I synthesize 2 different solutions at different pH values ​​(pH 3 and 4.5), but at pH 3 the color of my solution is red, and although I get a color from colorless to yellow in my solution at pH 4.5, the darker red color appears at lower absorbance values ​​in my UV -vis readings. I use absorbic acid as a reductant and tween 20 as a stabilizer. And before readings, I set the baseline and use it 20-30 minutes after turning on the UV vis device. I get absorbance values for ph 3 and red solution around 0,385- 0,500 max and 1,091 and 1,400 max for my colorless to yellow ph 4.5 solution. I use same precusor and reagents for both. the colour change for this nanoparticle is colorless- yellow to red Can someone please tell me why is it like that? Thanks a lot.