Ap d8

The reference compounds AP and MA were purchased from Cerilliant (Round Rock, TX, USA) at a concentration of 1000 µg/mL in methanol. Methanolic solutions of the deuterated IS AP-d₈ and MA-d₁₁ in each vial at a concentration of 100 µg/mL were also purchased from Cerilliant. HPLC-grade acetone, ethyl acetate, and methanol were supplied by J. T. Baker (Phillipsburg, NJ, USA). Methanolic HCl (HCl, 1.25 M) was obtained from Fluka (St. Gallen, Switzerland). PFPA was acquired from Acros Organics (Geel, Belgium). HybridSPE phospholipid cartridge (30 mg/1 mL) was purchased from Supelco (Bellefonte, PA, USA). Strata-X 33 µm polymeric reversed phase cartridge (60 mg/3 mL) was purchased from Phenomenex (Torrance, CA, USA), while Oasis HLB extraction cartridge (60 mg/3 mL) was from Waters (Milford, MA, USA). All other chemicals were of analytical grade or higher. Polypropylene tubes (2 mL) were obtained from Eppendorf (Safe-Lock tube, Hamburg, Germany). Water was purified with a Millipore AFS-16 water purification system (Molsheim, France).
Stock solutions of the target compounds were mixed and diluted in methanol to prepare final mixed standard solutions at 10 µg/mL of AP and 20 µg/mL of MA. A working solution of IS (AP-d₈ and MA-d₁₁) at 0.3 µg/mL was also prepared in methanol. All these solutions were stored at −20 °C before use.

AP, 4HA, and AP-d₈ were obtained as solutions from Cerilliant (Austin, TX, USA). HPLC-grade methanol was purchased from J.T. Baker/Avantor (Center Valley, PA, USA). Water (LiChrosolv-grade) was supplied by Merck (Darmstadt, Germany). Formic acid (LC–MS LiChropur-grade) was purchased from Sigma Aldrich (St. Louis, MO, USA). All other chemicals were of analytical grade or higher. The AP and 4HA working standard solutions (10 µg/mL) were prepared by dilution with methanol. The IS working solution was prepared in methanol to obtain an AP-d₈ solution (0.1 µg/mL). These solutions were stored at −20 °C in amber bottles before use.

AP, 4HA, and AP-d₈ were obtained as solutions from Cerilliant (Austin, TX, USA). HPLC-grade methanol was purchased from J.T. Baker/Avantor (Center Valley, PA, USA). Water (LiChrosolv-grade) was supplied by Merck (Darmstadt, Germany). Formic acid (LC–MS LiChropur-grade) was purchased from Sigma Aldrich (St. Louis, MO, USA). All other chemicals were of analytical grade or higher. The AP and 4HA working standard solutions (10 µg/mL) were prepared by dilution with methanol. The IS working solution was prepared in methanol to obtain an AP-d₈ solution (0.1 µg/mL). These solutions were stored at −20 °C in amber bottles before use.