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Rapid parameter optimization of low signal‐to‐noise samples in NMR spectroscopy using rapid CPMG pulsing during acquisition: application to recycle delays
Author(s) -
Farooq Hashim,
CourtierMurias Denis,
Soong Ronald,
Masoom Hussain,
Maas Werner,
Fey Michael,
Kumar Rajeev,
Monette Martine,
Stronks Henry,
Simpson Myrna J.,
Simpson André J.
Publication year - 2013
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.3923
Subject(s) - chemistry , pulse sequence , excitation , analytical chemistry (journal) , signal (programming language) , chemical shift , biological system , nuclear magnetic resonance spectroscopy , nuclear magnetic resonance , spectroscopy , physics , chromatography , quantum mechanics , computer science , organic chemistry , biology , programming language
A method is presented that combines Carr–Purcell–Meiboom–Gill (CPMG) during acquisition with either selective or nonselective excitation to produce a considerable intensity enhancement and a simultaneous loss in chemical shift information. A range of parameters can theoretically be optimized very rapidly on the basis of the signal from the entire sample (hard excitation) or spectral subregion (soft excitation) and should prove useful for biological, environmental, and polymer samples that often exhibit highly dispersed and broad spectral profiles. To demonstrate the concept, we focus on the application of our method to T 1 determination, specifically for the slowest relaxing components in a sample, which ultimately determines the optimal recycle delay in quantitative NMR. The traditional inversion recovery (IR) pulse program is combined with a CPMG sequence during acquisition. The slowest relaxing components are selected with a shaped pulse, and then, low‐power CPMG echoes are applied during acquisition with intervals shorter than chemical shift evolution (RCPMG) thus producing a single peak with an SNR commensurate with the sum of the signal integrals in the selected region. A traditional 13 C IR experiment is compared with the selective 13 C IR‐RCPMG sequence and yields the same T 1 values for samples of lysozyme and riverine dissolved organic matter within error. For lysozyme, the RCPMG approach is ~70 times faster, and in the case of dissolved organic matter is over 600 times faster. This approach can be adapted for the optimization of a host of parameters where chemical shift information is not necessary, such as cross‐polarization/mixing times and pulse lengths. Copyright © 2013 John Wiley & Sons, Ltd.