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Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

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If you need any help for any Technical problem related to Waters HPLC , UPLC, MS systems, Feel free to contact me..

I provide full maintenance/ Qualification services/Free telephone support

I'm Waters service Engineer (with +8 years experience): "Chromatoghraphy@gmx.com"
Hi, what advice do you have for keeping check valves ticking over nicely? I use a binary Waters UPLC and my buffer is 20mM potassium phosphate, I always wash down system after run but often my check valves need to be replaced regularly, is there a sound technique to flush or maintain check valves so they last a bit longer? Thanks.
Do you mean you have to change this defective primary check valve only after some time of working with buffer? Do you change or replace any others components like seals, plunger, Intelligent intake valve,...etc?

If you are talking about primary check valve, you can easily wash it with water/methanol 50:50%, then if you got a small needle and try to enter it into the big mouth of this check valve and try to press for some time, then try to reconnect it again, and it should be work.
Hi and thanks for the reply,

Yes, to clarify, its almost always the primary check valve that acts up after a few runs using strong buffers, even when the buffer line is washed out for a few hours after the run. No I don't ever change seals or plungers etc, only the check valves when the pressure goes up and down mid run its normally the only thing that will rectify the issue. Is there any indication in the UPLCAcquity screen that shows a faulty check valve, maybe the performance screen and compression ratio, are these values important?

What would you recommend is the best way to clean out check valves in terms of a washdown at the end of a run which uses a buffer?

You should wash your system with at least 90% Waters + 10% organic, in addition to apply Waters procedure for acidic cleaning, which as I remember (prepare 4 solvents: water100%, phosphoric acid 30%, Methanol100%, ACN 100%), and prepare samples vials from the same solvent,and start to make injections for every mobile phase, so you can start washing with water for 15 min and make sime sample injections using sample vials, then transfer to phosphoric solution for 15 min, then water again for 15 min, then AcN for 15 min, then Methanol for 15 min, and try also to make check valve cleaning for at least one time every month by sonicate it into water+ organic, and get a small needle and try to press into big mouth of check vlv.

For Compression C/D, it should be less than 1.8 when you get small delta psi less than 1% of total pressure

I recommend to try to make leak test for pump (check until vent valve) from consule >> select pump>> maintain>> leak test, and see if it will pass or not.
I`m using a Waters Class H UPLC with Xevo TQD Mass Spectrometry for a while. In the lab we are doing some research with pesticides residue. I noticed that the chromatogram, for the last couple days, has that weard and huge noise in the 6 first minutes. Dont know whats going on. Some suggestion?Image
Did you try to clean ion source, check the collision cell, Did you perform Pm kit for Ms, or Sm Ftn, Did you run tuning solution for MS1 and Ms2, or mass calibration check?
Hello, I wonder could you help me with a UPLC issue? I need to use one tomorrow and its been 2 weeks since this UPLC has been used- the last run was completed as normal and the buffer was flushed out afterwards plus the check valves were flushed in 50:50 Methanol: Water then the instrument was powered off. When I start it up tomorrow, should I run the pump seal for 10 or 20 minutes followed by a check valve flush before setting up with fresh washes, mobile phase and running samples? Is it better to run some blanks and test injections to test baseline and retention time/peak shape before running? Thanks.
It shouldn't be a problem. You will want to equilibrate (as long as it was properly cleaned) your system (10X column volumes) and perform some test injections.

I have a problem with low pressure on the UPLC system. On the dynamic leak test, both A and B are showing "Unable to compress". In the beginning, I thought the air in the line is a problem. I did prime all lines for 20mins. But it was not progressive. Then I changed check valves at Accumulators but it is still showing the same response. There is no sign of leakage from the front side. Upon checking the volume before mixer from A and B, it is 25-50% less.


What is delta PSI?
Can you able to put pin plug into vent valve of Binary pump and re-run your test again?
Do you have any problems in shift of peaks at retention time ?
which solvent do you use them during this test?
Is there way to transfer HPLC method to UPLC method?
Mohamad wrote:
Is there way to transfer HPLC method to UPLC method?

This has been covered here and at many other sites. Check the sticky postings, references and google for guidance. There are also online calculators that can help you.
Some waters system have a way of calculating focused gradients.

    What algorithm is this based upon?
    Why does it start at a low concentration of organic solvent before the focused gradient?

It is good to know how/why things work.

Thanks in advance.
SHERIFV4 wrote:

If you need any help for any Technical problem related to Waters HPLC , UPLC, MS systems, Feel free to contact me..

I provide full maintenance/ Qualification services/Free telephone support

I'm Waters service Engineer (with +8 years experience): "Chromatoghraphy@gmx.com"

l can not access to the certificate of analysis section in waters site, please send me the pdf file or figure of the certificate of analysis of waters column with this specification:
bondapak c18 column (4.6 *250 mm, 10 micometer)
part NO. wato52860
serial number: w92521c22
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