Liquid chromatography and NMR

The solid complexes were decomposed in aqueous KOH. The recovered amines were analyzed by gas-liquid chromatography and NMR (benzene-TMS). Complex A contained n-HMTP (82.6% pure) its NMR spectrum had two N—CH3 singlets (2/3 ratio) at t 7.79 and 7.85, respectively. Complex B contained N,N -c-PMPP (94.8% pure) its NMR spectrum had three N—CH3 singlets (1 2 2 ratio) at t 7.80, 7.86, and 7.87, respectively. The original 11-component mixture contained 48.8% n-HMTP and 11.4% N,N -c-PMPP. 

In many cases a combination of liquid chromatography and NMR spectroscopy allows an exact quantification of small amounts, even trace amounts (ppm). This method is used to quantify neutral lipids in highly enriched phospholipid mixtures (Fig. 4.5). 

Dissolved in water and extracted with -heptane to remove ethylene glycol dimethacrylate (checked by gas-liquid chromatography and by NMR) and distilled twice under reduced pressure [Strop, Mikes and Kalal J Phys Chem 80 694 1 976]. 

NMR and IR are powerful spectroscopic techniques, which provide additional information about the compositional details of a sample. However, they are often unable to differentiate between a polymer blend A + B and a copolymer consisting of A and B. For such complex polymer compositions a combination of liquid chromatography and spectroscopic methods is helpful. In his recent review Pasch [57] discusses a couple of examples. 

Hyphenated analytical techniques such as LC-MS, which combines liquid chromatography and mass spectrometry, are well-developed laboratory tools that are widely used in the pharmaceutical industry. Eor some compounds, mass spectrometry alone is insufficient for complete structural elucidation of unknown compounds nuclear magnetic resonance spectroscopy (NMR) can help elucidate the structure of these compounds (see Chapter 20). Traditionally, NMR experiments are performed on more or less pure samples, in which the signals of a single component dominate. Therefore, the structural analysis of individual components of complex mixtures is normally time-consuming and less cost-effective. The... 

PfO Eight phenolic compounds. .. were... obtained by reversed-phase high-performance liquid chromatography, and their structures were elucidated by NMR spectroscopy and mass spectrometry analyses. (Adapted from Ey et ah, 2006)... 

In the present context correlation means chemically relating a compound of unknown configuration with a compound of known relative configuration. In this section correlation sequences which do not directly affect the chiral units are discussed. Relations of this type, if carefully applied, are unambiguous and do not depend on mechanistic and/or stereochemical assumptions (also see Sections 4.3.4.1.2. and 4.3.4.1.2.1.). In contrast to the constraints in methodology mentioned in Section 4.3.4.1.2., comparison with the reference sample can be performed by any suitable analytical method, such as gas or liquid chromatography, or NMR spectroscopy. Some examples are ... 

Modern analytical techniques have been developed for complete characterization and evaluation of a wide variety of sulfonic acids and sulfonates. Titration is the most straightforward method of evaluating sulfonic acids. Spectroscopic methods for sulfonic acid analysis include ultraviolet spectroscopy, infrared spectroscopy, and lH and l3C nmr spectroscopy. Modem separation techniques of sulfonates include liquid chromatography and ion chromatography. See also Chromatography. 

The coupling of LC (liquid chromatography) with NMR (nuclear magnetic resonance) spectroscopy can be considered now to be a standard analytical technique. Today, even more complex systems, which also include mass spectrometry (MS), are used. The question arises as to how such systems are handled efficiently with an increasing cost and a decreasing availability of skilled personal. LC-NMR and LC-NMR/MS combine the well-established techniques of LC, NMR and MS. For each of those techniques, various automation procedures and software packages are available and used in analytical laboratories. However, due to the necessary interfacing of such techniques, completely new demands occur and additional problems have to overcome. 

The chromatography and NMR systems perform completely independent by of each other. The only necessary link is the liquid connection between the column and the NMR detection cell. The NMR spectrometer can act as a detector for the chromatographic system, so that even a conventional LC detector in the chromatographic system is not necessary. 

Undoubtedly, NMR is the most informative method for characterization of organic compounds. However, it has limited application in combinatorial chemistry due to several factors. NMR is a relatively insensitive and slow method, requires homogeneous samples, and consumes quite expensive deuterated solvents. Here we will discuss the most recent developments of this method that overcome the major limitations and make NMR one of the promising techniques in combinatorial chemistry. It relates to the application of NMR, not only for analyzing compounds attached to polymer support and for monitoring reactions on a solid phase, but also as a detector for liquid chromatography (LC/NMR). For the most recent review, see [10]. 

Analytical Procedure. The structures of silicate anions in the solutions and solids have been examined with the trimethylsilylation technique combined with gas-liquid chromatography and "Si NMR. The molecular weight distribution was measured by applying gel permeation chromatography to the trimethylsilylated derivatives. 

The product from Step 2 (2.3 mmol) was dissolved in 10 ml N,N-dimethylformamide, NaH (340 mg, 50% suspension) added, stirred 15 minutes, and 4-methoxy-6-methyl-2-methylsulfonylpyrimidine (526 mg) added. The reaction stirred 3 hours at ambient temperature, water was then added, and the mixture extracted with diethyl ether. The aqueous phase was acidified with 1 M HCl, extracted with diethyl ether, dried, and concentrated. The residue was purified by liquid chromatography, and the product isolated in 52% yield. H-NMR and MS data supplied. 

J. M. Characterization of a thermally induced irreversible conformational transition of amylose tris(3,5-dimethylphenyl-carbamate) chiral stationary phase in enantioseparation of dihydropyrimidinone acid by quasi-equilibrated liquid chromatography and solid-state NMR, Anal. Chem., 2003, 75, 5877-5885. 

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