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To experienced Bruker users: I often get the following message in ICON-NMR while running HSQC/HMQC: "zg: DRU warning: n ADC-overflow warnings received during acquisition (DRU1)!", with n being a variable number between measurements. Any idea what it means? Is there anything wrong with my acquisition parameters? I mean, my spectra seem ok but maybe because of it I'm suffering from sensitivity loss, or else. I wonder if there is something i could easily do to solve this. |
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This means that sometimes during the measurement the signalis too sstrong for the analog to digital converter. Can you provide a few more details about the sample, solvent etc. If there is no detrimental effect on the data you can also just disregard the message. Hi Clemens, some more details about the problem: Samples = small molecules, 200-600Da, 2-10mg range Solvents = either DMSO-d6 or CDCl3 Experiment = standard HSQCEDETGP from Bruker, run in ICON-NMR - Sylvain Demanze (Mar 09 '11 at 05:10) + I sometimes get a zg pop-up window stating "DRU warning, ADC flow during last scan (DRU1! This will lead to a loss of quality of the FID. Reduce the receiver gain to avoid this problem" - Sylvain Demanze (Mar 09 '11 at 05:16) I checked the RG value in the acqpars: set at 2050 for all spectra measured (limit?) and 18390.4 in the exppar before measurement. - Sylvain Demanze (Mar 09 '11 at 05:16) |
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This can be common in 2D pulse programs where the first increment is not the biggest FID in the experiment. Under these circumstances, if you use RGA your receiver will be set too high and you will get an overflow in later increments. To get around this, it is worth setting a fixed receiver gain for these experiments. Set the receiver gain to a sensible level (e.g. half what RGA would set) and store it in your parameters. The change the automation program (AUNM) to "au_zgonly". This will prevent RGA setting the wrong value... |
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A common mistake is to tune the probe after you have don RGA. be sure not do do so, a badly tuned probe will not be as sensitive as a tuned one and consequently, your RG will be larger, tuning the probe after RGA has been done often causing reciever overflow (and FID clipping). Also, keep in mind that RGA automation program should be au_zgonly as said before, as gradients tend to attenuate the signal and cause the selection of a larger than needed RG. |
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As a side-note, our cryoprobes have in the past often had a large spike at the start of the fids, which if you use RGA, will give an artificially low value. In 2d's we've always avoided RGA for the reasons John mentioned above. The signs of clipping the spectra signals due to incorrect digitization (rg is too high) I've seen are :- for mild clipping; slight distortions in the baseline and the base of peaks; for severe clipping big distortions to the peak shape and spurious peaks in the baseline. Also maybe its not to be recommended, but you can use the 'ha' tool to log into the DRU and switch the warning off... Duncan |
If you have max RG = 2050 (e.g.) and get overflow then just set it to 1030. If you still get overflow then set RG = 600. And so on - rga doesn't work properly for 2D experiments, you have to copy it from corresponding 1D experiment. - Dmitry Mainichev (Mar 22 '11 at 18:51)