I would like to do product analysis of phenol hydrogenation products: cyclohexanone and cyclohexanol using GC-MS. I tried creating a calibration for a mixture of cyclohexanone and cyclohexanol (concentrations ranging between 0.325mM to 5mM) and find that since their respective peaks evolve at very similar times, I cannot get proper peak separation when they are in a mixture to do any quantification. I have tried using dichloromethane and ethyl acetate as solvents. A co-worker has seen some peak separation using acetonitrile, however, I will be extracting my products from the aqueous phase and acetonitrile is miscible with water. I am using an Agilent 8890 GC system and Agilent 5977B GC/MSD with a HP-5MS UI column. My method is start at 33C, hold 2 mins, and ramp at 26C/min to 150C. I have tried decreasing ramp rate as well. If anyone has any advice how I can get this peak separation it would be greatly appreciated.
You need to use a column with a more polar bonded phase. See for example;
V. F. Knupp, Y. M. Idernori, Z. L. Cardeal. A headspace gas chromatographic method for the analysis of cyclohexanone and cyclohexanol in a system involving metalloporphyrins as catalyst. Chromatographia (2001) 53(9):529-533. DOI:10.1007/BF02491617
Please look at the following below links which may help you in your analysis:
https://www.eurekaone.com/wp-content/uploads/2012/09/258_GC19310en.pdf
http://www.rsc.org/suppdata/ra/c3/c3ra21663b/c3ra21663b.pdf
Thanks
Dear Brianna Markunas
I have 3 possible solutions that could be successful.
1. use the possibilities of the MS to generate extracted ion chromatograms (EIC).
The mass spectra of both substances show differences like masse 55 (ketone) - 57 (alcohol), mass 98 (ketone)- mass 82 (alcohol), you will find some more. By extracting significant masses you produce a mass-dependent separation, even if your separation column does not physically separate the analytes cleanly. However, the calibration must then also be performed with the extracted masses.
2. adding salt to the aqueous phase. This method is used in various Quetchers methods to be able to shake out with ACN. The salt concentration in the water is then correspondingly high.
3. extraction with ethyl acetate or dichloromethane followed by derivatization of the OH group of the alcohol with a silylating agent, e.g. 1,1,1,3,3-hexamethyldisilazane. Silylation takes about 20 minutes at 70°C and has the advantage of changing the retention time of the alcohol so that separation occurs. The ketone is not derivatized in the process.
I would try method 1 first, since the effort is minimal.
If this is not successful, try the alternatives.
Best regards and stay healthy
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