Ammonium iodide nh4i

The internal standards (d3-testosterone, d4-cortisol, d9-progesterone, d7-cholesterol, 13c3-androstene-3,17-dione, and 13c3-estrone) were purchased from Cerilliant (Round Rock, TX, USA). L-ascorbic acid, sodium acetate, acetic acid, β-glucosaldosidase/arylsulfatase, ammonium iodide (NH4I), dithioerythritol (DTE), and N-methyl-n-(trimethylsilyl)trifluoroacetamide (MSTFA) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Commercial standards of steroids (dehydroepiandrosterone, testosterone, 11-deoxycorticosterone, cortisone, cortisol, 16α-hydroxyestrone, pregnenolone, 17α-hydroxypregnenolone, epipregnanolone, dihydrotestosterone, 21-hydroxyprogesterone, androsterone, epiandrosterone, corticosterone, estrone, 17β-estradiol, estriol, 16-epiestriol, progesterone, 17α-hydroxyprogesterone, desmosterol, cholesterol, etc.) were purchased from Sigma-Aldrich, J&K Chemical Ltd. (Beijing, China), or Santa Cruz Biotechnology, Inc. (Santa Cruz, CA). Chromatographic pure hexane, methanol, and ethyl acetate were purchased from Merck (Fairfield, OH, USA). The Oasis HLB SPE cartridge was obtained from Waters (1.5 ml, 60 mg; Waters, Milford, MA, USA).

Cholesterol, CEs, and OHCs were purchased from Sigma (St. Louis, MO, USA). Deuterium-labeled internal standards, 2,2,3,4,4,6-d₆-cholesterol, 2,2,3,4,4,6-d₆-cholesteryl stearate, 25,26,26,26,27,27,27-d₇-4β-hydroxycholesterol, and 25,26,26,26,27,27,27-d₇-27-hydroxycholesterol were obtained from C/D/N Isotopes (Pointe-Claire, Quebec, Canada) and Avanti Polar Lipids (Alabaster, AL, USA). The trimethylsilylation (TMS) reagent, N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), ammonium iodide (NH₄I), and dithioerythritol (DTE) were acquired from Sigma. The hybrid solid-phase extraction (SPE)-precipitation cartridge (H-PPT, 1 mL, 30 mg) was supplied by Supelco (Bellefonte, PA, USA). All organic solvents were analytical, high-performance liquid chromatography-grade chemicals, and were purchased from Burdick & Jackson (Muskegon, MI, USA).