TAILIEUCHUNG - Understanding NMR Spectroscopy phần 3

Tính toán góc độ nghiêng, θ, một spin với điều này bù đắp. Đối với phạm vi bình thường của sự thay đổi proton (0 - 10 ppm), là lĩnh vực này đủ mạnh để cung cấp cho những gì có thể được phân loại như là xung cứng 25 kHz? E 3-2 Trong một thí nghiệm để xác định độ dài xung của một nhà điều hành quan sát thấy một tín hiệu | 3-20 The vector model Exercises E3-1 A spectrometer operates with a Larmor frequency of 600 MHz for protons. For a particular set up the RF field strength w1 2n has been determined to be 25 kHz. Suppose that the transmitter is placed at 5 ppm what is the offset in Hz of a peak at 10 ppm Compute the tilt angle d of a spin with this offset. For the normal range of proton shifts 0-10 ppm is this 25 kHz field strong enough to give what could be classed as hard pulses E3-2 In an experiment to determine the pulse length an operator observed a positive signal for pulse widths of 5 and 10 s as the pulse was lengthened further the intensity decreased going through a null at s and then turning negative. Explain what is happening in this experiment and use the data to determine the RF field strength in Hz and the length of a 90 pulse. A further null in the signal was seen at s to what do you attribute this E3-3 Use vector diagrams to describe what happens during a spin echo sequence in which the 180 pulse is applied about the y axis. Also draw a phase evolution diagram appropriate for this pulse sequence. In what way is the outcome different from the case where the refocusing pulse is applied about the x axis What would the effect of applying the refocusing pulse about the x axis be E3-4 The gyromagnetic ratio of phosphorus-31 is X 108 rad s 1 T 1. This nucleus shows a wide range of shifts covering some 700 ppm. Estimate the minimum 90 pulse width you would need to excite peaks in this complete range to within 90 of the their theoretical maximum for a spectrometer with a B0 field strength of T. E3-5 A spectrometer operates at a Larmor frequency of 400 MHz for protons and hence 100 MHz for carbon-13. Suppose that a 90 pulse of length 10 Ịxs is applied to the protons. Does this have a significant effect of the carbon-13 nuclei Explain your answer carefully. E3-6 Referring to the plots of Fig. we see that there are some offsets at which the .

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