Low-voltage mass spectra

The rate of formation of oxidation intermediates was followed by withdrawing aliquots during oxidation runs and determining intensities of the parent peaks in low voltage mass spectra as measures of the relative concentrations of starting hydrocarbon and products. Although sensitivity—i.e., the proportionality factor between parent-peak intensity and concentration—differs from one compound to another, peak heights for any one compound in the spectra of samples of equal size (0.6ft) are... 

Minor oxidation products are shown in Table V the numbers are relative intensities in the low-voltage mass spectra. The trimeric products... 

The authors acknowledge the assistance of J. K. Phillips for the low voltage mass spectra analyses. 

Low voltage mass spectra of subfractions 1-15 were obtained on an Extranuclear 5000-1 quadrupole mass spectrometer with Curie-point heating inlet using 1/4 jiil glass capillary probe tips as described by McClennen et al. (4). The inlet was heated to 200 C, electron energy was set at 12 eV. Samples were scanned from m/z 20 to m/z 300. All spectra were recorded with an IBM 9000 computer. 

Figure 2. Low voltage mass spectra of (a) subfraction 1 and (b) subfraction 12.

Low-voltage mass spectrometry has been used to identify ferrocene and its derivatives, for by using an ionizing voltage of 8 eV only the molecular ion peaks are observed (44,189). Reed and Tabrizi studied the mass spectra... 

Figure 11 Comparison of high-voltage and low-voltage El spectra of the diesel fuel. In the high-voltage El spectrum (top), significant amounts of fragment ions, shown as odd masses, are present. In the low-voltage El spectrum (hottom), essentially molecular ions, shown as even masses, are present.

The mass spectra of the substituted [2.2]paracyclophanes at low ionizing voltages show distinct peaks for the chief radical fragments of the two p-xylylene... 

Although the mass spectra of dibenzothiophene, its sulfoxide, and its sulfone have been recorded, the bulk of published work in this area is mainly of a general nature concerned with the identification of types and classes of sulfur compounds. As a result, detailed fragmentation patterns of dibenzothiophene derivatives are few in number. Mass spectrometry, particularly low electron voltage mass spectrometry, has, however, been extensively used for the identification of dibenzothio-phenes in petroleum. ... 

Numbers are maximum intensities in low-voltage (7.5 volts, uncorrected) mass spectra, scaled to original intensity of hydrocarbon = 500. 

The low-voltage, high-resolution mass spectra (LVHRMS) were obtained on a Kratos MS-50 high-resolution mass spectrometer interfaced to a Kratos DS-55 data system. The Rasa coal extract was vaporized directly into the ion source by a direct-insertion probe. Spectra were recorded at probe temperatures of 100°C, 200OC, 300°C, and 350°C. The instrument was scanned from 700 to 60 amu at a scan... 

The spectra of various disubstituted ferrocenes were examined by Clancy and Spilners (44) at low ionizing voltage, and they observed only the molecular ions. They have also used mass spectrometry to identify products from the reaction of lithioferrocene with benzyl chloride one of the products was dibenzylferrocene (189). The mass spectra of [5]-ferroceno-phanes show very intense molecular ion peaks and fragmentation is limited (9, 10). The ketone derivatives (LXXXT) and (LXXXII) fragment by elimination of carbonyl groups first. 

Relative intensities in the low-voltage spectra, normalized to a value of 100 at mass 380 for intercomparison. 

MALDI mass spectra were acquired on a Broker Reflex mass spectrometer equipped with a 337 nm nitrogen laser and a multiple sample stage source. The spectra were acquired in linear mode, represent the sum of 20 laser shots, and are un-smoothed. All ions were desorbed at a laser power just above threshold, at an ion extraction voltage of 30 kV. The matrix used was a saturated solution of 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, Aldrich Chemicals) in a 1 1 water/acetonitrile solution. Low-mass matrix ions were deflected by the application of a voltage pulse. 

Measurement by Mass Spectroscopy. Mass spectra of the GPC subfractions, Fr-M, D, and T, were obtained by a low-resolution and low-ionization voltage (10 eV) method using gas chromatography-mass spectroscopy (GCMS) techniques for Fr-M-3 to 7 and Fr-D-3 to 7 and by a direct insert technique for high-... 

The positive-ion ESI mass spectra of six imidazolinone herbicides, e,g, imazapyr and imazaquin, showed protonated molecules at low cone voltages (40 V),... 

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