Have you ever colleccted NMR data and found that the signal-to-noise ratio was very poor even though you just KNOW that there is absolutely nothing wrong with your sample? If so, the following note may help you figure out the problem. The flow chart in the note is especially helpful.
Daniel D. Traficante, "Elementary Trouble-Shooting for Poor Sinal-to-Noise Ratios of NMR Spectrometers" Concepts in Magnetic Resonance, 2, 63 (1990).
http://scholarsportal.info/cgi-bin/sciserv.pl?collection=journals&journal=10437347&issue=v02i0002&article=63_etfpsrons
I must admit that when students come to me with poor signal-to-noise ratio problems, the first thing I check is the sample. Most often this is the problem as many people really have no idea how much sample they have in their tube or the sample is cloudy or has precipiate or is not filled properly or is paramagnetic or is a complex mixture......... If the sample appears OK, I use the logic in the note above to help isolate the problem.
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2 comments:
Hi Glenn, I am having an issue with Noise in my spectrum. I observe a noisy baseline particularly at the base of every peak. Also the sweep line in lock window is very noisy. Many time it takes a lot of time to shim the magnet. Some times it does not shim at all, says that 'signal-to-noise ration is too low, Shim failed'. Can you help me to solve this issue?
Bharat,
The problem with poor S/N in the lock may be a separate problem compared to that in other channels of the spectrometer. The lock problem may be with the 2H transmitter board or the lock preamplifier.
From the information you give, it is difficult to make a guess as to what the problem may be. Here are some questions you should address to help troubleshoot the problem.
Is the problem with noise you observe in your spectrum common to both the 1H and broadband channels?
Is the noise uniform across the baseline?
Are your pulses still calibrated correctly?
Do you see excessive noise in your wobble tuning curves?
Does the problem persist if you use a different SGU?
Does the problem persist if you unplug the gradient cable?
Does the problem persist if you unplug the VT heater?
Does the problem only occur when you use 1H decoupling?
Does the probe tune well?
Is the sample sitting properly in the probe? (maybe VT gas is lifting sample)
Good luck
Glenn
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