Queuine standard was dissolved in ultrapure water to prepare 1 mM stock solution.
Phosphate buffered saline (PBS) with 4% bovine serum albumin (BSA) was sued as surrogate matrix. Both q and Q stock solutions were aliquoted and stored at -20 ֯ C. Calibration standards (1, 0.3, 0.1, 0.03, 0.01, 0.003, 0.001 and 0.0003 µM), and 3 quality controls (QCs; 0.8, 0.02 and 0.0008 µM) were prepared freshly either in ultrapure water; or spiked in matrix surrogate and then extracted using a PBA cartridge on the day of analysis.
Phosphate buffered saline (PBS) with 4% bovine serum albumin (BSA) was sued as surrogate matrix. Both q and Q stock solutions were aliquoted and stored at -20 ֯ C. Calibration standards (1, 0.3, 0.1, 0.03, 0.01, 0.003, 0.001 and 0.0003 µM), and 3 quality controls (QCs; 0.8, 0.02 and 0.0008 µM) were prepared freshly either in ultrapure water; or spiked in matrix surrogate and then extracted using a PBA cartridge on the day of analysis.
