Chromatography Forum

I received a waters 2795 HPLC unit with a 486 uv detector last week. It was purchased from an on-line auction. It is up and running but I seem to have a problem with reproducibility in-between std injections. With a reliable method that I use on our 2695 waters HPLC with the same detector, method, and column, I can get a RSD of below 1 on regular bases for 6 std injections. With the 2795 I am having a tough time getting a RSD below 7.
When we purchased the instrument I changed out all of the plumbing, cleaned the filters and frits and check valves. I did have a problem with the clogged injector valve but I believe that I fixed it. Everything else seems to be working fine on it. Since I am new to this model of instrument I am looking for ideas on what else may be causing the reproducibility problems.
Thank you in advance

Chuck

I would replace all filters/frits/check valves and also the syringe. Run compression test to check for leaks in the system.

Disclaimer:I am not sure what changes have been made between the 2695 to the 2795 models.

Hi,

How did you clean the inject valve? also have you verified the inject port and the needle placement. If the needle isn't correctly aligned then you will get issues. The 2795 and 2695 are completely different from each other. Is the system throughly purged and primed? You should be able to get the same RSD results from this system.

Regards,
Bull76

I did check for leaks and I did not detect one. I also tried replacing the syringe without any positive result.

When we received the instrument I was unable to make an injection. The needle and syringe seemed to be working fine, so I took off the injection port and sonicated it with warm water. The problem was acutely with a clog in the faceplate of the injection valve. I am guessing that the people that ran the instrument before we received it ran something threw it they probable should not of and it turned into a gummy mess. I used a syringe cleaning wire and then sonicated it with warm water till I could see light pass thru each of the holes in the faceplate.

I am sure that is not the proper way to clean it, but I only have about 6 months of hands on experience with HPLC’s and that is 6 months more than anyone else that I work with.

What is the best way to check for needle placement? When I check the septums of the sample that ran the holes are mostly in the middle of the septum.

Thank you for your help

Chuck

Chuck,
Did you perform the compression test to check for leaks in the system, as suggested by LC_labrat? If so, what values/results did the system return to you?

Best Regards

Hi,

You need an alignment tool to align the needle and then you need to Calibrate the deck offset. You can Replace the stator and rotor in the inject valve. Sonicate the inject valve face for any period of time is better than not.
Also there is a inject port seal and this needs to be in place. You can test the inject port by placing the needle into the port, connecting a syringe to the needle and putting the inject valve into bypass. When you now manually inject solvent through the needle in should flow through the needle into the port with no overflow and out to waste.

Regards,
Bull76

What volume were you trying to inject. the stanard sample loop fitted to the 2795 is generally smaller than the 2695 unless you upgrad. the max injection volume is 50 µL if I recall

Thank you for all of your suggestions. I found a leak at the injection port. I am going to buy new injection port seat, injection port seal wash and the injection valve re-build kit.
While I have it dismantled is there any other suggestions as to what preventive maintance I should perform, or other areas I should troubleshoot.

Thanks for everyone’s help

Chuck