Extraction and analysis of polycyclic aromatic hydrocarbons and benzo[a]pyrene metabolites in microalgae cultures by off-line/on-line methodology based on matrix solid-phase dispersion, solid-phase extraction and high-performance liquid chromatography

This paper describes the development and validation of an analytical methodology to determine the presence of four PAHs: benzo[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene and benzo[a]pyrene in cultures of the green microalgae Selenastrum capricornutum. The metabolites of benzo[a]pyrene (BaP), 4,5-dihydrodiol benzo[a]pyrene, 9,10-dihydrodiol benzo[a]pyrene, 3-hydroxy benzo[a]pyrene and 9-hydroxy benzo[a]pyrene were also included. The methodology consisted of three parts: (1) separation of liquid media from biomass samples by centrifugation of pure cultures, (2) off-line extraction of analytes from biomass by a miniaturized matrix solid phase dispersion (MSPD) method and from liquid media by a solid phase extraction (SPE) method and (3) on-line SPE preconcentration and analysis of the MSPD and SPE extracts, separately, by high performance liquid chromatography with fluorescence detection (HPLC-FD). The off-line/on-line (MSPD/SPE–HPLC-FD) method was validated over a concentration range of 20–200 pg mg−1 obtaining good linearity (r2 > 0.9912) and precision values measured as relative standard deviation (RSD) < 5%, recovery values were in the range of (40–66%) and the limits of detection (LODs) ranged from 2 to 6.5 pg mg−1. The off-line/on-line (SPE/SPE–HPLC-FD) method was validated over a concentration range of 5–120 pg mL−1; r2 > 0.9913 and RSD < 7.36%, recovery values were in the range of 38–74% and LODs ranged from 0.8 to 2.3 pg mL−1. This methodology was applied to samples from cultures exposed to BaP at 5 ng mL−1 with different exposure times (0.75, 1.5, 3, 6, 24 and 48 h). The analytical methodology was suitable for measuring the very low amounts of residual BaP and metabolites produced in bioassays. Results showed that some of the metabolites favored by the microalgae are the dihydrodiols. The microalgae cultures were able to decrease the BaP level in the liquid medium below the United States Environmental Protection Agency (USEPA) limit (<0.2 ng mL−1).