Factors involved in the acquisition and processing of data in pulse Fourier transform NMR are re-examined and results presented graphically. Included in the discussion are the effects on signal/noise of data acquisition time and exponential filtering, the characteristics of analog filters, and the use of quadrature phase detection. Particular attention is given to the choice of optimum pulse repetition time and magnetization flip angle. The effects of zero-filling on signal/noise, resolution, and lineshape are analyzed.Pulse and Fourier transform methods have been widely adopted in NMR, particularly as a means for enhancing signal-to-noise (S/N) through coherent time averaging; and equipment for carrying out pulse FT studies has become standard in many laboratories. The chemist approaching pulse FT studies for the first time, however, often encounters a rather bewildering array of parameters that must be selected for each experiment. On the basis of intuition, advice from colleagues, and ultimately experience, he normally arrives at reasonable sets of conditions for carrying out different types of experiments. Of course, the parameters needed for such studies are subject to mathematical analysis; indeed, a number
The pulsed NMR technique for rapid and nondestructive determination of oil in oilseeds has been developed. The effects of spin‐lattice relaxation time, spin‐spin relaxation time, seed moisture, angular position of the seeds, sample tube thickness, and sample height upon the magnitude and reproducibility of the NMR signal were studied. Based upon these studies, various parameters for seed oil analysis have been fixed. The oil content of Brassica, peanut, and sunflower seeds was determined. The reproducibility of the measurement is ± 1 %. The technique was tested by measuring the oil content of the same seeds by the cold percolation method (CCl4 extraction). It was further tested by determining the oil content of 60 Brassica seed samples independently at three laboratories. The results of these tests are given.
Proton spin-spin relaxation times (T 2 ) of peel (albedo and flavedo) and juice sacs (flesh segments) of navel oranges were measured at 10 MHz using a Bruker Minispec PC 110 NMR spectrometer. The oranges were subjected to chilling (5 • C) and freezing (−7 • C) temperatures for 20 h and warmed to room temperature before peeling for T 2 measurements. The exposure to chilling or freezing temperature did not affect the T 2 values of peel, but freezing caused an appreciable decrease (∼15%) in the T 2 values of flesh segments of the varieties of navel oranges studied. When the peel was exposed to −20 • C, the T 2 showed a drastic reduction suggesting that the peel did not freeze at −7 • C. The possible cause of reduction in the T 2 values when exposed to freezing temperature may be damage to the juice sac membrane and leakage of juice out of the sac. The difference in the T 2 values between juice sacs of freeze-affected and normal oranges can potentially be used for detection of freeze-damaged fruits.
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