Chromatography Forum

I have a 5890 dual-ECD setup for PCB analysis with two columns. Out of the blue (from one run to the next, no maintenance or anything) the response on the first detector dropped to about 1/10th of its normal value. The response on the second detector is fine.

Did maintenance on both injection ports (septum/liner/gold seal); no change.

I swapped columns between the two injection ports. Now Detector B's signal has a low response and Detector A's signal is back to normal.

So signs point to something with the first injection port or maybe the gas supply. Any suggestions on what to check next?

Check gas flows for both inlets (esp. split ratios, total and split flows).
If they are equal check with flow meter.
If autosampler is present check both syringes whether they inject equal volumes.

Also check that your split vent valve is functioning. If it's stuck open, then you'll think you're running splitless but will actually be running split. I think the 5890 inlet was still back pressure regulated so you will have the same flow out the split vent whether the valve is open or shut (gas just comes from either before or after the inlet) but you should hear it move when you manually activate it.