Chromatography Forum

I moved column/ mobile phase/samples to a clean system, the blank injection were free of carry-over, but carry-over came back after sample sequence.

Flora, I don’t think you have a flow-cell problem/contamination – if you’re seeing peaks anyway.
When you say; you tried the method on another system, do you mean another system including the column or did you take mobile phase and column from the current system and installed it on the other system?
Also if you are correct in thinking the column’s not involved in the case, why don’t you remove the column and try to run the test/s with no column in the flow path?

Best Regards

Then I think you’re probably dealing with inadequate injection system wash. Sometimes (mostly it’s more sensible to find the right washing solvent as opposite to extend the washing sequence/procedure. For instance I’ve seen people wash the injector with almost pure organic (ACN or whatever) in protein separations context, thinking “it must be good” since it’s a strong solvent. But actually they cause precipitations by that.

Best Regards

I am using Waters system, extended needle wash applied to the method -- but seems still not enough for cleaning.

Then I think you’re probably dealing with inadequate injection system wash. Sometimes (mostly it’s more sensible to find the right washing solvent as opposite to extend the washing sequence/procedure. For instance I’ve seen people wash the injector with almost pure organic (ACN or whatever) in protein separations context, thinking “it must be good” since it’s a strong solvent. But actually they cause precipitations by that.

Best Regards

Maybe that underlines my point, which is: Standard washing liquids/mixtures are not necessarily the best solution in every situation. I'm not aware of the composition of the utilized liquid/mixture but it might be less suitable than just water for instance, since you say your compound is extremely soluble in water.
If you need more concrete suggestions, you might have to tell us more about your compound and the washing mixture's composition.

Best Regards

If you need more concrete suggestions, you might have to tell us more about your compound and the washing mixture's composition.

...and more about the system itself.

if using Alliance 2695, there is a Needle-Wash-filter, which might be contaminated.
It's located within the black plastic knob seen in the sample compartment.

I've used 20% phorsphoric to clean our old Varian PDA...
I don't think it'd be a good idea to have it constantly cleaning the needle though...

BTW Hollow, where is this filter? I only see the foam padding on the roof inside the sample compartment...I'd like to change the filter as I've had some carryover issues before as well.

cody:
if you take out the carousels, then, on the very right side where the needle comes down, you should see this black "cap" that can be unscrewed.
Maybe push the foam padding a bit up, if it has lowered itself by time.

Within this retainer is this outer part of the needle wash.

It's not really a "filter" but rather kind of a frit.
Waters itself seems to interchange the naming.

Waters has a SOP document as well as demo videos of how to replace this frit on their website.

Search for "needlewash" (maybe have to be logged on)
- look for the "self service procedure"; scored second top for me
- at third place, the replacement frits itself showed up