Luna silica

The collected blood samples were immediately processed and stored at −80°C until analysis. Plasma TMAO levels were quantified by stable isotope dilution liquid chromatography tandem mass spectrometry (6460 Series Triple Quadrupole LC/MS; Agilent) using a d9-(trimethyl)-labeled internal standard, as previously described (23 (link)).
In total, 50 μL of plasma was added to a 1.5 mL Eppendorf tube and mixed with 200 μL of 10 μmol/L internal standard composed of d9-TMAO in methanol. The samples were vortexed for 1 min, and then the supernatant was aliquoted following centrifugation at 15,000 g and 4°C for 25 min. Two microliters of supernatant was injected directly into a silica column (4.69 × 250 mm, 5 μm Luna silica, catalog no. 00G-4274-E0; Phenomenex) at a flow rate of 0.5 mL/min⁻¹ with 80% solvent A (0.1% formic acid in water) and 20% solvent B (methanol). TMAO and d9-TMAO were monitored in the positive multiple reaction monitoring mass spectrometry mode using characteristic precursor–production transitions including m/z 76/58 and m/z 85/66, respectively. To calculate TMAO concentrations, serial concentrations of TMAO standard were added to control plasma to prepare a calibration curve.

Analysis of tocopherols was performed by HPLC according to Brazaityte et al.’s [25 (link)] methodology with some modifications. About 1 mg of oil was weighed in an Eppendorf tube, and then 1 mL of n-hexane with 1% of BHT was added to the tube. Afterward, the samples were filtrated through a 0.45 µm polytetrafluoroethylene (PTFE) membrane syringe filter (VWR International, Radnor, PA, USA) and were analyzed by HPLC/FLD (fluorescence detector) (Agilent Technologies, Santa Clara, CA, USA). The HPLC measurements were performed using a normal phase column (Phenomenex Luna Silica, 5 μm, 250 mm × 4.6 mm). The HPLC 10A system, equipped with an RF-10A fluorescence detector (Shimadzu, Japan), was used for analysis. Peaks were detected at an excitation wavelength of 295 nm and an emission wavelength of 330 nm. The mobile phase (0.5% isopropanol in hexane) was used at a flow rate of 1 mL min⁻¹. The α-tocopherol, γ-tocopherol, and δ-tocopherol were identified according to the analytical standard. The α-tocopherol, γ-tocopherol, and δ-tocopherol content were expressed per 100 g of oil.