Page 30 - Pharmaceutical Analytical Chemistry II - Pharm D Clinical- 07-PA202

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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