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ACID-BASE TITRATION IN VEGETABLE OIL SAMPLE

ACID-BASE TITRATION IN VEGETABLE OIL SAMPLE


Gupta (2017) Vegetable oil is oil consisted free faty acid, triglycerides, monoglycerides, diglycerides, triglycerides, poly aromatic hydrocarbon, colour compound such as chlorophyll which given green colour and β-carotene which given red colour with trace metal. Free fatty acid can be analyzed through titration acid – base. Analysis of free fatty acid is conducted by dissolving oil with neutral ethanol 96% and steaming rapidly into enhance solubility oil into alcohol. The mixture is added phenolphthalein indicator 1% with 1-2 droplets until pink colour is appearing. The mixture is titrated with base solution. Base solution usually apply is standardized sodium hydroxide. The formula of determination of free fatty acid and acid value is described below

Changing colour of sample before and after adding alkali solution

Where [NaOH] is sodium hydrozide concentration had been standardized according to AOCS H 12-52, VNaOH is sodium hydroxide volume, w is sample’s weight, and MW is molecular weight of mayor component of faty acid (AOCS Ca 5a-40). Coconut and palm kernel oil is abundantly contained lauric acid (C12H24O2) with molecular weight is 200 g/mol. However palm oil is dominantly consisted palmitic acid (C16H32O2) with weight of molecular is 256 g/mol. The formula of acid value is contrary with definition of acid value which apply potassium hydrogen as titrator and its definition of its parameter (AOCS Cd 3d-63). Actually potassium hydroxide and sodium hydroxide has same properties. They are both strong base and in same group (alkanity). Actually potassium hydroxide is able to precipitate. However sodium hydroxide can’t. The other side sodium hydroxide is environmental friendly and less harmfull. It leads sodium hydroxide is regulary applied in cooking oil company    

Besides free faty acid, acid value is analysis of edible oil which consumes base solution as titrator. Eventhough they apply base solution as titrator. Oil sample doesn’t steam like free faty acid. Acid value uses solvent neutral mixture toluene and iso-prophyl alcohol (1:1). Both these parameters use neutral solvent in order to the acidity of solvent isn’t affected the analysis process. 

Another parameters in edible oil ultilize acid base principle are saponification value and analysis soap content. Both these method ulitilize hydrochloric acid as titrator. Saponification value spend phenolphthalein as indicator. Sample is added precisely 25 mL potassium hydrogen 0,5 M alcoholic. It reacts with triglycerides, monoglycerides, diglycerides, and fatty acid so it produces soap. Saponification value applies 0,5 M hydrochloric acid. Saponification value is applied for all oil sample (AOCS Cd 3-25). It’s differently with soap content which ultilizes hydrochloric acid 0,01 M and it only is applied for refined oil. Soap content use bromophenol blue as indicator (AOCS Cc 17-95, 2009).    

We conclude that free fatty acid, acid value, saponfication value, and soap content are parameter apply acid base titration principle. Free fatty acid, acid value, and saponification value utilize phenolpthalein as indicator. While soap content only uses bromophenol blue indicator. The final titration is marked with changing colour of mixture like phenolpthalein from transparant into pink soft. However blending of bromophenol blue and sample converting green into yellow. 

Reference :

AOCS Ca 5a-40, 2009, Free Fatty Acid

AOCS Cc 17-95, 2009, Soap in Oil with Titrimetric Method

AOCS Cd 3-25, 2009, Saponification Value

Gupta, M, 2017, Practical Guide to Vegetable Oil Processing, 2nd Edition, London, Elsevier Inc

https://www.walshmedicalmedia.com/open-access/process-parameter-estimation-of-biodiesel-production-from-waste-frying-oil-vegetable-and-palm-oil-using-homogeneous-catalyst-44558.html

 

 

 

 


Comments

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