This may be a daft question, but how do I go about identifying the probe in our NMR machine, and hence whether it's capable of measuring (simple 1D) 19F spectra? It is a Bruker Avance 500, and I was under the impression that it might be capable of this with a little fiddling (http://www.chem.uic.edu/nmr/downloads/Avance-19F_Guide.0201.pdf), if I'm lucky wrt to what probe we have.
Addition (1724, 260911): I have now confirmed that it is a BBO probe. What else is needed for the linked protocol to work (specific preamplifiers?), and is there a software method to check whether we have it?
(Background: our NMR tech seemed to suggest that it's not possible, but has also in the past said that VT and DOESY were not possible, and thanks to people working it out, they are now standardish here. I won't necessarily have a problem, but want to ener the conversation armed with the info, references/instructions)
It is certainly possible to observe 19F on most Bruker Avance spectrometers. In many cases, it is as easy as selecting a fluorine parameter set, setting the probe/solvent calibration parameters, and then acquiring the data. A lot will depend on the exact hardware that you have.
Probes: The 1H channel on many probes will tune to 19 F. You will have to check yours to be sure. There are dual 1H/19F probes available, and many of the newer broadband probes (BBFO, BBO+ and QNP) will observe 19F through the X port on the probe. This enables you to do 1H/19F double resonance. These probes will be clearly identified on the label.
To check whether the proton channel of a regular BBO probe will tune to fluorine, the best tool is a network analyzer. If you don't have access to one, you can use the software tuning program 'wobb'. This requires that the console be properly set-up for fluorine.
Note that a lot of probes have a 19F background from teflon.
Pre-amps: The normal 1H pre-amp isn't typically used for 19F. It is the X pre-amp that will cover 19F (to match with 19F on the X port of the probe). Check that your X pre-amp covers 19F. The sticker on the back of the pre-amp will tell you. It will say something like XBB19F. Our system also has a separate 19F pre-amp that we can use for 19F of solids, as it has a 4 kW power limit. It can also be used for liquids if we want.
Console: The 19F transmit signal is routed through the 1H amplifiers. However, it often then goes through something called a "QNP switchbox" to make sure the RF is automatically routed to the X port on the probe. On some systems (like our AV 300), it is part of the amplifier, and on others it is a separate unit (like our AV III 500). You can clearly see if this unit is there in the edasp dialog. If you don't have this unit, then you will have to do a bit of recabling to accomplish the same thing.
Filters: You will also need some filters if you intend to do 1H/19F double resonance.
That's about all I can say without knowing exactly what hardware you have. If you send me some details, I can give you some more tips.
On our systems (AV 300 with QNP probe and AV III 500 with BBFO ATM probe), running 19F with or without 1H decoupling, and 1H with 19F decoupling, is as simple as running normal proton and carbon spectra. A lot just depends on making sure that the software, cabling and calibration files have been properly configured. Bruker probably did this at installation.
I have found that there's three types of probes for Bruker (double resonance):
BBO - Broad Band Observe probe. This probe have inner coil for BB and outer for 1H. BB can be tuned up to 15N frequency. Unfortunately one can't make any experiments with fluorine resonance.
BBOF - Broad Band Observe probe with Fluorine. It's the same like the one above but it has additional feature that allows to tune X chanel (BB coil) for fluorine. So you can make 1H (with 19 decoupling), 19F (with 1H decoupling), 19F (with 19F decoupling), 1H-19F HETCOR, 1H-19F HOESY.
BBOH&F (or BBOH%F) - Broad Band Observe with Proton & Fluorine common coil. Outer coil can be tunned for 1H and 19F frequencies, BB coil to 15N. With this probe one can't obtain two resonance 1H-19H spectra (including decoupling) but it's possible to obtain wide range 19F spectra instead of 1H, for example 19F-13C HMBC, 19F-15N HMBC, 13C-19F HSQC etc.
I hoped i have BBOH&F to obtain 19F-13C HMBC but unfortunately there's only BBFO.
answered May 30 '14 at 03:24