Solid Phase Extraction (SPE) with elution by a small amount of Hexane and then direct injection into a GC. See Waters, Phenomenex, Restek, and Agilent websites.

You will need to 'spike' the Hexane with a small amount of an internal standard (ISTD) that is similar to Benzene so you can calculate a % Recovery. Drying down Hexane is a 'pain' and will highlight the massive losses of Benzene occuring during the drying process.

See the attached article. Great minds think alike! However, they use DCM (Dichloromethane or Methylene Chloride).

Article Determination of Benzene, Toluene, Ethylbenzene and Xylene i...

I would recommend purge-trap or head space or SPME analysis.

example of the head space method from Agilent

https://www.agilent.com/cs/library/applications/5990-3285EN.pdf

Great and thank all for valuable suggestions

C18 - SPE conditioning with a series of organic solvents

You can use Purge And Trap (P&T) as well as Head Space technique. P&T will be quite expensive and hence HS will be a more affordable technique.