Chromatography Forum

I am having an issue trying to draw up a 0.2 uL sample with a salvaged CTC A200 autosampler. I can easily draw that amount consistently with a hydrocarbon matrix but when I try to draw that with water I usually get nothing.
I switched to a gas tight syringe but that did not help.

I am using 50/50 xylene acetone for the rinse solvent. I have tried pre-rinsing the syringe with water sample as well as only pumping sample (without pre-rinsing) but that does not seem to do it either.

If I manually sample, I can pull a water sample, just not on the CTC.

Suggestions?

AICMM

* Decrease drawing speed
* Change syringe (needle tip may be clogged)
* Use "sandwich" - i.e. air gaps before and after sample

Would an intermediate rinse with Methanol or Acetone be possible to remove any traces of the xylene that may be causing a problem with the water entering the syringe?

Probably the vacumm created by a 0.2 ul movement of the pluger is not enough to break the surface tension of the water across the bore of the needle. Can you overfill and then eject all but 0.2 ul with that sampler ?