Negative peaks with regular interval

[vahur]

Hi

The method is used daily and this is the first time I encountered this problem. At first I thought it could be an air bubble, but the pressure graph was normal for the whole run

Thanks in advance


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[tom jupille]

Details, details, details, we need details!

Mobile phases & gradiemt?
High- or low-pressure mixing?
Detector & settings?
Do the dips always occur st the same times in the run?

[vahur]

Details, details, details, we need details!

Mobile phases & gradiemt?
High- or low-pressure mixing?
Detector & settings?
Do the dips always occur st the same times in the run?

My apologies, thought this could be a textbook type of problem. Mobile phase is 10 mM ammoniumformiate pH=9,5/MeOH with a 90/10 start to 15min and then up to 10/90 in 5 minutes. Column is waters Xbridge c8 (150 mm 5 um). Detector is DAD (220nm). I don´t know if its High- or low-pressure mixing (machine is Agilent 1260 infinity). The dips have occured in one run only so far so I can not say if they have the same tr every time.

[Gerhard Kratz]

The Dips come every 3 minutes. What is your flow rate????????

[vahur]

The Dips come every 3 minutes. What is your flow rate????????

1 ml/min

[Peter Apps]

Details, details, details, we need details!

Mobile phases & gradiemt?
High- or low-pressure mixing?
Detector & settings?
Do the dips always occur st the same times in the run?

My apologies, thought this could be a textbook type of problem. Mobile phase is 10 mM ammoniumformiate pH=9,5/MeOH with a 90/10 start to 15min and then up to 10/90 in 5 minutes. Column is waters Xbridge c8 (150 mm 5 um). Detector is DAD (220nm). I don´t know if its High- or low-pressure mixing (machine is Agilent 1260 infinity). The dips have occured in one run only so far so I can not say if they have the same tr every time.

Rule number two of troubleshooting:

A problem that only occurs once is not a problem.

Peter

[juddc]

What Peter said...though if the non-problem can be understood it can be avoided more successfully in the future.

Your 1260 appears to be a low pressure mixing unit, by the way.

With that said, I do find it interesting that the duration of the dip decreases as time goes on, but the time between dips is constant. I have a a potential suspect in mind.

Does your instrument have a seal wash? How often does your seal wash cycle? What's in it? What was in it before? Did you change the seal wash solvent before the run? Was it empty? Had the seal wash and associated tubing perhaps not been flushed prior to the run?

The 'Ghetto Chromatographer' wants to know.

Cheers!

CJ

[vahur]

What Peter said...though if the non-problem can be understood it can be avoided more successfully in the future.

Your 1260 appears to be a low pressure mixing unit, by the way.

With that said, I do find it interesting that the duration of the dip decreases as time goes on, but the time between dips is constant. I have a a potential suspect in mind.

Does your instrument have a seal wash? How often does your seal wash cycle? What's in it? What was in it before? Did you change the seal wash solvent before the run? Was it empty? Had the seal wash and associated tubing perhaps not been flushed prior to the run?

The 'Ghetto Chromatographer' wants to know.

Cheers!

CJ

The instrument has it but we don´t use it. I´ll just wait and see if it happens again in the future.