Corona detector

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. 

The Cl is analyzed by high performance liquid chromatography (HPLC) with UV detection. The brine composition and pH of the eluting solutions have to be adjusted to minimize the associated matrix effects. Besides, Cl analyses suffer from low UV-absorption of key components, which limits their quantitation. The use of a Corona detector in conjunction with HPLC to achieve desired sensitivity is evaluated, with emphasis on peak separation of key Cl components. 

P) content. ICP method will not be addressed here. The potential use of a Corona detector to determine base 4 that is not detected by the UV detector will be discussed. The quantitation of the Cl bases is based on one single predominant peak for each base. We have used an Agilent Model 1200 HPLC instrument and an Acclaim surfactant column (5 pm, 4.6 x 150 mm) to evaluate the method. Typical retention times observed for Cl based on UV detection are 2.4 minutes for base 1, 17.1 minutes for base 2, and 15.2 minutes for base 3. A typical chromatogram is presented in Figure 1. The small peak that tails the predominant peak at 2.43 minutes was included in the calculation of the peak area for base 1. 

With the exception of base 1, UV absorption by other Cl bases is very low, limiting their determination using a UV detector. Corona Aerosol Detector (CAD), which is a universal detector with good detection performance, was implemented to improve the characterization of the Cl bases. Preliminary findings indicate the good potential of Corona for the identification and quantification of Cl base 2, base 3, and base 4. The response feetors (peak area/ concentration) for selective peaks for base 2 and base 3 by corona detectors are 10-fold higher than those by the UV detector at 280 nm. Presence of KHI does not interfere in Cl determination when UV detection is used however KHI has strong interferenee in the determination of Cl when Corona deteetor is used. At this... 

Many types of detectors can then be used. However, contrary to the FID in GC, there is no sensitive and universal detector. The most used system is the UV/Visible detector and it requires that the compounds absorb characteristic wavelengths of an incident light. The diode array detector is more powerful. It helps scan the entire UV/Visible domain. Therefore, by spectral analysis, it is possible to carry out peak purity calculations. The Evaporating Light Scattering Detector (ELSD), and more recently the Corona detector, by its universality is increasingly used in the analysis of natural extracts. ELSD is based on the partial evaporation of the effluent as a way to obtain a mist of solid or liquid particles of the solute, which passes... 

Heller and Tabibian (13) noted that errors, due to laterally scattered light and the corona effect, as large as to cause a 30 reduction in measured turbidity, may result if instruments which are perfectly suitable for ordinary absorption measurements are used for turbidity measurements without proper modifications. To evaluate the performance of our turbidity detector, particle suspensions of various concentrations of several polystyrene latex standards were prepared. Their extinction coefficients were measured using both a bench-top UV spectrophotometer (Beckman, Model 25) and the online detector (Pharmacia). 

The data shown in Figures 6 A-D indicate that while the smaller particles 85, 98 eind 109 nm are indistinguishable from the dissolved solute, sodium dichromate, in as far as detector behaviour is concerned, the detector response differs significantly for the larger diameter particles. The reduced peak area and hence t irbi-dity indicated for the larger particles is a direct result of the optical effects noted earlier. The observations are consistent with the findings of Heller and Tabibian that the corona effect... 

An ion mobility spectrometer consists of a sample-introduction device a drift tube where ionisation and separation of ions takes place and a detector. Ionisation sources of choice include radioactive sources (e.g. a 63Ni foil), photoionisation methods, corona-spray ionisation, flame ionisation and corona discharge. The most common detection method used to measure the... 

All of the ionizing air systems at Longhorn are located in areas where ultraviolet sensors are used in conjunction with deluge systems for fire protection. Care must be taken to shield the ultraviolet detectors from the ion generating corona source. The systems used at Longhorn are individually shielded with PVC tubing or with hoods. 

Ozone decay was measured in an office, a home, and several metal test facilities. Measurements were carried out with a Mast ozone meter and an MEC chemiluminescence ozone detector. The latter was calibrated with a stable ozone source and the epa neutral buffered potasaum iodide procedure. (It was noted over a wide range of concentrations that the mec meter measurements were consistently higher than those of the Mast meter by a factor of 1.3. That this is essentially identical with the findings of the DeMore committee is interesting.) Ozone generated by a positive corona ionizer was introduced into the test facilities. Ozone decay in a metal-walled room was found to be first-order, with the rate constant... 

Various mass spectrometer configurations have been used for the detection of explosives, such as ion traps, quadrupoles and time-of flight mass analyzers and combinations as MS/MS systems. The ionization method is usually APCI with corona discharge [24, 25]. An example is given in Figure 20, which shows the schematic diagram of an explosive mass spectrometer detector [25]. It is based on an ion trap mass analyzer, an APCI source with corona discharge and a counter-flow introduction (CFI) system. The direction of the sample gas flow introduced into the ion source is opposite to that of the ion flow produced by the ion source. 

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)...

TABLE 53.7. Detection performance of corona discharge-type IMS detector LCD-3.2E... 

Choice of the proper detection scheme is dependent on the properties of the analyte. Different types of detectors are available such as ultraviolet (UV), fluorescence, electrochemical, hght scattering, refractive index (RI), flame ionization detection (FID), evaporative light scattering detection (ELSD), corona aerosol detection (CAD), mass spectrometric (MS), NMR, and others. However, the majority of reversed-phase and normal-phase HPLC method development in the pharmaceutical industry is carried out with UV detection. In this section the practical use of UV detection will be discussed. 

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],... 

Detector MS, SCIEX API III, atmospheric pressure ionization, nebulizer probe 450°, 2.5 (juA Corona discharge needle, quadrupole mass filter, 0.002 inch pinhole aperture, SIM m/z 749 and 752... 

Detector MS, PE Sciex API III, heated nebulized interface, corona discharge needle +4 xA, nebulizer probe 500°, nebulizing gas was air at 2 L/min and 80 psi, curtain gas flow was nitrogen at 0.9 L/min, sampling orifice +45 V, dwell time 400 ms, interface heater 60°, electron multipher-3.7 kV, collision gas was argon 355 x 10 atoms/cm, first quad-rupole filter admits m/z 276 (cyclobenzaprine) and 295 (trimipramine, collisional fragmentation at second filter, monitor m/z 215 (cyclobenzaprine) and 208 (trimipramine) at third quadrupole filter... 

Detector MS, PE-SCIEX API III triple quadrupole, heated nebulizer, corona discharge (+5 pA), positive ion APCI, nebulizer probe 500°, collision gas argon at 350 X 10 mole-cules/cm, nebulizing gas nitrogen at 80 psi and 2 L/min, curtain gas nitrogen at 0.9 L/min, orifice -1-50 V, electron multiplier -3.8 kV, dwell time 400 ms, interface heater 60°, m/z 317... 

Detector MS, Sciex Model API III triple quadrupole, nebulizer probe 500°, nebulizing gas 80 psi, auxiliary flow 2 L/min, corona discharge needle -1-3 p,A, 0.1143 mm orifice, orifice 40 V, collision gas argon... 

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