I synthesized a transparant membrane from chitosan which was modified with tannic acid ligands and cross-linked with tripolyphosphate to detect Cu (II) metal in solution. When I dip this membrane in a Cu (II) solution with an alkaline pH and stir, the membrane will turn brown due to the reaction of the tannic acid-Cu (II) complex in the membrane. What I ask is, why when I measure the absorbance of the membrane with a thickness of 0.09mm in Uv-Vis Spectrometer, the resulting peak is not smooth or fluctuates? but the peak is correct in the wavelength range of 400-500 nm. Thank you.
Gaby Aprilia Kusumawati
A thin layer of surface water with a special structure exists near the membrane surface. It also exists around DNA, in the human body between molecules. Due to its small size, it fluctuates. Therefore, the spectrum changes. You can read about such water in
Preprint Quantum and thermal liquid -liquid phase transitions in aque...
This is result of membrane cts-tannic acid-tpp who contacted with Cu(II) solution in pH base who measured from UV-Vis spectrofotometer.
@Dr. S. Kalidhasan thank you for your respon sir. And sorry for the late answer. I use variations concentration of Cu(II) solution, from 1ppm-10ppm, Sir. And the shape of the peak remains the same as that, not stable. I used a blank is a chitosan-tannicacid-tpp membrane which was not immersed in a Cu(II) solution, and it was true that there was no peak.
@Dr.S.Kalidhasan I also made a chitosan membrane without ligands tannic-acid (TA), only modified with tripolyphosphate (TPP). Then I dipped it in a 10 ppm Cu (II) solution and the result was my membrane was blue, then I measured the absorbance with UV-Vis 900-500 nm. But the peak results are smooth, unlike the membrane with a ligand TA.
If the pH was influence. I was try with variation pH of Cu(II) solution Sir. I try in pH 7 (netral), the peak is same with pH alkaline, the different is its absorbance.
@Dr. S. Kalidhasan Oh it's like that, sir. Okay, thank you. But I still don't understand, sir. In theory, the brown color of the membrane is due to the formation of the tannic acid-Cu (II) complex in the membrane. And I tried made solution of tannic acid - Cu(II) complex then I measured in Uv-Vis, the peak is good or smooth. If TA is what causes it to be unstable, why is it that when it's peak solution is stable? Do you mean because the TA in the membrane so changes and affects the UV vis analysis?
@Dr. S. Kalidhasan oh okey sir, thank you.
For the brown color by TA-Cu(II) complex on membrane marked by the peak in uv vis analysis sir. Does not the presence of a peak in the uv vis test indicate the formation of a complex compound, sir?
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