We experience a massive baseline drift, it more or less looks like a hill, when injecting human serum albumin purified from Pichia pastoris in a Q-TOF SYNAPT G2 HDMS (Waters). I have attached a spectrum. The buffer was exchanged from PBS to 50% acetonitrile, 0.1% formic acid for the measurement and the protein was diluted 1:50 before injection. So, why do we see this hill? Normally if we would have protein impurities we expect more peaks. With salt, we expect broader peaks. But with what can we expect this "baseline hill"?
Hi,
Looking at your spectrum and the protein you're analyzing, I'd say the hill is caused by the enormous heterogeneity in HSA. So not so much protein impurities, but more the vast amount of different variants (modifications, for example), for which you appear to have too little resolution to resolve them.
Hope this helps!
Hi Eef,
thank you for your answer. What I don't understand is why this heterogeneity pushes the baseline. Shouldn't it be like many many different peaks but a flat baseline?
Eef Dirksen is correct. The instrument would need much higher resolution to show baseline separation for the many signals there from the various modifications. In fact, this is a fairly typical mass spectrum (from many instruments) for albumin , i.e., it's not a baseline shift, it's just reality.
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