1. R. Provost and R. V. Jardine Defence Research Establishment Sufiield Ralston, Alberta, Canada
A Simple, Convenient Method to Obtain NMR Spectra on Milligram Samples
A simple and convenient method for obtaining the nuclear magnetic resonance (nmr) spectra of milligram quantities of material is by the use of a meltina-. mint tube (1.5-2.0 X 100 mm) with a well-rounded end. A solution of as little as 4-8 mg of material in 0.04 ml of a suitable solvent is introduced into the capillary tuhe with amicro-syringe and centrifuged to remove occluded air. The tuhe is then sealed off as symmetrically as possible approximately 7 mm from the end and introduced into a standard nmr cell containing sufficient deuterochloroform/tetramethylsilane solution (-5%) to cover the ampoule. Optimum working conditions with a Varian A-60 instrument for a 20% sample were a filter bandwidth of 0.2-0.4 and sweep time of 500 sec, amplitude 50-60, while for a 10% solution the amplitude was adjusted to
Figure 1. NMR spectrum of diethyl phtholote obtained in deutemchioroform. External ~tandordTMS.
100. To maintain capillary symmetry, the sample tube was spun a t approximately 50 cps. Figures 1 and 2 demonstrate that the spectra obtained in this manner compare favorably with those obtained from standard samples. At the amplitude required to produce useful spectra, the appearance of spinning sidebands (SSB) and carbon-13 (13C-H) satellites of TMS must be recognized in order to avoid confusion in spectral interpretation. (Obviously spinning sidebands and carbon-13 satellite signals could he removed by omission of TMS, and referring to CHC1,. However, from a pedagogical standpoint, inclusion of TMS is instructive.) Spinning sidebands can be readily recognized by variation of spin rate. The 13C-H satellite hands appear as a doublet, J13c-x = 158 Hz spaced symmetrically about the TMS peak (see Figs. 1and 2).
Figure 2. NMR spectrum of ethyl methylbanrylpharphinote obtained in deuterochloroform. External standard TMS.
Volume 45, Number 10, October 1968
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