Optimisation of contamination-control, extraction and analysis of trace levels of phthalic acid esters in seawater

Quantification of phthalates and phthalic acid esters (PAEs) in seawater is challenging due to matrix overlaps, self-absorbance and contamination from plastic laboratory materials that release PAEs. Plastic materials are ubiquitous in sampling devices, analytical instruments and the laboratory environment, thereby making it more difficult to reliably analyse trace concentrations of PAEs in collected seawater samples. In the current study a reliable protocol was established for OAE analysis in seawater including control of blank contamination and optimisation of experimental conditions. The mass of PAEs in blank tests of selected materials ranged from 3 ± 0.7 to 35 ± 6 ng for liquid-liquid extraction (LLE) and from 5 ± 1.8 to 63 ± 15 ng for solid-phase extraction (SPE). Higher blank values were measured for dibutyl phthalate (DBP, 35 ± 6 ng, 12 ± 3 ng), and di(2-Ethylhexyl) phthalate (DEHP, 63 ± 12 ng, 23 ± 5 ng) in LLE and SPE, respectively. Recoveries of PAEs in LLE were 90–97%, and up to 86–90% for SPE. The method quantification limits (MQL) for PAEs were 10–20 ng L^–1 for LLE and 10–35 ng L^–1 for SPE. In coastal seawater samples from Sharm Obhur, PAE concentrations obtained using SPE ranged from 138–282 ng L^–1 (Di(2-ethylhexyl) phthalate, BEP), 143–276 ng L^–1 (diethyl phthalate, DEP) and 8.9–238 ng L^–1 (DBP). The method shows lower MQL values for LLE and SPE than reported values of 10–100 ng L^–1 and 30–100 ng L⁻¹, respectively. The MQL values meet the requirements for PAEs analysis in seawater. The results suggest that LLE or SPE combined with GC-MS form efficient methods to quantify PAEs concentrations in seawater.