Thanks to all who responded to my inquiry about boron NMR background
signal from the probe.
My original questions were: How effective are boron-free glass inserts?
Can you buy them separately from the probe and install them yourself?
Would such an installation void the probe warranty? What is a good
source and how much do they cost? Do they have an effect on other
nuclei?
A summary of the responses I got:
The source of the background signal seems to be boron-containing probe
ceramics (true for Bruker, don't know about Varian), the probe glass
insert, and the sample tube (in this order of decreasing contribution).
Use of quartz sample tubes does little to reduce the problem.
The probe boron signal comes in the 10 to 100 us range. A major
contribution are receiver recovery effects such as ringing.
Depending on the sample, modification of standard acquisition can help:
increasing the probe ring-down / receiver gating time to a few hundred
us and/or using a Hahn spin echo with a delay of 0.5 - 1 ms.
A popular approach is a sample - solvent subtraction, using identically
acquired spectra. It worked very well here for a polymer sample with
broad B11 peaks.
Boron-free probes can be purchased from probe manufacturers, at an extra
cost of ca. 15% vs. a regular probe.
Modification of a regular probe is an alternative. No info about cost.
Nobody identified a source of probe glass inserts. Replacing an insert
yourself would likely void any service contract / warranty coverage
for the probe.
The boron-free alternative to the commonly used pyrex glass insert is
made of quartz which has a significant aluminum NMR background signal.
Fortunately for us the whole issue lead to the (re)discovery of a rarely
used broadband probe that is boron-free: no background signal at all.
Best regards,
Lazaros Kakalis
Rutgers University at Newark
Department of Chemistry
73 Warren Street
Newark, NJ 07102-1811
Tel: (973) 353-5040 (office, lab)
Tel: (973) 353-5329 (secretary)
Fax: (973) 353-1264
Email: kakalis_at_andromeda.rutgers.edu
Received on Tue Dec 18 2001 - 18:58:57 MST