John,
Another comment came to mind:
(6) If the 1090 high pressure pump is leaking oil into the solvent path, you
can get a very steep absorbance climb as %B increases and what you described
is a very steep absorbance climb. It happened here a few months ago. The
problem developed suddenly and was corrected by replacing the booster pump
diaphragm. In addition to the strong absorbance up slope, the DPTU and
PTH-Lys peaks were strongly suppressed and did not recover after the pump was
fixed (i.e., the C18 column had to be replaced). There were also numerous
artifact peaks in the chromatogram while the pump was leaking oil.
Hope that helps,
Steve Tindall
Argo BioAnalytica Inc.
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