Hi!

I have been using for a long time a semi-preparative method with a normal-phase column in order to get 2 different eluates from the same sample, and then I analyze each eluate using CG-ECD. Suddenly, I´ve started to find extremely low recoveries (or no recovery) in most of the 16 analites, although 3 of them remain OK. I´ve checked the autosampler, the loop, changed the column, there are no leaks, and I´ve checked that the flow is OK in each pump.
Mobile phases are Hexane and Hexane/Chloroform/Isopropanol

Could ou please give me some advice about what else could I do?

Thanks a lot!