Our thanks to everyone who responded to our inquiry about three
artifact peaks in our Edman sequencer's chromatograms (one coeluting
with PTH-Gly, one with PTH-Glu, and one between PTH-His and PTH-Ala).
We eventually traced the problem to the acetonitrile used in making the
10% acetonitrile/water (S4) and standards (R5) by running a modified
blank (no R4 loaded to flask) with pure water in the S4 position. The
acetonitrile in question is Baker HPLC grade, lot # M48802. For today
we are using some American Bioanalytical DNA Synthesis grade
acetonitrile, but will switch back to Baker as soon as we can get a
different lot as there is a different (single) artifact in the
chromatogram with the Amer. Bio. acetonitrile. The new artifact
coelutes with DMPTU, so we are running with it for now.
Thanks again for all of your suggestions and information,
Myron Crawford
Keck Biotechnology
Yale University