LCMS: MS Signal Only in Negative Mode. Positive Mode Dead.
Posted: Thu Aug 10, 2017 5:21 pm
Hello,
I'm encountering a problem with our Sciex API 2000 ESI Mass Spec (hooked up to an Agilent 1100 LC). We recently stopped getting any signal whatsoever in positive mode. No noise, no small triangular peaks, just a flat dead line. When I switched the method over to negative mode, the standard I ran had perfect signal, beautifully resolved peaks, and accurate masses. We tried replacing the electrode, unclogging the spray nozzle, cleaning the spray plate. We are thinking the electron multiplier might be bad, but why would it be bad solely in positive mode? We aren't sure where to test voltages either, as the SciEx manual is very unhelpful.
So..Does anyone know what would cause a dead signal in positive mode, but allow perfect spectrometry in negative mode? Our instrument is 14 years-old and is way out of warranty. SciEx won't even respond to e-mails from us at this point, so any information would be extremely helpful.
Thank you,
Dan
I'm encountering a problem with our Sciex API 2000 ESI Mass Spec (hooked up to an Agilent 1100 LC). We recently stopped getting any signal whatsoever in positive mode. No noise, no small triangular peaks, just a flat dead line. When I switched the method over to negative mode, the standard I ran had perfect signal, beautifully resolved peaks, and accurate masses. We tried replacing the electrode, unclogging the spray nozzle, cleaning the spray plate. We are thinking the electron multiplier might be bad, but why would it be bad solely in positive mode? We aren't sure where to test voltages either, as the SciEx manual is very unhelpful.
So..Does anyone know what would cause a dead signal in positive mode, but allow perfect spectrometry in negative mode? Our instrument is 14 years-old and is way out of warranty. SciEx won't even respond to e-mails from us at this point, so any information would be extremely helpful.
Thank you,
Dan