NMR Samples

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NMR Samples

• Types of NMR tubes
• Sample preparation

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Types of NMR Tubes
Solution NMR Sample Tube Spinners
Solid State Sample Rotors
NMR Sample Tubes with Caps
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NMR Sample Preparation

• Use clean dry NMR tubes and caps (tubes can
  be re-used, caps should not!)
• 0.5 ml deuterated solvent (i.e. CDCl ,C D
  , acetone-d ,etc.)
• substrate requirements for routine spectra
  10 mg for proton NMR 100 mg for carbon-13 NMR
• min. filling height of tube 2 inches (5 cm)
• Cleaning of tubes 1. rinse with solvent you
  were using 2. rinse with acetone 3. dry in
  (vacuum-)oven at low temperature

5 mm
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NMR Sample Preparation
Clean clear solution
Suspension or opaque solution
Precipitate
Not enough solvent
Two phases
Concentration gradient

GOOD!
B a d S a m p l e s !
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Good and bad NMR Spectra

• are the result of
• Sample preparation
• Choice of solvent
• Homogeneity of magnetic field
• Data acquisition parameters
• Processing procedures

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Good spectrum
ppm
ppm
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Good spectrum
ppm
Peak picking
Integrals
ppm
ppm scale
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Good spectrum
ppm
ppm
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Bad spectrum ?
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Bad spectrum !
No units specified for axis and peak picking
Signal/Noise ratio bad
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Bad spectrum ?
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Bad spectrum !
Tall signals are cut off
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Bad spectrum ?
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Bad spectrum !
Signals too small (only allowed to
compare signal intensities between different
spectra)
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Bad spectrum ?
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Bad spectrum !
Broad signals(bad sample, poor shimming, wrong
processing parameters)
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Bad spectrum ?
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Bad spectrum !
Signals are distorted (automatic phase
correction is often insufficient)
Excessive peak picking (low p.p.
threshold,also due to improper phasing)
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Bad spectrum ?
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Bad spectrum ?
Areas without signals should be excluded. (If you
want to print all your spectra with a default
range, i.e. 0-10 ppm, dont forget to print
detailed expansions.)
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Lab Assignments
Duration Spectrometer Experiment
sample requirement
(per 0.5 ml solution) 1. 2X2 hrs 100
360 MHz Comprehensive 1H NMR Indirect 13C
Observation 100 mg 2. 3 hrs 100 or
360 MHz Pulse Width Calibration and B1 100 mg
3. 2X2 hrs 100 360 MHz Rare spin
NMR concentrated (80-90) 4. 3 hrs 360
MHz Decoupling 1H from 13C and B2 100 mg 5. 2
hrs 100 300 MHz Spin Echo and
Spin/Spin Relaxation, T2 100 mg 6. 2 hrs
100 300 MHz Spin/Lattice Relaxation,
T1 100 mg 7. 3 hrs 360 MHz Nuclear
Overhauser Effect 25 mg 8. 2 hrs 360
MHz Polarization Transfer and DEPT 100 mg
9. 3 hrs 300 MHz 13C CP/MAS in Solids (sample
provided) 10. 2 hrs 360 MHz HETCOR (1H/13C
COSY) 100 mg 11. 2 hrs 360 MHz 1H COSY /
NOESY (optional) 25 mg Use your own samples,
if possible. Familiarize yourselves with the
procedures for each experiment, before you come
to the lab. Print the manuals.