Spectrum of a mixture

MS is a means of examining a compound, also in the gas phase, so that its stmcture or identity can be deduced from its mass spectrum. MS alone is not good for examining mixtures because the mass spectrum of a mixture is actually a complex of overlapping spectra from the individual components in the mixture. 

Figure 8.25 shows the AXn,m. ii,iii Auger spectrum of a gaseous mixture of SFe, SO2 and OCS, all clearly resolved. The three intense peaks are due to sulphur in a >2 core state, but there are three weak peaks due to a core state also. The S 2p X-ray photoelectron spectrum of a mixture of the same gases is shown for comparison, each of the three doublets being due to sulphur in a 1/2 or 3/2 core state. 

Because of disproportionation, Pu02 is never observed on its own and its colour must therefore be deduced from the spectrum of a mixture involving Fhi in several oxidation states. 

The spectrum of a mixture of compounds is essentially that of the sum of the spectra of the individual components, provided association, dissociation, polymerisation, or compound formation does not take place. In order to detect an impurity in a substance, comparison can be made of the spectrum of the substance with that of the pure compound impurities will cause extra absorption bands to appear in the spectrum. The most favourable case will occur when the impurities present possess characteristic groupings not present in the main constituent. 

In toluene at —60° C the NMR spectrum of a mixture of HjSiBr and 7flMi-(Et3P)2PtHCl showed that all of the H3SiBr is converted into HjSiCl prior to formation of a Si—Pt product. 

Figure 9.8 UV MALDI-MS spectrum of a mixture of polymer additives. After Jackson et al. [57]. Reprinted from A.T. Jackson et al., Rapid Communications in Mass Spectrometry, 10, 1449-1458 (1996). Copyright 1996 John Wiley Sons, Ltd. Reproduced with permission...

Solutions of the alkylammonium salts of Cl , Br , r in acetonitrile show no visible absorptions beyond 300 nm. The aromatic it-acceptor, tetracyanopy-razine (TCP) is characterized by strong absorptions in the 220-300 nm range and a shoulder at 350 nm. However, the electronic spectrum of a mixture of the bromide salt and TCP reveals a new absorption band at Xct = 400 nm... 

This peak is broadened and contact shifted down field by the unpaired electron (Fig. 24). A spectrum of a mixture of methylcobinamide and free nitroxide shows broadening of the methyl resonance but no shift in resonance position. Thus the nitroxide must remain attached to the cobalt atom in solution. 

Figure 2.7 Mass spectra recorded at different resolutions. Mass spectrum obtained by a two dimensional ion trap at low resolution (a) and by an Orbitrap at resolving power 50000 (b). Mass spectrum of a mixture of three isobaric species [C19H7N]+, [C20H9]+, [C13H19N302]+ obtained at low resolution (black line) and at resolving power 50000 (grey line) (c). It is noteworthy that at low resolution the three peaks are completely unresolved...

Fig. 9 The FT-Raman spectra of a paracetamol-dicalcium phosphate dihydrate mixture A, spectrum of pure paracetamol B, spectrum of pure dicalcium phosphate dihydrate C, spectrum of a mixture of paracetamol (5% w/w) in dicalcium phosphate dihydrate D, spectrum C minus spectrum B to identify pure paracetamol (compare with A). 

Recording the MALDI spectrum of a mixture of two polymers having different backbones, one finds that MALDI peak intensities reflect in a distorted manner the abundances of the chains and the composition of the blend. In some cases, the distortion is small and thus MALDI is semiquantitative. The main cause is that the ionization efficiency (i.e., the probability of ion production) for the two polymers is not the same. Furthermore, it has been shown that instrumental parameters can affect peak intensities, thus falsifying the composition of the blend. For instance, some authors [5] studied an equimolar mixture of PEG and PMMA, recorded the MALDI spectrum of the mixture and found, on changing instrumental parameters, that the apparent blend composition changed from 100/0 to 50/50 to 0/100. 

