We were once doing ES MS on smallish peptidomimetics and were getting
very strong anomalous peaks in the 200-500 m/z range. It turned out
these were coming from the 50ml tubes in which we were preparing the MS
buffer (50% acetonitrile, 0.1% formic acid). Specifically, the problem
turned out not to be from the polypropilene tube itself, but from the
cap. We now use glass for storing buffer but still prepare samples in
eppendorf-like tubes without apparent problems, on immediate use.
Bye Alex