Analysers using pulsed NMR

Other applications follow the same principle and are based upon the detection of phosphorus or fluorine elements. 

1 Often in tables the values describing a nucleus magnetic moment are represented as lying upon an axis parallel to S, the applied magnetic field. Therefore, if for a proton, = 1.41 x 10 J calculate the constant y for the proton. 

3 In the NMR spectrum from a 200 MHz spectrometer the scale along the abscissa is represented by 1 ppm = cm. 

What is the distance between two signals with a separation of 7 Hz  

If it is known that y H/y C = 3.98, what would happen to the distance calculated above if a C spectrum were to be recorded on the same apparatus  

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Figure 9.28— ll NMR instrument used for routine analyses. Automatic analyser based on pulsed NMR used to quantify water and lipids in food technology. (Reproduced with authorisation of Bruker.)... 

Chapter 6 introduces the product operator formalism for analysing NMR experiments. This approach is quantum mechanical, in contrast to the semi-classical approach taken by the vector model. We will see that the formalism is well adapted to describing pulsed NMR experiments, and that despite its quantum mechanical rigour it retains a relatively intuitive approach. Using product operators we can describe important phenomena such as the evolution of couplings during spin echoes, coherence transfer and the generation of multiple quantum coherences. 

Figure 15.32 Low resolution JT NMR instrument for routine analyses. The analyser operates on the principle of pulsed NMR and is used for quantifying water and fat in numerous food products (model minispec, reproduced courtesy of Bruker).

Over the last three decades, in particular gas chromatographs, electrochemical detectors and gas analysers have found their way to the process environment. Most recently, various analytical techniques that were formerly only used in the laboratory have become suitable for implementation in manufacturing. Examples are UVA IS absorption spectroscopy, near-IR spectroscopy, refractive index measurements and more recently mid-lR spectroscopy, Raman spectroscopy, pulse NMR and mass spectrometry. In particular, the number of spectroscopic applications has increased, sometimes replacing more established measurement methods (like GC or gas analysers). In addition, other traditional laboratory/off-line methods are now moving towards in-process applications e.g. rheometry and XRF). 

The oilseed section uses a three-tiered system in order to ensure accurate results obtained with the pulse-NMR method. First, the checksamples are analysed with every analysis and the rapid method results are compared with the reference method results. Second, throughout the year, samples are randomly taken, analysed by both methods and the results compared. Finally, verification samples are made annually and analysed using both the methods. The results from the 2011 verification... 

The temperature dependent H, H, and chemical shifts of NH3 and ND3 have been calculated.The pressure and temperature dependence of self diffusion in fluid ammonia have been investigated using the NMR pulsed field gradient method. Substituent effects on the P chemical shifts of PX2Y, X, Y = F, OH, NH2, CH3, BH2, BeH, Li, H, have been analysed. The quadrupole spin relaxation of in NNO in collision with various molecules has been determined.chemical shifts and some /( P N) values have been reported for three classes of compounds containing P-N bonds. The relations of P chemical shift with degree of substitution and substituent have been determined for cyclotriphosphazenes. and NMR spectroscopy has... 

The use of a probe molecule to study the properties of micellar medium requires the knowledge of the micellar binding site of the probe molecule, with absolute certainty under a specific condition, which is almost impossible to achieve by any experimental or theoretical technique. Pyrene, a highly hydrophobic water insoluble hydrocarbon molecule, has been used to determine the polarity of micellar medium, but its precise micellar binding site is not known with absolute certainty. For instance, pulsed Fourier transform NMR and chemical shift analyses used to determine the dynamic solubilization site of the pyrene in cationic micellar solutions show that pyrene is solubilized in the interior of the... 

Pulsed nuclear magnetic resonance (NMR) has been used for such analyses due to the speed, repeatability, and nondestructive nature of the measurement. Additionally, the method requires no solvents, an important consideration for environment friendliness. Modern benchtop NMR systems are highly automated and computerized, which allows unskilled personnel to be trained to run the measurements. 

NMR analyses were done on an IBM Instruments NR-300 spectrometer and an Oxford 7 Tesla superconducting narrow-bore magnet. Silicon-29 (Si-29) NMR spectra were recorded at 59.6 MHz and hydrogen (also commonly called proton or H-l) NMR spectra at 300.13 MHz. Spectra were recorded using conventional single-pulse techniques with proton decoupling for Si-29 acquisitions. Si-29 experiments were structured so as to suppress nuclear Overhauser enhancement (NOE). For Si-29 acquisitions, spectral widths were 50 kHz and Fourier transform (FT) sizes were 4K points. For protons, spectral widths were 7.5 kHz and FT sizes were 16K points. Si-29 rf pulse widths were approximately 12 fits and proton rf pulse widths were 8 jj.s. 

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