Stability with Method SW8082 (PCBs by GC-ECD)

Discussions about GC and other "gas phase" separation techniques.

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Hello, I am using a 5890 GC with dual ECDs and a single inlet for PCB analysis but it seems that my calibrations do not last very long (about a week). I'm using the pesticide columns from Restek (Stx-CLPesticides 1 and 2) and the peak shapes look nice and sharp but after running for a few days the response will climb on one detector and drop on the other forcing me to recalibrate. I am using hydrogen as the carrier gas set at constant flow of 2.2 mL/min through the column and nitrogen as the detector gas at 50 mL/min for each detector. Has other people had stability issues with PCBs? Can anyone offer any insight?
More information is needed. What type of liner are you using? What are the column dimensions? Oven and inlet parameters? I run gobs of PCB's so I might be able to help you out.
I'm using a spitless single taper goosneck liner 4mm x 6.5 x 78.5 with glass wool inserted halfway down. The columns are Stx-CLPesticides (30m 0.32 mmID 0.5 um df) and Stx-CLPesticides2 (30m 0.32 mmID 0.25 um df). My oven parameters are 130 C inital hold for 1 min, then 8 C/min up to 270 C hold for 2.50 minutes. Thanks for the reply!
I would try operating in split mode. Bump your makeup gas flow down to about 30mL/min to achieve higher sensitivity and inject 2uL at a 5:1 split. I calibrate down to 100ppb with every Aroclor and get very good stability running in split mode. Also, make sure your inlet is clean! If your 8082 extracts are anything like mine they are very dirty. I recommend at least changing the liner and clipping clipping the column routinely to further improve your stability. Not sure if you are doing this, but you could perform a sulfuric acid clean up on the extracts. This will also help protect your column from "junk". If you try any of this, let me know how it works for you.
I'll give those a try. I actually have problems even keeping a calibration curve when running QC samples (MDL, LOD/LOQ) that I know are clean. I'll drop the nitrogen flow down to 30 mL/min and see how that looks. I calibrate down to 25 ug/L for A1016/1260 and do a single point calibration for the other aroclors. Do you use glass woool in your inlet liner? What kind of liner are you using? Thanks for the advice!
I have really good luck with single taper liners from restek. I pack the liners myself with deactivated glass wool. Just a small plug of wool in the center of the liner helps the sample to completely vaporize.
While ECDs are inherently unstable, our calibration for PCBs lasts at least a month, depending on what we dump on it of course. PCBs don't degrade in the instrument the way pesticides do. Using single taper liners, no glass wool, dual column setup with helium carrier. Our samples are cleaned with acid.
Also consider your ECD- PCBs 'eat' the source foil, we refoil every 2-3 years. Oily samples do a number on them as well.

Good luck, TW
If the response increases on one detector and decreases on the other then you must have a change in the split between the two columns. How are you doing the split ? - two-hole ferrule into the inlet ?, Y-splitter ?. How big are the response changes ? Do you see any (even very small) changes in retention time - if it is a column split issue they will get shorter on the increasing side and longer on the decreasing column.

Peter
Peter Apps
Twanger - if you do not mind, who are you using to refoil the ECDs? Thanks.
Only two options I know of in the US- for 5890s you need CJBruyn in Washington, but be ready to wait, she has a large backlog at times. 6890 uECDs can be exchanged through Agilent.
Thanks, twranger. I have used CJBruyn in the past, she does great work.
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