Re: [AMMRL] Artifact: processing or acquisition?

From: Anklin, Clemens via groups.io <clemens.anklin=bruker.com_at_groups.io>
Date: Sun, 6 Oct 2024 01:52:55 +0000

Hi all,

here a few more comments on this topic.

The udeft pulse sequence as implemented has basically no phase cycle. This
means that any eventual DC offset in the FID is not eliminated. This is usually
done by at least inverting the pulse and the receiver as the DC offset will
not change and thus be cancelled out. There are probably ways to include a
basic phase cycle to get rid of the DC offset.

The data included in Luke's mail is acquired in the QSIM mode. Setting AQ_mod
to DQD would also eliminate the DC offset. DQD acquires the data at an offset
and digitally demodulates. This also eliminates the DC offset.

Finally setting bcmod to "quad" will also almost completely eliminate this center spike.
    BC_mod = no BC-mod = quad
[cid:part1.VRreqklu.ua1dELMT_at_bruker.com][cid:part2.PQbiNPWk.kfGTaqq0_at_bruker=
.com]

I hope this clarifies some issues.

Regards

Clemens


On 10/4/2024 12:53, Fulton, Luke via groups.io wrote:

Hi all,

Turns out my predecessor(s) fought this problem tooth and nail before finding
a suitable workaround. The artifact is indeed from the carrier frequency. It
crept up long ago in the lab and eventually affected all of our Bruker systems.
This being the first time I've run into it myself I assume some degree of
intermittence. From what I hear it's a common issue many labs have experienced.
It's removable by applying linear prediction in TopSpin processing, and then
in Mnova loading the 1r file to receive the same benefit. There's still some
mystery why this happens at all, but with a fix in place I can live not knowing.

Thank you all for the rapid feedback, your numerous offers to help are highly
appreciated. I've attached an example raw data file here for the several
who were curious to take a look themselves.

Kind regards,
Luke


Luke Fulton,
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticutâ
Storrs, CT 06279

email: fko24003_at_uconn.edu<mailto:fko24003_at_uconn.edu>
(alias): luke.fulton_at_uconn.edu<mailto:luke.fulton_at_uconn.edu>
mobile: (603) 953-5275
Office: (860) 486-4069
________________________________
> From: main_at_ammrl.groups.io on behalf of Fulton, Luke via groups.io
> Sent: Thursday, October 3, 2024 5:54 PM
> To: main_at_ammrl.groups.io
> Subject: [AMMRL] Artifact: processing or acquisition?

Hi all,

A user has reproduced a strong singlet centered at o1p in udeft carbon spectra.
I'm reminded of center spectra phantom peaks that appeared on varian's
when number of transients wasn't a power of 2. But those "signals" only contained
a single data point, and in this case the "signal" has plenty of points. It
appears on Mnova, is absent in TopSpin, and we've confirmed independently with
multiple computers. I'm certain it's an artifact rather than sample contents.
What I'm less sure of is whether it stems from the instrument and acquisition
conditions, or file transfer and data processing. We've encountered both sorts
of issue previously. The console's TCU B cable has known problems right now.

If no has heard of this before then I'll push them to repeat the measurement
on a different magnet. They're itching to submit and won't want to chase the
ghost. I just don't want them relying on questionable data.

Kind regards,
Luke

Luke Fulton, PhD
CHEM BLDG R003
NMR Core Facility Director
Unit 3060
COR2E & Department of Chemistry
55 N Eagleville Road
University of Connecticut
Storrs, CT 06279
email: fko24003_at_uconn.edu
(alias): luke.fulton_at_uconn.edu
mobile: (603) 953-5275


--
==========================
==========================
====================
Clemens Anklin Ph.D. Vice President
Bruker BioSpin NMR Applications & Training
15 Fortune Drive NEW Phone: 978-313-5NMR(5667)
Billerica MA 01821 twitter: _at_canklin
web: http://www.bruker.com
e-mail: clemens.anklin_at_bruker.com
==========================
==========================
====================


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Received on Sun Oct 06 2024 - 10:01:51 MST