Retention time shift of HCH

[astroguille]

Hi people!

I work at GC 6890, I analize pesticides in fruits and vegetables.

The standard has 30 pesticidas, and that includes HCH (α, β, γ, δ).

I noticed gladually a shift of HCH β and γ: now, those co-elute, but the retention time of the others pesticides are ok.

What can the problem be?

Thanks

[Don_Hilton]

First guess is that you have run many injections on the column - and the residual junk from injections has changed the stationary phase.

(I am also assuming that you are keeping up with changing liners, septa and such.)

Assuming there have been no other changes in the column and column conditions, like column length, gas flow rate or temperature program, try baking out the column. If that does not work, trimming off the front end of the column may work. And, if either of these techniques works, be sure you have a new column on hand or on order. The column's days are numbered.