Seven2go

Octanoic acid (Acros Organics, Pittsburgh, PA, USA) and trihexylamine (Sigma Aldrich, St. Louis, MO, USA) were used as received for the preparation of the T6A OA organic mixture. Hydrochloric acid (37%, Merck, Kenilworth, NJ, USA), nitric acid (65%, Merck), bromic acid (47%, Merck), hydroioidic acid (55%, BDH Chemicals, Radnor, PA, USA), and perchloric acid (70%, Acros Organics) were diluted with Milli-Q water (deionized with Simplicity Millipore deionizer, Millipore, Burlington, MA, USA) to the pH values at which they were used. Sodium hydroxide (>99%, Merck) and potassium hydroxide solution (87.5%, J. T. Baker, Radnor, PA, USA) were similarly diluted.
trihexylamine and Octanoic acid were mixed in 1:1 mole ratio, based on weighings with an analytical balance. After initial mixing, samples were stirred 20+ hours, using a magnetic stirrer.
For the extraction experiments, 4.00 mL of the organic phase were mixed with an equal volume of the aqueous phase and shaken, overnight on a Beun De-Ronde wrist-shaker. Phases were then isolated using a Medilite centrifuge, and the resulting phases were separated by a syringe.
pH measurements of the aqueous phase were conducted with a Mettler-Toledo Seven2Go apparatus (Columbus, OH, USA) and a a Mettler-Toledo InLab Expert electrode. The pH meter was calibrated, prior to each round of measurements, using Certipur buffer standards (Merck).

A pH electrode (InLad Micro, Mettler Toledo®) connected to the pH/ORP meter (Seven2Go, Mettler Toledo®) was calibrated using standard solutions of pH 4, pH 7, and pH 11. After the calibration, the electrodes were inserted directly into the vacutainer tube to take the measurement. The pH of the soil solution samples were measured within 24 h of sample collection.