title: Rapid parameter optimization of low signal-to-noise samples in NMR spectroscopy using rapid CPMG pulsing during acquisition: application to recycle delays.
abstract: 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.
authors: Department of Chemistry, University of Toronto, 1265 Military Trail, Toronto, ON, Canada, M1C 1A4.
authors: Hashim
authors: H
authors: Farooq
authors: Denis
authors: D
authors: Courtier-Murias
authors: Ronald
authors: R
authors: Soong
authors: Hussain
authors: H
authors: Masoom
authors: Werner
authors: W
authors: Maas
authors: Michael
authors: M
authors: Fey
authors: Rajeev
authors: R
authors: Kumar
authors: Martine
authors: M
authors: Monette
authors: Henry
authors: H
authors: Stronks
authors: Myrna J
authors: MJ
authors: Simpson
authors: André J
authors: AJ
authors: Simpson
mesh_terms: D017743:Equipment Reuse; D009113:Muramidase / Q000737:chemistry* / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D009930:Organic Chemicals / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D013997:Time Factors
chemical_list: D009930:Organic Chemicals; D011108:Polymers; D009113:Muramidase