Tetrabutylphosphonium hydroxide

Potassium citrate tribasic monohydrate (K₃C₆H₅O₇.H₂O, purity ≥ 99 wt%) was obtained from Sigma-Aldrich Chemical Co. (USA). Prostate Specific Antigen from human semen (purity ≥ 95%) was obtained from Sigma-Aldrich Chemical Co. Methanol (purity > 99.9%) was acquired from Fisher Scientific. Acetonitrile (purity > 99.7%) was supplied from Lab-Scan. The buffers required for the ILs synthesis, namely n-cyclohexyl-2-aminoethanesulfonic acid (CHES, purity > 99 wt%), 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES, purity > 99.5 wt%), 2-(N-morpholino)ethanesulfonic acid (MES, purity > 99 wt%), n-(tri(hydroxymethyl)methyl)glycine (Tricine, purity > 99 wt%) and 2-[[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]amino]ethanesulfonic acid (TES, purity > 99 wt%) were purchased from Sigma-Aldrich Chemical Co. The cation precursor, tetrabutylphosphonium hydroxide ([P₄₄₄₄][OH], 40 wt% in H₂O) was supplied by Sigma–Aldrich Chemical Co. Tetramethylsilane (TMS, purity > 99.9 wt%) and deuterium oxide (D₂O purity > 99.9 wt%) were obtained from Sigma–Aldrich Chemical Co. Purified water passed through a reverse osmosis and a Milli-Q plus 185 water purifying system was used in all experiments. For the quantification of PSA using the Blitz Pro System, Super Streptavidin biosensors acquired from VWR were used.

Microcrystalline cellulose (MCC), 1-ethyl-3-methylimidazolium acetate ([Emim][Ac]), 40% tetrabutylammonium hydroxide (TBAH), 40% tetrabutylphosphonium hydroxide (TBPH), thiourea, Span^® 85, iron oxide (Fe₂O₃), lipase from Candida rugosa (Type VII, 1176 U/mg), p-nitrophenyl butylate, and p-nitrophenol were purchased from Sigma Aldrich (St. Louis, MO, USA). Sodium hydroxide, ethanol, hexane, isopropyl alcohol, Congo red, and water (HPLC grade) were obtained from Samchun Pure Chemical (Gyeonggi-do, Korea). Soybean oil was purchase from SAJO Daerim (Incheon, Korea). All other chemicals used were of analytical grade and were used without further purification.