What is in the wells? Is it standard curve? What are the concentrations?

You need to have a row of standard solutions in the Wells, which came with bioassay kits. This can then be used to extrapolate the concentrations of your experimental concentrations (absorbance).

If you are using an enzymatic glutathione recycling assay, these values don´t look too bad, do they? (If they are a glutathione standard curve)

The differences in the totals most likely stems from a certain latency introduced by pipetting (I am guessing without a multipipette).

Usually one would use the slope of the curves for gutathione calculations => These values look rather o.k. for the curves depicted as F,G, and H.

So probably you should try to improve the workflow in order to focus on the quality of the samples (trying to be as fast as possible), rather than the quanitity.

Thereby, you should be able to avoid slopes with delta = 0 etc. because not all glutathione used for the standards will be consumed upon measurement.

But that is just a wild guess right there => A little more information about your procedures and the curves would be great!