Regular peaks in baseline when heating column

Question

Hi All, 
 I am having an unresolved issue of ghost peaks and irregularities in my GC traces. I have tried bringing the column up above the final temperature and letting it sit with no injection. During this there are regular peaks in the bassline. These peaks fade as time goes on, but are still visible even after an hour at temperature. The bassline is also a bit noisy, fluctuating by about 0.5 pA after an hour. II replaced the septum. Haven't done any other maintenance but this column and inlet have not been used much since installed (maybe 20 runs total). Pictures of the traces are attached. 
 Some set up details: 
 Column: DB-1HT, 30m, 0.32 mm ID, 0.1 um film thickness 
 Cool on column inlet 
 Hydrogen carrier gas flowing at 1.6mL/min 
 Max program temp is 380. These images taken at 390. 
 
 Any help is much appreciated. 
 
 Zoomed out baseline showing temp ramp 
 
 Zoomed in once temp stabilized. See regular peaks. 
 
 Close in of bassline. Regular Peaks visible and very noisy.

Hany Al-Sayed · Answer

Hi Dear, 
 Firstly, Cheking the carrier gas purity, 
 Checking the Columen condition, 
 check injector and Cleaning it, 
 And my be changing the Delta Sensor. 
 
 Best Regard's

CMZainea · Answer

Hello vtpolywood , 
 
 What type of GC do you have, if I may? If it's an 8890 for example there are some Diagnostic tests built-in that you can run on the Cool On Column inlet. Have you recently changed gas tanks (whether carrier, FID fuel, air or makeup gas)? 
 
 Make sure that the air gas supply is set at an appropriate pressure. Somewhere between 60-80 psi usually is good, but as a rule, gas supply pressure needs to be at least 20 psi higher than what the FID pressure needed during the run. Obviously, make sure you have enough gas left in the tank (if you have a tank, and not a generator). 
 You could do the same with all the gases (inlet: carrier, detector: fuel, air and makeup gas), always good to check appropriate gas supply pressure. 
 If all gas supply pressures are fine, consider adding gas traps/filters to the gas supply lines. 
 
 inlet, column and detector maintenance are always good ideas too, but with this sort of regularity, my best guess would be either a gas supply or an electrical problem.