Sample preparation

Appropriate sample preparation is essential to obtain good quality spectra.

• The sample for analysis should be labeled and delivered with a completed and signed order.
• The sample should be dissolved in a deuterated solvent; e.g. from Deutero GMBH (http://www.deutero.de), Sigma-Aldrich (http://www.sigmaaldrich.com) or other manufacturers.
• For sample preparation, use undamaged tubes (diameter 5 mm, length 7 inches) of a quality compatible with the spectrometer used (500 MHz or 700 MHz).
• For routine measurements for the above-mentioned tubes of the "Economy" or "Standard" series can be used. These can be, for example, test tubes from Norell (http://nmrtubes.com/), Wilmad (http://www.wilmad-labglass.com) or other manufacturers.
• Pasteur pipettes with an elongated thin tip (310 mm) are very useful for sample preparation and then for "recovery" of the solution
• The volume of the solution in the tube should be approx. 0.6 ml (height of the liquid column approx. 40 mm). A "significantly" smaller or larger liquid volume may cause deterioration of the quality of the recorded spectra.
• The solution in the tube should be homogeneous and free of sediment.
• The tube must have a tight cap and must not be dirty on the outside.
• The correct preparation of the sample for measurement is the sole responsibility of the user.
• Poorly prepared samples and in the wrong tubes may not be accepted for measurement.
• The solutions should have the correct concentration. Too high concentration of the solution causes broadening of the signals in the proton spectrum. Too low a concentration extends the accumulation time of the carbon spectra.
• Recommended minimum amounts of substances to be measured (500 MHz):

          - 1H spectra -1-5 mg
          - 13C spectra - 5-10 mg
          - heteronuclear spectra with 1H detection (e.g. HSQC, HMBC) - 5-10 mg
          - homonuclear 2D spectra (e.g. COSY, TOCSY, NOESY, ROESY) - 1-5 mg

The given amounts of substances for individual experiments are very indicative. Spectra can also be recorded for smaller amounts of substance, but this requires more "measurement time". For very small amounts of substances, it is advisable to record the spectra on a 700 MHz spectrometer using a cryoprobe.

• Calibration of chemical shifts can be performed by adding an internal standard (e.g. TMS), using a solvent signal or according to the scale recommended by IUPAC (Pure Appl. Chem., Vol. 73, No. 11, pp. 1795-1818, 2001; http: //pac.iupac.org/publications/pac/pdf/2001/pdf/7311x1795.pdf).
• When using an internal standard (eg TMS), its concentration should be low (0.05% - 0.1%, i.e. 1-2 drops per 100 mL of solvent). It is more convenient to buy solvents with an added internal standard.
• In case of any doubts regarding sample preparation, it is advisable to contact the operator.
• Free programs available on the Internet and the TopSpin program, which will be available from October 2013 from computers in the WCh network, can be used to process the spectra.