Have a look at Application Note 5990-3451EN from Agilent. You should be able to almost separate and quantify (i admit there is no baseline separation) benzo[b]flouranthene and benzo[k]flouranthene by means of gas chromatography. By means of mass spectrometry You can not distinguish the two substances, they are too similar.

The link fyi https://www.agilent.com/library/applications/5990-3451EN.pdf

MS pattern will be same for both compounds. If you come up with good oven temperature programme it will be able to resolve the two peaks with respect to RT for lower concentration of analytes. Usually it is better to start low oven temperature with low ramp. This will be tricky but probably possible.

Good luck for your PAHs analysis.

Db5ms - thin film and best 60,0m column.

Regards

GB

Is there any big difference between mass spectra of the compounds analyzed?

no

both molecular weight are 252.3 g/mol

I agree with most of the above answers. It is better to optimize the GC conditions using a suitable column and get a good separation between the two so that they can be identified on the basis of RT.

Optimize the separation conditions. C18 columns have the ability to recognize the different length to width ratios even if they re isomers yielding different retention time. Then you do not have to depend on the MS to recognize them.

Sorry your question was on GC/MS . I talked about HPLC. You will find selective columns which differentiates isomers with different geometry.

Hi Mahsa,

You can almost seperate benzo[b]fluoranthene and benzo[k]fluoranthene as Ludwig writes. The problem is that in a real life sample benz[j]fluoranthene will be in the middle. So if you analyze a standard with only b and k you will see 2 peaks with a small gap, in a sample however that gap between b and k j will be filled with the overlapping j.

With a HP5 column the amounts of b and k will be higher due to the overlap of j.

With a PAH-Select column benzo[j]fluoranthene will elute after b and k, so that would be an option.

Regards, Alex

I agree with Alexandre. I worked a lot with Rxi-PAH column and it gives an excellent separation on the crysene/triphenylene critical pair, too