Aerosol, charged

The motion of a charged aerosol particle in a gas is governed by the electrostatic force and the aerodynamic forces. The theory dealing with the particle motion has been discussed in several books (see, e.g., Hinds- ). The electrostatic force F caused by the electric field E is given by... 

FI. Foster, W. W., Deposition of unipolar charged aerosol particles by mutual repulsion, Brit. J. Appl. Phys. 10, No. 5, 206 (1959). 

G6. Gordieyeff, V. A., Some properties of unipolarly charged aerosols, Arch. Ind. Health 14, 471 (1956). 

K6. Kraemer, H. F., Properties of electrically charged aerosols, Univ. of Illinois, Eng. Exptl. Sta. Tech. Rept. 12, AEC Rept. COO-1013, Contr. AT(ll-l)-276 (1954). 

Z2. Zebel, G., On the theory of the behavior of electrically charged aerosols, Kolloid Z. 

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. 

Charged Aerosol Luna C-18 > Thermo Hypercarb > ZirChromCarb > PLRP-S > TiOj-Carb... 

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. 

The most common LC-MS interface. Flow rates up to 1 ml/min but best at 200 pl/min or below. A charged aerosol is generated at atmospheric pressure and the solvent is largely stripped away with a flow of N gas. The charged molecules are drawn into the MS by eiectrostaticaiiy charged plates. 

Aikin, A. C and W. D. Pesnell, Uptake Coefficient of Charged Aerosols—Implications for Atmospheric Chemistry, Geophys. Res. Lett., 25, 1309-1312(1998). 

There are many types of HPLC detectors available today with the most popular ones including UV and UV-photodiode array (PDA), fluorescence, refractive index, evaporative light scattering (ELSD), charged aerosol (CAD), and the mass spectrometer. Of these, the most commonly used detector for pharmaceutical analytical methods is the UV detector since a majority of pharmaceutical compounds have some type of chromophore. Multiple detectors in series can also be utilized in order to obtain more information per chromatographic run. For example, a PDA detector can... 

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 15.5 Instrument schematic of the CAD (charged aerosol detection). (Reproduced...

Tadeusz G, Frederic L, Roman S, Pat S. 2006. Universal response in liquid chromatography using charged aerosol detection. Anal. Chem. 78 3186-3192. 

Charged aerosols and aerosol charging Microcontamination electrostatic precipitation atmospheric electricity aerosol sampling and measurement ion-particle interactions. 

The physical quality of samples is assessed via analytical methods. Liquid chromatography with mass spectrometry (LC-MS) is the most common instrumentation used to determine sample presence and purity (Kerns et al., 2005). Chemiluminescent nitrogen detection (CLND), charged aerosol detection (CAD) and other techniques have also been used to determine concentration (Popa-Burke et al., 2004 Gamache et al., 2003). 

Gamache, P.H. et al. 2003. HPLC analysis of nonvolatile analytes using charged aerosol detection. LC/GC N. Am. 23, 150-155. 

Radioactive sources can also be used for charge neutralization, since these produce large numbers of bipolar ions that can then rapidly neutralize highly charged aerosols (Cooper and Reist, 1973). 

Figure 12.5 Electric field around a partially charged aerosol particle.

The denominator will equal 2.121 for all positively charged aerosol particles n = +, 2.121 for all negatively charged aerosol particles n = -, and 1.0 for all neutral aerosol particles n = 0. Then... 

---