comparision of three different make GC's

[Chandresh K. Soni]

Hello everyone,
we are in process of purchasing 2-3 gc with FID and capillary split/splitless injector
I checked these three different vendors GC
agilent 7890
thermo trace 1310
Varion 450 which I have

I prepared one sample of the following component in dichloromethane as solvent

a. diethylethanolamine
b. octylamine
c. nepthalene
d. 2,4-dinitrophenol

when I injected this sample in all the three GC one by one using the same column, liner,all the gc parameters like oven, injector, detector and carrier I found some unexpected results which has:

agilent varion thermo
a. diethylethanolamine 11.1% 10.8% 11.3%
b. octylamine 14.6% 14.0% 11.4%
c. nepthalene 63.9% 62.0% 69.6%
d. 2,4-dinitrophenol 10.2% 13.5% 7.5%

now I am confusd that if I just want to analyze any sample for area% which GC is giving me right results and also what is the cause for variation in the area %.
as I can do quantification also but I don't want to do this and just want to understand the reason behind the difference in the % area difference as in my opinion all the FID are working on the same principle.

if anybody can suggest me the reason please suggest us.

[Peter Apps]

When you say "the same column, liner...." do you mean that you took the column and liner out of one instrument and put them into the next one ?, of that you used the same type of column and liner in each instrument.

Thermo inlets have larger hot zones than Agilents or Varians - what was you inlet temperature, split or splitless, split ratio, concentration of the sample, injection volume, amount of each component on the column ?

Are these differences repeatable ?

Peter

[Chandresh K. Soni]

yes peter,
i removed from one instrument and installed on another instrument ( GC column, Liner)
split injection, split ratio, concentration , injection quantity each and every parameter is same.
even data collection rate in the detector is also same.

sample prepared in hundred ml volumetric flask and same one solution is injected on each GC. Even the injection syringe is also same.

i analysed it five times and every time we found same results with 0.2% difference in the area % results. we also checked the effect of liner but not able to find the reason of % area difference

[cleh]

Please give us the parameters for each instrument:
Carrier gas type and flow
Make up gas type and flow
Split or splitless injection (if splitless, what time is the split valve opening?)
Purge flow
H2 flow
Air flow
Injector and detector temps

Thanks,
Cathy

[Peter Apps]

yes peter,
i removed from one instrument and installed on another instrument ( GC column, Liner)
split injection, split ratio, concentration , injection quantity each and every parameter is same.Yes I know that already, because that was in your first post. You are asking for reasons why the results are different, one of the possible reasons is inlet discrimination, but to judge whether that is likely to be the reason I need to know the conditions that you are using. Telling me that they are the same on each instrument does not provide me with the information that I need to help you
even data collection rate in the detector is also same.

sample prepared in hundred ml volumetric flask and same one solution is injected on each GC. Even the injection syringe is also same.Similarly, you might be overloading the column or the detector with some or all of the components. whether or not there is overloading depends on how much of the compound you are putting on the column, that depends on the concentration of the sample and the injection conditions; particularly the split ratio. That is why I asked for the information. That the sample is the same for all the instruments does not provide the required information

i analysed it five times and every time we found same results with 0.2% difference in the area % results. we also checked the effect of liner but not able to find the reason of % area difference

The more you don't tell us, the more we can't help you.

Peter