contamination with UPLC-MSMS

[aldij]

when working with our UPLC-MSMS-system i sometimes get this problem. a sample injected is very concentrated and after this injection every blank-injection contains the analyte-peaks. so i think the system gets contaminated somewhere. it takes days of injecting blanks before my blank are blank again.
at what point of the system sits the contamination?
does anybody know any easy procedure to get rid of this contaminations?

thanks i.a.

albert

[DR]

Depends on the sample... if it's a pretty clean sample, I'd look into the injector. If it isn't so clean, I'd check the MSD...

[aldij]

the problem is not related to the matrix. it also hapened if e highconcentration in clean methanol was injected. the problem must be in the UPLC becouse i get a nice peak at the right RT, if the contamination hapened in the MS i would expect a steady background. But where in the LC did it hapen? and what is the easy way to solve the problem?

[Mark Tracy]

Since the retention time of the carryover is the same as the sample, it has to be coming from the injector. I have noticed that carryover tends to get worse as the column pressure goes up. I attribute this to fittings and seals flexing slightly and allowing the sample to penetrate into places it would not normally go. I suspect in your case that there is something on the injection valve that is not quite tight enough.

Also, check out the discussion on needle wash.

[DR]

^ yep - check the needle wash - is it full? primed? appropriate?

[Newman768]

I'm a little late, but let me add a hint anyway.

If your really doing uplc as I understand uplc (means high! pressure) then you have to be sure that the injection part of the autosampler has NO dead volume at all.
If you change for example the rheodyne but don't use a new sample loop you get a dead volume and ANY high conc injection results in carry over problems which may last for up to 100 injections!

To chech if this is your problem run the system with e.g. 100% of acetonitrile and open the fittings of the sample loop so that any contamination / carry over is flushed out. After this procedure the carry over problem should be solved.

Hope this helps