we have one online GC for measurement Syngas components concentration(H2、CO、CO2、N2、CH4), with external calibration method. We have two bottles standard gas, the same components but difference concentration.Usually,we use bottle A to be calibration gas, bottle B only for validation after calibrated GC.
At recently weeks, I found a interesting thing , I used bottle B to calibrated GC, let bottle A as validation gas, and confirmed all the analysis result were normal! Then, we put the GC in process gas working status, but found the analysis result was not correct, CO and H2 concentration value drifted! CO always great than normal process value, H2 less it, but other three components value are normal! we observed this result a few days, CO and H2 value not become normal, so I calibrated the GC again, but this time used bottle A calibration it, bottle B validation, then put GC in process gas working status, and found all components concentrations were normal in the analysis result!
We knew the difference calibration gas concentrations will cause GC analysis result, but our doubting is why only CO and H2 value are drifted in this case?
please help us analysis why?

the parameters as below:

typical process gas value: CH4 2.3-vol%; CO 17.76-vol%,
H2 69.85-vol%; CO2 9.85-vol%; N2 0.24-vol%

bottle B: CH4=4-vol%,CO=19.08-vol%,CO2=12-vol%,

bottle A: CH4=2-vol%,CO=17-vol%,CO2=8.08-vol%,
N2=0.5-vol%, H2= blance.