Agilent 1200 baseline puzzle!

[derboyl]

hello all,

i have a puzzling baseline shift occuring randomly on two of our HPLCs. i am finding it hard to find a pattern or pin it down to one cause.

the shift is slight (1-10mau) but is enough to interfer with our impurity analysis and %recoveries.
I did a forum search and found an entry (fri,mar 04 2005 by jzt) with a very similar effect although not as large a shift. But we are getting the same "cliff" effect which when it arises at the rt of our peaks is very troublesome.

In our case the shift has occured in two different instruments with the same set up(1200, DAD,ALS, Quart pump), which were installed at the same time. in both cases the shift began 4-5 months after 1st use and up to present.
It occures with completly different methods, different columns, different wavelenghts, different chemists. the hplcs are even in different rooms!
but it occurs periodically from time to time, often not for weeks.

However they are all isocratic methods. the only common factor not including electricity supply!

We aquired two Agilent 1200 systems a year ago, oct 07.

We had an agilent engineer out to take a look, he changed seals,needle seat and needle but it made no difference.

Has anyone any ideas? or has anyone had similar issues?

many thanks,
derek

[zokitano]

Your problem seems like the one I had several months ago with an Agilent 1100 Series (also with ALS, DAD, Quat pump).
The problem turned to be electrical interference from the electrical devices in nearby. I just "balanced" the detector via Chemstation software and the excessive drift of the baseline disappeared.

Do you have any electrical devices nearby your "problematic" HPLCs or any sources of electromagnetic field in your lab? It seems too easy and stupid, but also a mobile phone left at the bench beside your HPLC could give an electromagnetic interference with HPLC's electronic parts.

Regards

[derboyl]

hello zokitano,

yes both systems are close to other electrical devices, in fact the labs are quite small and cluttered with instrumentation including other HPLCs.

you could be correct however because we have a glasswasher close to the most problematic HPLC.
It is hard to know for sure because we were never watching the baseline when the shift occured, so far it has happened while away from the monitor and so envirmental conditions were not recorded so far.

but thanks for you comments, its definitly something to investigate further!

derek

[yaoguocan]

firstly since such a lottle shift ,which can be caused by slightly temp shif ,ph variance ,column equibration and soon ,can affect your determination ,the method need to be further optimized .
second, it need detailed further investigation.your hplc intrument should be placed in a seperated room with temp and humity controling device,free from electricmagnic filed

[derboyl]

hello Yaoguocan,

many thanks for your comments.
it is very probable that the problem stems from the ergonomics of our lab!
the most problematic HPLC is closest to both a window and other instrumentation. The HPLCs that are housed away from most disturbances are not giving trouble yet!
Since the problem transends methods, columns and chemists im inclined to think you might be correct.
i will investigate along those lines.

thanks,
derek

[Bintang]

I have seen this kind of problem with UV detectors sitting in direct sunlight, if you cast a shadow on the detector the baseline goes down!
It could also be a lamp problem.

[detox]

Are you using chemstation to control the 1200 HPLC's? If so you could try many tests from the software to troubleshoot your problem:

1. The Agilent 1200 DAD's come shipped with the 1000 hour lamps, as these lamps age they will have "stepping" and "plateau" type appearances to the baseline> check your lamp hours.

2. Remove the flowcell and close the flowcell door, this will remove the flowcell and the mobile phase flowing through it from the troubleshooting. Monitor the baseline/collect data. Is the baseline problem still there? If so, you now have isolated the problem to the detector and or the power supplied to the detector. The problem may be lamp related, power supplied to the detector from the outlet optics/mainboard (not likely). Move the detector only to another location on a different circuit and monitor the baseline.

3. If the problem goes away when you remove the flowcell, then you know that either your flowcell is contaminated or the mobile phase passing through your flowcell is causing the problem. Stop the pump flow while the flowcell is still in the detector. If the problem persists then its your flow cell, if it goes away then its the flow going through the flowcell meaning something is coming through the system (possible contaminate).

Hope that helps.