Physics Lab Report
CROATICA CHEMICA ACTA
CCACAA 78 (1) 99¿103 (2005)
ISSN-0011-1643
CCA-2984
Original Scientific Paper
Acid Value Determination in Vegetable Oils by Indirect Titration in Aqueous-alcohol Media
Elena Kardash* and Yakov I. Tur’yan
National Physical Laboratory of Israel (INPL), Givat Ram, Jerusalem 91904, Israel
RECEIVED JANUARY 16, 2004; REVISED JULY 21, 2004; ACCEPTED OCTOBER 28, 2004
Keywords acid value vegetable oils indirect titration
A new method of acid value determination in vegetable oils has been developed. The method is based on (a) simple, rapid and complete extraction of acids from an oil test portion into reagent
(0.05 mol dm–3 triethanolamine (B) in the mixture of 50 % H2O + 50 % 2-PrOH) and (b) indirect titration of acids in BH+ form against aqueous alkali in the presence of a phenolphthalein indicator. Suitable metrological parameters of acid value determination have been obtained.
The advantages of the method are (i) absence of a toxic solvent, (ii) extraction and titration of acids at room temperature, and (iii) no need for preliminary neutralization of acid admixtures in a solvent.
INTRODUCTION
Acid value (AV) is an important indicator of vegetable oil quality. AV is expressed as the amount of KOH (in milligrams) necessary to neutralize free fatty acids contained in 1 g of oil.1,2
The majority of national and international standards for AV determination in vegetable oils are based on the acid-base titration techniques in non-aqueous solvents.1,2
These techniques have a number of drawbacks:
(i) Currently used non-aqueous solvents are toxic,
e.g., ethanol or isopropanol heated up to 60 °C or higher
(exact temperature is not indicated),1 or diethyl ether– ethanol solvent (1:1 vol. ratio).2
(ii) Incomplete solubility of a test oil portion in alcohol (even under heating)1 caused by the formation of a dispersed system.3
(iii) Conditions for accurate acid-base titration in hot amphoteric solvents might deteriorate
CCACAA 78 (1) 99¿103 (2005)
ISSN-0011-1643
CCA-2984
Original Scientific Paper
Acid Value Determination in Vegetable Oils by Indirect Titration in Aqueous-alcohol Media
Elena Kardash* and Yakov I. Tur’yan
National Physical Laboratory of Israel (INPL), Givat Ram, Jerusalem 91904, Israel
RECEIVED JANUARY 16, 2004; REVISED JULY 21, 2004; ACCEPTED OCTOBER 28, 2004
Keywords acid value vegetable oils indirect titration
A new method of acid value determination in vegetable oils has been developed. The method is based on (a) simple, rapid and complete extraction of acids from an oil test portion into reagent
(0.05 mol dm–3 triethanolamine (B) in the mixture of 50 % H2O + 50 % 2-PrOH) and (b) indirect titration of acids in BH+ form against aqueous alkali in the presence of a phenolphthalein indicator. Suitable metrological parameters of acid value determination have been obtained.
The advantages of the method are (i) absence of a toxic solvent, (ii) extraction and titration of acids at room temperature, and (iii) no need for preliminary neutralization of acid admixtures in a solvent.
INTRODUCTION
Acid value (AV) is an important indicator of vegetable oil quality. AV is expressed as the amount of KOH (in milligrams) necessary to neutralize free fatty acids contained in 1 g of oil.1,2
The majority of national and international standards for AV determination in vegetable oils are based on the acid-base titration techniques in non-aqueous solvents.1,2
These techniques have a number of drawbacks:
(i) Currently used non-aqueous solvents are toxic,
e.g., ethanol or isopropanol heated up to 60 °C or higher
(exact temperature is not indicated),1 or diethyl ether– ethanol solvent (1:1 vol. ratio).2
(ii) Incomplete solubility of a test oil portion in alcohol (even under heating)1 caused by the formation of a dispersed system.3
(iii) Conditions for accurate acid-base titration in hot amphoteric solvents might deteriorate
References: 1. D. Firestone (Ed.), Official Methods and Recommended Practices of the American Oil Chemists Society, 4th ed., American Oil Chemists Society, Champaign, 1996, Method Ca 5a–40 3. W. Horwitz, J. Assoc. Off. Anal. Chem. 59 (1976) 658–661. 4. R. A. Robinson and R. H. Stockes, Electrolyte Solutions, Buterworthy Scientific Publications, London, 1959. 5. Ya. I. Tur’yan, O. Yu. Berezin, I. Kuselman, and A. Shenhar, J. Am. Oil Chem. Soc. 73 (1996) 295–301. Kuselman, Croat. Chem. Acta 76 (2003) 329–334. 8. H. S. Harned and B. B. Owen, The Physical Chemistry of Electrolytic Solutions, 3rd ed., Reinhold Publishing Corporation, New York, 1958, p 9. H. A. Laitinen, Chemical Analysis, Khimiya, Moscow, 1966, p Croat. Chem. Acta 78 (1) 99–103 (2005)