Mass spectrometric detection photoionization

Figure B2.3.7. Schematic apparatus of crossed molecular beam apparatus with synclirotron photoionization mass spectrometric detection of the products [12], To vary the scattering angle, the beam source assembly is rotated in the plane of the detector. (By pemrission from AIP.)...

In this chapter we have discussed the successful implementation in our laboratory, for the first time, of the soft (i.e. low energy) electron-impact ionization method for product detection in crossed molecular beams reactive scattering experiments with mass spectrometric detection. Analogous to the approach of soft photoionization by tunable VUV synchrotron radiation,... 

Intense laser sources have been used to induce ionization or fluorescence of products in several kinds of photolytic experiments. Welge and his colleagues have used these sources to detect NO by multiphoton ionization (MPI) of the product. They have also used lasers that have been extended to the VUV region by various nonlinear mixing schemes as photoionization sources for mass spectrometric detection of reaction products. 

Less effort appears to have bear expended on studies of F, Q, Br, and I atom reactions, although the e.p.r. spectra of the P states of F, Cl, Br, and I have all been described. Spectra of F, Q, and Br in P states have also been desmbed. Mass spectrometric detection of atoms also has bemi reviewed fairly recently. Certain indirect methods, e.g. using detection of OF produced by the reaction of F with O2 to detomine [F], have been described above. Direct detection of atoms, using reduced electron enmgies in electron impact, or using photoionization, A. A. Westcnberg, Progr. Reaction Kinetics, 1973, 7, 23. 

Another PHg source is benzylphosphane CgHsCHgPHg. Its thermal decomposition starts at 650 C [49] or 600°C [50] and was approximately complete at SSO C [49] or 800 C [50]. The PHg fragment was mass-spectrometrically detected following either electron impact [49] or photoionization with the Lyman-a line [50]. The formation of PHg was confirmed by its reaction with CH3 (from the simultaneous pyrolysis of ethyl nitrite) to CH3PH2 which was mass-spectrometrically detected [49]. 

The PH + ion formed by electron impact on PH3 was mass spectrometrically detected. An ionization efficiency curve between 30 and 50 eV led to appearance potentials of 34.0 eV (square root plot) or 32.7 eV (linear extrapolation) [1] both values are tabulated in [2] for the first value, see also [3]. Partial PH3 ionization cross sections for PH + and PD3 ionization cross section ratios, PDl /PD, were obtained for electron energies up to 180 eV and showed appearance potentials of 35.0 0.5 eV for PH + and 34.9 0.5 eV for PD + (square root plots) [4]. The PH + ion was also mass spectrometrically detected after ionization of PH3 by high-energy electrons (8 keV). Oscillator strengths were obtained by dipole (e,e+ion) spectroscopy simulating photoionization [5]. 

The basis for mass spectrometric fingerprinting is full-scan spectra within a mass range that covers the molecular weight (MW) of the compounds of interest. Different ionization techniques may be used prior to the mass spectrometric detection. ESI, atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI) will produce different... 

Pb(C2Hs)4 in air or other gas samples was determined, after appropriate sampling [428, 482] by gas chromatography using flame ionization [331, 357, 531, 565], electron capture detectors [239, 250, 306, 334], a photoionization detector [369], mass spectrometric detection [264, 531, 565, 574], or detection by atomic absorption spectrometric procedures [322, 328,... 

Yang X, Lin J, Lee Y T, Blank D A, Suits A G and Wodtke A M 1997 Universal crossed molecular beams apparatus with synchrotron photoionization mass spectrometric product detection Rev. Sc/. Instrum 68 3317-26... 

Mass spectrometric studies are not limited to the investigation of stable intermediates they have also been carried out on reaction transition states. The ultrafast studies by Zewail, for example, are nominally mass spectrometric based, where photoionization is used to detect reactive species on exceedingly short (femtosecond) time scales.Time resolved studies provide insight into the rates of unimo-lecular reactions, but do not provide direct thermochemical insight. 

Martens-Lobenhoffer et al. [119] used chiral HPLC-atmospheric pressure photoionization tandem mass-spectrometric method for the enantio-selective quantification of omeprazole and its main metabolites in human serum. The method features solid-phase separation, normal phase chiral HPLC separation, and atmospheric pressure photoionization tandem mass spectrometry. The internal standards serve stable isotope labeled omeprazole and 5-hydroxy omeprazole. The HPLC part consists of Agilent 1100 system comprising a binary pump, an autosampler, a thermo-stated column component, and a diode array UV-VIS detector. The enantioselective chromatographic separation took place on a ReproSil Chiral-CA 5 ym 25 cm x 2 mm column, protected by a security guard system, equipped with a 4 mm x 2-mm silica filter insert. The analytes were detected by a Thermo Scientific TSQ Discovery Max triple quadrupole mass spectrometer, equipped with an APPI ion source with a... 

LFP/UV, Excimer laser photolysis, UV absorption detection of hydrocarbon. LFP/PIMS, Excimer laser photolysis, photoionization mass spectrometric monitoring of hydrocarbon. RR, Relative rate determination. DF/MS Discharge flow production of radicals, mass spectrometric monitoring of hydrocarbon radicals. PR/UV, Pulsed radiolysis in 760 Torr H2, UV absorption detection of ethyl and ethyl peroxy. 

From Eq. (9) it is clear that correct determination of QY depends on accurate knowledge of the overall detection efficiency/, which is generally about 0.5. It can be determined in two ways. One is to compare the measured ratio C2+/C+ with the calculated ratio for an atomic rare gas such as Xe at a wavelength where the true relative production ratio A2+/N+ is known from photoionization mass spectrometric measurement of the ion yields. This method has been used in deriving the Xe data of Fig. 15. As expected, the quantum yield in the atomic case is unity (100%) within experimental error this must be generally true because deactivation of superexcited states by light emission is very rare. Thus the second and quicker method is simply to measure the apparent QY for an atomic gas and determine / accordingly. 

Dissociation and ionization by means of one or several lasers. Sensitive detection of fragments and ions with resonance photoionization and mass spectrometric techniques (tunable lasers). Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) with pulsed ablating laser sources. High lateral resolution enables molecular microprobing of biological cell compounds... 

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