On 6/13/2023 11:23 AM, Kenneth Sharp-Knott wrote:
> Can't say I've ever seen an EPR post on here, but here goes... I'm
> barely familiar with EPR but manage the instrument in our lab. Today,
> the users are observing a signal/feature/hump an the start of the
> spectra from 0-500G which should not be there. I have no idea where
> it is coming from, but it's present in all samples, including the standard.
> Anyone have any ideas? This is a Bruker EMXplus with the Premium X MW
> bridge.
Hi!
I do not recognize the 0-500 G signal in your PDF. So, feel free
to be very sceptical. However, I have dealt with a number of
background signals in resonators over the years. Perhaps these may
be useful checks.
Paramagnetic oxygen in the air can give a background signal (though I
think that this is usually at higher magnetic field values from my own
experiences). One can flush the waveguide and empty resonator with dry
nitrogen gas while acquiring data to see if the signal disappears.
Second, the thermocouple in a Bruker heater dewar may extend just high
enough into the cavity to yield a background signal. One can usually
lower the tip of the thermocouple to keep it out of the cavity...or
just remove the heater dewar entirely, at least as a check.
Third, there can be user contamination of the cavity. For me this usually
results from users running samples in containers other than a quartz EPR
tube, i.e., samples mounted in "straws" used with the SQUID, single crystals
mounted on the end of an EPR tube, etc. If part of the sample breaks off
or flakes off, that flake may remain in the resonator. You might wish to
check with Bruker first before attempting to clean out a resonator yourself..
The three basic cleaning procedures than can usually be done by a user are
the following:
1) With the resonator removed from the instrument, try blowing the resonator
out with dry nitrogen gas. Outside of the instrument, you can
turn the resonator to various angles to help anything fall out of the
resonator.
2) If that fails, the resonator might be rinsed with ultrapure water,
i.e. water with conductivity in the megaohms.
3) If that fails, EDTA might be added to the ultrapure water to act as
a chelating agent.
If all that fails, you might have to send the resonator back for
re-manufacturing.
Bob
--
Robert E. Taylor, Ph.D.
Department of Chemistry and Biochemistry
University of California, Los Angeles
607 Charles E. Young Drive East
Los Angeles, California 90095-1569
E-mail: taylor_at_chem.ucla.edu
Telephone: (310) 206-2074
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Received on Tue Jun 13 2023 - 12:38:18 MST