Nuclear magnetic resonance sample tube

Human bile sample (500 pi) is placed into a 5-mm nuclear magnetic resonance (NMR) tube. The pH of the solution is adjusted at 6 0.5 using HC1. This range of pH is the optimal value to avoid lowering of the amide integral due to the chemical exchange (alkaline pH) or to precipitation of bile salts (acidic pH). 

Solid Fat Content. Similar method as described previously (3) was used. In this method, the samples were melted in nuclear magnetic resonance (NMR) tubes therefore it was essentially the lUPAC method 11.B.6 (4). To measure changes in solid fat content during storage, samples were not melted but instead, they were transferred to the NMR tubes using a rod and a piston. Measurements were taken directly at ambient temperature (23°C) at weeks 4, 8, and 12 of storage. 

All NMR spectra were recorded on a Varian A-60 spectrometer at room temperature by Nuclear Magnetic Resonance Specialties, Inc., New Kensington, Pa. Benzene soluble fractions were recorded in deuterated chloroform solution (CDCls) while dimethyl sulfoxide-dc (DMSO-dr.) was the solvent employed for other fractions. (Deuterated chloroform with enrichment of 99.8% was purchased from Bio-Rad Laboratories and dimethyl sulfoxide-dr, with enrichment of 99.6% from Merck, Sharp, and Dohme of Canada.) The internal standard used with the CDCla solutions was tetramethvlsilane and hexamethyl-disiloxane (chemical shift 7 c.p.s.) with DMSO-d . Prior to preparation for NMR recording, the samples were thoroughly dried in a vacuum at 110°C. The NMR tubes were sealed to minimize the absorption of atmospheric moisture. The chemical shifts given in c.p.s. are referred to tetramethylsilane. 

In addition, this procedure was quite tedious and time consuming. Therefore, in recent years when physical methods for assaying molecules in mixtures—methods such as nuclear magnetic resonance (NMR), gas chromatography, and others—have become available, a renaissance in the study of redistribution reactions has taken place. These methods allowed a rapid, quantitative, and precise determination of all of the reaction products present in a mixture. Also, equilibrium reactions could be carried out in much smaller sample sizes, thus permitting the study of exotic, hard-to-obtain compounds. Redistribution reactions—the kinetics as well as the equilibria—can now be measured directly in sealed NMR tubes. Furthermore, the relatively recent widespread availability to chemists of high-speed computers, in addition to these modern analytical tools, has facilitated the use of the appropriate mathematics even when highly complicated. 

It is a common practice to seal a sample in a closed glass tube for storage or for further study by means of EPR (electron paramagnetic resonance) or NMR (nuclear magnetic resonance). Although it is not difficult to tip off a sample, if done poorly, the NMR tube will spin very badly. If done badly, the sample may be destroyed along with hours, weeks, or months of work. 

Transfer the ether to a tared reaction tube and evaporate the solvent to leave crude triphenylmethane. Remove a sample for melting point determination and recrystallize the residue from an appropriate solvent, determined by experimentation. Prove to yourself that the compound isolated is indeed triphenylmethane. Obtain an infrared spectrum and a nuclear magnetic resonance spectrum. 

Fig. 2.3. Outline of a conventional one-dimensional nuclear magnetic resonance experiment, (a) A sample in a nuclear magnetic resonance tube (b) a magnet into which the sample is placed (c) the outline of a simple experiment (d) the free induction decay (FID), which is Fourier-transformed to a spectrum (e).

A) Schematic diagram of a simple nuclear magnetic resonance (NMR) spectrometer. The sample is placed in solution in a long, thin tube and spins in a probe sitting in a magnetic and surrounded by radio-frequency (RF) coils B) proton NMR spectrum of ethanol (QH O) with tetramethylsilane (TMS) added as internal standard. On the 8-scale of chemical shifts,... 

Small Scale Reactions When the reaction mixture occupies a few milliliters, the reaction can be carried out in a tapered centrifuge tube to facilitate recovery of a solid or liquid product after removal of solvent. On a still smaller scale, sections of small glass tubing sealed at one end are often used, and the course of the reaction may be followed by a spectral technique. For example, if an exploratory reaction can be conveniently followed by nuclear magnetic resonance (NMR) spectroscopy (Sec. 3.3.1), the reaction can be performed in an NMR sample tube and its progress checked periodically by NMR. 

C Nuclear Magnetic Resonance Spectroscopy. Carbon-13 NMR spectra were obtained at 22.5 MHz on a JEOL FX-90Q Spectrometer using a 5000 Hz window. Approximately 30,000 transients were accumulated for each sample consisting of 0.1 to 0.2 grams of copolymer in 2 mL of D2O in 10 mm tubes. 

Pyrex nuclear magnetic resonance (NMR) sample tubes (0.4 mm -w all thickness) are suitable for containing the sample to be irradiated. These can be purchased from Kontes Glass Co. in several different grades. The tubes can be stoppered with rubber septa during experiments requiring anaerobic conditions. 

The fat in margarines and shortenings consists of liquid and solid components. The solids consist of fat crystals that incorporate the liquid oil in a crystal network. The amount of crystals present or, in other words, the amount of solids, the crystal size, and the strength of the network are important in determining the texture. The solid fat content (SFC) is determined by either nuclear magnetic resonance spectroscopy (NMR) or dilatometry. The dilatometry method is old and cumbersome but is still in use. NMR can also be used to estimate the SFC in the finished product by transferring a tube of the finished product into the NMR tube by means of a stainless steel open probe [3]. The manner in which the solid fat content is determined is very important. There are two official methods, the American Oil Chemists Society (AOCS) method, which is used in the Americas, and the lUPAC method, which is used mainly in the rest of the world. In the AOCS method the fat is cooled at 0°C for 15 min, tempered at 26.1°C for 30 min, and cooled again to OX for 15 min, and then measurements are taken at the various temperatures after the samples have been left for 30 min at those temperatures. In the lUPAC method samples are not tempered instead, the fat is cooled at 0°C for 30 min and then measurements are taken as in the AOCS method. There is quite a difference in the SFC values obtained at temperatures... 

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