Page 31 - Pharmaceutical Analytical Chemistry II - Pharm D- 02-06-07102
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The interference of Cl- is avoided by addition of Zimmermann-
Reinhardt reagent (ZR – reagent)
ZR Reagent: MnSO4 + H2SO4 + H3PO4
Mn(II):
It reduces the potential of MnO4−/ Mn2+ couple sufficiently so that will notoxidize
Cl−
MnO4− + 8H+ + 5e Mn2+ + 4H2O
0.059 [Mn2+]
E = E0 – log
5 [MnO4–] [H+]8
[Mn2+] ↑ E↓
H3PO4:
1. It complexs Fe3+ (Fe(HPO4)+ is nearly colorless) thus prevent
formation of yellow Fe3+–chloride complexes → sharp ep color
change.
H3PO4 + Fe3+ ⎯→ Fe (HPO4)+
yellow colorless
2. Complexation of Fe3+ reduces the potential of Fe3+/Fe2+ couple,
so increase the reducing power of Fe2+ (readily oxidized with
MnO4−)
Fe3+ + e- Fe2+ [Fe2+]
E = Eo –
0.059 [Fe3+]
H2SO4: log E↓
for acidification
1
[Fe3+] ↓
[2] Determination of H2O2
H2O2 O2 (g) + 2H+ + 2e
5H2O2 + 2MnO4- + 6H+ ⎯→ 2Mn2+ + 5O2 + 8H2O
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