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Unsaponification Method

 Differences Unsaponificafion matter with AOCS methods and ISO method

 

Unsaponification means compounds that are unable to react saponification reaction such as hydrocarbon, chromophor compound like beta-carotene and chlorophyl, and polyaromatic. Faty acid, monoglycerides, diglycerides, and triglycerides in oil will be produced soap if oil is added with base solution in steam condition. Parameter unsaponification matter applies potassium hydroxide as base solution in order to generate soap. Ultilization sodium hydroxide less use since it will be precipitate however potassium hydroxide is more radically than sodium hdroxide. That’s why potassium hydroxide is more applicable than sodium hydroxide.

The mixture after saponification will be extracted with non polar solvent like n-hexane or petroleum benzene in separating funnel. The image will shown below. It is conducted to seprate soap (bottom layer) and organic phase. Organic phase will be dissolved with organic solvent. Extracting the mixture is done six time so that litte amount soap is given. Organic phase is collected and washed with ethanol 10% which had been blended with phenolpthalein indicator 1%. The first washing step will be given magenta colour on bottom layer since there’re still soap inside the mixture. Washing it completely until bottom layer is colourless. Colourless bottom layer means no soap in the mixture. The mixture is putted in erlenmeyer flask and evaporated in oven with high temperature.

separating funnel

After evaporating the mixture, Erlenmeyer flask is weighed until its mass is stable. If it’s stable, hot alcohol is putted in erlenmeyer flask and titrated with low concentration base solution. The purpose is ensuring small free faty acid. This parameter consider faty acid dominantly in sample is oleic acid C18:1.

We explain the differences method unsaponification with AOCS Ca 6a-40 and ISO 18609:2000. AOCS Ca 6a-40 uses potassium hydroxide 50% 5 mL and ethanol 96% 30 mL although ISO 18609:2000 applies potassium alcoholic 1 M 50 mL. Adding alkali solution is carried out through volumetric pipette due to precisely react with sample. In AOCS methods, sample is saponified then added hot water, cold water, ethanol, and petroleum benzene. This is done to ensure nothing residue left in saponify. Petroleum benzene as solvent is applied to extracting sample at least 6 times. Sample extracted is washed with ethanol 10% to remove soap residue. Sample is evaporated. Sample is weighed until its constant value. If sample isn’t constant, sample is putted in oven with temperature 80 °C for 30 minutes and desicator for 15 minutes. Constant weighed sample is titrated with sodium hydroxide 0.02 M to ensure small free faty acid. 

However in ISO 18609:2000 sample saponified is swirled with cold water through condensor. It’s conducted to catch evaporated soap and volatile content of oil. Sample is extracted with n-hexane or petroleum benzene 6 times and washed with ethanol 10%. Sample is evaporated and weighed in constant weight at 105 °C. Constant weighed sample is titrated with 0,1 M potassium alcoholic.

Formula of unsaponification matter :

Where W1 is constant weighed sample, W2 is mass of oleic acid is titrated, W3 is weight of erlenmeyer flask and W is weight of sample. Unsaponification matter of refined oil is below 0,15%. However in crude oil is 0.3-0.5% and fad oil is above 0.5%.          

 Therefore we get interferences that both of unsaponification method with AOCS Ca 6a-40 and ISO 18609:2000 are firstly potassium hydroxide as alkali solution, petroleum benzene is applied as organic/non polar solvent which is dissolved six times, alcohol 10% is washed organic phase.

References :

AOCS Ca 6a-40

ISO 18609 : 2000

https://www.chem.ucla.edu/~bacher/General/30BL/tips/Sepfunnel.html

  

 

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