Comparison of 1.7 mm submicro and 3 mm micro gradient NMR probes for the acquisition of1H13C and1H15N heteronuclear shift correlation data

Abstract

A variety of specialized probes are now available for the NMR characterization of small samples. The performance characteristics for 3 mm gradient micro inverse and 1.7 mm submicro inverse-detection gradient (SMIDG) NMR probes for the characterization of small samples using gradient inverse heteronuclear shift correlation methods are compared. Results of three 48 min 1H13C GHSQC experiments performed using a 0.5 µmol sample of the drug ibuprofen dissolved in either 30 or 150 µl are compared. A similar set of 12 min 1H13C GHSQC experiments were performed using 1 µmol samples of strychnine. The results of both sets of GHSQC experiments demonstrate an ∼2.3 fold improvement in the signal-to-noise ratio attainable using the 1.7 mm submicro vs a 3 mm micro NMR probe with a given molar quantity of sample when data are accumulated for the same length of time. Data acquired using a 1.7 mm sample in the 3 mm probe gave intermediate results that represent a significant advantage relative to data for a 3 mm sample in the 3 mm micro NMR probe. These results parallel those reported in 1992 for a comparison of the then new 3 mm NMR probe vs a conventional 5 mm NMR probe. Finally, results are also compared for the acquisition of a series of 18 hr 1H15N GHMBC spectra on a 3 µmol (1 mg) sample of strychnine at natural abundance. The 3 µmol sample of strychnine represents about the practical limit of the 3 mm micro NMR probe for 1H15N at natural abundance overnight. The results obtained with the 1.7 mm submicro probe were ∼2.3 fold better than with the 3 mm micro probe. Furthermore, the signal intensity of the weaker responses in the spectra was significantly better, relative to the noise floor of the spectrum, than were the corresponding responses in the 3 mm micro probe data. Copyright © 1999 John Wiley & Sons, Ltd.