Hi all,
I am measuring acetate (C2), butyrate (C4) and caproate (C6) in my biological sample. Initial concentration of C2 was expected to be ~25,000ppm, and zero for C4 and C6. My standard range is from 10ppm to 200ppm. So, I prepared two samples, which one has been diluted 200 times to measure C2, and another has no dilution to measure C4 and C6.
However, the results I got were very confusing because the concentration of C2 from 200x dilution and 0x dilution did not match, and also C4 was detected in 200x dilution but not in 0x dilution.
Because C4 and C6 will be produced from C2, so isnt that C4 and C6 should be detected in 0x dilution instead of in the 200x dilution sample? Besides, my technician also mentioned that "Quantification for all analytes could only be done on the diluted samples". Does that mean, if the concentration difference between two analytes is too big, the measurement will be inaccurate?
Hope to hear from you all soon.
Cheers,
Kai
Dear Kai,
are you sure about "25,000mM" (25M) ?
Define you concentration as m/m (mass of analyte per mass of solvent), next make dillution on the scale.
For any further help, please post chromatograms and prepared calibration curves.
regards,
GB
Grzegorz Boczkaj
Hey Grzegorz, thanks for replying. I have corrected, its 25,000ppm. I have also attached an excel sheet of the GC-FID analysis.
You said "my technician also mentioned that "Quantification for all analytes could only be done on the diluted samples". It sounds like your technician knows more about this, why don't you question him/her?
I suspect that quantification was done on the dilute sample in order to operate in a linear calibration region, and that is also why there is a discrepancy between the dilute and concentrated sample.
As others mentioned above, you did not give a lot of information in order to really help solve this mystery. If I were you I would want to look at the chromatograms and make sure there are no mis-identifications of the peaks, and look at the raw data for the calibrations.
Dear Kai
We are happy to help you and I agree with above mates, could you please elaborate your methodological approach? To me, it is suspicious from the sample preparation, here, I assume type II error from prepared instrumental sampling are well-prepared.
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