NMR and Mass Spectrometry

The spectroscopic methods, NMR and mass spectrometry for predicting cetane numbers have been established from correlations of a large number of samples. The NMR of carbon 13 or proton (see Chapter 3) can be employed. In terms of ease of operation, analysis time (15 minutes), accuracy of prediction (1.4 points average deviation from the measured number), it is... 

Both PS-A and PS-B have a tendency to hydrate like panal, and they also form adducts with methylamine. The adducts, PS-A/MA and PS-B/MA, are prepared by incubating PS-A or PS-B in 75 % methanol containing an excess amount of methylamine hydrochloride plus some sodium acetate to neutralize the HC1, at 45°C for 30 min. The adducts can be purified by HPLC on a PRP-1 column (80% acetonitrile containing 0.05% acetic acid). Their chemical structures have been determined by NMR and mass spectrometry as shown in Fig. 9.8 (p. 288). Both adducts are colorless and show an absorption maximum at 218 nm. 

Nuno, M. et al.. Identification of anthocyanin-flavanol pigments in red wines by NMR and mass spectrometry, J. Agric. Food Chem., 50, 2110, 2002. 

Only H NMR, 13C NMR, and mass spectrometry, the three most important spectroscopic methods for the tropane alkaloids, will be treated here. 

A number of minor components present in commercial neomycin have been separated by column chromatography on a carboxylic cation-exchange resin, Amberlite CG-50 99. The components were eluted from the resin with ammonium hydroxide solution. T.L.C. of the eluent fractions showed the presence of two previously unreported impurities which were then isolated on Dowex 1X2 and tentatively identified using NMR and mass spectrometry. 

Modern spectroscopy plays an important role in pharmaceutical analysis. Historically, spectroscopic techniques such as infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS) were used primarily for characterization of drug substances and structure elucidation of synthetic impurities and degradation products. Because of the limitation in specificity (spectral and chemical interference) and sensitivity, spectroscopy alone has assumed a much less important role than chromatographic techniques in quantitative analytical applications. However, spectroscopy offers the significant advantages of simple sample preparation and expeditious operation. 

Recently, the compound 1, 3-deph-enyl-2-methylaminopropane hydrochloride was identified in two different samples of methamphetamine powder. The identification was based on a combination of UV, IR, NMR and mass spectrometry. The presence of this compound in methamphetamine indicates that the clandestine operators were syn-... 

Elemental composition S 25.23%, H 0.79%, N 11.02, 0 62.95%. Nitrosylsulfuric acid may be analysed by IR, NMR and mass spectrometry, as well as by elemental microanalysis. Wet analysis involves hydrolyzing the compound in the presence of excess NaOH and measuring excess base by potentiometric titration. 

Ru(0)(0jR)2 (R=7,8-didehydrocholesteryl acetate and cholesteryl acetate). These esters were isolated from RuO (as RuO /aq. Na(I04)/acetone) and R, and were shown by H and NMR and mass spectrometry to be Rn(VI) diesters similar to those obtained from the alkenes R with OsO. Their isolation, despite the absence of X-ray structural studies, suggests that such diesters could be involved in reactions of RuO, as indeed they are in the corresponding reactions with OsO. In each case a pair of isomeric diesters was formed (Fig. 1.31) [323, 346]. 

Hansen, S.H. et al.. High-performance liquid chromatography on-line coupled to high-field NMR and mass spectrometry for structure elucidation of constituents of Hypericum perforatum L., Anal. Chem., 71, 5235, 1999. 

Electron paramagnetic resonance spectroscopy (EPR) (also called electron spin resonance spectroscopy, ESR) has been scarcely applied in the field of art and art conservation. Some work can be found in which EPR is used as complementary technique to SEM-EDX, NMR, and mass spectrometry (MS) for studying free radicals occurring in polymerization, pyrolytic, oxidative, and other radical degradative processes in artwork, as well as in the characterization of varnishes and oleoresinous media [42]. 

The dimer [ In(NEt2)3 2] was synthesized by reaction of LiNEt2 with InCl. " It was characterized by NMR and mass spectrometry. Oddly, the detailed synthesis and stnicture... 

Catalytic Experiments. Activities were performed in a 1 liter Parr reactor. A typical experiment was performed as follows at a temperature of 100 °C, 100 mg of the catalyst and 1.5 /. wt of (-)-carvone (Aldrich) in n-hexane solution (100 ml) were Introduced in a high pressure Parr reactor equipped with mechanical stirring and automatic temperature control. Before introducing the hydrogen the system was purged 2 or 3 times with Nz> The total hydrogen pressure was 21 atm. The reaction products were analysed by gas chromatography. NMR and Mass Spectrometry and identified as unreacted carvone, carvotanacetone, carvomenthone and three carvomenthol stereoisomers (axial-equatorial, equatorial-equatorial and equatorial-axial). 

Nitroxides (T, general formula R2NO ) have been used extensively to provide evidence for radical mechanisms through their ability to couple with (i.e. trap) reactive carbon-centred radicals (R ) to form alkoxyamines, R—T, e.g. Scheme 10.6. The elusive radical, R, may thus be identified, characterised and quantified through analysis of the stable non-radical alkoxyamine by the usual spectroscopic techniques such as NMR and mass spectrometry. 

Spectroscopic methods like infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), and mass spectrometry (MS) are described in other chapters of this textbook. 

Figure 4 Coenzymes of methanogenesis. F-430, coenzyme M (2-thioethanesulfonate), and coenzyme B (7-thioheptanoyl-threonine-O-phosphate [sometimes abbreviated HS-HTP]). Methyl-reducing factor is a structure proposed on the basis of NMR and mass spectrometry, in which the phosphate group of CoB is linked by a carboxylic-phosphoric anhydride to a UDP disaccharide, uridine 5 -(2-acetamido-2-deoxymannopyranuronosyl)-2-acetamido-2-deoxy-glucopyranosyl-diphosphate [171]. The CoB moiety without it appears to be functionally active in the enzyme reaction.

H, 13C, and 31P nuclear magnetic resonance (NMR), and mass spectrometry play a dominant role in the characterization of C2E2 heterocycles, and carefully investigated spectroscopic parameters are included in the majority of the preparative papers dealing with this chemistry. The general trends can be extracted from earlier reviews . 

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