Low peak area with On Column Inlet

[AZBiodiesel]

I am using an HP 6890, the back inlet is On Column. How should my valve settings be in my method in chemstation? I ask because it looks like I am getting drastically reduced peak areas. The retention times, symmetry, and correlation coefficients for my standards are all good. But the peaks are giving 600 pA where I am used to getting 2 million. All my connections from inlet to detector are good, gas flows are good. The front inlet is split/splitless. It just seems that I am losing some sample somewhere in the inlet. I am using a capillary column, maybe its a make up gas issue/leak in the FID?

Thanks

[GasMan]

I seem to remember from some of your earlier postings that you were working with a 5890. Is it the case that you have moved from a 5890 to a 6890?

Gasman

[AZBiodiesel]

Yes, I used to have 3 5890s, one with EPC, one with no EPC, and one with the regulators on the side. Now I have a 6890 and 7694 HSS. I was wondering if it was a unit issue but I have seen loss of my high boilers in my low level standards, so I am suspecting I am losing sample somewhere or not getting enough on the column, I have looked through the valve list on the unit and we have no valves installed (makes sense for the on column inlet). My baseline is at 20-30 pA...wondering now if it is an FID issue, not enough sample getting to the jet maybe due to makeup gas flow...

[GasMan]

Are the readings the value on the GC screen, or are you using a data system?

Gasman

[AZBiodiesel]

those are the integrated peak areas. went back and found some old chromatograms/data and the old area was 2 mil new is 600. but proportionally they are still the same...

[GasMan]

My guess is that with the 5890 you had an A to D converter box between the 5890 and your data system. You now have a 6890 with a lan connection and you connect the 6890 directly to your data system. If I am correct, there is nothing to worry about. At first it is a bit concerting, but you will see no overall difference in your results when you calibrate your system.

Gasman

[LCbob]

Also I would advise leak checking with the column installed ( stick a septum on the exit of the column ), especially if you are using a retention gap.

[AZBiodiesel]

Gasman,

Thanks for the info, we are using a 6890N with lan connection. I am using a retention gap with the full 5m installed. I may cut it down to 1-2m and see what happens. Also, I found that the inlet was not set to "track oven" I am hoping some of the high boilers were getting stuck on the inlet.

Thanks again.