NMR manager
Johns Hopkins School of Medicine
312 WBSB
Department of Pharmacology
725 N Wolfe St
Baltimore, MD 21205
410-502-4803(office)
Varian NMR trouble shooting
- I can not see the acqi button nor can I see the window.
Go to the macro window and type acqi, then enter¿. It should show up.
- After integration, I can not see the full spectrum.
Type ds and then click full button.
- My middle mouse button does not work, I couldn’t use it to increase the peaks in the window.
This is because you are in integration mode. Use mouse to click at the button full int/part int until it becomes no int. Try the middle mouse button. It should work.
- My spectrum looks strange. There are some other peaks which are not supposed to show up.
Check sw (spectral width), our 400MHz machine is set to 6400. If it is small, then type sw=6000, and then run the spectrum again. Then wft, f full, aph. If you still see something strange, type sw=sw*2, run spectrum again and then wft, f full. You need to reference the spectrum. Then put the cursors a little farther away from the side peaks. And then type movesw, and then collect the spectrum again.
Oh, it is too complicated. Then try to load an FID you previously saved, and type wft, then use these parameters to run the experiment by typing ga.
- My spectrum baseline is so thick, should I run more scans.
You can use line broad width to edit your spectrum. Type lb=1, wft f full.
- I tried to save my FID, but the computer does not do the job for me.
You are in vnmr directory. You need to go back to your own directory. To do this, use your mouse to click the following buttons: main menu, file, set directory, home. You will be redirected to your own directory. You need to check where you are. Type pwd and then eneter, you will get a message on top.
7. When I run an experiment, I get a message saying ACD overflow. How can I avoid this.
It is a gain-related problem. To solve this problem, type gain? and you will get a number showing on top. type nt=1 gain='n' ga to get a spectrum. Now type gain? one more time, you will see that gain not in use (xx), but there is a number in the brackets. Now type gain=xx ( the number in the brackets) and nt=16 bs=4 ga. wft aph.......
8. My spectrum looks to have a fat baseline. What is going on?
It is because you applied too much noise into the fid. Type df (display fid) to take a look at your fid. Then type dscale (or click at dscale ), you can see that your magnetization relaxed to Z in 0.5 s. There is an additional 1.5 seconds (if your at is set to 2 s). To make your baseline thinner, type at=0.8, d1=3 then type dg (display group parameters)to have a look at the parameters. Then type ga.
You can also set lb(line broadwidth) to at/2, (at=acquizition time and then type wft when you process the spectrum.
9. How long does gradient shimming take?
Usually one cycle takes 20 seconds when you use the default nt of 4(nt= number of transients). If you think it is too long, you can change nt to 2.
Gradient shimming takes about 3 to 4 times and will stop when RMS (root mean square error) is less than 1. It will try up to 10 times and then stop.
See the picture.
