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 751.0010

date 97-02-25 time 14:24 4

U(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

============