I'm analyzing some compounds using GCMS. The analytes are beta-Myrcene and D-Limonene, and the internal standard is benzophenone. By three-point calibration, the RRF of beta-Myrcene and D-Limonene are 0.11 and 1.05, respectively. Is this reasonable, or is the difference too large, considering that they are isomers?
Thank you.
Although they have the same empirical formulas their structures are very different, and so it is likely that they would have different ionisation efficiencies in an electron impact source, and consequently different response factors. Nearly an order of magnitude difference is unlikely though, unless you are omitting to tell us that you are monitoring single or selected ions, in which case it is entirely possible.
MS is all about structure! The impact pattern (and thus the daughters) can be totally different.
While a 3 point calibration is nice (3 times lucky), I use 5 or 6 points in my linear curve.
They both have a very strong 69 and 93. They are quite different structurally, but you should get similar response in the MS. While I would expect the limonene to give you higher response, I would certainly expect that both would give you RRFs significantly higher than 0.11, even if you are using EICP instead of TIC for the quantification. I would check the standard.
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