Chromatography Forum

I have searched and read lots of posts regarding injector problems on this forum. They are very helpful.

Here is the problem from our waters 2767 autosampler:

Long story short: By injecting a dye sample (with deep blue color), I was able to locate the problem.
I first disconnected the inlet to the column and collected the solvent with a glass bottle. Then I injected 10 ul of the dye sample to the analytical injector (20 ul loop, mobile phase: 100% methanol, 1 ml/min). I didn't get any dye sample collected in the glass bottle. I could see that the dye sample went directly to the waste line. After consulting with the waters tech support, I did the injector rebuilt (replaced the stator face assembly and the rotor seal). But the problem isn't solved. Then I thought maybe there was a blockage in the stator face. I checked the stator face and no blockage found. Plus the system pressure is normal. There is no leaking from the injector either.

The injection to the prep injector (there are two injectors in the 2767 autosampler) works fine, which excludes problems from the probe. Any suggestions or comments? What caused the problem? The waters support suggested me to replace the whole injector valve, which costs ~$3000.

Thanks very much your time and help.

There can be some software reasons for this.

Check that syringe you have on the 2767 has the same volume that is configured in the software.

Confirm the the loop volume is configured correctly in the software.

I cant quite remember, but in the software there is a check box that is something like "center injection in loop", I think that needs to be unchecked.

There can be some software reasons for this.

Check that syringe you have on the 2767 has the same volume that is configured in the software.

Confirm the the loop volume is configured correctly in the software.

I cant quite remember, but in the software there is a check box that is something like "center injection in loop", I think that needs to be unchecked.

Hi AA,

Thanks for your suggestions. I checked the software configurations. The loop volume and the syringe size are all set correctly.

You were right. There is an option in the autosampler setup: central in loop. I unchecked it as you suggested. But still no sample being injected.

Any further suggestions? I really appreciate your help.

Hi,

If when you make the injection to the analytical inject port the dye over flows and out to waste at the inject port then the needle placement needs adjusting. But if you do the injection and the dye goes to waste via the Inject valve then the valve is suspect.

Regards,
Bull76

Hi,

If when you make the injection to the analytical inject port the dye over flows and out to waste at the inject port then the needle placement needs adjusting. But if you do the injection and the dye goes to waste via the Inject valve then the valve is suspect.

Regards,
Bull76

Hi Bull76,

I fully agree with you. From what I have tested, it is clearly the latter case. Plus the needle works on the prep injector. Now I doubt that the problem might be from the injector port. After I replaced the stator face assembly and the rotor seal, I didn't replace the injector port because we don't have any in the lab. What do you think?

Thanks very much for your help.

Hi,

The inject port position for the analytical and prep are taught and can differnet but usually they aren't. To best view the inject port you would need to remove the guard from above the inject ports. Carry out an injection and view the inject port and see if your sample bubbles/flows up in the port. If it does then you need to re-teach the position. If it doesn't and the needle is in the correct depth then the issue is the inject valve. But if it is the inject valve then the valve assy is faulty. By replacing the stator and rotor seal you have ruled out these. Do you hear the inject valve change position during an injection? The inject port is just an inlet to the inject valve. You need to be sure the dye is coming out the waste of the inject valve, if so then you need a new inject valve.

Sorry to stretch this out.

Bull76.

Hi,

The inject port position for the analytical and prep are taught and can differnet but usually they aren't. To best view the inject port you would need to remove the guard from above the inject ports. Carry out an injection and view the inject port and see if your sample bubbles/flows up in the port. If it does then you need to re-teach the position. If it doesn't and the needle is in the correct depth then the issue is the inject valve. But if it is the inject valve then the valve assy is faulty. By replacing the stator and rotor seal you have ruled out these. Do you hear the inject valve change position during an injection? The inject port is just an inlet to the inject valve. You need to be sure the dye is coming out the waste of the inject valve, if so then you need a new inject valve.

Sorry to stretch this out.

Bull76.

Hi,

I didn't take out the guard to view if there was any overflow from the injector port. I will do that to confirm.

Regarding the inject valve, something seems very strange to me. I replaced the stator face assembly and the rotor seal. The system pressure is normal. There is no leaking. I do hear the inject valve change positions. I even followed each turn. When the needle was inserted the inject port, the inject valve rotated, the flow of the mobile phase from the loop outlet was stopped. Then the syringe moved to inject the sample. Then the inject valve rotated again, the flow of the mobile phase from the loop outlet continued. Finally, the needle went to wash the injector port and the injected sample came out from the waste line. It seems to me that everything works fine. I just couldn't figure out which part is wrong with the inject valve.

Thanks again for your time and suggestions? Any other thoughts?

Best.

Wild guess: Is it possible that you have either the rotor or the stator 60 degress out of alignment ? - the valve will then do exactly the opposite to what you want because the internal channels will be connecting the wrong ports. All the valves that I have ever seen had pin locations to prevent this, but maybe yours is different.

Peter

Wild guess: Is it possible that you have either the rotor or the stator 60 degress out of alignment ? - the valve will then do exactly the opposite to what you want because the internal channels will be connecting the wrong ports. All the valves that I have ever seen had pin locations to prevent this, but maybe yours is different.

Peter

Ours too. Only can be installed in one direction.
Thanks.

Dear all,

The injection problem of our 2767 sample manager is solved. First, I would like to thank you all for your great suggestions and professional analysis. You guys are more helpful than the waters tech supporting people.

Today I took off the guard and observed the injector port for any signs of overflow when making an injection as Bull76 suggested. I did see some overflow from the analytical port when the needle was injecting the dye sample. The prep port also had a little overflow but much less compared with the analytical port. I think this is why the dye sample was injected from the prep port. I replaced the injector port and readjusted the needle position. Then the injector works without any problem.

Excellent suggestion from Bull76 on viewing overflow: The guard needs to be removed in order to see the truth.

Thanks again for your time and help!!

Best,
jjliy

Glad the issue is resolved for you. Thats what were here for.

Regards,
Bull76.