Rogue injections on Waters 2695

[StephenO]

Hi we are having problems with a Waters Alliance2695 autosampler. The system suitability are failing due to one injection giving a higher area than the other five injections. This is happening even though the injections are taken out of the same vial or if they are being taken out of different vials. It is happening very randomly and if it doesn't happen in the system suitability it is happening between bracketing Standard injections.

We have had the engineer from Waters out and he has been troubleshooting by replacing the injector, the pressure valve the injection loop but the error is still occurring.

Any body any ideas or experience with this problem before.

Thanks

[AA]

First, if you have not already done so, replace the syringe. Confirm that there are no air bubbles in the syringe (remove them if they are present). Run the compresibility routine from front panel. That should help.

Is the bad injection the first injection? Or is it random. If it is the first, sometimes using pre-slit septa can help in that situation.

Sometimes carryover can cause this kind of issue too, make sure you have needle wash in place and primed. Run some blanks and confirm that you dont have carryover.


AA

[unmgvar]

what is the type of septa that you are using?
slit or not?
is the higher area result at the end of the 5-6 reps?
what is your injection volume?

does it happens on other applications right now or just the one

has the tech person checked the centering of the needle?
did he check the tip of the needle, to see if it s now "dull"

[StephenO]

Hi it seems to occur randomly its never happened on the first injection it is always the 4/5 injection and then on the bracketing Standards but not all bracketing standards. It has never occured on the sample injections although this could just be coincidance.

The engineer has replaced the Syringe already but the problem still occured.
We use Septums with no slits
Injection volume is 10ul
It doesnt happen on the other HPLCs but it is ocurring on different methods of analysis on this one HPLC.
Needle Wash is working fine on this HPLC

What does it mean if the needle is "Dull"?
When you talk about the blanks do you mean inject the Mobile phase or the diluent?

Thanks for your help

[Peter Apps]

There was a similar post fairly recently in which I speculated that random high results could be due to particles in the samples / standards. After that the OP went silent so there is no way of knowing whether that explanation was valid. What filters are you using on the standards ?

Peter

[StephenO]

We are just using Whatman No1 filter paper

[Peter Apps]

Try a syringe tip filter - it should also give a much cleaner solution in terms of dissolved contaminants.

Peter

[StephenO]

Thanks for your help Peter but this Method works fine on several other HPLCs we are just having this problem with one specific HPLC. We are sure it is the system.

[Peter Apps]

Thanks for your help Peter but this Method works fine on several other HPLCs we are just having this problem with one specific HPLC. We are sure it is the system.

This is very similar to the other thread - they also only had the problem on one instrument, and it may have been due to a difference between side-hole and tip-hole needles. Are the other instruments the same make as the problem one ?

And as a general trouble-shooting tip; if something is easy and cheap to implement then it is worth a shot even if you have reasons to believe that it is not going to solve the problem, even if only to eliminate another possibility for the cause of the trouble.

Peter