We have online GC-FID and GC-TCD (Mod: 2014) connected with flow reactor system.
This GC-FID/TCD is connected to a gas line coming from flow reactor system which I used for cascade reaction. In this flow reactor system ethanol is pumped with constant rate & heated at 160 oC and an inert gas (flow controlled by MFC) is using as carrier gas for ethanol. To prevent from condensation of ethanol, the line is wrapped with heating tapes. Further, the gas/ethanol flow through a loop in the GC-FID and GC-TCD, and when the sampling process starts, the GC takes the gas in the loop to column by pressing the switch (activate sampling at same time).
In this system, I flow the gas/ethanol at constant conditions in flow reactor for the long time as well, but I get instable peak area of ethanol in GC-FID as depicted in attached figure.
I tried a lot by changing the flow reactor parameters, checked gas leak, pressure regulators, sampling time. but facing the same problems.
Could anyone suggest me, where is the problem or anyone facing such type of issues?
Thanks in advance
First, make sure the column and detector are intact. Then, perform pre-sampling/sample preparation according to the protocol (AOAC). After that, ensure the purity of the solvent used (laboratory grade for GC). Eventually/finally you will achieve a better result.
Dear Hamid Reza Farhang , thanks for the response. I used to do the pre-sampling to make sure any impurities or not. Then only, starting ethanol pumping and obtained the results as attached histogram. Here, I am using only pure ethanol (99.8%, GC grade) and N2 gas as carrier gas. Therefore, it has gas phase sampling through loop to FID column. And the condition is intact of the flow reaction such as Temperature, gas flow rate and ethanol pump rate etc. But still obtained instable peak area of ethanol.
Dear Raju Kumar ,
Unfortunately, you do not describe how to mix ethanol and nitrogen before adding the sample to the GC. From my point of view the fluctuations can also be caused by incomplete mixing.
In my opinion, the relative standard deviation of your measurements is not necessarily high at around 8%. Laboratory GC`s with autosampler achieve relative standard deviations between 1-10 %, depending on the analyte and method, i.e. values comparable to yours.
In our laboratory we spent a lot of time and experiments with the calibration of thermodesorption systems. Here, too, the mixing of gas phase and analyte was a significant problem. Maybe you can optimize the mixing by using silanized glass wool in the gas path.
Good luck in solving the problem and stay healthy
Grzegorz Boczkaj Thanks for the response. I am using Pora PLOT capillary column and the temperature condition column is as follow: Ramp rate 5oC, temp-200 oC and holding for 3 min.
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