ECD detectors - changing response

Chromatography Forum: GC Archives: ECD detectors - changing response
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, January 12, 2004 - 03:29 am:

We're measuring a chlorinated aldehyde as a trace impurity in a chlorinated alcohol using GC ECD. The problem is that the ECD detector response seems to be matrix dependant i.e. in the presence of the alcohol the response for the aldehyde grows with each subsequent injection. I realise this is a 'normal' pitfall of ECD (matrix dependant response i.e). Injecting blanks in between samples seems to reduce the effect - has anyone got any other suggestions. I've tried standard additions to 'standardise' the matrix but got drift with that as well.
Thanks
John


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Monday, January 12, 2004 - 08:45 am:

I suspect you have active sites on your injection port or column which cause the aldehyde to be adsorbed and released in an inconsistent manner and not just a matrix effect.
If the solvent is causing a decrease you would be seeing the classical lowering of response of the ECD. You state the response is INCREASING with repeated injections and that it returns to a near normal state if you inject blanks between samples. That does not sound like the classical ECD response problem.

I would experiment with different spiked samples and see how the concentration of the aldehyde effects the linearity and consistency of the response. In other words, if the response increases each injection of a 100ppm aldehyde solution, does the response increase quicker with a 10000ppm aldehyde solution? If you inject an 10,000ppm solution first, what response does the 100ppm solution have immediately after that injection versus the response of an injection of it before a 10,000ppm solution injection?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Tuesday, January 13, 2004 - 01:28 am:

Thanks - i'll try that
John


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