Determination of Peroxide Number with Potentiometric Method

Determination of Peroxide Number with Potentiometric Method

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0431.100 Pt Titrode; input 1

Reagents
c(Na2S2O3) = 0.01 mol/L; D0
Prepared daily from c = 0.1 mol/L

Sample
app. 5 g sunflower oil
50 mL glacial acetic acid / chloroform (3 : 2)
1 mL KI saturate
100 mL dist. water

Remarks
· Calculations:

Perox.No=(EP1-C01)*C02/C00;2;meq/kg

Perox.No = peroxide number in meq.O2/kg
C01 = consumption of blank sample (0 mL)
C02 = factor (10)

. Answer

Perox.No = 0.8874 x 10 / 5.0188 = 1.77 meq/Kg

EP1 = 0.8874 mL
C00 = 5.0188 g

· Sample preparation:
Weigh out accurately 5 g sample in an Erlenmeyer flask and add 50
mL of the glacial acetic acid / chloroform mixture. Then add 1 mL of
the KI solution and shake during 5 s. Now allow the mixture to stand
for about 1 min. in a dark place. After this, rinse the contents of the
Erlenmeyer flask out into a beaker with 100 mL dist. water and
immediately back-titrate the iodine thus liberated with sodium
thiosulphate. A blank control sample should be prepared and treated
in the same way. Enter the blank value as C01.
· The sample must be stirred well during the titration, in order to obtain
a good emulsion.

Literature
· Metrohm Application Bulletin No. 141: Analysis of edible oils and fats.

Method documentation

'pa
751 GPD Titrino 15215 751.0010
date 97-02-25 time 14:25 4
DET U Perox.No
parameters
>titration parameters
meas.pt.density 4
min.incr. 10.0 ml
dos.rate max. ml/min
signal drift 50 mV/min
equilibr.time 26 s
start V: OFF
pause 0 s
dos.element: internal D0
meas.input: 1
temperature 25.0 °C
>stop conditions
stop V: abs.
stop V 99.99 ml
stop U OFF mV
stop EP 1
filling rate max. ml/min
>statistics
status: OFF
>evaluation
EPC 5
EP recognition: all
fix EP1 at U OFF mV
pK/HNP: OFF
>preselections
req.ident: OFF
req.smpl size: value
activate pulse: OFF
------------
'fm
751 GPD Titrino 15215 751.0010
date 97-02-25 time 14:25 4
DET U Perox.No
>calculations

Perox.No=(EP1-C01)*C02/C00;2;meq/kg

C00= 5.0188
C01= 0.0
C02= 10
------------
'fr
751 GPD Titrino 15215 751.0010U(init) 20 mV DET U Perox.No
smpl size 5.0188 g id#1 Suprema id#2 Oil
EP1 0.8874 ml 80 mV
Perox.No 1.77 meq/kg
stop #EP reached
============
'cu
751 GPD Titrino 15215 751.0010
date 97-02-25 time 14:24 4
start V 0.0000 ml DET U Perox.No
0.5 ml/div dU=20.0 mV/div
============