Direct determination of ultra-trace polycyclic aromatic hydrocarbons in water by liquid chromatography coupled with online solid phase extraction

A method was developed for the direct determination of 16 ultra-trace polycyclic aromatic hydrocarbons (PAHs) in water by liquid chromatography (LC) coupled with online solid phase extraction (online SPE). The water sample was centrifuged at a high speed to remove the particulate matter and prepared into an aqueous solution containing 40% (v/v) methanol. A 2 mL-sample was directly injected into the online SPE flow path. Online purification and enrichment of the samples were carried out on the SPE column (Acclaim PA II, 50 mmx4.6 mm, 3 mu m). The PAHs eluted from the SPE column were transferred to the analytical flow path by valve switching, and were separated on a Hypersil Green PAHs column (150 mm x 3 mm, 3 mu m). Water and acetonitrile were used as the mobile phases. The flow rates of 1.0 mL/min and 0.4 mL/min were used in the extraction and balance processes, respectively. The flow rate of 0.6 mL/min was used to separate the PAHs in the analytical flow path. Acenaphthylene without a fluorescent signal was detected at the ultraviolet absorption wavelength of 220 nm, while other PAHs were measured by the fluorescence signal via the special excitation/emission wavelength program. The entire analysis could be completed within 37 min. The linear correlation coefficients of the 16 PAHs were greater than 0.996. The limits of detection of the PAHs were 0.14-12.50 ng/L (S/N=3) with only 0.38 ng/L for benzo(a) pyrene (B(a) P). The recoveries of PAHs at spiked levels of 10, 40 and 200 ng/L in the water samples were 76.1%-134.9%. The RSDs (n=3) were 0.3%-16.6%. Furthermore, the recoveries and RSDs (n=3) of B(a) P were 71.8%-92.7% and 3.9%, respectively. The proposed method is simple, rapid, solvent-saving, stable and sensitive, and can meet the ultra-trace analysis requirements of the PAHs (especially B(a) P) in various water samples.