Page 233 - Natural Antioxidants, Applications in Foods of Animal Origin

212 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir TABLE 6.1 (Continued)

Potentio metric determination of peroxide values
Titrant [Analyte] [Analyte] [Titrant] [Titrant] Eo Constant n E system
(Liters) Ox. Red. Red. Ox. V
0.0253 0.0336 0.003 0.08 0.0592 2 0.050
0.0260 0.0342 0.003 0.08 0.0592 2 0.090
0.0300 0.0375 0.003 0.08 0.0592 2 0.050
0.0350 0.0412 0.004 0.08 0.0592 2 0.050
0.0400 0.0444 0.004 0.08 0.0592 2 0.050

Components for potentiometric titration are:

1. Buret containing the titrant (sodium thiosulfate).
2. Known volume of the sample containing the analyte (extracted fat
or oil).
3. Reference electrode (saturated calomel or hydrogen electrode).
4. Electrode for measuring the potential, working electrode.
5. Meter to record the change during titration.

To demonstrate the application of the Nernst equation, titration of
hydrogen peroxide (H O ) with sodium thiosulfate (Na S O ) in a model
4
2
2 2
2
system was calculated with Microsoft Excel 2010 spreadsheet, E value
o
®
™
sourced from CRC Handbook of Chemistry and Physics 71st edition.
Rxn. in aqueous system 2S O –2 + H O – 2e <–> 2H O + 2e + 2S O –2
–
–
4 6 2 2 2 2 3
RT
( )
K eq = E cell = nF × ln K eq (6.6a); solving for K (rxn driven strongly to the right)
o
E = (E Red.) + (E Ox.) (6.6b)
o
o
(Redox)
E (analyte at T=0) = 0.281 V
o
ne E o ne E o
+
=
Eq. point = 0.200;vol. to eq. pt. M × M × V 2 (6.6c)
V =
=
ne ne 1 1 2
+
K = 1.43 × 10 57
eq
E (Redox) 1.69 V
E eq. pt. 0.200 V (estimate)