Chromatography Forum

Hi All,

I am having some problems recovering low for cis-1,2-Dichloroethene in proficiency samples. I am doing a 5mL purge and running on an 8100 archon as a soil. I use a K trap and am running on a 6890/5975 agilent system with a DB624 column (20m/0.18/0.18). All other analytes within the regulated compound list recovers fine (some are exactly 100% recovery) except for this one. It is recovering around 75%. I run a primary and secondary source and have also checked the system with a tertiary source and they all recover within 15%. I am at a loss and am trying to see what I can change to make this analyte recover.

This is a new problem for the last 2 proficiencies, before that I had never had a failure for this compound.

I have lost the double bonded analytes before when there is salt contamination in the transfer lines or internal system lines. If you have already put in a new trap, you can try changing the transfer line from the purge and trap to the inlet. I just purchase some Silcosteel tubing from Restek and pull out the old line and cut to the same length and slide it back in the heated line.

Which purge and trap concentrator are you using and is your transfer line to the GC Silcosteel or Nickle? The Nickle ones are really bad about becoming active with salt contamination.

The concentrator is an old Tekmar Velocity. Thanks for the idea about replacing the transfer line. I have rinsed the one I have with Methanol, but am not sure when it was replaced last.

Another thing to check is to see if 1,1,2-Trichloroethane is breaking down into 1,2-Dichloroethene. Normally the same thing that causes this also causes similar breakdown such at Pentachloroethane into Tetrachloroethene, through the loss if a Cl and addition of a double bond. If the breakdown is consistent the calibrations and second source will all agree, but when you have an unknown without the corresponding Ethane, the Ethene version will report out as a failure.