Polystyrene as a Medium in Reverse-Phase Separation Of Polycyclic Aromatic Hydrocarbons

by Mantha, Madhavi

The purpose of the research was to design a method using high-performance liquid chromatography (HPLC) that would separate the sixteen polycyclic aromatic hydrocarbons (PAHs) designated by Environmental Protection Agency (EPA) as priority pollutants on two different kinds of polystyrene (PS) in the reversed phase. One was a zirconia-based column coated with polystyrene. The other was a polystyrene divinylbenzene (PS-DVB) column. The idea behind using these columns was to take advantage of extreme retention of PAHs by these columns by using high temperatures or temperature programming in order to reduce the amount of organic modifier in the mobile phases to perform analytical separations and achieve faster LC separations. Separation of the sixteen PAHs was attempted using PS-coated zirconia and the optimum conditions consisted of thermal programming as well as mobile phase gradient by running the sample at 60oC for the first 15 minutes and then at 50oC for the next fifteen minutes and using 30% acetonitrile (ACN) from 0-10 minutes, 30-50% ACN from 10-15 minutes and 50-75% ACN from 15-30 minutes. Co-elution of geometric isomers, benz(a)anthracene with chrysene and benzo(b)fluoranthene with benzo(k)fluoranthene was observed. The optimum conditions using the PS-DVB column were temperature 70oC isothermal for 5 min, 70-110oC gradient at 5.33oC min-1 for the next 7.5 min and 110oC isothermal for the next 17.5 min, mobile phase 50-90% ACN, remaining H2O:MeOH 1:1 (v/v), flow rate 2 mL min-1. Again co-elution of geometric isomers, benz(a)anthracene with chrysene and benzo(b)fluoranthene with benzo(k)fluoranthene was observed. The last three anlaytes, dibenz(a,h)anthracene, indeno(1,2,3,cd)pyrene and benzo(ghi)perylene had better separation with one peak and two shoulders, but could not be resolved completely. No combination of mobile phases containing THF, ACN, H2O and/or MeOH and no temperature program was able to completely resolve the EPA 16 PAHs better than typical silica-based C-18 columns. The PS columns did, however show potential for separation of PAHs and their environmental derivatives with two to three rings, such as those found in the vapor phase in the environment.