Eicosanoic d39 acid

NaCl
(99.999% trace metals basis), NaI (99.999%,
trace metals basis), NaBr (99.99%, trace metals basis), NaSCN (99.99%,
trace metals basis), NaOH (99.99%, trace metals basis), Na₂S₂O₃ (99.99%, trace metal basis), ethylenediaminetetraacetic
acid (EDTA, 99.995%, trace metals basis), eicosanoic-d₃₉ acid (97%, dAA for deuterated arachidic acid), eicosanoic
acid (99%, AA for arachidic acid), and chloroform (anhydrous grade,
stabilized with ethanol) were obtained from Merck. HCl, 36.5% (99.999%,
trace metal basis), was purchased from Alfa-Aesar. Before use, NaCl,
NaBr, and NaI were baked at 500 °C for 1 h and slowly cooled
to eliminate any traces of organic compounds. As NaSCN decomposes
at a significantly lower temperature, the salt was cleaned using an
approach similar to that proposed by Lunkenheimer for purifying surfactants,^{35 (link)−37 (link)} where the surface of NaSCN stock solutions are repeatedly aspirated
to remove traces of surface active contaminants. The remaining compounds
were used as received. Ultrapure water was obtained from an Integral
15 Millipore system featuring a constant conductivity (18.2 MΩ·cm)
and low total organic content (<3 ppb). The glassware was cleaned
beforehand by a three-step sonication procedure with, subsequently,
ethanol, Deconex (Borer Chemie), and ultrapure water, alternated with
10 times rinsing with water between each step.

NaCl (99.999% trace metal basis, Merck) was baked at 500 °C for 1 h in order to remove traces of organic contaminants. HCl 36.5% (99.999% trace metal basis, Alfa Aesar), deuterium oxide (D 99.9%, <0.8 μS cm⁻¹ in conductivity, Cambridge Isotope Laboratories, Inc., MA, USA), chloroform (anhydrous grade, stabilized with ethanol, Merck), methanol (anhydrous, 99.8%, Merck), eicosanoic-d39 acid (97%, dAA for deuterated arachidic acid, Merck), and sodium eicosyl sulfate (>95%, Santa Cruz Biotechnology, TX, USA) were used as received. The electrolyte solutions were prepared by serial dilution in either D₂O or ultrapure water from an Integral 15 Millipore system (resistivity of 18.2 MΩ.cm and TOC < 3 ppb). The solvents used for the fatty acid and fatty sulfate spreading solutions consisted of pure chloroform, and a mixture of chloroform-methanol in a 10:1 proportion, respectively.