Does anybody have experienced reproducibility problems with a JASCO AS-1559 autosampler when injecting less than 20µL per injection?
Our vendor detected some month ago a problem that has been related to our UV detector, however it seems the reproducibility of injections by the autosampler is still changing from day to day being some days excellent and some days bad. This has been found with benzophenone standard on C18 column with water/acetonitrile as mobile phase.
Any suggestion to solve that problem as the vendor is not able to find any defect of the autosampler when he performs tests under our conditions (probably he always get the lucky hit!)?
Thanks in advance,
CCL

A few years ago, we had major reproducibility problems with our Jasco AS-950 autosampler. We twice sent our AS-950 back to Jasco for servicing but they could never find anything wrong with it. Our problem was finally solved when one of the reps came to visit the lab and realised that the problem was due to the type of autosampler vial caps that we were using! We were using the screw top caps with the PTFE/rubber septa (for standard 2mL vials). Apparently, the septa was forming such a tight seal around the needle that air couldn't enter the vial as the sample was drawn out and this was causing the irregular injection volumes. When we ran several injections from a uncapped vial, the reproducibility was excellent. We subsequently changed to either polypropylene snap caps or caps with pre-cut septa (available from Chromacol) and have had no problems since. I hope you get to the source of your problem, good luck! :o)

Ann

We don't have Jasco, but we only fill our sampler vials half way up, maximum for similar reason.