Nuclear magnetic resonance qualitative analysis

The analysis of lipids is dominated by chromatographic methods such as gas chromatography (GC) and high-pressure liquid chromatography (HPLC) and some other physical methods such as thermo analysis. Nuclear magnetic resonance (NMR) spectroscopy covers only a small part of lipid analysis. In most cases it is used for qualitative analysis such as structure elucidation of lipids. Unlike the other methods NMR spectroscopy is coupled with computer technology, and its development is as fast as that of computer software and hardware. In 1991 the Nobel Prize for chemistry was given to Professor Ernst for the development of Fourier Transform NMR spectroscopy (FT-NMR). The capabilities of these methods even for the elucidation of the three-dimensional structures of small molecules up to macromolecules are impressive. 

Both infrared and Raman spectroscopy are extremely powerful analytical techniques for both qualitative and quantitative analysis. However, neither technique should be used in isolation, since other analytical methods may yield important complementary and/or confirmatory information regarding the sample. Even simple chemical tests and elemental analysis should not be overlooked and techniques such as chromatography, thermal analysis, nuclear magnetic resonance, atomic absorption spectroscopy, mass spectroscopy, ultraviolet and visible spectroscopy, etc., may all result in useful, corroborative, additional information being obtained. 

Nuclear magnetic resonance (NMR) spectrometry has seldom been used as a quantitative analytical method but can have some practical importance in the characterization of surfactants [296-298]. 13C-NMR spectrometry has been used for the qualitative and also quantitative analysis of dodecyl, tetradecyl, and cetyl sulfates [299]. H- and, 3C-NMR spectra of sodium dodecyl sulfate are given by Mazumdar [300]. 

Many techniques for the analysis of anthocyanins have been used for almost a century and are still of importance, along with considerable advances in technologies such as mass spectroscopy (MS) and nuclear magnetic resonance (NMR). This section summarizes the analytical procedures for quantitative and qualitative analyses of anthocyanins, including classical and modem techniques. 

Many methods are currently available for the qualitative analysis of anthocyanins including hydrolysis procedures," evaluation of spectral characteristics, mass spectroscopy (MS), " nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectroscopy. - Frequently a multi-step procedure will be used for... 

Gerstein BC, Dybowski CR (1985) Transient techniques in NMR of solids an introduction to theory and practice Academic Press, Orlando, 295 pp Hatcher PG (1987) Chemical structural studies of natural lignin by dipolar dephased solid-state nC nuclear magnetic resonance Org Geochem 11 31-39 Hatfield GR, Maciel GE, Erbatur O, Erbatur G (1987) Qualitative and quantitative analysis of solid lignin samples by carbon-13 nuclear magnetic resonance spectrometry Anal Chem 59 172-179... 

G. P. Moloney, D. J. Craik, and M. N. Iskander, Qualitative analysis of the stability of the oxazine ring of various benzoxazine and pyridooxazine derivatives with proton nuclear magnetic resonance spectroscopy, J. Pharm. Sci. 81, 692-697(1992). 

Instmmental methods of analysis provide information about the specific composition and purity of the amines. Qualitative information about the identity of the product (functional groups present) and quantitative analysis (amount of various components such as nitrile, amide, acid, and determination of unsaturation) can be obtained by infrared analysis. Gas chromatography (gc), with a liquid phase of either Apiezon grease or Carbowax, and high performance Hquid chromatography (hplc), using silica columns and solvent systems such as isooctane, methyl tert-huty ether, tetrahydrofiiran, and methanol, are used for quantitative analysis of fatty amine mixtures. Nuclear magnetic resonance spectroscopy (nmr), both proton ( H) and carbon-13 ( C), which can be used for qualitative and quantitative analysis, is an important method used to analyze fatty amines (8,81). 

Qualitative Analysis involves determining the nature of a pure unknown compound or the compounds present in a mixture. Quantitative Analysis involves measuring the proportions of known components in a mixture, and the chemical techniques include volumetric analysis and gravimetric analysis. Instrumental Analysis include several physical techniques including spectroscopic techniques, mass spectrometry, polarography, nuclear magnetic resonance, etc. 

A number of methods are used in classical analysis to perform these tasks. Qualitative as well as quantitative analysis of mixtures can be achieved by chromatographic methods such as gas chromatography (GC) and liquid chromatography (LC). Chemical sensors or biosensors can also be employed for selectively quantifying a compound in a mixture. However, such analysers have only been developed for a very limited number of analytes. Identification of pure compounds can be achieved by nuclear magnetic resonance (NMR) measurements, by mass spectrometry (MS), infrared spectroscopy (IR), UV/vis spectroscopy or X-ray crystallography, to name a few. 

Nuclear Magnetic Resonance Spectroscopy. Like IR spectroscopy, NMR spectroscopy requires little sample preparation, and provides extremely detailed information on the composition of many resins. The only limitation is that the sample must be soluble in a deuterated solvent (e.g., deuterated chloroform, tetrahydro-furan, dimethylformamide). Commercial pulse Fourier transform NMR spectrometers with superconducting magnets (field strength 4-14 Tesla) allow routine measurement of high-resolution H- and C-NMR spectra. Two-dimensional NMR techniques and other multipulse techniques (e.g., distortionless enhancement of polarization transfer, DEPT) can also be used [10.16]. These methods are employed to analyze complicated structures. C-NMR spectroscopy is particularly suitable for the qualitative analysis of individual resins in binders, quantiative evaluations are more readily obtained by H-NMR spectroscopy. Comprehensive information on NMR measurements and the assignment of the resonance lines are given in the literature, e.g., for branched polyesters [10.17], alkyd resins [10.18], polyacrylates [10.19], polyurethane elastomers [10.20], fatty acids [10.21], cycloaliphatic diisocyanates [10.22], and epoxy resins [10.23]. 

Infrared spectroscopy has been extensively used in both qualitative and quantitative pharmaceutical analysis [1-3], This technique is important for the evaluation of the raw materials used in production, the active ingredients and the excipients (the inert ingredients in a drug formulation, e.g. lactose powder, hydroxypropyl cellulose capsules, etc.). Although nuclear magnetic resonance spectroscopy and mass spectrometry are widely used in the pharmaceutical industry for the identification of drug substances, infrared spectroscopy can provide valuable additional structural information, such as the presence of certain functional groups. 

Since conclusions reached in forensic laboratories are used in the criminal justice system, they must leave no room for doubt. Thus, analytical methods must meet strict criteria. They must be extremely selective, reproducible, sufficiently sensitive, and suitable for qualitative and quantitative analysis. It is also highly desirable for the method to call for the minimum number of pretreatment steps and to be applicable to compound mixtures without preliminary separation of their components. Nuclear magnetic resonance (NMR) spectroscopy meets these criteria. It is well... 

If the objective is identification (qualitative analysis), it suffices to compare the spectrum of the analyte with that of a standard, both recorded in the same solvent and at an identical pH. This is not the main application of UV-Vis spectrophotometry as the best results in this context are provided by spectroscopic methods considered more effective for the study of the molecular structure of organic compounds (infrared, nuclear magnetic resonance, mass spectrometry, and X-ray diffraction). However, UV-Vis spectrophotometry is a source of relevant supplementary information that helps in the elucidation of molecular structures of drugs, impurities, metabolites, intermediate compounds of degradation, etc. 

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