Gradient experiments

Holz, M Lucas, O Muller, C, NMR in the Presence of an Electric Current, Simultaneous Measurements of Ionic Mobilities, Transference Numbers, and Self-Diffusion Coefficients Using an NMR Pulsed-Gradient Experiment, Journal of Magnetic Resonance 58, 294, 1984. Hooper, HH Baker, JP Blanch, HW Prausnitz, JM, Swelling Equilibria for Positively Ionized Polyacrylamide Hydrogels, Macromolecules 23, 1096, 1990. 

Stationary phase. Supelcosil Cig ABZ (Supelco Scientific, Bellefonte, PA, USA) was the most often employed support and gave the best correlations. This stationary phase should be selected in a first instance with a geometry adapted to the application for conventional gradient experiments, supports of 150X4.6 mm, 5 pm represent a good choice while a shorter column (i.e. 50 mm or lower) with smaller particle size (i.e. 3-3.5 pm) must be preferentially selected for fast gradient analysis. 

Fig. 1.19 Spin-echo based pulse sequence to each gradient pulse, A the separation between encode velocity change. The gradients are each pair of bipolar gradient pulses and tm the stepped pair-wise independently (2D VEXSY) mixing time between the bipolar gradient pairs, or simultaneously (1 D VEXSY). For a VEXSY The opposite polarity of the bipolar gradient experiment, 7q to k4 are usually applied along pair is realized by an inversion 180° pulse, the same spatial direction. 8 is the duration of...

Fig. 2.5. Measurement of pKas of serotonin by target factor analysis (TFA). (A) 3-D spectrum produced by serotonin in pH gradient experiment (equivalent to A matrix). (B) Molar absorptivity of three serotonin species (equivalent to E matrix). (C) Distribution of species (equivalent to C matrix). In this graph the three sets of data points denote the three...

Curtis GP, Roberts PV, Reinhard M. 1986. A natural gradient experiment on solute transport in a sand aquifer 4. sorption of organic solutes and its influence on mobility. Water Resources Research 22 2059-2067. 

Fig. 10.14. Gradient-enhanced HMQC pulse sequence described in 1991 by Hurd and John derived from the earlier non-gradient experiment of Bax and Subramanian. For 1H-13C heteronuclear shift correlation, the gradient ratio, G1 G2 G3 should be 2 2 1 or a comparable ratio. The pulses sequence creates heteronuclear multiple quantum of orders zero and two with the application of the 90° 13C pulse. The multiple quantum coherence evolves during the first half of ti. The 180° proton pulse midway through the evolution period decouples proton chemical shift evolution and interchanges the zero and double quantum coherence terms. Antiphase proton magnetization is created by the second 90° 13C pulse that is refocused during the interval A prior to detection and the application of broadband X-decoupling.

Fig. 10.16. (A) GHSQC spectrum of strychnine (1) using the pulse sequence shown in Fig. 10.15 without multiplicity editing. (B) Multiplicity-edited GHSQC spectrum of strychinine showing methylene resonances (red contours) inverted with methine resonances (black contours) with positive phase. (Strychnine has no methyl resonances.) Multiplicity-editing does have some cost in sensitivity, estimated to be 20% by the authors. For this reason, when severely sample limited, it is preferable to record an HSQC spectrum without multiplicity editing. Likewise, there is a sensitivity cost associated with the use of gradient based pulse sequences. For extremely small quantities of sample, non-gradient experiments are preferable.

D. Canet, Radiofrequency field gradient experiments, Prog. NMR Spectroc., 1997,30, 101-135. 

Using initial scouting gradient experiments for efficient development of final gradient or isocratic methods... 

The molecular weight of muscle FDPase, based on sucrose density gradient experiments, was estimated to be 133,000, similar to that of liver FDPase (64)- However, the muscle enzyme did not react with antibody prepared against purified rabbit liver FDPase (63), and its amino acid composition differed significantly (74). In particular, the muscle enzyme contained fewer histidine and methionine residues but was richer in tyrosine and arginine. Tryptophan is absent in all of the mammalian FDPases thus far examined, with the possible exception of FDPase from swine kidney (65). The muscle and liver enzymes could also be distinguished on the basis of their electrophoretic mobility (74) ... 

A simple way to view a pulsed field gradient experiment is to add up the twist acquired by the sample magnetization in each gradient pulse and make sure they add up to zero for the desired pathway. If the twist is not zero at the beginning of acquisition of the FID, there will be no observable signal. For example, in the INEPT experiment (Fig. 8.26)... 

Thorbjarnarson KW, Mackay DM (1994) A forced gradient experiment on solute transport in the Borden aquifer 3. Nonequilibrium transport of the sorbing organic compounds. Water Resour Res 30 401-419... 

Linear gradient experiments can also be employed to determine K and v.52 Equation (3) relates a solute retention volume (Vg) to initial and final carrier salt concentrations (x xf), the gradient volume (Vg), the column... 

This expression can be employed with two or more gradient experiments to determine v and K (using a least-squares fit). The gradient technique is better suited for simultaneously determining parameters for several components of a complex mixture. 

Table 8-1 contains sample data for this experiment. You should create your own Table 8-1. It should be filled in with your experimental results and the various terms calculated. One table should be made with the data you collected for each experiment performed (e.g., if you did Sections A and B, you should construct two tables, if you did A, B, and C you should have three tables). Do not prepare a Table 8-1 for the gradient experiments.

An automated tracer injection system was utilized to dispense tracers into the fracture regime of well 4014 under natural gradient conditions (Figure 1.2(b)). Two long-term, steady-state natural gradient experiments, each with a duration of 1.5 to 2... 

Nishioka, M. and Morkovin, M.V. (1986). Boundary-layer receptivity to unsteady pressure gradients Experiments and overview. J. Fluid Mech., 171, 219-261. 

Sensitivity improved gradient experiments are available, however, the increased length of the pulse sequences allows for dephasing of the desired magnetization. Therefore, the theoretical sensitivity enhancement is not always obtained. Furthermore, the sensitivity improvement is often restricted to a particular spin system (usually one I spin and one S). 

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