Detection photo-ionization

IP Ionization potential is the amount of energy needed to remove an electron from a molecule of chemical vapor. The resultant ion is a charged particle that is detectable by various instrumentation such as photo ionization or flame ionization detectors. 

Additional detectors currently available use other technologies such as electrochemical detectors for blister, nerve, blood, and choking agents, and infrared spectroscopy detectors or photo ionization detectors for the detection of blister and nerve... 

If reasonable amounts of negative quarks could be had in a sample, energetic photons just above the threshold can ionize the quark to a free state with moderate kinetic energy. One advantage of such an experiment liberating photo-ionized quarks is that a high-resolution spectrometer (or related multi-channel device) can detect the well-defined X-rays emitted by the capture of the quark to a definite heavy atom (such as gold or thorium). 

Photo-induced electron-transfer decarboxylation reactions have been reviewed. A variety of methyl- and methoxy-substituted phenol radical cations have been generated by either photo-induced electron transfer or photo-ionization in dry solvents such as acetonitrile. In the presence of small amounts of water the radical cations are not detected and the phenoxyl radical is the only transient species observed. The 2-methoxyphenol radical cation was found to be more reactive than the 4-methoxy radical cation. 

The gas-phase structure of f-BuLi has also been probed by McLean and coworkers using photo ionization mass spectrometry". At room temperature, they detected only tetramers and determined the ionization potential of (f-BuLi)4 to be 6.2 eV. Other ions were detected above 8 eV with general formulae R Li4+(n = 1-3) and RLi2+(R = f-Bu). Both R3Li4+ and RLi2 had also been observed by Brown and coworkers in the H spectra of f-BuLi vapor, while R2Li4 and RLi4+ had not . 

Resonant 3-photon ionization with pulsed laser (Cu-vapor pump laser) ion detection after photo-ionization rare earth in preparation (P78)... 

Two-step photo ionization with CW laser via Rydberg states ion detection In tested (P77)... 

A small fraction of the orthopositronium atoms produced pass through the cw-excitation beam, where they are promoted to the 23Si level and then through a multi-pass doubled-YAG beam at 532 nm, where they are photo-ionized. The photo-ionized positron is electro-statically accelerated and magnetically-guided into a channel-electron multiplier array (CEMA) where it is detected. The time-of-Hight between the incident positron pulse and the photo-ionization pulse determines the range of positronium velocities detected. 

All aluminum clusters react with CO, but Alg reacts about twice as fast as any other cluster. The Alg cluster is nearly a hundred times more reactive toward CO than Hj. In addition no Al —CO adducts are detected. Studies of CO chemisorption on aluminum surfaces ° indicate that the bond strength is only about 8 kcal/mol, consistent with theoretical calculations.The fact that Al —CO and Cu —CO are not observed as products may be due to unimolecular decomposition in the beam, or dissociation during the photo-ionization/detection process. The answer must await further experiments. 

The primary method of analyzing carbon disulfide in air is by adsorption on an activated charcoal tube followed by solvent elution for subsequent quantification. GC equipped with either an electron capture detector (ECD), photo-ionization detector (PID), or FPD has been used for measuring carbon disulfide after elution from the solid phase. Detection limits of low ppm levels of carbon disulfide in the air sample were achieved with these techniques (McCammon et al. 1975 Peltonen 1989 Smith and Krause 1978 UK/HSE 1983). NIOSH has recommended GC/FPD (method 1600) for determining carbon disulfide in air. The range of quantification is 3-64 ppm for a 5-L air sample (NIOSH 1984b). 

When a very high sensitivity is needed the pump/probe technique using photo-ionization was employed [46J. The atoms were excited by the pump beam and then a delayed probe beam was applied to ionize them from the excited state. The ion signal versus delay time is detected. Advantages of this technique are a high sensitivity and a time resolution limited only by the duration of the pump and probe pulses, but not by the time resolution of the detector. 

The detectors used in gas chromatography for the detection of individual VOCs can also provide information about a mixture without a separation step. These VOC detectors include, for example, the flame-ionization detector (FID) and the photo-ionization detector (PID). Other direct-reading instruments have also been used for determining VOCs, such as photoacoustic spectroscopy (PAS) (see Chapter 1.6). Other types of sensors (e.g. electronic noses ) may become important in the future. 

Much of today s technology has been developed into commercially available detection equipment, however, and this equipment should allow first responders, whether they be police, fire, Hazmat, or EMS units, to detect the presence or absence of CWA. This equipment is available, reasonably priced, and will detect a wide array of chemical agents. The M9 paper and the M256 kit are simple and inexpensive devices that enable responders to rapidly detect classical CW agents. The photo-ionization detector, the ion mobility detector, the surface acoustic wave detector, and the colorimetric tubes give medical personnel an ability to deal with a wider array of chemicals. As a market evolves for these items of detection equipment, modifications for the civilian community will be made to simplify their usage and the costs associated with their acquisition and maintenance should decrease. 

Medical personnel must rely on accurate and timely information provided by the earliest responders on the scene. If medical teams are expected to be the earliest responders to the scene of a mass casualty incident involving chemical agents, then they should be provided with reliable detection equipment as well as training on the use of the equipment. There should be continued support for the Public Health Service efforts to equip Metropolitan Medical Strike Teams with effective and currently available chemical agent detection equipment. These detectors are reliable, relatively inexpensive, and provide for the detection of all classical chemical agents that may be utilized in a domestic terrorist incident. Furthermore, efficient and cost-effective portable hand-held CWA detectors employing photo ionization detectors, surface acoustic wave microsensors, or ion mobility spectrometry should be readily available to all Hazmat units expected to respond to a potential CWA incident. 

Kanu, A.B. Thomas, C.L.R, The presumptive detection of benzene in water in the presence of phenol with an active membrane-UV photo-ionization differential mobility spectrometer, AnaZy f 2006, 131, 990-999. 

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