Chloroform dissolves the NMR caps. We haved used only red caps for a number
of
years on an old JEOL 400MHz spectrometer. The bore tube had a red ring
around
it from where the chloroform dissolved a bit of the caps.
Standard DISPOSABLE 5mm Caps (usually red, but also available in numerous
other colors) are made from Ethylene Vinyl Acetate, which dissolves in
Chloforom (this fact has been stated for over 10 years in the Wilmad
catalog). Even Chloroform vapor can soften this material and it is possible,
as confirmed by Bob's observations, that the material can coat spinner
housings. Thus, it's recommeded that for Chloroform, use another cap
material, such as PTFE, available from a number of reliable sources,
including Wilmad.
The plastic DISPOSABLE caps are made from Polyethylene (such as the 10mm
size) so this precaution is not applicable except for 5mm tubes.
Regards:
Paul Cope
Manager of NMR Accessories and Supplies
Bruker Instruments, Inc.
______________________________________________
PLEASE NOTE - WE HAVE A NEW AREA CODE!!!
______________________________________________
Telephone: 1-978-667-9580 x443
FAX: 1-978-667-0985
e-mail: pwc@bruker.com