Dispersion with time delay

As in the case of the HN(CO)CA-TROSY scheme, the HN(CO)CANH-TROSY experiment can be readily expanded to a four-dimensional HN(CO)CANH-TROSY experiment without increasing the overall length of the pulse sequence. This can be accomplished by labelling the 13C (f) chemical shift during additional incremented time delay, implemented into the 13C — 13C INEPT delay. As a result, a well-dispersed 13C (i- 1), 13C (i- 1), 15N(i), Hn(0 correlation map is obtained with minimal resonance overlap albeit with the inherent sensitivity loss by a factor of y/2. 

All solutions were stored for 60 days before use. This delay was necessary for accurate results since Narkis (10) had already shown that poly(l-amidoethylene) solutions are not molecularly disperse until 54 days after preparation. These solutions age by losing intermolecular entanglements and becoming monomolecular solutions (10). Poly( 1-amidoethylene) solutions are known to lose viscosity with time (11). Several authors have attributed this viscosity loss to oxygen or radical degradation of the polymer (11), but Francois (12) has shown that changes in viscosity only... 

Gradient dilution [275, 338], which was first described and used in 1982 [264, 338], is based on the selection of a suitable element of the dispersed sample zone to become the source of the analytical readout. This is done by selecting a time delay (e.g., 10, 12, 14, 16, or 18 s), elapsed from the point of injection 5, as illustrated in Fig. 2.18, right. Since the selected elements of the dispersed sample zone have different dispersion coefficients (Di, D2, I>3,. . . , Fig. 2.18, left), which yield, for a series of injected standard solutions, a sequence of corresponding calibration curves with decreasing slopes, the sensitivity of measurement can be... 

Zone penetration is an ideal tool for measuring selectivity coefficients, since the method allows readouts to be taken (1) at that vertical slice of the composite zone where the dispersion coefficients are equal (Da = Db at point M Fig. 2.26, bottom) and (2) at the peak maximum of the pure A component. The concentrations within such a composite zone and position of the point M at a time tM are readily established by an experiment where zone A is first injected alone and peak A is recorded by a detector of choice. (If chemical reactions are involved, like a reaction with a suitable reagent for colorimetric detection, a suitable manifold and colorimetric detector are used—cf. Section 4.5.2). Next, zone B is injected alone and peak B is recorded. Provided that the same solution of analyte is injected in both runs A and B, and that the detector responds linearly to the injected species, this experiment yields, (a) the isodispersion point M within the time concentration rnatrix, which is identified via time delay tM, and (b) the peak height Ha for the response of the pure species A at the time Im, because it equals the horizontal distance between point M and the baseline (Fig. 2.26). 

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