Liquid chromatography-NMR spectroscopy

The molecular structure of thiophene has also been determined by liquid crystal LC (liquid chromatography) NMR spectroscopy <1984MP779, 1988MCL267> as well as ED and rotational spectroscopy. 

RM Holt, MJ Newman, FS Pullen, DS Richards, AG Swanson. High-performance liquid chromatography/NMR spectroscopy/mass spectrometry further advances in hyphenated technology. J Mass spectrom 32 64-70, 1997. 

Czerwenka, C., Zhang, M. M., Kaehlig, H., Maier, N. M., Lipkowitz, K. B., Lindner,W. Chiral Recognition of Peptide Enantiomers by Cinchona Alkaloid Derived Chiral Selectors Mechanistic Investigations by Liquid Chromatography, NMR Spectroscopy, and Molecular Modeling, J. Org. Chem., 2003, 68, 8315-8327. 

C. Alvarez-Lorenzo, R. A. Lorenzo-Ferreira, J. L. Gomez-Amoza, R. Martinez-Pacheco, C. Souto, and A. Concheiro, A comparison of gas-liquid chromatography, NMR spectroscopy and Raman spectroscopy for determination of the substituent content of general nonionic cellulose ethers, J. Pharmaceut. Biomed. Anal, 20 (1999) 373-383. 

Czerwenka C, Zhang MM, Kahlig H, Maier NM, Lipkowitz KB, Lindner W. Chiral recognition of peptide enantiomers by cinchona alkaloid derived chiral selectors mechanistic investigations by liquid chromatography, NMR spectroscopy, and molecular modeling. J. Org. Chem. 2003 68 8315-8327. 

An understanding of the recognition of chirality at a molecular level has become of interest in many fields of chemistry and biology. In the past decade, many attempts to clarify the mechanism of chiral recognition on CSPs for liquid chromatography have been made by means of chromatography, NMR spectroscopy,199 202 X-ray analysis, and computational methods.203 - 206 The successful studies have been mostly carried out for the small-molecule CSPs, especially cyclodextrin-based CSPs and Pirkle-type (brush-type) CSPs. In contrast, only a few mechanistic studies on chiral discrimination at the molecular... 

In the present chapter, various tools such as thin-layer chromatography, high performance liquid chromatography, mass spectroscopy, and NMR used in analysis of flavonoids are discussed. In addition, the relevance and application of such tools in the analysis of flavanones, with emphasis on citrus flavanones, is discussed. 

Tremendous advances have been made in the past few decades in both the range and sensitivity of the analytical methods now available. For the purpose of solubility measurement, solution compositions can be measured by any eonvenient analytical technique, among which may be listed liquid chromatography (HPLQ, spectroscopy (UV, IR, NMR and mass), differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermogravimetric analysis (TGA), refractometry, polarimetry, and most recently capillary electrophoresis (Altria, 2000). 

There are quite a few variations of 2D NMR experiments in which properties such as retention time (in liquid chromatography-NMR, LC-NMR), distances (imaging) or diffusion coefficients (diffusion ordered spectroscopy) are the variables along one or more axes in the spectra. 

The modern electronic industry has played a very important role in the development of instrumentation based on physical-analytical methods As a result, a rapid boom in the fields of infrared, nuclear magnetic resonance (NMR), Raman, and mass spectroscopy and vapor-phase (or gas-liquid) chromatography has been observed. Instruments for these methods have become indispensable tools in the analytical treatment of fluonnated mixtures, complexes, and compounds The detailed applications of the instrumentation are covered later in this chapter. 

Very little in the way of advances has occurred since 1971 in the applications of ultraviolet or infrared spectroscopy to the analysis of fluonnated organic compounds Therefore, only gas-liquid chromatography, liquid chromatography, mass spectrometry, and electron scattering for chemical analysis (ESCA) are discussed The application of nuclear magnetic resonance (NMR) spectroscopy to the analysis of fluonnated organic compounds is the subject of another section of this chapter... 

In this context it is important to note that the detection of this land of alkali cation impurity in ionic liquids is not easy with traditional methods for reaction monitoring in ionic liquid synthesis (such as conventional NMR spectroscopy). More specialized procedures are required to quantify the amount of alkali ions in the ionic liquid or the quantitative ratio of organic cation to anion. Quantitative ion chromatography is probably the most powerful tool for this kind of quality analysis. 

Using IR spectroscopy and NMR, one can analyze the chemical structure of PA. The molecular weight and molecular weight distribution can be analyzed by endgroup analysis, viscometry, and high-pressure liquid chromatography (HPLC). The crystalline order can be analyzed by WAXS, small-angle X-ray spectroscopy... 

Although saponification was found to be unnecessary for the separation and quantification of carotenoids from leafy vegetables by high performance liquid chromatography (HPLC) or open column chromatography (OCC), saponification is usually employed to clean the extract when subsequent purification steps are required such as for nuclear magnetic resonance (NMR) spectroscopy and production of standards from natural sources. 

Because carotenoids are light- and oxygen-sensitive, a closed-loop hyphenated technique such as the on-line coupling of high performance liquid chromatography (HPLC) together with nuclear magnetic resonance (NMR) spectroscopy can be used for the artifact-free structural determination of the different isomers. 

In the case of heterogeneous polymers the experimental methods need to be refined. In order to analyze those polymers it is necessary to determine a set of functions / (M), which describe the distribution for each kind of heterogeneity i This could be the mass distributions of the blocks in a diblock copolymer. The standard SEC methods fail here and one needs to refine the method, e.g., by performing liquid chromatography at the critical point of adsorption [59] or combine SEC with methods, which are, for instance, sensitive to the chemical structure, e.g., high-pressure liquid chromatography (HPLC), infrared (IR), or nuclear magnetic resonance spectroscopy (NMR) [57],... 

Spiroaziridinium compounds have also been synthesized under photochemical conditions. For example, the photolysis of piperidine 83 in acetonitrile resulted in 3-azoniaspirooctane 85 (Equation 19) <1997JOC6903>. Its presence was detected by H NMR spectroscopy and mass spectrometry. This azoniaspiro species was thought to be transient and went on to form N-substituted piperidines which were qualitatively identified by gas liquid chromatography (GLC). 

Liquid and paper chromatographies as well as mass spectrometry (MS) are used for the identification and analysis of hydroperoxides [60]. Nuclear magnetic resonance (NMR) spectroscopy is used for identification of diacyl peroxides. 

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