Chromatography Forum

Hello,

I have a Perkin Elmer GC-ECD instrument. I am trying to measure nitroglycerin (NG) in soil. I use the below method:

Injector temp: 150 oC
Oven Temp: 35 hold for 3min, 250 hold for 1 min
ECD temp: 300
SETPOINT 1.50
Carrier gas: He
Column: 30m, elite-5 , 0.25, 0.25

I used to get good results with the above settings. Starting 2 weeks ago I noticed that the base line goes up when the temperature reaches about 110-140. NG peaks comes out in 15.2 min (temp:~ 155). I also get false positive and noise. When I use only alcohol sample and injcet it I get noise and false positive. I already replaced the septum, replaced the injector liner, washed and cleaned the syringe, Backed the column at 320 for 2hrs, cut about 6 inches of both end of the column and baked it again. Nothing worked. Now even I don't get the noise. If I do not inject anything or inject alcohol I get flat base line until the temperature reaches 110 and then the base line goes up to 1000mv and saturate and keep going straight at 1000mV.




PLEASE HELP ME

Thanks

Change liner ,Septa, remove column from detector. Block the ECD from bottom bake ECD at 350 degree set make up gas 45 ml overnight. Conditioned the column overnight still problem persists change the column.
(Make sure make up gas N2 & He carrier GAS is of good quality & no leak in the gas pannel/filterstation )

sanjay

For the noise issues, I would suggest checking the connections to the detector (we recently had this problem). Make sure that the connections are clean and snug.

Thank you all

I have another question. I ran several 100ppm standards andalthough I calibarated my method several times, I get different concenterations each time I ran the same (100ppm) standards. I got 54, 71, 85, 112, 114, 156, 276, 219, 186,.. I use GC-ECD.

Thanks

I have another question. I ran several 100ppm standards andalthough I calibarated my method several times, I get different concenterations each time I ran the same (100ppm) standards. I got 54, 71, 85, 112, 114, 156, 276, 219, 186,.. I use GC-ECD.

Thanks