Minivap

The direct digestion of the samples in the glass slides were performed by focussed microwaves in a microwave unit Explorer Hybrid from CEM Corporation (Matthews, NC, USA). The hair samples were treated with 25% tetramethylammonium hydroxide (TMAH) (Sigma-Aldrich) for 4.5 min at a fixed power of 35 W. After digestion the resultant supernatant was transferred to a vial containing 4 mL of acetic acid/sodium acetate buffer (pH 4). For derivatization, 0.8 mL of a 2% w/v sodium (tetra-n-propyl)borate (LGC-Standards, Wesel, Germany) in Milli-Q water and 1 ml of hexane (Sigma-Aldrich) were added for liquid-liquid extraction. The derivatization and extraction into hexane was accomplished by five minutes of manual shaking. Then, the sample was centrifuged (5000 rpm for 5 min), and the organic layer was transferred to a glass vial and stored at -18 ºC until analysis. Just before the GC-ICP-MS injection of the samples an additional step of pre-concentration under a gentle stream of nitrogen was carried out in a dedicated unit (Minivap, Supelco, Bellefonte PA). The samples were pre-concentrated until a final volume of approximately 20 µL.

Aliquots of 100 mL of wastewater were vacuum-filtered through 0.7 μm glass microfiber filters GF/A (47 mm diameter, Whatman, Kent, UK) and 0.45 μm cellulose filters (47 mm diameter, Merck Millipore).Samples were spiked with 20 ng of every IS after filtration. SPE was performed using a standard vacuum manifold Visiprep™ (12-port model, Supelco, Steinheim, Germany) maintaining a pressure of approx. 5 inches Hg.
Samples were loaded onto mixed-mode reversed-phase strong anion-exchange cartridges (Oasis MAX-60 mg, Waters, Milford, MA, USA) previously rinsed with 3 mL of MeOH followed by 3 mL of ultrapure water. Sorbents were dried under nitrogen during 30 min and analytes eluted with 5 mL of 2% formic acid in MeOH. Eluates were evaporated to dryness under nitrogen using a Turbo-Vap II (Zymark, Hopkinton MA, USA) and a Mini-Vap (Supelco, Steinheim, Germany) concentrator. Extracts were reconstituted in 100 μL of MeOH, filtered through 0.22 μm PVDF syringe-driven filters (Millex, Merck Millipore) and injected into the UPLC ® system.