Potentiometric Determination of the Iodine Number

Potentiometric Determination of the Iodine Number

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

Reagents
c(Na2S2O3) = 0.1 mol/L; D0

Sample
app. 0.5 g sunflower oil
15 mL CCl4
25 mL c(ICl) = 0.1 mol/L (according to Wijs in glacial acetic acid / CCl4,
e.g. Merck No. 9163)
10 mL w(Hg acetate) = 0.025 (2.5%) in glacial acetic acid
15 mL w(KI) = 0.10 (10%)
30-50 mL dist. water

Remarks
· Calculations:

Iod.No=(C01-EP1)*C02/C00;2;g/100g

Iod.No = iodine number in g iodine / 100 g sample
C01 = consumption of blank sample (0 mL)
C02 = molecular mass of I * concentration titrating agent * 100g
sample / factor mL -> L (126.9 * 0.1 *100/1000 = 1.269)

. Answer

Iod.No = (0 – 6.149) x 1.269 / 0.5204 = 104.61 g/100g

EP1 = 6.149 mL
C00 = 0.5204 g

· Sample preparation:
According to the expected iodine number, weigh out 0.10 ... 1.00 g of the sample in an Erlenmeyer flask and add 15 mL CCl4.
Add 25 mLiodine monochloride solution and add 10 mL mercuric acetate solution, mix and allow to stand for 5 min. in a dark place.
Then add 15 mL KI solution, rinse into a beaker with dist. water and back-titrate the excess iodine with sodium thiosulphate.
A blank control sample should be prepared and treated in the same way. Enter the blank value as C01.
· You may add a solution of w(Mg-acetate) = 0.03 (3%) instead of the Hg-acetate solution.
· 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
DET U… Iod.No
parameters
>titration parameters
meas.pt.density… 4
min.incr…. 10.0 ml
dos.rate max…. ml/min
signal drift …20.0 mV/min
equilibr.time …38 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 ….20 ml
stop U ….OFF mV
stop EP ….9
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
DET U Iod.No
>calculations

Iod.No=(C01-EP1)*C02/C00;2;g/100g

C00= 0.5204
C01= 0
C02= 1.269
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) -16 mV DET... U Iod.No
smpl size ....0.5204 g
EP1… 6.149 ml …92 mV
Iod.No ….104.61 g/100g
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml DET U Iod.No
2.0 ml/div dU=50.0 mV/div
============