Determination of the iodine value of oils and fats: results of a collaborative study

Abstract

-This report outlines the study protocols and compares the results obtained for the iodine values of a wide range of fats and oils when using the published standardised method (which specifies the use of carbon tetrachloride) with the results obtained when using a mixture of cyclohexane and glacial acetic acid. The values reported for the iodine values indicate that the latter solvent system can be recommended for use in place of carbon tetrachloride in the determination of iodine value without loss of precision. INTRODUCTIONAs a consequence of the recognition of the potential carcinogenic risk when using carbon tetrachloride for analytical purposes, the Commission decided to carry out an investigation into whether this solvent could be satisfactorily replaced by a non-toxic reagent when determining iodine values by the published standard method which specifies the use of carbon tetrachloride.Before organising a comprehensive interlaboratory study it was considered advisable to conduct a preliminary investigation involving three laboratories experienced in the determination of iodine values. For this investigation, samples of crude fish oil, tung oil, tallow and sunflower seed oil were provided. Each sample was required to be analysed in duplicate, with each solvent, and when determining the iodine value of the tallow the effect of adding tetrachloroethane immediately before the titration of excess iodine was to be checked. The volume of Wijs' solution and solvent to be used were 25 ml and 15 ml as specified, respectively, in the present IUPAC and IS0 standardised methods. [Nofe:tThe AOCS method prescribes a reaction solvent volume of 20 ml.]The results of this preliminary investigation are given in Table 1. It will be seen that the agreement between the overall mean values obtained for the determined iodine values by both solvents was generally satisfactory. The difference in the results obtained for duplicate analyses (not shown in the table) by each laboratory appeared to indicate that the precision of the method was unaffected by the choice of solvent. It was not established that the use of tetrachloroethane, when determining the iodine value of the tallow, made a significant improvement to the performance characteristics of the method and this aspect was not studied further. On the basis of these preliminary results it was decided to proceed with a comprehensive collaborative study. s t COLLABORATIVE S T U D Y A N D RESULTSFor the 1st study (1 989), which was undertaken in co-operation with members of ISO/TC 34/SC 1 1, eleven fats and oils were selected to represent the wide range of lipid materials for which the determination of iodine value is of commercial importance viz.: 7 vegetable oils (olive oil, refined palm kernel oil, crude and refined palm oil, tung oil, sunflower seed oil, hydrogenated soya bean oil), 3 animal fats (crude and hydrogenated fish oil, tallow) and a used frying oil. Each of the 11 materials were provided as blind duplicates (i.e. a total of 22 samples) and participants wer...

Physicochemical Characterization of Cucumis sativus L. seed oil

“…This suggests that seed oil is highly unsaturated. The refractive index (1.4685) of the oil is in close range with the values obtained for some conventional oils such as palm kernel oil (1.449-1.451), Soya bean oil (1.466-1.470) etc [12,13,14]. Since the refractive index of the oil is greater than that of water (1.330) at room temperature, this property suggests the use of the oil in studies relating to optics.…”

“…The acid value was determined following established procedure of AOAC [3]. Iodine value was estimated by applying Wijs method [4,5]. Moisture content was determined by oven drying a known quantity of the oil in the oven at 105 o C for 24 hours after which the percentage moisture was calculated as follows: o C using a rotary vacuum evaporator to yield the crude oil.…”

Molecular iodine/polymer complexes

“…As with the above polymers, the species found in the I 2 nylon complexes such as I 2 nylon6 were the polyiodide ions I 3¯a nd I 5¯a s spectral analyses ( 13 C NMR, 14 N NMR, IR, Raman, XRD) suggested [199,200]. In the I 2 nylon6 complex prepared by treating nylon6 with I 2 /KI solution, the I 3¯ ions were normal to the chain axis and the I 5¯ units were oriented along the polymer chain.…”

“…Iodine is one of the components of Wijs reagent used for the estimation of the iodine value (IV) of fats and oils [14,15]; Wijs reagent is a solution of iodine monochlo ride in acetic acid and can be prepared from a mixture of iodine trichloride and iodine.…”

Blend Characteristics of Biodiesel Obtained from Four Virgin Tropical Seed Oils

“…The mixture was reacted for the required time of mixing (5 or 30 mins) after which the blender was switched off and the mixture immediately transferred into a separatory funnel and closed tightly. The mixture was allowed to settle for 24 h after which a dark color glycerin settled at the bottom while a pale liquid layer which is the methyl ester separated at the top (Wu et al, 1998 Kirk, 1965;Pockington, 1990;IPMAN, 1983;Chevron, 2007;Lewkowitsch, 1921Lewkowitsch, , 1923Paquot, 1979;Tat & Gerpen, 2000). Weight of given volume of sample at desired temperature (20 o C) was determined using a pycnometer previously calibrated at same temperature.…”