Glucose Assay Problem

This was a problem we were having with the glucose standards (and presumably with the treatment samples as well) resulting in a non-linear standard curve. It the colour change induced by the glucose in the higher concentration standards appeared to reverse resulting in a reduced colour change for the higher concentration samples compared with the lower conentration samples.
The solution for us was that you have to vortex the samples as soon as they come off the heating block in order to get the colour change to develop throughout the solution and then immediately add the sulfuric acid in order to stabilise the colour change.