retically,one may obtain complet e2D NMR dataset er BioSpin 200 ral days af h lor a n the ab sigmals of a dilut 72Mk 园 I prod ions are use of lo 3 43 The technique is challenging to learn but wonderfully powerful for the determination of organic and biochemical structure. 44 900 MHz NMR 伯明翰HWB￾NMR中心的 900 MHz核磁 谱仪 45 46 Theoretically, one may obtain complete 2D NMR datasets on, say, ca. 1 mg of a natural product of MW ca. 1000 (1 nmol) if several days of acquisition time are available, but few can afford this luxury. A more important limitation for a natural products chemist working with small-molecular mass samples is dynamic range – the ability to detect weak signals of a dilute solution of a natural product from strong background signal (e.g. residual NMR solvent signals or even impurities within the NMR solvent). Dynamic range limitations are ameliorated by the use of low-volume probes in which relatively high sample concentrations can be maintained. 47 5 mm (600 µL), 1.7 mm (35 µL) and 1 mm tubes (7 µL). Right, a gas-tight sample syringe fitted with an extra long needle. Image credit: D. S. Dalisay. Fig. 1 Relative NMR sample tube diameter (OD) and sample volumes. From left to right, Tadeusz F. Molinski. NMR of natural products at the ‘nanomole-scale’. Nat. Prod. Rep., 2010, 27, 321-329. 48 Fig. 1 Approximate time-line and qualitative comparison of recent milestone NMR probe innovations.Mass sensitivity (Sm, linear ‘y’ scale) for 1H NMR of a hypothetical fixed-mass sample as a function of probe fill volume (Vf, note the logarithmic ‘x’ scale) for room temperature probes (red line) and cryoprobes (blue line) at fixed field, Bo. See text for key references. NanoprobeTM is a trademark of Varian Inc