Inject pure standards for each of these compounds under the separation conditions you are using to get a reference for their relative retention times and accurate spectra for a searchable library. These 2 compounds give very similar EI spectra so for identification you will need to verify their retention times and spectra under the exact conditions you are using. You can then mix the 2 compounds and inject this mixture to see how well they can be separated at different concentrations and determine if the spectra change at different concentrations. You can look up the spectra for both compounds in the mass spec database, see link.

http://www.massbank.jp/

What are your chromatographic conditions?  This has always been a difficult separation (see peaks 62 and 63 below).  Call your Agilent rep.

https://www.researchgate.net/profile/Kenneth_Lynam/publication/239569492_Semivolatile_Organics_Analysis_Using_an_Agilent_JW_HP5ms_Ultra_Inert_Capillary_GC_Column/links/5565dc3f08aeccd77735995f.pdf?origin=publication_list

Article Semivolatile Organics Analysis Using an Agilent J&W HP5ms Ul...

In order to separate these pairs you will need a different column.  Review this article (its been done before);

https://www.researchgate.net/publication/244073097_Gas_chromatography_of_the_system_phenanthrene-anthracene-carbazole_on_a_column_of_cadmium_chloride_modified_with_Carbowax_20M

Article Gas chromatography of the system phenanthrene-anthracene-car...

I agree with Bruce. What is your GC conditions, like column, solvent, gas and the gas flow rate etc. However, under very ordinary conditions these are difficult to separate. You may try a simple capillary PORAPAQ Q column. 

Dear Eda,

in the past, I used  Restek Rxi 5-ms capillary (of same dimensions as yours) as general-purpose column for semivolatile organics.

I alwas had a baseline separation of PHE-ANT  ( even on old, worn out  column).  IMHO, PHE-ANT is not a critical pair on this column.

Now, I prefer Restek Rxi-PAH, which provides better separation of some toxicologically relevant PAHs on mass 252. Again, the  separation of PHE-ANT is OK, and using 17-Sil MS phase, you must succeed, too. 

Dear Eda,

   i am also struggling for separation of chrysene and benzo a anthrencene in HP-5 ms,

then we realized that ZB-5 msi 30 meters 0.25 mm 0.25 thickness film is giving good separation in pah compounds. low noise and high lifetime, we are getting separation for all  PAH compounds, very stable for herbal matrices,

Inject pure standards for each of these compounds under the separation conditions you are using to get a reference for their relative retention times and accurate spectra for a searchable library. These 2 compounds give very similar EI spectra so for identification you will need to verify their retention times and spectra under the exact conditions you are using. You can then mix the 2 compounds and inject this mixture to see how well they can be separated at different concentrations and determine if the spectra change at different concentrations. You can look up the spectra for both compounds in the mass spec database, see link.

http://www.massbank.jp/

I agree with John Carney. These two compounds can be separated on a Restek  Rxi-17 Sil MS column. This is a medium polar column with 50 % phenyl modification and with extremely low bleeding. You should be able to get a comfortable separation using this column. You will have to adjust the temperature conditions for the column and also the concentration of the sample solution. 

Thank you for your responses..

They are all very illumunating for me.

Finally I have splitted that peaks from each other with the same column, only changing the method. If you interested in with this, i can share my GC-MS method.

Again, thank you very much.

Using GC/MS also and  I am not sure if I am seeing peak splitting or separation here - the mass spectra are nearly identical. I do not have access to either in pure form (we only purchased a mix of compounds). Seeing similar for the later PAH separations as well. 

Although these compounds elute close together it should be NO problem to seperate them on a "standard" DB1 or 5 column with a "standard" oven program. No special columns or oven programs required. They have very similar spectra, but that is not something unusual in GCMS. Many other PAH have very similar spectra, nothing to be concerned about. Tailing on an older column can make it difficult to quantify anthracene.

In environmental samples you can easily identify phenanthrene and anthracene by looking at the "GC-pattern". You will see one big peak followed by a smaller peak (mass 178). The big peak (phenanthrene) will be ~5-10 times higher than the small peak (anthracene). Although this will be true for many environmental samples there can be exception to this rule.

Experienced analist identify PAH not only based on there spectra and retention times but also the "GC-pattern" they see. Using deutered PAH as internal standards will make it even more easy to identify your PAH.

There are special PAH columns to help seperate PAH that really are a problem to seperate.

Regards, Alex