title: Microflow NMR: concepts and capabilities.
abstract: The principles and parameters to consider when choosing an NMR probe for analysis of a volume- or mass-limited sample are identified and discussed. In particular, a capillary-based microflow probe is described which has a mass sensitivity comparable to cryoprobes (observe volume approximately 40 microL), but with several distinct advantages. The microflow probe has a flowcell volume of 5 microL and an observe volume of 1.5 microL and is equipped with proton and carbon observe channels, deuterium lock, and z-gradient capability. The entire flow path is fused silica; inlet and outlet capillary inner diameters are 50 microm to minimize sample dispersion, making it well-suited to volume-limited samples. An injected sample of 1 nmol of sucrose (0.34 microg in 3 microL, 0.33 mM; MW = 342 g/mol) yields a 1D proton spectrum in 10 min on a spectrometer of 500 MHz or higher. In another example, 15 microg of sucrose (in 3 microL; 15 mM, 45 nmol) is injected and parked in the probe to yield a heteronuclear multiple-quantum coherence (HMQC) spectrum in less than 15 h. The natural product muristerone A (75 microg in 3 microL, 50 mM, 150 nmol; MW = 497 g/mol) was delivered to the flow cell, and a gradient correlation spectroscopy spectrum was acquired in 7 min, a gradient HMQC in 4 h, and a gradient heteronuclear multiple-bond correlation in 11 h. Four basic modes of sample injection into the probe vary in degree of user intervention, speed, solvent consumption, and sample delivery efficiency. Manual, manual-assisted (employing a micropump), automated (using an autosampler), and capillary HPLC modes of operation are described.
authors.affiliation: Protasis/MRM Corporation, 101 Tomaras Avenue, Savoy, Illinois 61874, USA. dolson@microNMR.com
authors.forename: Dean L
authors.initials: DL
authors.lastname: Olson
authors.forename: James A
authors.initials: JA
authors.lastname: Norcross
authors.forename: Mark
authors.initials: M
authors.lastname: O'Neil-Johnson
authors.forename: Paul F
authors.initials: PF
authors.lastname: Molitor
authors.forename: David J
authors.initials: DJ
authors.lastname: Detlefsen
authors.forename: Aaron G
authors.initials: AG
authors.lastname: Wilson
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Peck
mesh_terms: D001331:Automation; D002244:Carbon / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D004441:Ecdysterone / Q000031:analogs & derivatives* / Q000032:analysis; D008832:Microchemistry / Q000379:methods*; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011522:Protons; D012680:Sensitivity and Specificity; D012997:Solvents / Q000737:chemistry; D013395:Sucrose / Q000032:analysis*
chemical_list: D011522:Protons; D012997:Solvents; C055348:muristerone A; D004441:Ecdysterone; D013395:Sucrose; D002244:Carbon