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| Figure 1: Effect of organic solvents and formic acid concentration on analytical sensitivities of 6β-hydroxycortisol (6βHC) and free cortisol (FC) by gradient-elution UPLC-ESI-QTOF MS. (A) Peak area comparison using methanol, acetonitrile, and isopropanol as the eluting solvents. (B) Peak area comparison with different percents of formic acid in the mobile phases, and with isopropanol as the eluting solvent. (C) Comparison of 6βHC and FC peak areas obtained with isopropanol/0.01% formic acid and acetonitrile/0.1% formic acid as the mobile phases, respectively, using the same linear gradient. |
