Online water sampling-Mix-assisted miniscale liquid-liquid extraction coupled with full evaporation dynamic headspace concentration of polybrominated diphenyl ethers.

Polybrominated diphenyl ethers (PBDEs) are commonly used as flame retardants in daily household products and have been found to be detrimental to human and animal health. Being highly stable, accumulation can take place easily in the environment. In our previous studies, an innovative sample preparation method named miniscale liquid-liquid extraction (msLLE) coupled to full evaporation dynamic headspace (FEDHS) concentration was developed, and then successfully coupled to an online water sampling system, allowing full automation from water sampling to sample preparation, sample detection and analysis. In the present work, the fully automated online sampling-Mix-assisted-msLLE-FEDHS platform was optimized and applied to PBDEs in environmental aqueous samples. The online sampling system was set up with a modified sample vial (to have an inlet and outlet), two tubings and a peristaltic pump which was programmed to control the water flow into and out of the vial. After adding 2 mL of the extractant (n-hexane), and 7 mL of sampled water to a 10-mL vial, msLLE was enabled, assisted with a Mix module to ensure a quick and efficient mode of mixing between the organic and aqueous phases. The organic extract was then transferred to the FEDHS setup for selective trapping and concentration of the PBDEs, while the solvent was removed. The trap consisted of Tenax TA adsorbent, which has favorable π-interaction with the PBDEs but not with n-hexane. Subsequently, the adsorbent tube was automatically transported to the injector of the gas-chromatography mass-spectrometric (GC-MS) system to thermally desorb the trapped PBDEs for detection and analysis. The optimized methodology was found to achieve low limits of detection (0.0031 to 0.018 µg/L) with good linearity (r ≥ 0.9932) and satisfactory absolute extraction recoveries (between 61.4% and 80.9%). The analysis of PBDEs in spiked genuine water sample attained satisfactory and repeatable relative recoveries (between 106.1% and 132.6% with%RSDs ≤ 8.6%).