CCV is increasing when everything else is fine

[barneyjo]

We are running EPA method 508 for pesticides on 5890's and are having a recurring problem. We do all the standards, degradation check, etc, but when we get to the CCV - the results are too high. Chromatography and RT's are right on and the ICV passes fine - just the CCV. I am not sure if it is an inlet problem or something on the detector end. We do pesticides standards, chlordane, and pcbs at the same time. I kind of remember 10 years ago or so, that I would do pests and then do pcbs to avoid a similar problem - but I honestly cannot remember. Could there be a problem with make up gas flow rate? Any input would be appreciated. Thanks

[AICMM]

Barneyjo,

Are you using an internal standard? My experience has been that the 5890 ECD had a signficant amount of drift over time as the oven top plate becomes hotter and hotter. I think this has to do with the overall detector temperature getting higher over time. To test this, put a long delay in between preliminary runs like breakdown and your CCV in order to let the top plate cool off. Also make sure that your detectors are well insulated. If you can run an IS this will compensate somewhat for this phenomenon.

I will be curious to hear more about your plight.

Best regards.