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Lecture
Methods in Magnetic Resonance
We will use the 200 MHz Varian NMR to demonstrate a standard 1H Block Decay (1 Pulse) Experiment. A PDF TUTORIAL CAN BE FOUND AT: http://nmr.asu.edu/nmr/opguides.html
Once you are trained you will receive a username and password for the Sun Blade Computer that runs the 200 MHz NMR.
The program that controls the NMR is called vnmr.
So, the first thing we need to do is login and start vnmr. Once you do this it will start 4 windows.
The top window should look something like:
The "Seq" gives the loaded sequence and "Exp" tells you what experiment # you are currently in. The command line allows you to type all commands needed to control, process and print NMR spectra. Also, most common commands can be accessed from the menu buttons shown below the command line…. NEVER PRESS THE GLIDE BUTTON!!
The second window is a black background window that will typically be blank when you first start. It is the window for displaying your data, fid or spectrum.
The bottom window is the place where most information about the acquisition and processing settings can be found. The startup bottom window for the standard 1 H NMR (Seq: std1h) is shown below:
Chm598 - Prof. Yarger Thursday, February 08, 2007
The last window that shows up (typically on the upper right part of the screen) is the acquisition status window:
As the acqu. Window states, we are currently Idle. Hence, lets setup an run a standard 1 H 1-pulse NMR experiment on 95% D 2 O, 5% H 2 O in a std 5mm NMR tube.
Click the following sequence:
Or type: setup('H1','D2O')
Type: dg
You will see that the standard parameter set has you running 16 transients, 16k data points, 3kHz spectral width. Also, the spectrometer will also auto lock, auto shim and auto set the receiver gain.
If you are ready to go, Type: ga And the spectrometer will collect a std 1H NMR data set. It will also auto lock, auto shim
Now lets go back and look at the processed data. First I type ds to display the spectrum, then type aph , to auto phase the spectrum.
Now I will turn the integral off (since this is a one peak spectrum, where relative integration is not useful)) and show the scale ( dscale ):
Okay, we have run a std 1H NMR of water. What did the pulse sequence look like? Type dps , to display pulse sequence:
So, we pulse for 16.5 microseconds and then collect data for 2.7 seconds. Why are we pulsing 16.5 μs? Why not 10 μs or 30 μs? Typically, we want to obtain the maximum signal and this is achieved by using a (^) π/w pulse (90o^ pulse). So lets do an experiment to tell us the π/2 pulse length for this spectrometer (with the current power settings and probe).
The easiest way to do this is array the parameter pw. This is typically called a nutation experiment.
So, to array pw, type pw=1,5,10,15,20 … With our 95:5, D 2 O:H 2 O sample, lets just use one transient ( nt=1 ) and we will set the gain way down ( gain=2 ). Also, lets narrow the sweep width ( sw=1000 ) and add a delay between experiments to insure the system is back to equilibrium before starting the next array point ( d1=10 ). Basically, we need to way 5*T1 to ensure the spins are back to equilibrium.
Now type dg (to display parameters in lower window)
It shows the pw parameter is an arrayed list. To display the values of this array type arraylist :
The spectrometer is still locked and shimmed. So, type ga. It will take several minutes to collect all 20 data sets. Type time to find out the total exp. Time. This will collect 20 separate FIDs and when you type ft , will process 20 separate spectra. Specifically, type lb=1 wft and then phase the first spectra ( phase ). Now type ai to put the y-axis in an absolute intensity mode (otherwise it scales on spectra by default) and type dssh to display the spectra horizontally:
