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

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'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

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