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NMR Samples

Types of NMR tubesSample preparation

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Types of NMR Tubes

Solid State Sample Rotors

Solution NMR Sample Tube Spinners

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

3 6 6 6

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 preparationChoice of solventHomogeneity of magnetic fieldData acquisition parametersProcessing procedures

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Good spectrum ppm

ppm

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Good spectrum

Integrals

Peak picking

ppm scaleppm

ppm

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Good spectrum

ppm

ppm

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Bad spectrum ?

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Bad spectrum !

Signal/Noise ratio bad

No units specified for axis and peak picking

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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, don’t 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.