Title:
NMR Manual for Cross Polarization Magic Angle Spinning (CPMAS) Experiment
Purpose
This CPMAS manual will help NMR users to understand the advantages of Cross Polarization Magic
Angle Spinning and to follow the procedures to conduct this experiment with little or no NMR staff
assistance
Introduction
Solid state NMR is very different from solution NMR. The significant difference is the NMR peaks
are much broader. The broad peaks are caused by three anisotropic nuclear spin interactions:
 chemical shielding anisotropy
 dipole-dipole coupling
 quadruple coupling
To overcome these broadening factors, CPMAS with high power proton decoupling is applied as the
most common technique in solid state NMR. Even with this technique, the peaks are still hundred
times broader in solid NMR than that in solution NMR.
Why do we need to do solid state NMR, since there seem no advantages? There are two occasions:
 if a sample is not soluble in any solvent
 if there could be a structural change to the sample in the solution
In such a case, solid state NMR is the only choice. Although not many users are doing solid state
NMR (only about 5%), the technique is still a powerful tool to help NMR users get structural
information.
CPMAS is commonly applied to C13 NMR, but can be applied to the other hetero-nuclei also, such
as Al27, Si29, P31, Sn119, etc. There are two advantages from CP:
 to assist in observing dilute spin, such as C13 (natural abundance 1.1%), and increasing
peak intensity
 to shorten the delay time, and therefore, to shorten the data acquiring time
The advantage of MAS is that to reduce the dipole and quadruple interactions, and therefore, to
make NMR peaks sharper.
Preparation
Spectrometer: NMR-S400 only
Probe: 5mm HXY probe or 3.2mm HXY probe
Prerequisite: users have done the basic and solid NMR training; also users should understand the
differences between solution and solid NMR, such as hardware, T1 and T2, etc.
Sample: must be in powder form; and 160 mg or more are required
Reading:
http://www-f9.ijs.si/~krizan/sola/sempod/0607/rangus-seminar.pdf
http://en.wikipedia.org/wiki/Solid-state_nuclear_magnetic_resonance
http://mutuslab.cs.uwindsor.ca/schurko/ssnmr/ssnmr_schurko.pdf
Experiment Setup
1)
2)
3)
4)
Login on FOM system and login as walkon on Solid400 computer
Load solid sample into a rotor, put rotor into the probe, insert probe into magnet
Open a standard file, e.g. C13_tancpx, into the current buffer, e.g. exp1
Check all the parameter values are the newly updated, e.g. pwX90 (Figure 1)
Check probeConnect on screen is ’H1 C13 Si29’, for instance (Figure 1)
Check hardware cable connections correct, e.g. cable channel 2 connected to X on probe
5) Start spinning the sample to appropriate rpm by pressing 'Start', as shown in Figure 2
Figure 1. Parameters in Channels Panel.
Figure 3. Manual tuning Interface.
Figure 2. Parameters in Spin Panel.
Figure 4. Parameters in Acquisition Panel.
6) Tune the nuclei, e.g. C13 and H1, by a command mtune. Usually, tune C13 first in Channel 2,
then H1 in Channel 1 (Figure 3). Hit button Start Probe Tune, then tune it manually using the
rods on the probe (2 red rods always for H1, and X and Y depend on probe mode) and watch the
dip position moving; if it’s good, stop and quit
7) Acquire data with appropriate nt and bs (Figure 4), then hit Acquire button
8) Preview the spectrum by wft when bs1 is completed; decide to stop or keep running
9) Save data into a correct folder, i.e. /walkon/PI_name/user_netid/
Ending Work
1) Stop acquiring and stop spinning
2) Take rotor out of probe
3) Take sample out of rotor and clean up the rotor
4) Write a note in Log Book
5) Keep desk top clean
6) Logout from S400 computer and FOM
Manual Created by: IMSERC Lab, Department of Chemistry, Northwestern University
Manual Revised Date: March 2014