Detremination of the Saponification Number with Potentiometric Method

Determination of the Saponification Number with Potentiometric Method

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0232.100 combined pH glass electrode; input 1

Reagents
c(HCl) = 1 mol/L; D0

Sample
app. 2 g sunflower oil
25 mL c(KOH) = 0.5 mol/L in ethanol
app. 10-20 mL dist. water

Remarks
· Calculations:

Sapon.No=(C01-EP1)*C02/C00;1;mg/g

Sapon.No = saponification number in mg KOH per g of sample
C01 = consumption of blank sample (12.199 mL)
C02 = mg KOH / 1 mL titrating agent (56.1)

. Answer

Sapon.No = (12.199-5.271) x 56.1 / 2.0224 = 192.2 mg/g

EP1 = 5.271 mL
C00 = 2.0224 g

· Sample preparation:
Weigh out approx. 2 g sample in a round-bottomed flask. Add 25 mL
alcoholic KOH solution plus a few boiling beads and allow to boil
lightly for at least 30 min. Shake from time to time. Finally rinse the
content of the round-bottomed flask into a beaker with a small
quantity of dist. water and back titrate the excess of potassium
hydroxide with HCl. A blank control sample should be prepared and
treated identically. Enter the blank value as C01.

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

Method documentation
'pa
751 GPD Titrino 15215 751.0010
DET U Sapon.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
DET U Sapon.No
>calculations

Sapon.No=(C01-EP1)*C02/C00;1;mg/g

C00= 2.0224
C01= 12.199
C02= 56.1
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) -357 mV DET U.... Sapon.No
smpl size…. 2.0224 g
EP1 ….5.271 ml…. -203 mV
Sapon.No ….192.2 mg/g
stop #EP reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml DET U Sapon.No
1.0 ml/div dU=50.0 mV/div
============