Discoloration – buffers
More discoloration experiments. No wafers were RTP’ed, and I looked at different wafer numbers. For each experiment, I looked at discoloration in the oven at 37C and the incubator. The labelling might be a bit confusing. For the top right pictures, I looked at 4.4 mg/mL KHCO3 (left chip) and 0.35 mg/mL NaHCO3 (right chip).
KHCO3 causes discoloration at about the same concentration as NaHCO3. Also, chips in the oven always discolor faster than chips in the incubator, and the pH always falls in the incubator. Notice that even at high initial bicarbonate concentrations, the pH falls into physiological range in the incubator.
I also looked at more buffers in the oven vs. the incubator:
Here, Tris-HCL, sodium borate and glycine/NaOH buffers (and low NaHCO3) caused discoloration within a day in the oven, but only sodium borate and glycine/NaOH caused discoloration at 24 hours in the incubator.