Fast Spectrophotometric Determination of Iodine Value in Biodiesel and Vegetable Oils

Abstract

Iodine value is an important quality parameter for evaluation of the oxidative stability of biodiesel and vegetable oils, but the official methods are time-consuming and demand large amounts of reagents and solvents. The present work describes a novel procedure for determination of iodine value based on the discoloration of a triiodide aqueous solution due to halogenation of the unsaturated compounds in the samples. Iodine is extracted to the organic phase and consumed proportionally to the amount of unsaturated compounds in the samples. Thus, the remaining fraction of I 3 quantified by spectrophotometry in the aqueous phase is inversely proportional to the concentration of unsaturated compounds. For biodiesel samples, responses were linear from 10 to 106 g I 2 per 100 g, with coefficient of variation and limit of detection estimated at 5.0% (n = 8) and 2.5 g I 2 per 100 g, respectively. The corresponding values for vegetable oils were 20 to 140 g I 2 per 100 g, 3.0% (n = 10), and 7 g I 2 per 100 g, respectively. The procedure consumed only 1.2 mL of sample, 365 μg of I 2 , and 42 mg of KI with ca. 2.4 mL of waste generated per determination. The results agreed with those obtained by the official methods at the 95% confidence level.

The Evaluation of Deep Frying Oil Quality With the Spectrophotometric Method for the Rapid Assessment of Total Polar Compounds

“…In this respect, fluctuation values in peroxide value can be related to the rate of peroxides formation were more than their degradation, and vice versa when decreased. These findings could be supported by Wu and Nawar (1986), Andrikopoulos et al (2003) and Soares and Rocha (2018). Peroxide value fluctuated and increased slowly during the frying process for 20 -40 hr., which was related to the formation of secondary oxidation products.…”

“…These results could be supported by Tompkins and Perkins (1999), Hassan and Abou-Arab (2004) and Kalogianni et al (2016). This suggests that oxidation, polymerization and polar compounds formation are strongly and positively related with one another whereas hydrolysis and therefore free fatty acids (acid value) formation is independently related to repeated oil use (Li et al, 2016;Soares and Rocha, 2018). Several European countries use this spectrophotometric method for evaluating frying oil quality and the critical value for an oil regarded as deteriorated is 0.7-1%, which is equivalent to threshold range of polar components (Kalogianni et al, 2016).…”

“…Although the changes of acid value were correlated with the changes in TPCs content during frying in this study, it is not recommended to use acid value as indicator for evaluating the frying oil. Iodine value is proportional to the degree of unsaturation of the oil and indicates its oxidative stability (Soares and Rocha, 2018).…”

“…Chemical analyses measure decomposition compounds reliably in the frying oil (Qing, 2000), but are very timeconsuming, costly, tedious usually require reasonable analytical expertise. During frying, unsaturated compounds formed in the oil are believed to absorb electromagnetic energy over the visible spectrum (Osawa et al, 2007;Soares and Rocha, 2018).…”

Investigations on a novel collector for anionic reverse flotation separation of quartz from iron ores

“…Iodine value (IV) is an important characteristic for the content of unsaturated fatty acids in fats, fixed oils, emulsifiers and solubilizers (Hilp, 2002). Iodine value is proportional to the degree of unsaturation of the product, so iodine value can be used to characterize the content of the double bond of fatty acid and its oxidation products (Muniyappan et al, 2019;Soares and Rocha, 2018). In present article, the iodine values were analyzed by Hanuš method according to the official method of China (GB/T 13892-2012, Standardization Administration of P.R.C.).…”