I am a user of a Thermo Scientific Surveyor HPLC system with an autosampler. Since we came back from end-of-year festivities vacation, the system is not working anymore, because of unexpected behavior, described as follows.
The Thermo Scientific system is analytical, and thus the autosampler system only starts when the baseline of detectors/flow/pressure is completely stable. We are not able to inject samples presumably because the system feels the baseline is not OK (we keep getting a "Waiting for Trigger" message indefinitely).
From monitoring the detectors with a preview run function, we have noticed that the detector signals at 220 nm and 254 nm are not stable, while pressure and flow are normal. We think this instability prevents the autosampler from injecting. We have changed solutions and columns, but the detector signal remains unstable nonetheless. The signals are behaving in a characteristic way:
1) Overall tendency is a continuous decrease in absorbance with some oscillations. The line keeps going down below zero.
2) The behavior of detectors is the same in both 254 nm and 220 nm wavelengths, suggesting the "disturbance" is on the detector itself, not in the solution (as contaminants should absorb in different wavelengths).
3) Curiously, moving the front doors of the upper PDA detector module cause marked interference in the detector signal lines -- opening either left or right doors cause a sudden decrease in absorbance, and putting a hand in front of the right open door causes a continuous increase in absorbance until the hand is removed (then signal line goes back to the slow decrease behavior).
I am not sure how to deal with this behavior, yet I think it might be something quite simple to adjust. I am not sure if originally the interference from moving the front PDA doors was normal. Maybe someone who uses the same system could give me some hints, please?
This is a peculiar problem you are having. In our laboratory we have a lot instruments from Thermo, including Thermo Scientific Surveyor HPLC system, but we have never encountered a problem such as yours. Given your information, I strongly believe there is something wrong with your detector cell or detector, respectively. You state that the signal drops as you open your detector doors, and rises as you close them. It seems to me that white light is "leaking" into your detection cell/detector, I don't know how to put it otherwise. It is just like when an analyte goes through the detector cell, it absorbs the light, therefore, less light reaches the detector which results in signal increase. On the other hand, when analyte exits the detector cell, less light is absorbed and the light that reaches the detector has higher intensity, hence, the signal drop. When you open your PDA detector doors, you increase the incident light, so the signal decreases. In my opinion, this should not be a problem if the detector cell would be isolated properly, so that the ambient radiation cannot affect the signal.
I don't really know how to approach this problem. Maybe you should look for cracks in the PDA housing or just additionally wrap/isolate the detector with the aluminium foil.
But thean again, something completely different could be the cause of your problem.
Good luck... Cheers!
Eduardo,
can you check with ChromQuest the energy of the lamps?
the topic you described about the door position, etc...must be related with the cell position ( is it correctly screw?) and/or the fact you have in place the flat panel in front of the cell
I have never used Thermo HPLC but you may have a bubble in your flow cell. Remove the column and connect the pump directly to UV ( no column) and run Isopropyl alcohol through flow cell.
Like Pierre Roland-Gosselin, I would guess that it is a lamp issue. Do you know the last time that the lamp was replaced?
Many thanks for all useful insights. Please note that I have attempted i) changing columns; ii) changing solutions, iii) purging the system, iv) deaerating (hope this spells right) the solution, v) changing flow. The obtained interference pattern did not change, thus I am convinced the problem lies not in the column/solution/method.
Also, the fact that signals at different wavelengths vary in the same way indicates that the interference is not chemical.
What I find truly awkward is that I can interefere in the signals by moving in front of the detector module, and this makes me think the source is not a contaminant or bubble.
Please, I can see that Alen and maybe Pierre have similar or identical systems -- could one of you make a simple test when using the system and tell me what happens, please?
I monitor the baseline before injecting using the preview run mode. It is unstable since after vacation. When I open the front doors of the PDA module, there is a noticeable steep decrease in the absorbance, like a small inverted peak. When I close it, it makes a positive "peak". With the right door open, if I cover the opening with my hands (need not touch the module), absorbance starts increasing untill I remove my hand, when it slowly goes back to normal. I cannot say if this was happening before. Please, if one of you could just try it out and tell me, it would be great.
Thanks for all attention, everyone. Will let you know what happens.
Dear Alexander, yes I have thought this over, however the program says the lamp still has only been going for 200h. Anyway I will try to clean and replace it, but I do not know if this would cause a higher sensitivity to external interference... Will let you know here when I found out the issue, thanks!
Eduardo, no, this does not normally happen, I have never experienced this in our lab at least. As I said before, I don't think that your problem is of chemical nature, nor do I think you have a bubble in the detector cell, nor do I think that the lamp age has to do anything with your problem because in these instances the signal should not change by simply standing in front of your detector.
Does your PDA module have a transparent door? I still believe that you have a problem with the incident light at the detector cell and like Pierre suggested, check the position of the detector cell in the detector module. Is it correctly positioned, screwed properly, covered with the plate? Double check everything, and then try to completely isolate the detector cell from the surrounding radiation (day light, laboratory light, etc.). If my suspicions are correct you should get a stable signal then.
