Is there a problem with my calibration curve of GSH and Total GSH for Amplite® Fluorimetric Glutathione GSH/GSSG Ratio Assay Kit? Why does my standard curve not make sense?

In theory, the calibration curve of GSH and Total GSH should match fairly closely. An important thing to keep in mind is that [GSH] is 5, 2.5, 1.25, 0.625, 0.3125, 0.1563, 0.0781, and 0 µM after serial dilution whereas [TGSH] is 10, 5, 2.5, 1.25, 0.625, 0.3125, 0.1563, and 0 µM. after the same serial dilution. This is because of the GSSG/GSH molar ratio: 1 GSSG ⟶ 2 GSH. Thus when plotting the standard curves, the x-axis values for TGSH needs to be twice that of GSH.