Figure 14.6. Infrared spectra of a KBr pellet of 3% sodium humate (Aldrich) and an NMR spectrum of a mixture of toluene, hexanoic acid, and octanal. The functionalities responsible for the absorption features are labeled. 

There are also a number of powerful NMR experiments that yield detailed information about the structure of pure organic molecules. However, as with other regions of the spectrum (see Figure 14.4), chemical mixtures produce spectra that are combinations of all of the absorption features of all of the components in the mixture. The H NMR spectrum of a mixture of toluene, hexanoic acid, and octanal is shown in Figure 14.6. This spectrum shows the unique absorptions of each of these functional groups and also illustrates that mixtures of compounds give spectra containing the absorption bands of all the components. If an impure sample had such a spectrum, it would not be known... 

Fig. 2.11.30. ESI—FIA—MS(— ) overview spectrum of a mixture of perfluoro derivatives of alkyl phosphonic acid (CnF2n+i-P(0)(OH)2) and alkyl phosphinic acid (CnF2n+i...

The vibrational spectrum of a typical organic molecule is quite rich (with many peaks that are specific to the chemistry and environment of the species) thus, numerous wavelengths may be used to monitor any individual species. Conversely, using the entire spectrum of a mixture and using chemometric algorithms are useful for the simultaneous determination of several components. 

Similarly, the spectrum of a mixture of Fe(tpps)H20 and Fe(tpps)(OH) can be measured by rapid scan/stopped-flow at various pH s within a few milliseconds after generation (Fig. 3.9). In this short time, dimerization is unimportant so that the spectrum of Fe(tpps)OH can be measured and the pAi of Fe(tpps)H20 estimated. 

Although the kinetics of imidazole exchange between NP2 and its low-spin imidazole adduct are very slow and no chemical exchange cross peaks in the NOESY/EXSY spectrum of a mixture of the high-spin and low-spin forms of NP2 are observed, the V-methylimidazole complex... 

A 400 MHz NMR spectrum of a mixture of common organic solvents consisting of... 

A 100 MHz NMR spectrum of a mixture of ethanol (C2H6O) 5 18.3 (CH3), 5 57.8 (CH2) and bromoethane (C2HsBr) 5 19.5 (CH3) and 6 27.9 (CH2) in CDCI3 solution is given below. The spectrum was recorded with a long relaxation delay (300 seconds) between acquisitions and with the NOE suppressed. Estimate the relative proportions (mole %) of the 2 components from the peak intensities in the spectrum. 

The NMR spectrum of a mixture of 1-iodobutane and 1-butanol recorded at 298K in CDCI3 solution is given below. There is some overlap between the spectra of the components of the mixture. The TOCSY spectrum and the COSY spectrum are given on the facing page. Use the TOCSY and COSY spectra to determine the chemical shifts of all of the protons in 1-butanol and 1-iodobutane. 

Fig. 2. (a) Raw 300 MHz proton spectrum of a mixture of acetone and ethanol in deuteri-ochloroform (b) after reference deconvolution using the acetone signal as reference and an ideal lineshape of a 1 Hz wide Lorentzian and (c) after reference deconvolution with an ideal lineshape characterized by a negative Lorentzian width of 0.1 Hz and a Gaussian width of 0.4 Hz. The 0.1 Hz Lorentzian term represents the approximate difference in natural linewidth between the ethanol and acetone signals, and is responsible for the wings on... 

Figure 3 NMR spectrum of a mixture containing -90% of trans-isomex of ester.

The infrared spectrum (especially the near-infrared) has assumed great importance in chemical and biological research because of the highly specific absorption of chemical compounds at these wavelengths. The infrared absorption of a given organic compound may be used to characterize that particular compound. The infrared spectrum of a mixture of several compounds among which there is no interaction, does not lie between the spectra of the individual compounds, but consists of a direct superposition of the spectra of the individual compounds... 

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