Dear Colleagues,
We recently begin to work on peptides with our Inova 500 (installed last year), and we have a big problem with the probe tuning. For a peptide in a 50mM salt buffer solution, the reflected power in the tuning meter could not reach lower than about 300 in our HCN probe at attenuation of 9; the reflected power can not be lower than 500 for a 100mM salt, and the water suppression works very poorly. We tried with another probe we have, a HCNP penta probe, it is a little better, the reflected power is above 90 for 50mM buffer, and about 190 for 100mM buffer. In both probes, turning the matching knob counter-clockwise (if one faces the bottom of the probe) reduced the reflected power quickly, but the matching knob reaches its limit at the above mentioned reflected power. The tuning is still adjustable, but only increases the reflected power in either direction.
Both probes can be tuned well with normal organic solvent or D2O without salt. I have very little experience with salted solution, and I know that having salt will result in detuning of the probe, but I did not expect such a big effect even for 50mM salt. I was told that in the literature, people have used salt concentration as much as 300mM, which will be completely unworkable on our probes. So my question is:
1. Are both of our probes bad for salt samples? What are the acceptable reflected power for high salt concentrations in your experience, especially with Varian's probe?
2. Our magnet have a drift rate of 5~6Hz/hour, and the probe has been delivered for about a year now. The current proton frequency is about 499.700MHz. Could the field becomes in compatible with the probe electronics now? What are the lowest field that functions well you have seen with the Varian Inova 500 system?
Any suggestions will be greatly appreciated.
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Wei Li, Ph.D
Dept. of Pharmaceutical Sciences
University of Tennessee HSC
847 Monroe, Room 327
Memphis, TN 38163
Phone 901-448-7532 (Office) Fax 901-448-6828 (Office)
Phone 901-753-6978 (H)
Received on Fri Sep 28 2001 - 12:31:57 MST