Proton nuclear magnetic resonance spectrometers

Proton nuclear magnetic resonance spectra of 15-20% solutions of polymers in CC14 were obtained with Varian T-60 or HR-300 spectrometers. Chemical shifts are reported... 

Another method (ASTM D-4808) covers the determination of the hydrogen content of petroleum products, including vacuum residua, using a continuous-wave, low-resolution nuclear magnetic resonance spectrometer. Again, sample solubility is a criterion that will not apply to coal but will apply to coal extracts. More recent work has shown that proton magnetic resonance can be applied to solid samples and has opened a new era in coal analysis by this technique (de la Rosa et al., 1993 Jurkiewicz et al 1993). 

Although the determination of HA or HB selectivity is relatively straightforward the techniques for isolation of pyridine nucleotides from the reaction mixtures are tedious and time consuming. Two more recent techniques use either proton magnetic resonance or electron impact and field desorption mass spectrometry. The technique of Kaplan and colleagues requires a 220 MHz nuclear magnetic resonance spectrometer interfaced with a Fourier transform system [104], It allows the elimination of extensive purification of the pyridine nucleotide, is able to monitor the precise oxidoreduction site at position 4, can be used with crude extracts, and can be scaled down to /nmole quantities of coenzyme. The method can distinguish between [4-2H]NAD+ (no resonance at 8.95 8) and NAD+ (resonance at 8.95—which is preferred) or between [4A-2H]NADH (resonance at 2.67 8, 75 4B = 3.8 Hz) and [4B-2H]NADH (resonance at 2.77 8, J5 4A = 3.1 Hz). 

Purification and characterization The crude NHS esters were recrystallized to a constant melting from either chloroform-hexane or chloroform-acetone mixed solvents. Product purity was confirmed by proton nuclear magnetic resonance using a GE QE 300 spectrometer. 

The proton nuclear magnetic resonance spectrum of lomefloxacin mesylate obtained in D2O at 25° C is given in Figure 5 (9). The spectrum was obtained on a Bruker AM-500 NMR Spectrometer operating at 500.13 MHz and was referenced to external TSP [3-(trimethylsilyl)propionic-2,2,3,3-d4 acid]. The chemical shifts and spectral assignments are provided in Table 2 (9,10). The effect of increasing concentrations of Al3+ on the... 

The 300-MHz proton nuclear magnetic resonance spectrum of tolnaftate was obtained on a Bruker AM 300 NMR spectrometer and is shown in Figure 2. The spectrum was recorded... 

Instruments Batch experiments for obtaining CL profiles were performed using a Microtec NITI-ON Lumicounter 2500 (Chiba, Japan). Proton nuclear magnetic resonance ( H-NMR) spectra were obtained on a JEOL JNM-EX270 spectrometer (Tokyo, Japan) with tetramethylsilane as an internal standard. Mass spectra (FAB-MS) were measured on a JEOL JMS-LXIOOO (Tokyo, Japan) with w-nitrobenzyl alcohol as a matrix. 

The liquid products were quantified by GC-FID (gas chromatograph with flame ionisation detector) and characterised with GC-MS (gas chromatograph with mass spectrometer). The aromatics content was monitored on-line with a near infrared spectrometer that was calibrated by proton nuclear magnetic resonance spectrometry. 

Thus protons in a field of one tesla should absorb energy at 42.6 MHz. A popular design frequency for a nuclear magnetic resonance spectrometer is 60 MHz for a proton to absorb at this frequency requires that B = 1.41 tesla. 

Proton nuclear magnetic resonance (NMR) spectra (60 MHz) were recorded on a Varian EM-360L spectrometer. Carbon-13 (25 MHz) and 100 MHz proton NMR spectra were obtained on a Jeol JNM-FX-100 instrument. 1-H NMR (300 MHz) and 75 MHz 13-C spectra were determined on a Nicolet NT-300 instrument. Chemical shifts are given in parts per million (ppm) on a 6 scale downfield from tetramethylsilane (TMS) or solvent peaks [(dimethyl sulfoxide-d ) ... 

The sample was prepared by the neat technique on KBr plate or by the KBr pellet technique. The proton nuclear magnetic resonance (NMR) spectra were obtained at 60 MHz with a JEOL-PMX 60 spectrometer. Deuterochloro-form and carbon tetrachloride were used as solvents with tetramethyl-silane (TMS) as the internal reference standard. The X-ray diffraction patterns of the powdered samples were taken in the region of 5 to 3 o by a Rigakudenki Model DC-8 X-ray diffractometer, using Ni-filtered Cu-Ka radiation. 

In proton nuclear magnetic resonance spectrometry, the levels are separated by about AE = 6.6 x 10 J. Therefore, at room temperature Ny/Nj, = 0.99998, which indicates that the levels are very nearly equally populated. An NMR spectrometer will need a very sensitive detection system, and precautions must be taken to prevent the population of the upper level becoming greater than that of the lower. 

Proton nuclear magnetic resonance spectra are recorded on a Bruker WB UM 360 or a Bruker SP200 spectrometer with tetramethylsilane as internal standard the signals are described as s, singulet d, doublet t, triplet q, quartet, m, multiplet br, broad Ar-H, aromatique. 

Proton and carbon-13 nuclear magnetic resonance (NMR) spectra were recorded on a IBM Instruments 270 MHz NMR Spectrometer on 6-8 weight percent solutions in deuterated chloroform. Ultraviolet spectra were recorded on an IBM Ultraviolet Spectropluitometer Model 9420 using chloroform solutions containing 2 x 10-5 g/ml of the copolymers. 

If one wishes to obtain a fluorine NMR spectrum, one must of course first have access to a spectrometer with a probe that will allow observation of fluorine nuclei. Fortunately, most modern high field NMR spectrometers that are available in industrial and academic research laboratories today have this capability. Probably the most common NMR spectrometers in use today for taking routine NMR spectra are 300 MHz instruments, which measure proton spectra at 300 MHz, carbon spectra at 75.5 MHz and fluorine spectra at 282 MHz. Before obtaining and attempting to interpret fluorine NMR spectra, it would be advisable to become familiar with some of the fundamental concepts related to fluorine chemical shifts and spin-spin coupling constants that are presented in this book. There is also a very nice introduction to fluorine NMR by W. S. and M. L. Brey in the Encyclopedia of Nuclear Magnetic Resonance.1... 

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