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Nuclear Magnetic Resonance Determination of Reaction Rates

IP.com Disclosure Number: IPCOM000034460D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 4 page(s) / 48K

Publishing Venue

IBM

Related People

Feig, E: AUTHOR [+2]

Abstract

A method for determining nuclear magnetic resonance reaction rates is provided and comprises: a) selectively exciting a body along a desired plane; b) reexciting the body with a spin-echo at a point in time halfway between the selective excitation of the body and the rephasing of the induced free induction decay (FID); c) measuring the free induction decay (Eµ(t,u)) of the body over time; d) Fourier transforming the measured free induction decay with respect to time to obtain E(f,u); e) computing the time-dependent concentration of the molecules of the body that have not yet reacted (hk (u)) according to the equation E(f,u) = hk (u) Ek (f,u) where Ek (f,u) are values along a support set strip obtained from previously conducted excitation, reexcitation, and measurement experiments which correlate the Fourier transform of the measurements of individual species (k) to support sets, and where the species k present are determined from a comparison of the obtained plot of said Fourier transformed data to the individual species support sets; and f) repeating steps a) - e) with different spin-echo and rephasing times.

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Nuclear Magnetic Resonance Determination of Reaction Rates

A method for determining nuclear magnetic resonance reaction rates is provided and comprises: a) selectively exciting a body along a desired plane; b) reexciting the body with a spin-echo at a point in time halfway between the selective excitation of the body and the rephasing of the induced free induction decay (FID); c) measuring the free induction decay (Eµ(t,u)) of the body over time; d) Fourier transforming the measured free induction decay with respect to time to obtain E(f,u); e) computing the time-dependent concentration of the molecules of the body that have not yet reacted (hk (u)) according to the equation E(f,u) = hk (u) Ek (f,u) where Ek (f,u) are values along a support set strip obtained from previously conducted excitation, reexcitation, and measurement experiments which correlate the Fourier transform of the measurements of individual species (k) to support sets, and where the species k present are determined from a comparison of the obtained plot of said Fourier transformed data to the individual species support sets; and f) repeating steps a) - e) with different spin-echo and rephasing times. The excitation, refocusing, and induced free induction decay measurement of a body are seen with reference to Fig. 1. Thus, as shown by pulse 10, at time zero a desired plane of the body is selectively excited. At pulse 20, a refocusing spin-echo pulse is applied at time s/2. Measurements F(s,t) (which is the same as E(t,u) where u = s + t and denotes the Fourier transform in the first variable) are made over time at 30, with rephasing of the FID occurring at time point 40 (s).

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Once the measurements are obtained, reaction rates (i.e., the time dependent concentration of the molecules of the body that have not yet reacted) may be computed.

Thus, the obtained measurements Eµ(t,u) are inverse Fourier transformed in time to provide a value E(f,u). By making a two-dimensional plot of E(f,u), and having previously conducted excitation, reexcitation, and measurement experiments which correlate the Fourier transform of the measurements of individual species (k) to support sets, the species k present are determined from a comparison of the two-dimensional plot of Fourier transformed data with the individual species support sets. Because the inverse Fourier transformed measurements are related to their summands by the reaction rates, the reaction rates are determined.

The theoretical basis of the above-disclosed method is as follows. If nuclei are subjected to a uniform external magnetic field of intensity H, any local field which deviates in the intensity by W H will deviate due to the chemical shift f and due to the coupling effects g between excited nuclei. For nuclear magnetic moments described in coordinates rotating at the Larmor frequency w = - qH, at time t = 0, the moments are all aligned along the same direction. Under the influence of f alone, moment...