How to account for variation in purge-trap GC-FID? - (Oct/21/2012 )

Hi,

I'm currently doing research on anaerobic biodegradation of hydrocarbon. Now, some of my treatments have produce some interesting results. I extracted some of samples from the microcosms on Day 0 to get the initial amount of alkanes that I spiked into my microcosms and I extracted some samples from those microcosms that are producing some methane, again on Day 200+. The results that I got show that there are quite a lot of biodegradation that has occured. But when I compared my measured methane and the theoretical amount of methane (where I calculate by deducting the amount from day 0 and day 200+), the percentage of my measured methane is ranging from 10-58%, which is, according to my supervisor, too low. He said that I should be comparing my live treatments with my autoclaved control and not from Day 0 with Day 200+ due to variation in the measurement. He said something like biodegradation of my spiked hydrocarbon expressed in % of autoclaved control. He did not explain further but instead ask me to look into literatures. Of course literature won't explain how to do the calculation. Any of you guys know how to do the calculation? My math and analytical chemistry is kinda rusty as I've left these subjects for quite sometime..

O_o
Not sure how you did the calculations for the 10-58% methane, I worked in biodegradation but we accounted degradation by substrate depletion not product formation.
Autoclaved control is used to normalize the results as you may have spontaneous formation, degradation, volatilization etc, so you have to use as baseline the measurements of the controls

Check this link at the end of the page 8
https://www.wastereduction.gov.hk/en/materials/info/container/HS_2001.pdf