Hi All

I am still fairly new to GC analysis but I am having an issue with a difference in retention time for the ammonia component between our Reference Gas standard and the ammonia component of the Synthesis gas we produce. The ammonia component of the ref gas standard appears at 6 mins, the ammonia component of the syn gas sample appears after 7 mins and is not giving a result. This is leaving the operators over night with no result for ammonia.

We are running a Shimadzu GC-2014 with Molesieve and Porapak QS columns and the following conditions.

Injection temp: 120
Molesieve Pressure: 96.5kPa column Flow: 20mL/min
Porapak QS Pressure: 51.9kPa column Flow: 20mL/min

Column Temperature: 50

FID (Ch 1)
Detector Temp: 390
Flame on

DTCD (Ch 2)
Detector Temp 120
Temperature (Pre) 390

FID (Ch 3)
Detector Temp: 390
Flame off

Carrier Gas is Hydrogen
Ammonia is detected on channel 3 using a FID with the flame off.

The other parameters we measure are Carbon Monoxide, Methane, Carbon Dioxide, Argon, and Nitrogen. The retention time shift is not evident in the other parameters, it only appears in the ammonia component.

Has anyone got any suggestions on what would be causing this shift in retention time and how I can address it?