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Presaturation delay

Conversely, the decoupling effect of v2 requires only that v2 be on during FID acquisition. Therefore, if v2 is on during the presaturation delay but off during FID acquisition, most of the NOE enhancement would be preserved but all decoupling would be lost. The net result is a coupled spectrum with improved signal-to-noise ratio. [Pg.196]

MHz H NMR spectra were measured on solutions of ca 25 mg pectin/0.5 ml D2O on a Bruker AMX600 NMR spectrometer. The temperature was 350 K to diminish the viscosity of these solutions and 32 scans were measured. Solvent suppression was performed using presaturation during the recycle delay. [Pg.794]

Pre-saturation In this technique prior to data acquisition, a highly selective low-power rf pulse irradiates the solvent signals for 0.5 to 2 s to saturate them. No irradiation should occur during the data acquisition. This method relies on the phenomenon that nuclei which have equal populations in the ground and excited states are unable to relax and do not contribute to the FID after pulse irradiation. This is an effective pulse sequence of NOESY-type pre-saturation that consists of three 900 pulses RD - 900 - tx - 900 - tm - 90° - FID, where RD is the relaxation delay and t and tm are the presaturation times. [Pg.476]

Standard onedimensional NMR One-dimensional NMR — simple one-pulse experiment, typically with presaturation of solvent during the recycle delay with a weak RF field To quantify small molecules To identify some simple small molecules... [Pg.308]

Equation 1 was derived assuming that the nuclear spin magnetizations are at thermal equilibrium values prior to the start of the presaturation. In practice, due to time constraints on the instrument, this condition may not usually be reahzed and the nuclear spin magnetization can generally be in a quasiequilibrium state prior to presaturation. If (tj + t) is the delay between two consecutive 90° observe pulses, where t is the presaturation period and fa is the time delay before presaturation (this includes the data acquisition time for the previous pulse), then the appropriate expressions for STD and for control NMR spectra are given by ... [Pg.23]

ID NOESY spectra (b) and (c) were acquired using the pulse sequence of fig. 1(a). A 59.2 ms half-Gaussian pulse was applied to proton H-ld. Mixing time was 25 ms in (b) and 200 ms in (c). Water presaturation was applied during the relaxation delay and the NOE mixing... [Pg.76]

The use of 2.5 1 ratio (instead of 10 1) of PDMS prepolymer to prepare the PDMS chip has reduced liquid loss by absorption into PDMS by 2.5 times. This has delayed the time for complete liquid absorption from 2.7 h to 6.3 h. Presaturating the PDMS with the liquid has also prolonged the liquid loss by absorption up to 22 h. This leads to less liquid loss problems in performing cell culture in PDMS chips [249]. [Pg.290]

Such NOE experiments work best when the more abundant (or sensitive) nucleus (e.g., H) is irradiated while the effect is observed on the less abundant (or sensitive) nucleus (e.g., 13C). It would be fruitless (as well as unnecessary) to carry out the reverse experiment, H 13C, and expect to see any enhancement of the hydrogen signal. Furthermore, remember that the NOE requires time to evolve. This is why, during a typical 13C 1H decoupling experiment, the v2 channel is left on not only during FID acquisition but beforehand as well (during the presaturation or preequilibration delay). [Pg.195]

The majority of pulse sequence variations focus on the events that precede detection (FID acquisition). The interval preceding detection is divided into a preparation time (which may include delays for preequilibration or presaturation), the initiating pulse, an evolution time (t), followed by one or more additional v, pulses and evolution times. During this entire period, plus the subsequent FID collection, the v2 (irradiating) channel may also be activated at various times. [Pg.203]

Varian VXR 500 NMR spectrometer operating at a proton frequency of 500 MHz. The spectral width was 6000 Hz with the carrier frequency at the HDO resonance. The solvent resonance was suppressed by presaturation. Each FID was composed of 16 k data points with 80 transients. The delay between successive transients was 2.8 s. The time domain data were processed by zero-filling to 32 k points, exponential multiplication (0.5 Hz) and Fourier transformation. Chemical shifts were referenced to internal sodium 3-(trimethylsilyl)-propionate-2,2,3,3-d4. The Kj values were obtained by nonlinear least square fit of the data to the equation... [Pg.681]

To simplify the interpretation of STMAS spectra, it is desirable to remove the CT—>CT correlation signal, particularly when studying nuclei subjected to distribution of local environments or weak quadrupole interactions. Several methods are available to remove the CT CT peak. In the first method, the CT transition is presaturated by a soft pulse, prior to the STMAS sequence (Fig. 12a) [38]. A sequence consisting of a selective soft pulse followed by a delay and a short excitation pulse maybe used for optimising the presaturation pulse. Unfortunately, this simple method only works when aU species present in the sample have very similar transverse relaxation times and quadrupole couphng constants. [Pg.167]

Fig. 5. Prostate biopsy. H MR spectra (8.5 T, 37°C), of human prostate biopsy specimens (a) cancer (Gleason s grade 3+3) (b) benign prostatic hyperplasia (BPH). MR spectra were collected with presaturation of the water signal. Acquisition parameters included number of scans, 256 or 640, sweep width 5000 Hz, delay 2.41 s, and time domain data points 4K. Reprinted from Cancer Research with permission from the American Association for Cancer Research. Fig. 5. Prostate biopsy. H MR spectra (8.5 T, 37°C), of human prostate biopsy specimens (a) cancer (Gleason s grade 3+3) (b) benign prostatic hyperplasia (BPH). MR spectra were collected with presaturation of the water signal. Acquisition parameters included number of scans, 256 or 640, sweep width 5000 Hz, delay 2.41 s, and time domain data points 4K. Reprinted from Cancer Research with permission from the American Association for Cancer Research.

See other pages where Presaturation delay is mentioned: [Pg.196]    [Pg.196]    [Pg.203]    [Pg.212]    [Pg.212]    [Pg.196]    [Pg.196]    [Pg.203]    [Pg.212]    [Pg.212]    [Pg.196]    [Pg.196]    [Pg.203]    [Pg.212]    [Pg.212]    [Pg.196]    [Pg.196]    [Pg.203]    [Pg.212]    [Pg.212]    [Pg.196]    [Pg.196]    [Pg.203]    [Pg.212]    [Pg.212]    [Pg.196]    [Pg.196]    [Pg.203]    [Pg.212]    [Pg.212]    [Pg.168]    [Pg.68]    [Pg.94]    [Pg.95]    [Pg.213]    [Pg.345]    [Pg.652]    [Pg.786]    [Pg.16]    [Pg.181]    [Pg.219]    [Pg.496]    [Pg.285]    [Pg.43]   
See also in sourсe #XX -- [ Pg.195 ]

See also in sourсe #XX -- [ Pg.195 ]

See also in sourсe #XX -- [ Pg.195 ]




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