tag:blogger.com,1999:blog-3300702123878659843.post3257990631950577102..comments2024-03-26T05:25:50.831-04:00Comments on University of Ottawa NMR Facility Blog: Weak Lock Signals and Distorted NMR SpectraGlenn Faceyhttp://www.blogger.com/profile/05146575170575279335noreply@blogger.comBlogger12125tag:blogger.com,1999:blog-3300702123878659843.post-13671812319847658312017-07-10T09:31:23.068-04:002017-07-10T09:31:23.068-04:00Hi Craig,
Thanks for the comment. We have been doi...Hi Craig,<br />Thanks for the comment. We have been doing this at uOttawa as well but have never set it up as solvent options from the lock table. <br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-3299439780566052072017-07-10T09:25:15.236-04:002017-07-10T09:25:15.236-04:00Glen,
we have, recently, set up non-deuterated so...Glen,<br /><br />we have, recently, set up non-deuterated solvent choices for our users on our Bruker instruments. We then link those to an edited shim routine (topshim 1H lockoff o1p=x.xx selwid=0.5) with the sweep and lock off. This works well for samples where users are taking aliquots from reactions and looking for quick 1H experiments.<br /><br />Craig.<br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-55582477077206551102017-01-18T08:48:02.697-05:002017-01-18T08:48:02.697-05:00Paul,
If you are asking if a spectrum is quantitat...Paul,<br />If you are asking if a spectrum is quantitative if the lock is not used, the answer is yes, providing that your acquisition parameters are appropriate for quantitative results. The quantitative nature of a spectrum is not dependent on whether or not a deuterium lock is used.<br />Glenn<br />Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-54916362262820869312017-01-17T20:47:15.836-05:002017-01-17T20:47:15.836-05:00Run you run a spectrum unlocked, but have the othe...Run you run a spectrum unlocked, but have the other necessary like relaxation, will running NMR unlocked be quantitative?Paul Khttps://www.blogger.com/profile/17322710073500185522noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-15450590611974097632015-10-07T20:45:37.845-04:002015-10-07T20:45:37.845-04:00Anonymous,
Thank you for the information. You are ...Anonymous,<br />Thank you for the information. You are correct. One can certainly improve the quality of the lock signal on a Bruker spectrometer with the loop adjust routine ("loopadj" command, if I recall correctly). I have seen this optimization make a remarkable improvement in spectral distortions when the lock signal is weak. <br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-61450895538539357912015-10-07T18:45:40.832-04:002015-10-07T18:45:40.832-04:00Hi Glenn,
You can usually compensate for a noisy ...Hi Glenn,<br /><br />You can usually compensate for a noisy lock by adjusting the lock averaging time. The lock system works exactly as Stan described it but it does not feedback instantaneously. Usually the signal is averaged over a period of time, from either a few milliseconds up to a few tens of seconds in a form of rolling average so such unwanted behaviour is avoided. The averaging time can be defined with some parameters, either more or less precisely depending on the instrument manufacturer. There are cases where people were able to obtain good lock on modern systems with cryogenically cooled probes using tap water! This depends heavily on the ...tap and it is said that for some reasons the water from the taps in Toronto is particularly good for that. Have you tried with Ottawa tap water?<br />But in any case having a high concentration of deuterium is the best thing to do and you should blame your sample preparation if it does not work and not the instrument;-)Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-62686559352337456072013-06-03T12:04:02.176-04:002013-06-03T12:04:02.176-04:00Christian,
Sometimes when a solvent mixture is use...Christian,<br />Sometimes when a solvent mixture is used or a deuterated solvent with more than one deuterium resonance is used, the spectrometer will lock on the wrong 2H resonance and the chemical shift scale on the spectrum will be displaced according to the difference in chemical shift between the the lock resonance and the other 2H resonance. This can be avoided by carefully editing the edlock table.<br /><br />I'm guessing here but perhaps resolution in the spectrum of a material in a solvent mixture may suffer due to the exhange of solvent shells around the molecule of interest at a rate that would produce line broadening.<br /><br />Glenn<br />Glenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-61268925677833954362013-05-31T02:46:17.944-04:002013-05-31T02:46:17.944-04:00Hi Glenn,
I hope my question(s) relate best to t...Hi Glenn, <br /><br />I hope my question(s) relate best to this entry of yours: We encounter difficulties to get proper spectra in CDCl3/CD3OD (let's say 3:1) mixtures in Bruker's automation - what is your advice to answer this problem on rare occations or as a routine job?<br /><br />Besides maybe necessary additional manual work, can there be any physical reason that a mixture-spectrum likde this can never be as good as a spectrum in a pure solvent?<br /><br />All the best, <br /><br />ChristianStettyhttps://www.blogger.com/profile/16274839844226746827noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-89998227318967439192012-04-30T10:48:48.912-04:002012-04-30T10:48:48.912-04:00Stan,
Thank you very musch for your explanation.
...Stan,<br /><br />Thank you very musch for your explanation.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-9693496948302669342012-04-30T10:48:14.553-04:002012-04-30T10:48:14.553-04:00Paulaner,
Thank you for your question. Please se...Paulaner,<br /><br />Thank you for your question. Please see Stan's comment for an excellent explanation.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-61957751059780874292012-04-30T04:13:17.514-04:002012-04-30T04:13:17.514-04:00Yes, Glenn, nice entry. People often forget that t...Yes, Glenn, nice entry. People often forget that the lock system is just an electronic circuit. It takes as input the 2D NMR signal, compares it to a fixed desired frequency and generates an output "error" signal driving an additional B0-correction coil located in the shims assembly. If the input is low quality (bad S/N) or if the circuit is defective, or oscillates, or otherwise misbehaves, it will actively produce field noise!!! On supercons, where inherent noise is very low, it is used primarily to compensate long-term drifts and environmental noise arising from the mains (lighting and other currents in the room). But it is a mixed blessing since it usually introduces more noise at frequencies over 100 Hz than what would be present without the lock. And that is normal operation - just imagine what happens when it is defective or when its input is inadequate.Stan Sykoranoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-86943259141391867092012-04-29T12:59:16.030-04:002012-04-29T12:59:16.030-04:00which is the explanation for that to occur? I mea...which is the explanation for that to occur? I mean, the bad spectrum quality while locking a weak signalpaulanerhttps://www.blogger.com/profile/07857139074876913309noreply@blogger.com