Dear ABRF People,
Has anyone noticed that Trp residues in proteins or peptides become oxidized in
a photodiode array detector (for example, the Waters 996)? The oxidized
products can be detected by on-line/off-line mass spectrometry (ESI-MS or
MALDI-MS). The slower the flow rate (HPLC) and the lower the amount of
proteins/peptides, the higher the percentage of oxidized products (components
with masses of +16 Da, +32 Da, and +48 Da etc.).. For example, the percentage
of oxidized Trp is greater when one separates proteins or peptides on a
capillary column than on a 1-mm-ID column. We currently use Waters 996 PDA
detectors with a 1- mm-ID column and a micro-flow cell.. Under these
conditions, major peaks in mass spectra for Trp-containing peptides were
oxidized products. We found the problem a year ago, and Waters has been trying
to solve it for more than a half year without success. Does anyone know any PDA
detectors that do not have the problem?
We also observed that micro-flow cell in the Waters 2487 dual wavelength
detector causes peak broadening. Does anyone know a better UV detector (less
dead volume and higher sensitivity) that can be controlled by Mass Lynx
software?
Thank you very much in advance.
Dingyi Wen, Ph.D
Biogen Inc.
12 Cambridge Center
Cambridge, MA 02142
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