brand spanking new GC calibration problem!

[sambo]

Hi
We have a new Perkin Elmer Clarus 500 GC with Turbomatrix autosampler with ECD and FID detectors for measuring N2O, CH4 and CO2. After a couple of weeks of running standards the RSD on both detectors is down from 100% to about 5-10%.

However,
1) The FID is showing downward baseline drift that hasnt been resolved by lowering the FID temp to 300 C from 350 C. The carrier is at 20 psi (N2) and 30 ml/min with air 450 psi and H2 50 psi. Unusal peaks in the signal appear when no samples are being run as well...for example this morning the mV reading jumped from 1.06 to 1.4?? Since the ECD baseline is not affected could it be due to the FID detector or the air/N2 gases rather than the column settings????

2) Low range standards (0.1 ppm N2O, 1 ppm CH4 and 10 ppm CO2) were run a few weeks ago and were detected perfectly. The instrument settings have not been changed but we are now unable to get a peak for the low N2O standard on the ECD. The CH4 was not integrated at first but was later resolved by lowering the noise and area settings. Could it have been a fluke to get peaks that low due to the high variability??

Does anyone have any suggestions for the drift on the FID and a suspected reason for the apparent change in detection of N2O on the ECD??

Many thanks
Sam

[MikeD]

Have you eliminated the Turbomatrix as a possible cause ?

[MikeD]

Do you mean Turbomatrix headspace sampler or Turbomatrix thermal desorber (ATD) ?

[sambo]

its a turbomatrix head space sampler..ive just increased the injection time from 0.02 min to 0.05 min to increase the mV reading. All of our calibrations appear to be polynomial which is ok but obviously is a problem if measuring high concentrations out of std range. Could there be a reason for a polynomial relationship rather than linear? I think we are still above the limits of detection.

[Reda HTDS]

For your FID, the optimum flows of Air & H2 recomanded by PerkinElmer are Air:450 ml/min & H2:45 ml/min. For you ECD, this is a typical problem when you use N2 as a carrier & MakeUp gaz at the same time. I recomand you to use He as carrier gaz & N2 as MakeUp gaz. Another important think with TurboMatrix HeadSpace, the pressure must be at least 5psi upper than head column pressure.