Dimethyldichlorosilane

Microscope slides of soda-lime glass (26 mm × 76 mm × 1 mm, Thermo Fisher Scientific Gerhard Menzel B.V. & Co. KG, Germany) were hydrophobized by chemical vapor deposition with trichloro(1H,1H,2H,2H-perfluorooctyl)silane (PFOTS, Thermo Fisher Scientific)^{22 (link)} or by coating with poly-dimethylsiloxane (PDMS) brushes by ‘grafting from’ using dimethyldichlorosilane (Sigma-Aldrich) as monomers.^{23 (link)} The reaction time for the polymerization was 1800 s. According to previous work^{23 (link)} a thickness of 7 ± 1 nm of the PDMS brush layer is to be expected. In the polymerisation reaction no catalyser or other initiator was added, it is a polyaddition reaction. Therefor no additional ionic components were added in the process which could influence the experiment.
Before being coated, the glass slides were first cleaned with acetone and ethanol in an ultrasonic bath, then treated with an oxygen plasma (Diener electronic FEMTO, Plasma-Surface-Technology, Germany, 6 cm³ min⁻¹ oxygen flow rate, 120 W) for 600s to remove organic contaminations and to activate the surface. Using stock solutions of concentration 1 M (mol L⁻¹) for NaOH, NaCl, CaCl₂ (VWR, Germany), KNO₃ (ROTH, Germany), and HCl (J T Baker Avantar, Germany) and deionized water (DI water, 18 MΩ cm, obtained from an Arium® Pro (Satorius, Germany)), solutions of concentrations of 0, 0.01, 0.1, 1, 10, 100 mM were prepared.

HPLC-grade methanol (MeOH), EtOH, AAC, (99%), FA (98%) were purchased from Sigma Aldrich (Cambridge, UK). HQ water was supplied by a Milli-Q system (PURELAB, Elga, UK).
The reference standards, rac-FL and rac-NFL and the internal standard (IS) FL-d₅ were purchased from LGC Standards (Teddington, UK). All standards and ISs were of the highest purity available (>97%). Structures, molecular formulae and molecular weights of target enantiomers are summarized in Table S15.
Stock solutions of the individual compounds were purchased in MeOH at a concentration of 1 mg mL⁻¹ or 0.1 mg mL⁻¹ and stored in the dark at −16 °C. Working solutions were prepared by diluting stock solutions in mobile phase or MeOH on a daily basis and stored at 4 °C.
All glassware was deactivated with dimethyldichlorosilane (5% DMDCS in toluene, Sigma-Aldrich) to minimize sample loss through adsorption of basic analytes onto –OH sites present on the glass surface^{46 (link)}. Oasis HLB (60 mg, 3 mL, Waters, UK) were used for solid phase extraction (SPE). HQ water, river water (collected in South-West England) and activated sludge (collected from a local wastewater treatment plant) were used for method development and validation.

After being washed 3×5 min with ddH₂O, the top coverslips were incubated with dimethyldichlorosilane (Sigma-Aldrich) for 5 min and then dried with an appropriate paper.