Water mass spectral peaks

The side-chain chlorine contents of benzyl chloride, benzal chloride, and benzotrichlorides are determined by hydrolysis with methanolic sodium hydroxide followed by titration with silver nitrate. Total chlorine determination, including ring chlorine, is made by standard combustion methods (55). Several procedures for the gas chromatographic analysis of chlorotoluene mixtures have been described (56,57). Proton and nuclear magnetic resonance shifts, characteristic iafrared absorption bands, and principal mass spectral peaks have been summarized including sources of reference spectra (58). Procedures for measuring trace benzyl chloride ia air (59) and ia water (60) have been described. 

Mass spectral peaks are often seen corresponding to loss of small, stable molecules. Loss of a small molecule is usually indicated by a fragment peak with an even mass number, corresponding to loss of an even mass number. A radical cation may lose water (mass 18), CO (28), C02 (44), and even ethene (28) or other alkenes. The most common example is the loss of water from alcohols, which occurs so readily that the molecular ion is often weak or absent. The peak corresponding to loss of water (the M-18 peak) is usually strong, however. 

The Mass spectral curing studies were done by heating each sample of polymer in the DIP consecutively at 100°C, 200°C, and 350°C for 1 hour each. The extent of cure at 200°C was estimated by taking the ratio of the area for the peak at 200°C in the TIC (or the ion chromatogram of water or isobutene) to the combined area of the peaks at 200°C and 350°C. The samples for the IR curing study were spun from dimethylacetamide solutions of the polyamic acid or its esters onto NaCl... 

The mechanistic basis for this phenomenon was explained in detail (Ivanovich 1994). Simply put, the uranium atoms occupy certain positions in the lattice of the mineral. When an alpha particle is emitted from U-238 (to form U-234), the parent atom recoils and its position in the lattice changes slightly and leads to creation of a fanlt in the lattice. Water that is in contact with the mineral wiU preferentially leach nranium atoms that lie close to these faults, leading to an increase in the fraction of U-234 in the leachate. This effect is clearly seen in alpha spectra of natnral samples where the U peak is often significantly larger than the U peak or in accurate mass spectral measurements. 

The luciferin produces a blue oxidation product during its purification process. In the DEAE chromatography of luciferin, this blue compound is eluted before the fractions of luciferin. The fractions of the blue compound were combined and purified by HPLC on a column of Hamilton PRP-1 (7 x 300 mm) using methanol-water (8 2) containing 0.1% ammonium acetate. The purified blue compound showed absorption peaks at 234, 254, 315, 370, 410, 590 (shoulder) and 633 nm. High-resolution FAB mass spectrometry of this compound indicated a molecular formula of C l C Nai m/z 609.2672 (M - Na + 2H)+, and mlz 631.2524 (M + H)+]. These data, together with the HNMR spectral data, indicated the structure of the blue compound to be 8. 

Figure 3.5. NMR spectrum of wood as a function of moisture content (Nanassy, 1974). The spectral intensity of the broad component is due to hydrogen nuclei in dry wood tissue (6% of oven-dry mass) and to a monolayer of strongly adsorbed water molecules. The intensity of this component increases somewhat with moisture content, at least to the fibre saturation point. This implies that new internal surfaces are being created as the moisture content increases. The narrow component corresponds to the more mobile multilayers of adsorbed water. The narrow component is truncated because the idea was to record the broad spectmm which required expanding the vertical scale, so that the peak of the narrow spectmm is well off scale. With quantitative NMR techniques the areas under the broad and narrow components of the spectmm provide a measure of the number of hydrogen atoms in these two states.

From other information concerning the molecular structure, such as isotope peak calculations, exact mass measurements, or spectral or chani-cal evidence, the presence or absence of nitrogen may be known. A compound known to be a steroid, for example, must have an even molecular weight. On the other hand, a substance that becomes water soluble under acidic conditions must contain at least one basic nitrogen function in this case, the molecular weight may be odd or even, depending on the number of nitrogen atoms actually present. 

The mass spectra of angusticraline (329) and alstocraline (330) displayed prominent ions due to methoxymacroline (m/z 368, 200) and cabucraline mjz 194) moieties. The NMR spectral data confirmed the presence of these units and further unravelled the point of attachment of the monomeric units. The substitution on the cabucraline moiety is at the aromatic C(IO ), which is linked to C(19) of the macroline part, a conclusion supported by the absence of signals normally due to these hydrogens, and the presence of a four-carbon fragment corresponding to the C(18)-C(21) unit in the NMR spectrum. It is also consistent with the presence of a hemiacetal function, which accounts for the observation of an OH in the IR spectrum as well as a peak due to loss of water in the mass spectrum of 329. 

The near-infrared spectrum of fully deuterated water is very similar to that of H2O, except that the peaks are all shifted because of the mass difference of the hydrogen atom. Table 6.2 summarizes the absorptions. Figure 6.4 shows a portion of the near-infrared spectral region, illustrating the isotope shift of the + V3 combination band (indicated by stars). 

Figure 8.3 is a comparison between a quadrupole and a magnetic sector instrument of one of the most common polyatomic interference—on Fe which requires a resolution of 2504 to separate the peaks. Figure 8.3a shows a spectral scan of 5 Fe+ using a quadrupole instrument. What it does not show is the massive polyatomic interference °Ar 0+ (produced by oxygen ions from the water combining with argon ions from the plasma) completely overlapping the Fe". It shows very clearly that these two masses are irresolvable with a quadrupole. If that same spectral scan is carried out on a magnetic sector-type instrument, the result is the scan shown in Figure 8.3b. ° It should be pointed out that in order to see the spectral scan on the same scale, it is necessary to examine a much smaller range. For this reason, a 0.100 amu window was taken, as indicated by the dotted lines.

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