Using a smaller diameter sample (3mm sample inside of a 5mm probe) can
have a dramatic reduction of the salt effect. If you have a 3mm turbine,
just use that turbine for a 3mm tube. You will, of course, have a hit on
filling factor, but the tuning should be closer to that of a non-lossy
sample, so you'll not suffer the full loss. You might be able to tune
the probe properly and determine the 90-degree pulse length.
If you don't have a 3mm spinner turbine you can place the 3mm sample
inside a 5mm tube. I recall doing this many, many years ago when I had
to have a 13C lock signal to do time averaging to do 13C (cw!) observe
on a 100MHz (proton) spectrometer. The S/N ratio was about 2 for this
lock, but it did work. I recall using a thin piece of teflon, cutting
out triangles that would fit inside a 5mm tube and then punching out
holes for a 2mm capillary containing the enriched carbon disulfide.
A side benefit for the 3in5 approach is that you can use any lock
solvent (non-salty organic, for example) in the outer space.
On 6/24/2025 9:33 AM, Vander Velde, David via groups.io wrote:
> Yes, assuming that's the 1H match control on your system (it's channel
> 6 on mine). High ionic strength samples drive the match towards its
> minimum value, and once you reach that in a particular probe, you're
> out of luck with getting the sample properly matched.
>
> Setting aside the question of whether it's necessary or advisable to
> prepare a sample like that, you can still get some kind of 1H spectrum
> by skipping probe tuning, taking some big hit on sensitivity. Some
> experiments are not going to work or not advisable, like 13C with 1H
> decoupling—you'd get high reflected power back from a mismatched
> probe, and the normal decoupling parameters will fail.
> ------------------------------------------------------------------------
> *From:* main_at_ammrl.groups.io on behalf of Stephen Nolte via groups.io
> *Sent:* Tuesday, June 24, 2025 8:13 AM
> *To:* main <main_at_ammrl.groups.io>
> *Subject:* [AMMRL] New Error on Varian 400MR
>
> Hi all,
>
> Summer research students elicited a new intermittent error this week
> on our Varian 400MR failed - rf signal too weak on tune chan#5.
>
> Can this be related to high levels of ionic salts in the sample?
>
> Thanks!
>
> _______________________________
>
> Stephen Nolte | Chemistry Technician
> Millersville University
> 717-871-7413
>
>
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