Chromatography Forum

Hi,
I have a 5890 ECD that I am having a problem obtaining a stable background on to run pesticides/pcb. I'm running single gooseneck Restek sky liner with wool to a 5m guard column to a universal press tight y connector which splits to Restek cl pesticides/ cl pesticides 2 analytical columns. I'm running H2 carrier at approx 2 ml/ min with N2 makeup gas at 60 ml/min. The injector is at 215C in split mode wither oven ramp from 150C to 300C with the detector at 300C. When I do a no injection run of the temperature program the baseline starts high but still acceptable but then as the oven goes through the ramp increases drastically but then sharply decreases when run finishes and the oven enters it's cooling cycle. I have leak checked the inlet and column connections and I have not found any leaks. I'm starting to suspect that this May have something to do with the makeup gas connections. Could this have something to do with the 1/4in ferrel that is around the makeup gas adapter? The siltek treated guide in the adapter? The whole makeup gas adapter?

Thanks for any insights,
Steve

All that stuff can and does occasionally get contaminated. Perhaps you can remove the detector ends and cap off at the adapter with a blank ferrule (or a paper clip and a .8 mm ferrule). That should help rule out the inlet and the columns, without driving you too crazy.

Hi,
I have a 5890 ECD that I am having a problem obtaining a stable background on to run pesticides/pcb. I'm running single gooseneck Restek sky liner with wool to a 5m guard column to a universal press tight y connector which splits to Restek cl pesticides/ cl pesticides 2 analytical columns. I'm running H2 carrier at approx 2 ml/ min with N2 makeup gas at 60 ml/min. The injector is at 215C in split mode wither oven ramp from 150C to 300C with the detector at 300C. When I do a no injection run of the temperature program the baseline starts high but still acceptable but then as the oven goes through the ramp increases drastically but then sharply decreases when run finishes and the oven enters it's cooling cycle. I have leak checked the inlet and column connections and I have not found any leaks. I'm starting to suspect that this May have something to do with the makeup gas connections. Could this have something to do with the 1/4in ferrel that is around the makeup gas adapter? The siltek treated guide in the adapter? The whole makeup gas adapter?

Thanks for any insights,
Steve

I have seen the 1/4 inch ferrule at the makeup gas fitting crack before and cause problems that are oven temperature dependent. As mentioned above, use blank ferrule to cap off detector and see if the problem is there when no column flow is present. If that looks good then check any traps you may be using in the carrier gas lines before the instrument.

I once helped someone with a problem where they thought they had no sensitivity when doing PCB analysis. He showed me chromatograms that were essentially flat baselines(it was on a chart recorder). When I went to see the instrument the first thing I noticed was when he turned on the chart recorder the pen went completely across the page from where it was parked. Instead of the flat baseline being low sensitivity, it was actually that the detector was at maximum signal. Looking at his setup, first I noticed the carrier gas was a plain small red tank of hydrogen, then part of the gas line from that tank to the GC was actually some rubber hose like what is used in brake lines on large trucks for air brakes. Using brake lines and industrial grade hydrogen does not give good results with an ECD

I am certain that your setup is nothing like that one, but just be sure to check the gas line traps often as any contamination there can cause problems similar to what you are seeing.