0
|
Hey all! We've got a serious problem because with our new probe (5mm bbo bruker) the t1 noise in the heteronuclear correlations is fucking high. Maybe i did something wrong by adjusting the pcpd sequence. As pulse power for pcpd i have chosen the pl of the calibrated decoupling pulse, was that right? Or has someone experience with this issues? I am working with an avance drx500 with xwinnmr. Thx a lot for EVERY hint! Cheers |
|
0
|
Hi, Firstly I suggest you to check some literature that concerns this topic, for example: Systematic sources of signal irreproducibility and t1 noise in high-field NMR spectrometers http://www.sciencedirect.com/science/article/pii/0022236492902648 Sources of t1 noise in two-dimensional NMR http://www.sciencedirect.com/science/article/pii/002223648490221X Regards, Arkadiusz |
|
0
|
Hi, Assuming you're using gradients, these should be fairly clean - the gradients should suppress the (large) signal from the uninteresting protons. The source of t1 noise is then modulation of the (small) real signals, and you do not normally see much t1 noise in heteronuclear 2D spectra. Things that can go wrong include: Gradients not working - but then you should also see that the quadrature detection has failed and you get mirror image peaks. Do you see the lock signal drop periodically during the experiment? Problem with 2H stop filter on/in the X preamp - if this is missing/damaged the noise from the decoupler will interfere with the lock and introduce t1 noise (this only applies to HSQC). If this is the problem setting the decoupler power to 120dB should give an improvement. Autoshim can cause t1 noise if set to change shims by a large amount and with a small time interval. If that's on, turn it off and see how that looks. Spinning - this will usually cause significant t1 noise Bad lock settings - if the lock regulation is really bad this could give t1 noise even when there are only relatively weak peaks. Does the lock signal look noisy? are the shims OK? You can try to improve the lock regulation by using the "loopadj" command after locking and before acquiring. This will set the lock regulation parameters based on the lock signal strength (this is a temporary operation - it will not update the parameters in the edlock table). If the lock is the issue then you may get better results in e.g. DMSO than CDCl3. Temperature instability - but this will normally cause more peak shape distortion (if just heating due to e.g. decoupling) or sidebands (if cyclic heating due to room temp fluctuations or poorly set PID parameters), rather than t1 noise. Can you post a picture of an example spectrum? |
