Menaquinone 7 mk 7

The following chemicals were used: citric acid (analytical grade) was from Serva Feinbiochemica GmbH, Germany, trisodium citrate pentahydrate (extra pure) was from Laborchemie, Apolda GmbH, Germany, disodium monohydrogen phosphate dihydrate (Na₂HPO₄·2H₂O) (≥ 98%), sodium hydroxide (NaOH) (≥ 99%), potassium chloride (KCl) (≥ 99.5%), chloroform (HPLC grade), and methanol (≥ 99.98%, ultra LC–MS grade) were from Carl Roth GmbH, Germany, monosodium dihydrogen phosphate dihydrate (NaH₂PO₄·2H₂O) (pure pharma grade) was from Applichem GmbH, Germany, disodium carbonate monohydrate (Na₂CO₃·H₂O) (> 99%) was from Fluka Chemika, Germany, sodium bicarbonate (NaHCO₃) was from Merck, Germany, DMPC (14:0 PC) (1,2-dimyristoyl-sn-glycero-3-phosphocholine) lipid was from Avanti Polar Lipids, USA, menaquinone 4 (MK-4) and menaquinone 7 (MK-7) were from Sigma Aldrich, Germany; menaquinone 9 (MK-9) was from Caymann Chemical, Germany. The buffer solutions were prepared using citric acid/trisodium citrate pentahydrate for pH 4, Na₂HPO₄·2H₂O/NaH₂PO₄·2H₂O for pH 6 and 7.4, Na₂CO₃·H₂O/NaHCO₃ for pH 9, Na₂HPO₄·2H₂O/NaOH for pH 11 and 11.4 and NaOH for pH 12–14.

Tetrahydrofuran (THF) for analysis, EMPARTA^® ACS (LiChrosolv, MERCK, Darmstadt, Germany); methanol anhydrous, 99.8%; methanol hypergrade for LC-MS, LiChrosolv^®; 2-propanol hypergrade for LC-MS, LiChrosolv^®; n-hexane hypergrade for LC-MS, LiChrosolv^®; ammonium acetate for LC-MS, LiChropur^®; acetic acid, 100%, for LC-MS, LiChropur^®; glacial acetic acid, 99.5%; menaquinone-7 (MK-7) United States Pharmacopeia (USP) reference standard; and vitamin MK-7 100 μg mL⁻¹ in acetonitrile, certified reference material (check standard) were purchased from SIGMA Aldrich (Gliwice, Poland).