Needle wash solvent in needle?

Hi per_oxid 

It sounds more like an equilibration problem than a needle wash issue.  Can you share more details about the run times and gradient times?

/Andy

__PRESENT

Thanks for reply. Will have to check the module part nr but its infinity model similar to G4226-90001. I cant see that its equilibration problem since method works great when I dont use needle wash or use 20%meoh as needle wash.

I did find a tech note that this wash design was not suitable for strong wash solvents since some solvent on needle exterior is injected.  I injected 2ul sample in water on 20%meoh mobilephase so perhaps a small volume of meho on needle exterior was the problem. The column was 2.1"100mm WatersT3, a c18 column. On the systems i used before i could use strong needle wash solvents but now i will consider that it can influence lc method.

The needle external wash was setup to use flushport for 6 seconds

On request i will provide the link to the evaluation of needle wash station design title

"NEEDLE WASH MECHANISM AND ITS
IMPACT ON HILIC ANALYSIS"

Hi per_oxid 

You could test your wash solvent mixing hypothesis by dissolving your sample in methanol or methanol/water, assuming that the analyte is soluble in methanol; I assume it must be, since you're using methanol as a wash solvent.  If you see the poor retention with the organic injection solvent then you have an answer.

How does that sound?

/Andy

Hi per_oxid 

You could test your wash solvent mixing hypothesis by dissolving your sample in methanol or methanol/water, assuming that the analyte is soluble in methanol; I assume it must be, since you're using methanol as a wash solvent.  If you see the poor retention with the organic injection solvent then you have an answer.

How does that sound?

/Andy

Thanks thats a good suggestion. The analyte is caffeine for a system commissioning test. The system works fine and no carry over problem so very strong wash solvents not needed. Still good to understand how system works.