Nuclear magnetic resonance pulse

Hahn, E. L. Pulsed Nuclear Magnetic Resonance in Solids, in, Faraday Symposia of the Chemical Society, 13, 8 (1978)... 

It is an unfortunate fact that several preexisting theories have tried to explain complicated mechanical phenomena of CB-reinforced rubbery materials but they have not been so successful." " However, a recent report might have a capability of explaining them collectively," when the author accepted the existence of the component whose molecular mobility is different from that of matrix mbber component in addition to the existence of well-known bound rubber component. The report described that this new component might be the most important factor to determine the reinforcement. These mbber components have been verified by spin-spin relaxation time 2 by pulsed nuclear magnetic resonance (NMR) technique, ° while the information obtained by NMR is qualitative and averaged over the sample and, therefore, lacking in the spatial... 

Schmidt, S.J. 1991. Determination of moisture content by pulsed nuclear magnetic resonance spectroscopy. In Water Relationships in Foods (H. Levine and L. Slade, eds), pp. 599-613. Plenum Press, New York. 

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. 

International Standard Organization (ISO) 10565. 1999. Oilseeds-Simultaneous Determination of Oil and Moisture Contents - Method Using Pulsed Nuclear Magnetic Resonance Spectrometry. International Organization for Standardization, Geneva. 

Rubel, G. 1994. Simultaneous determination of oil and water contents in different oilseeds by pulsed nuclear magnetic resonance. JAOCS 71 1057-1062. 

Pulsed nuclear magnetic resonance spectrometer (NMR), >20 MHz, with maximum dead time plus pulse width of 10 p.sec (e.g., Bruker Canada Minispec Oxford Instruments Analytical QP20+)... 

An assessment of emulsion stability involves the determination of the time variation of some emulsion property such as those described in the physical characteristics section above. The classical methods are well described in Ref. [9]. Some newer approaches include the use of pulsed nuclear magnetic resonance or differential scanning calorimetry [294]. 

Pulsed nuclear magnetic resonance (pNMR) has become the preferred method for measuring the percentage of solid fat in a partly solidified fat sample in most parts of the world because of its speed, precision and utility (Kaylegian and Lindsay, 1994). In contrast to dilatometry, pNMR measures the true solid fat content (SFC) rather than an index of this. 

Solid Fat Content of Fats and Oils by NMR (SFC) (Cd 16-81) estimates the percentage of solids in a semi-solid fat on the basis of the pulsed nuclear magnetic resonance (NMR) signal of hydrogen in the liquid fraction. The method is used in the palm oil industry and widely throughout the world. 

List, G. R., Steidley, K. R., Palmquist, D., and Adlof, R. O., Solid fat index vs. solid fat content A comparison of dilatometry and pulsed nuclear magnetic resonance for solids in hydrogenated soybean oil, in Crystallization and Solidification Properties of Lipids, N. Widlak, R. Hartel, and S. Narine (Eds.), pp. 146-152, AOCS, Champaign, IL, 2001. 

If the fat is cooled to some point below the melting point of the highest melting component and allowed to fully equilibrate (crystalhze to the maximum extent in the most stable polymorph), there will be some ratio of sohd to liquid fat dependent on the nature of the TAG mixture in the natural fat. This solid fat content (SFC) is often measured by a pulsed nuclear magnetic resonance (NMR) technique. A plot of the maximum amount of fat crystallized (SFC) at sequentially higher temperatures... 

Solid Fat Content Many methods for measuring SFC have been developed. These include dilatometry, calorimetry, and pulsed nuclear magnetic resonance (pNMR). Dilatometry and calorimetry use measurements of volume or heat content ratios between the completely liquid and the completely solid states (42). Dilatometry and calorimetry methods are time consuming and tend to be applicable only when the SFC is less than 50% (42). Therefore, pNMR has become the most commonly used method for SFC determination. 

The results of thermorheographic experiments presented in Table 7 show very high correlation with the pulsed NMR data in Table 2. Thus, Malaysian cocoa butter crystallizes quickly, and Brazilian is the slowest crystallizing, which correlates with the hardness of these cocoa butters as measured by pulsed nuclear magnetic resonance technology. 

The dilatometric method is time-consuming and subject to the bias introduced by the convention described. More recently pulsed Nuclear Magnetic Resonance (pNMR) has been used to measure the relative amounts of liquid and solid fat in a sample, based upon the difference in rates of relaxation of protons in the two phases after the sample has been pulsed (AOCS Method Cd 16-81). With proper calibration this gives a direct determination of the percentage of solid fat, and the results are termed sohd fat content (SFC). The analysis takes less time than dilato-metry, but the equipment is more expensive. 

Determination of crystallization rate and sohd fat index can be done conveniently using pulsed nuclear magnetic resonance (NMR) techniques (91). 

Fig. 2. Cooling curves for samples in pulsed nuclear magnetic resonance (pNMR), tur-bidimetric, light-scattering, and image analysis experiments.

Solid Fat Index vs. Solid Fat Content A Comparison of Dilatometry and Pulsed Nuclear Magnetic Resonance for Solids in Hydrogenated Soybean Oil... 

B. Determination of Water Structure by Pulsed Nuclear Magnetic Resonance (NMR) Technique... 

M. Hohwy and N. C. Nielsen, Elimination of high order terms in multiple pulse nuclear magnetic resonance specti oscopy Application to homonuclear decoupling in solids. J. Chem. Phys., 1997, 106. 7571-7586. 

A direct analogy can be drawn with the spin echoes formed in the more widely used pulsed nuclear magnetic resonance techniques. 

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