We have checked the injector, ECD for any contamination. However the engineer says both are alright. I am currently using an Equity 5 column.
Normally it is sign for high contamination of detector which is usually indicate the high concentration of sample has been injected.
always use very dilute solutions for GC.
first remove the detector end of column and condition the column according to the leaflet present in the box of column.
then connect the column to the detector and set the temperature of detector at 10C below it T-max with carrier gas flow for at least 1hrs.
then check the condition with dilute injection of chloroform.
if not better repeat the procedure.
I had similar problem and I decided to reset all the system, it was a problem with the communication between the computer and the GC. Clean the temporary memory in the computer and OK.
other question it is if your sample has water and if yo are using a FID detector
In most cases negative peaks in GC with ECD may occur after a positive peak due to an dirty or old ECD cell.
Follow the guidelines in the ECD manual for cleaning.
Another source are small leaks in the GC system. Try a sensitive leak detector - NOT liquids as Snoop or soap.
After removing even very small leaks, condition the detector for some hours at the max. temperature (for Ni-63 appr. 340 °C.
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