Clean NMR tubes are important because the only NMR signals observed should arise from your sample, not from tube contaminants. Also, such contaminants may render your peptide useless and only fit for waste. Wash all tubes (even new tubes received directly from the supplier) by following this procedure.
1. Soak your tubes in concentrated nitric acid for 1 h.
2. Carefully remove the tubes from the acid, and rinse well with high-purity water. Be rigorous in rinsing the tube, which is best achieved using a NMR tube washer that draws solvent from a reservoir to rinse the inside of the tube, as shown in Fig. 2.
3. If using a tube washer, rinse each tube with 500 mL high-purity water using this device (see Note 7). If a NMR tube washer is not used, take extreme care to ensure all acid is removed from the tube by rigorous manual rinsing.
4. Tubes can be dried inverted at room temperature by applying a vacuum or using dry nitrogen or argon-bottled gas to blow air into an inverted tube. Resist placing NMR tubes in an oven to dry, as this warps the camber and destroys all the costly craftsmanship.
3.4. Peptide NMR Sample Preparation
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