Collaborative test of determination of iodine value in fish oils. 1. Reaction time and carbon tetrachloride or cyclohexane as solvents

Abstract

Twenty‐two laboratories participated in a collaborative test to determine the iodine value (IV) of eight samples of fish oil (four with IV<150, four with IV>150) with either carbon tetrachloride (AOCS Official Method Cd 1–25) or cyclohexane (AOCS Recommended Practice Cd 1b‐87) as solvent and either 1 or 2 h of reaction time. Laboratories received coded duplicate samples (hidden duplicates) and carried out duplicate determinations on each oil by each solvent‐time combination (open duplicates). Replacing carbon tetrachloride with cyclohexane resulted in a lower IV (P<0.001). The decrease averaged 1.6 IV units for low‐IV oils and 3.8 IV units for high‐IV oils; this difference in response of 2.2 IV units between low‐ and high‐IV oils was significant (P<0.001). Increasing the reaction time had a relatively small effect (0.34±0.18). There was no interaction of reaction time with solvent or oil type. Cyclohexane caused emulsions, which made it difficult to titrate residual iodine and thus increased the variability of the determination. The repeatability standard deviations (sr), based on hidden duplicates, for 1‐h reaction time with carbon tetrachloride and cyclohexane were 2.17 and 3.35, respectively. The corresponding reproducibility standard deviations were 2.73 and 4.53.

Comparative Study on Oxidative Decomposition Behavior of Vegetable Oils and Its Correlation with Iodine Value Using Thermogravimetric Analysis

“…To reduce the use of toxic solvent, cyclohexane 3,4) has been substituted as a replacement for chloroform in Wijs method but longer reaction time is required especially for oils with higher IV. Other reported alternative methods with minimum solvent consumption were flow injection analysis (FIA) 5) , Fourier transform infrared spectroscopy (FTIR) 6) , near infrared spectroscopy (NIR) 7,8) , 1 H nuclear magnetic resonance spectroscopy ( 1 H NMR) 9) , differential scanning calorimetry (DSC) 10) and high performance liquid chromatography (HPLC) 11,12) .…”

Collaborative test of determination of iodine value in fish oils. 2. Carbon tetrachloride or cyclohexane/acetic acid as solvents

“…In the previous study (4), increasing the reaction time from 1 to 2 h had little or negligible effect, irrespective of IV. Consequently, the new test was conducted with 1 h reaction time only.…”

Characterization of oil-producing microalgae using Raman spectroscopy

“…Thus, the IV of oils measures the amount of C=C present in a sample; it is expressed as grams of iodine per 100 g of sample. However, this analytical technique involves several time-consuming steps, as is well described in [14][15][16][17][18], so that complete analysis takes about 30 -45 minutes [16]. Thus, a simpler and speedier analytical technique would be rather desirable, with potential benefits in food industry control-process applications, and in biofuel applications (for example, to estimate a fuel index [14]).…”