Determination of Acid Number with Potentiometric Method

Determination of Acid Number with Potentiometric Method

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0133.100 pH glass electrode; input 1
6.0726.100 Ag/AgCl double junction reference electrode
(LiCl sat. in ethanol)

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

Sample
app. 5-10 g sunflower oil
50 mL ethanol / diethylether (1 : 1), neutralized

Remarks
· Calculations:

Acid.No=EP1*C01/C00;2;mg/g
FFA=RS1*C02/C03;2;

Acid.No = acid number in mg KOH per g of sample
FFA = free fatty acid
C01 = mg KOH / 1 mL titrating agent (5.61)
C02 = relative molecular mass (282 for oleic acid)
C03 = factor (561)

. Answer

Acid.No = 0.150 x 5.61 / 10.3223 = 0.08 mg/g
FFA = 0.08 x 282 / 561 = 0.04

RS1 = 0.08
EP1 = 0.150 mL
C00 = 10.3223 g

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

Method documentation

'pa
751 GPD Titrino 15215 751.0010
DET U… Acid.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 …3 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 Acid.No
>calculations

Acid.No=EP1*C01/C00;2;mg/g
FFA=RS1*C02/C03;2;

C00= 10.3223
C01= 5.61
C02= 282
C03= 561
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) 35 mV DET U... Acid.No
smpl size ....10.3223 g
EP1 ....0.150 ml.... -201 mV
Acid.No .....0.08 mg/g
FFA 0.04
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml DET U Acid.No
1.0 ml/div dU=100.0 mV/div
============