Chromatography Forum

I'm running a 5890 for DRO/QAM analysis using an FID detector and I'm getting a very broad solvent peak that's starting at around 1.2mins and tails out to about 5mins till it reaches the baseline. This happens if I'm running in split or splitless. We checked the split vent (a little dirty but nothing significant that would cause a blockage) and we can here the split valve click on and off at the appropriate times. I recently changed the weldment on the instrument b/c the tubing snapped near the base and the FID has been recently cleaned. Any help would be greatly appreciated. Thanks.

Inlet-275C
Detector-325C
Headpressure-11psi
Flow~1.1mL/min

Your splitter is not venting the injection port, whether it is a function of time (splitless mode) or if it is continuous (split mode). That or your carrier gas flow rate is extremely low (0.1cc/min?).

Unless you are injecting 10 microliters of solvent with an extremely slow injection speed (5mcL per min) your column is still receiving solvent 2.5 minutes or more after the injection.

Find the reason why this is happening and fix it.

best wishes,

Rod

There should be a filter in the split vent line. When was it last changed? Alternatively have you put a flow meter on the split vent outlet and confirmed the flow is what you think it is?

But be aware that with a back-pressure regulated inlet there can be flow out through the split vent even though the split flow from the inlet is blocked.

Peter

Peter is correct.

You should find out why your inlet is not being vented. The most likely cause is a blockage. Review the pneumatics diagram of your inlet and take it apart and check for blockages.

best wishes,

Rod

Thanks guys,
I guess looks can be deceiving. Split line didn't seem that dirty but the solvent peak tightened up after it was changed out. Just happy it was an easy fix.

Thanks for the feedback - split outlets seem to be a definite Achilles heel.

Peter