Oh, and you can turn baseline monitoring off if I am not mistaken. Then the autosapmler will trigger the analysis run.
Cheers
I think the problem is in your flow cell. if you are using buffers in mobile phase and if cell is not cleaned properly then there are chances of formation of salts. which i think causing the problem. To solve this issue remove the column and directly connect the tubing. flush it at high flow rate (2ml/min) with filtered HPLC water and the reconnect the column and see what happens. if possible dis-assemble the flow cell and tubing and see for any salt builtup.
You should wash flow cell with plain water for at least 2-4 hours.
Eduardo,
I have used many PDAs from different vendors, but not this specific one. Still, the fact that opening the door immediately impacts detector signal reveals that this allows a change in "light detection" by the Photo diode array. While this may be caused by many things, here are a few to test: 1) The flow cell may not be properly seated in the cell holder: This will allow extraneous light into the optical bench, consistent with your observations. This is something you can easily fix yourself. 2) There may be a crack or break in the seal that isolates the optical bench or perhaps the flow cell cover is somehow misaligned (this will also allow extraneous light into the bench, resulting in your observations). A flow cell cover re-alignment you can do yourself, but a crack in the optical bench seal may require Thermo service. 3) there may be a leak in your flow cell area that results in the allows the eluent to seep into the flow cell chamber and/or optical bench that can redirect external light into the optical bench with the results you describe. The leak you can probably repair, but if eluent has leaked into the optical bench, there is a possibility of damage. That may also require Thermo service. I hope this information helps.
Dear everyone,
I still have not solved the problem, however I have made several minor adjustments to the system. Above all I have replaced tubing filters and washed the the light cell with milliQ water and isopropanol. Although there was a discrete decrease in back pressure, indicating some washing was necessary, this did not affect the issue. Also I have opened and cleaned the lightcell chamber, and this provided me with clues.
As Alen, Rajendra, and Jim suggested, I am quite convinced there is a problem with light incidence on the light cell/diode array. I have noted that fiddling with the in/out tubes affects the signal, and this was probably behind some interference from opening/closing the door, as it touches the tubes. Now my hand in front of the panel does not affect signal anymore, thus maybe some dirt/positioining issue may have been corrected from cleaning the detector chamber.
Indeed I noticed that the block that keeps the detector in place still allows some movimentation sideways, which probably will greatly affect signal output -- havent tried moving it during detection to avoid damage.
However still I do not feel signal is steady. I am going to call the guys from Thermo and hear their opinion...
Will let you know the outcome when they come.
Thanks to all!
Eduardo,
Thanks for the quick reply. You stated that the flow cell can move sideways. While I do not know the specific design of your PDA, movement of the cell, especially from side to side, will result in unstable absorbance output because it will change the PDA illumination angle. Typically, flow cells are mounted with screws to prevent this. However, I have one module where the cell holder snaps into a circular detail. The cell can rotate around the circular detail, but will not normally do so because it is mounted under a cover that eliminates tubing movement. It is possible (but difficult) to mismount this cell holder, and this causes unstable baselines, like those you describe. If you can remount your flow cell so that it applies the correct illumination angle, but does not move at all, that will likely fix your problem. Presumably, the detector manual will include instructions for how to do that properly. I hope this information helps.
I work with a Thermo PDA UV8000 and flow cell doesn't move at all. For all that has been said, it seems that you have a "Light leak"as someone mentioned before. Each time you open/close the module, the cell moves and causes a signal. In our system the cell is completly fixed and has a screw.
Dear colleagues.
I am both sorry and embarrassed to say I do not know what was causing the problem. The guys from Analitica came and had a look into it. They recalibrated the PDA detector. They checked if the PDA detector was fastened and secured inside the chamber. They checked if tubings were fine, and changed one plastic for a metal one.
Then we injected a standard solution and everything seemed fine.
They say these machines have the bad habit of coming back to normal as soon as they see the technicians coming. Well actually after some discussion, they think I might have had something trapped in the system from some sample that was removed when I cleaned the system, and that maybe the PDA detector was a bit wobbly until they laid their hands on it. Also they say some air conditioner air current can cause interference because of temperature changes in the PDA unit, and someone could affect this with a hand. We do not really know.
I will keep an eye on the HPLC and see if it starts misbehaving again, and will have you posted on the situation after a while.
At least they did not charge us for the visit! Sorry for not having anything solid to conclude...
Thank everyone for good tips, and know that probably one of you really hit the spot!
Best wishes,
Eduardo,
if the CQ software is waiting for trigger, it's because one element ( pump, As or detector) is not ready. So you can check via the status control what's append.
regarding the detector, you can check via instrument control the energy of the lamp .
i am waiting your feedback
regards
How was the system left prior to vacation? If running salt buffer mobile phases the system should be flushed with copious amounts of water and left in 50% MeOH. This will help to clean the system in your absence. Upon return flush with water and return to your normal solvent conditions. If left in buffer precipitation can occur and cause symptoms akin to what you describe. Also, precipitation in the flow cell can cause the cell to break giving random baselines.
- Badges
- Science method