Chromatography Forum

running some repeat injections without the pulse pressure. I'll see how it goes.

The pressure pulse should be ok I have used it myself with good results.

Those 10ul injections though could have caused some problems with split vent trap that is between the split vent port on the injection port and the pneumatics control at the end of the line. If the solvent overwhelmed the split vent trap it could have deteriorated the solenoids in the flow control module. The 6890s are much better at handling this but still not totally immune. We killed the solenoids in our first 5890 that came with EPC by injecting 2ul splitless injections, it wasn't long after we replaced it twice that they began to change the design.

Also injecting that much could be pushing crud over onto that split vent trap and making the flow through it erratic which would cause problems. Change the trap and solvent flush the split vent line to make sure it isn't clogged up. I have actually started replacing that piece of copper line with fresh precleaned copper tubing instead of trying to wash it out. Believe it or not, keeping that tubing clean will also help with breakdown of some analytes. In splitless mode the analytes do leave the injection port and return before going on column, which seems wrong until you think about how molecules move in a high temperature gaseous phase. Those molecules are moving really fast and in all directions, so it does matter how clean everything is, not just the liner.

Thanks James - that is the sentiment of my technician as well. We did actually replace the whole split line tubing so it may be a problem with the solenoid.

OK, it seems to be behaving itself after a good inlet clean-out and replacing the split line.

The troubleshooting was complicated by the fact that after changing the analyser, nobody did a target tune, so some of the SIM groups dropped responses.

We've changed our pulse parameters. We are still doing a 50psi pulse, but we have increased the time between the pulse ending and the pure flow kicking in.

Thanks for all your help.