Thank you to all of the great responses I have had to my query - if I didn’t
respond to your response directly it is because I couldn’t get your email
address off the message you sent.
I do want to clarify a couple of things:
- The background signal was acquired with no sample (no NMR tube) in the probe.
The sweep and the lock were off.
- I did run different RGs and p1s and can see that the ‘extra peaks ’
are not from pegged receiver gain.
As far as correcting for it, the primary suggestions are:
- Run a ‘blank’ and subtract that from the desired signal.
- Use a pulse sequence that is sensitive to the rf field of the sample, like
zgbs (DEPTH); there are some other methods like EASY that could also be tried
(in this case it tries to acquire the background fid separately immediately
after the desired fid).
- Try to correct the initial points of the fid, where the background signal
reveals itself. I do know that I can back predict the initial points in the
fid in TopSpin and remove the background, but don’t know yet how that
affects the quantitation. The AU program cryoproc1d also appears to incorporate
backward prediction, but I have not tried that.
Thanks again everyone for your help with this!
Tom P, SOU
> On Jan 10, 2024, at 3:24 PM, Tom Pratum via groups.io wrote:
>
> Hello All-
> We have a fairly new 400 MHz NEO Nano instrument with a broadband iProbe.
> One user is very interested in 27Al, and I note that in this probe there is
> a relatively significant 27Al background signal - I have seen 27Al background
> signals in pretty much every probe I have ever looked at. I have attached a
> plot of the signal (tuned empty probe) as acquired with a 2 usec pulse (around
> a 30 degree pulse at this power level), with the sw maxed out at 1.875 MHz,
> and 8 scans. The central component is around 11 kHz wide.
>
> I find the background signal relatively surprising due to the large number
> of components, and I am thinking the appearance could possible be due to one
> or more spin 5/2 powder patterns in which only the narrowest components appear
> due to how the spectrum was acquired, but really don’t know if that
> is the case. These components are not artifacts as they do move with the field.
>
> The user has some pretty broad signals they are interested in quantitating,
> and it would be good to remove the central component of this background signal
> if possible. I can think of a number of characteristics - such as T2 and rf
> inhomogeneity - that could be used to remove the signal, but they would also
> likely affect the quantitation to some degree,
>
> Does anyone have any experience in removing this background signal they can suggest?
>
> Thanks in advance.
>
>
> Tom Pratum,
> Southern Oregon University
>
>
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