There are many different methods you can consider. A very good starting point is that PAHs have excellent fluorescence properties. With a fluorescence spectrophotometer, you can measure PAHs with very good sensitivity but only poor selectivity (against matrix and the other PAHs). Using synchronous (2 dimensional) fluorescence, you can improve this to some extent. A very practical, rather simple and high performing approach is to use HPLC with fluorescence detection, which can be operated in different ways. I can particularly recommend using HPLC with multiband fluorescence detection, where you excite with one wavelength and monitor for instance 4 different wavelengths (you can find the details in many of my papers, e.g. Gouliarmou et al, Analytical Chemistry, 2012). It is often a good idea to add 20 or 50% of methanol to your aqueous samples, since this will protect them against biodegradation and sorptive losses. Finally, watch out with regards to light exposure of your samples, which can lead to photodegradation. I hope that some of this was helpful.

surface- enhanced Raman spectroscopy using silver nano particles could also be used.