to be a much more sensitive method. Electrochemical detection such as pulsed amperometric and coulometric (Uspitasari-Nienaber, 2002) has also proven to be sensitive and potentially valuable for the quantitative analysis of tocopherols and Tocotrienols (Abidi, 2000), especially for tocol analysis in blood and serum samples. HPLC mass detectors such as flame-ionization detectors, evaporative light-scattering detectors, and charged aerosol detectors have proven to be valuable for the quantitative analysis of many types of lipids, but because tocols have... 

Moreau, R.A. 2006. The analysis of lipids via HPLC with a charged aerosol detector. Lipids. 41 727-734. 

MS/ELSD/CAD Mass Spectrometry/Evaporative Light Scattering Detector/Charged Aerosol Detector ... 

In the introductory Section 2.1.3, it was discussed that an important aspect of optimization can be to improve a method for its applicability in trace analysis. The nature of the mode of detection is very relevant in this case whether the applied detector is concentration proportional like the very common UV detector or mass proportional hke nebulizer-based detectors, for example, evaporative light scattering detector (ELSD) or charged aerosol detector (CAD). This textbook contains dedicated chapters on nebulizer-based or aerosol detectors (Chapter 10 on trends in detection), as well as for the coupling of LC with mass spectrometry (Chapter 1). Here, the focus is on concentration proportional detectors UV detectors (VWD, DAD), fluorescence detectors (FLD), electrochemical detectors (ECD), and refractive index (RI) detectors. 

The charged aerosol detector in Figure 22-25 is a sensitive universal detector that responds to almost all analytes and is compatible with gradient elution. Eluate evaporates to leave an aerosol of nonvolatile solute. The fine particles mix with a stream of Nj ions formed in a high-voltage discharge, and the aerosol particles... 

Figure 22-25 Operation of charged aerosol detector. [Courtesy ESA, Inc., Chelmsford MA.]...

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... 

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