The document discusses the quantification of polyphenols (tannins) using potassium permanganate titration, emphasizing the effect of temperature on this process. It outlines the preparation of potassium permanganate and indigo carmine, along with the procedure for titration, which involves immersing pure grape extract in varying temperatures. The study highlights limitations, assumptions, and provides a formula for calculating total polyphenol concentration based on titration results.

1. Effect of temp on polyphenol (tannins) quantification using potassium permanganate titration (Lowenthal permanganate)
Polyphenols are antioxidants :
- found in blackberry, wines, blueberry, cranberry, grapes, cider, citrus fruits
- Tannins (TA), flavonoids, catechins, EGCG, EGC, ECG.
- quantification using potassium permanganate (titration)
- using indigo carmine indicator (blue) to green yellow
Antioxidants that can be quantified using permanganate titration
Procedure:
Potassium permanganate 0.004M (0.02N) was prepared.
0.1% (w/v) indigo carmine indicator 0.1g in 100ml acidified with H2SO4.
End point is greenish yellow.
Limitation : antioxidants like Vit C will be included
Assumption - all antioxidants esp polyphenol will be quantified.
Effect of temp (15, 45, 55, 65, 75) will be studied, using water bath.
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2. Green/red grapes – pure extract using cheese cloth
Indicator change from blue to greenish yellow
Procedure:
Potassium permanganate 0.004M (0.02N) was prepared.
0.1% indigo carmine indicator 0.1g in 100ml acidified with H2SO4.
End point is greenish yellow.
0.5ml of pure extract (grapes juice) added to centrifuge tube.
Extract was immersed into water bath at various temp for 10 mins.
After 10 mins, 2ml water and 200ul of indigo carmine were added. Blue sol obtained.
Titrated with 0.004M KMnO4 until end point is seen.
Ini and final vol recorded.
Blank titration was done – 2 ml water and 200ul indicator without any antioxidants
Temp/C Ini
vol
Final
vol
Vol (X)
KMnO4
Polyphenol
mg/L TA
15 3.9 4.7 0.8 498
45 11.5 12.2 0.7 415
55 12.3 12.8 0.5 249
65 18.0 18.6 0.6 332
75 20.9 21.4 0.5 249
Blank (Y) 4.7 4.9 0.2 --
End point
Effect of temp on polyphenol (tannins) quantification using potassium permanganate titration (Lowenthal permanganate)
Green grapes
Total polyphenol (mg/L TA) = (X – Y) x 4.157 x conc KMnO4 (N) x 10000
(0.8 - 0.2) x 4.157 x 0.02 x 10000 = 498mg/L
Formula that can be used. Click here for reference
Total polyphenol (mg/L TA) = (X – Y) x 4.157 x conc KMnO4 (N) x 10000
4.157 – conversion factor to TA equivalents
10000 – conversion factor from % to mg/L of TA.
N – normality for KMnO4 which is 0.02N or 0.004M
X – Vol KMnO4 used
Y – Vol blank titration
TA – tannic acid

3. Green/red grapes – pure extract using cheese cloth
Effect of temp on polyphenol (tannins) quantification using potassium permanganate titration (Lowenthal permanganate)
End point
Temp/C Ini
vol
Final
vol
Vol (X)
KMnO4
Polyphenol
mg/L TA
15 3.9 4.7 0.8 498
45 11.5 12.2 0.7 415
55 12.3 12.8 0.5 249
65 18.0 18.6 0.6 332
75 20.9 21.4 0.5 249
Blank (Y) 4.7 4.9 0.2 --
Total polyphenol (mg/L TA) = (X – Y) x 4.157 x conc KMnO4 (N) x 10000
(0.8 - 0.2) x 4.157 x 0.02 x 10000 = 498mg/L
Formula that can be used. Click here for reference
Total polyphenol (mg/L TA) = (X – Y) x 4.157 x conc KMnO4 (N) x 10000
4.157 – conversion factor to TA equivalents
10000 – conversion factor from % to mg/L of TA.
N – normality for KMnO4 which is 0.02N or 0.004M
X – Vol KMnO4 used
Y – Vol blank titration
TA – tannic acid
0
0.2
0.4
0.6
0.8
1
15 45 55 65 75 Blank
(Y)
vol
KMnO4
temp
Temp/C vs Vol KMnO4
0
200
400
600
15 45 55 65 75
Total
polyphenol/mg/L
TA
temp/C
Temp/C vs Total
polyphenol/mg/L TA
0
200
400
600
0 20 40 60 80
Total
polyphenol/mg/L
TA
Temp/C
Temp/C vs Total
polyphenol/mg/L TA

4. Oxidizing
Agent
Reducing
Agent
MnO4
- Fe2+
Cr2O7
2- SO2
HNO3 I-
H2O2 H2S
CI2 SO3
2-
KIO3 Vitamin C
OCI-/Cu2+ Oxalate/
C2O4
2-
Titration
Redox Titration
Acid Base Titration
Burette/Titrant
Oxidizing agent
?
Acid/Base Titration Redox Titration
Neutralization bet acid/base Redox bet oxidizing/reducing agent
Transfer proton/H+ from acid to base Transfer elec from reducing to oxidizing agent
Indicator for colour change No indicator needed
Redox Titration
- One reactant – must be standard (known conc) or capable being standardised
- Reaction bet Oxidizing agent/Titrant with Reducing agent/Analyte
- Titrant of known concentration
- Stoichiometrically equivalent amt titrant/titrand added
- No indicator needed. Detectable by colour change of Oxidizing/Reducing agent
Analyte/reducing agent
Titrand Redox Titration used to determine:
- Amount of copper in brass
- Amount Fe/iron in iron pill/food
- Amount H2O2 commercial peroxide solution
- Amount OCI - /hypochlorite/CI2 in bleach
- Amount Vitamin C
- Amount Dissolve oxygen content/BOD
- Amount ethanol in beer/wine
- Amount oxalate acid
?
MnO4
- + 5Fe2+ + 8H+ → Mn2+ + 5Fe3+ + 4H2O Cr2O7
2- + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ 7H2O
Iron determination using MnO4
- / Cr2O7
2-
purple colourless orange green
add MnO4
- till endpoint
↓
turn purple (excess MnO4
- )
add Cr2O7
2- till endpoint
↓
turn orange (excess Cr2O7
2-)