Dear Colleagues,
we would like to do a homonuclear decoupled phosphorous experiment, i.e.
31P {1H/31P} on our 3 channel INOVA spectrometer. Setting the second
decoupling parameters to phosphorous (i.e. dn2='P31', homo2='y' etc.)
the instrument automatically assigns the rf channels to
1: for P31 transmission
2: for 1H decoupling
3: for P31 homo decoupling.
This makes sense, as the second channel is 1H only.
The problem now arises from the fact that the decoupling comes out of
the 3rd channel connected to the second low frequency amplifier. When we
decouple C13 instead of P31, we feed the 3rd channel through a power
combiner (basically a sophisticated T) between the duplexer and the
probe and use the corresponding band pass filters for the transmission
and decoupling lines. Things work well this way.
When I hook up the system analogously for the P31 homo case (even with
dm2='n'), I do not get any signal. With homonuclear decoupling I now
have the problem, that I cannot use the filters to rout signals and
clean them up.
My questions are the following:
- How do I prevent the transmission pulse to go into the decoupling line
and amplifier.
- Do I need to worry about the decoupling pulse to go into the
transmission line (or does the homo gating and the duplexer switching
prevent this.)
- How do I prevent the signal from getting lost in the decoupling line
(I tried crossed diodes in line in the decoupler line, still no signal,
even when dm2='n')
- The amplifiers are way too dirty, even when turned off (dn2=' ') to be
connected into the transmission line. Just upon connecting, I get
receiver overflow, unless I use gain=0. Again, in the C13 decoupled
case, the filter cleans it up enough for this not to happen.
On our 2 channel Gemini2000 instrument, we have no problem doing this
type of experiment. The console itself is doing the gating because it
uses only the one available amplifier for that frequency. The same is
true on the INOVA for homonuclear proton decoupling. So alternatively
to solving the problems above, is there a way to force the INOVA to use
the same amplifier for P31 transmission and homonuclear decoupling?
Thanks for your help
Ulli
--
Ulrike Werner-Zwanziger
Dep. of Chemistry Tel.: (812) 856-4629
Indiana University Fax.: (812) 855-8300
800 E. Kirkwood Ave
Bloomington, IN 47405
Received on Thu Sep 20 2001 - 12:01:58 MST