Use of the NMR Spectrometer- A Practical guide

NMR tube cleaner
Vacuum pump
RB flask
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Use of the NMR Spectrometer by Roy Hoffman
Wash the cap
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Water and/or acetone in here Place cap on the bottom of the Use of the NMR Spectrometer NMR tube and insert the tube by
Effect of an rf pulse
z M θ z M 90 ° y
B1 x
y x
B1
θ log(B1)Tp
90°x pulse transfers the magnetization vector to the y axis
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Pulse power, on the spectrometer use the attenuation in dB: pl1, pl2, etc.
Too short yields poor spectrum
10 Use of the NMR Spectrometer by Roy Hoffman
Filter the suspension
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The residue stays in the filter
Use of the NMR Spectrometer by Roy Hoffman
and Z2 (with sample spinning). For more thourough shimming (nonspinning) adjust X & Y then XZ & YZ (if there is a large change redo X & Y) then adjust XZ2 & YZ2 (if there is a large change redo X, Y, XZ & YZ) then adjust XY & X2-Y2. Spin and readjust Z & Z2, acquire the spectrum and if it looks reasonable adjust Z3 then Z & Z2. Increase Z2 then adjust Z If there are problems with the spectrum Reduce Z2 then adjust Z use the lineshape as a guide The higher the lock signal the better the shimming
• Deuterated
– Solvent signal less likely to swamp sample signal – Allows field frequency lock – Easier to achieve homogeneity
• Solubility
– Preferably over 2 mg/mL for 1H – Preferably over 10 mg/mL for 13C • Cost: D2O and CDCl3 are the cheapest so used most often
Pulse duration on the spectrometer in µ p1, p2, etc. s:
Use of the NMR Spectrometer by Roy Hoffman
Acquisition of signal z
FID M y phase receiver y precession B1 x x phase receiver
Use of the NMR Spectrometer
A Practical guide
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Use of the NMR Spectrometer by Roy Hoffman
Choose NMR tube
• 300MHz
– Wilmad 507-PP-7 – Aldrich Series 300 – Kontes Grade 3
90°x pulse transfers the magnetization vector to the y axis
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Use of the NMR Spectrometer by Roy Hoffman
Fourier transform
downfield upfield
Fourier transform
Screen
BSMS for shimming, etc.
Display
Preamplifiers Probe tuning adjustment
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Cabinet not shown
Use of the NMR Spectrometer by Roy Hoffman
Adjustment wheel
• 400MHz
– Wilmad 528-PP-7 – Aldrich Series 400 – Kontes Grade 6
2 Use of the NMR Spectrometer by Roy Hoffman
Ensure that the tube is clean
First remove any labels then use an NMR tube cleaner
Frequency/Chemical shift
Time since pulse
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Sampling and folding
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Number of FID points (TD)
Slower sampling covers a narrower spectral range and causes peaks outside the range to fold in. Folding peak Spectrometer frequency (SF) 0ppm
Roy Hoffman
Wash the outside of the tube
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Insert the tube completely and Wash the inside of the tube
Use of the NMR Spectrometer by Roy Hoffman
If you are not sure it is now clean put some cotton wool on the end of a stick,
Put sample in spinner and clean with a dry tissue
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Use of the NMR Spectrometer by Roy Hoffman
Sample position
>4 cm depth 2 cm
Short sample Centered
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Use of the NMR Spectrometer by Roy Hoffman
and the sample is clear
Label it concentrically
Must be removed to run sample & may 12 lost get
Stuck on & does not fit in the magnet
Paper & magic tape
Aldrich NMR tube lable
• Overlapping signals: If the sample’s signals are near
the solvent signal consider another solvent
7 Use of the NMR Spectrometer by Roy Hoffman
The sample must be clear
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Field sweep Adjust width with SWEEP WIDTH
Use of the NMR Spectrometer by Roy Hoffman
Probe tuning controls
Matching Tuning
Adjustment tool
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Tuning screws for 1H
Use of the NMR Spectrometer by Tuning Roy Hoffman
sliders for 13C, etc.
How to tune the probe
Start tuning Adjust T Adjust M while correcting T
On screen
On preamplifiers
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Tuned frequency
Matching This is tuned This is tuned & matched
Use of the NMR Spectrometer by Roy Hoffman
Shimming For basic shimming start adjust Z
Soak it with acetone and insert it into the tube
Repeat with fresh cotton wool until it comes out clean
6 Use of the NMR Spectrometer by Roy Hoffman
Choose solvent
or the spectrum will yield broad and misshapen signals
Suspension yielution yields good spectrum
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Use of the NMR Spectrometer by Roy Hoffman
Filter it if there is precipitate
Insert a piece of cotton or glass wool into a pipette
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Wash it with a Pack it little solvent Use ofdown the NMR Spectrometer by
Use of the NMR Spectrometer by Roy Hoffman
NMR Spectrometer
Insert sample here Computer
Bruker DRX 400 spectrometer
RF pulse display
Printer Magnet Keyboard
Inserting the sample
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Use of the NMR Spectrometer by Roy Hoffman
Sample in probe
Tube
Turbine in bore of magnet
Inside of probe
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Use of the NMR Spectrometer by Roy Hoffman
Roy Hoffman
But never return the solvent to the bottle
Solvent depth 4.5 to 5 cm
Ideal depth 4.5 to 5 cm
Too long yields good spectrum but wastes solvent
BUT shimming OK here Just fix the phase
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Adjust Z3 then Z & Z2
Adjust Z3 & Z then Z2
Problem with X, Y, etc.
Use of the NMR Spectrometer by Roy Hoffman
Spin speed × 2
Field-frequency Lock
Adjust symmetry with LOCK PHASE Position of 2D signal Adjust position with FIELD Adjust height with LOCK GAIN and LOCK POWER Locked signal Adjust height with LOCK GAIN and LOCK POWER LOCK Enter lock solvent name e.g. lock cdcl3