ISO27107:2008(E) 9.3Determinationofperoxidevalue 9.3.1 Purge the carefully cleaned Erlenmeyer flask (6.7) with nitrogen or carbon dioxide. Weigh into the flask, to the nearest 0,1 mg: a) either a 5,0 g ± 0,1 g test portion for expected peroxide values from > 1 to 30; b)or a 10,0 g ± 0,1 g test portion for expected peroxide values from 0 to 1. The peroxide value is a dynamic value, dependent upon the history of the test sample. Furthermore, the determination of the peroxide value is a highly empirical procedure and the value obtained depends on the the fat/oil can be over 30 meq active oxygen per kilogram. In these cases, the user should choose a smaller test portion mass. As the test portion mass influences the result, report it together with the result. 9.3.2[ In the case of fats with high melting points (hard fats and animal fats), carefully add to the melted fat 20 ml of test portion gently, if necessary. medium speed to avoid spraying. 9.3.4Immediately add 30 ml to 100 ml of water (5.1). The amount depends on the apparatus used. NOTE end-point of the titration is bigger (~100 mV). This results in a titration curve with a sharp turning point. 9.3.5Immerse the combined platinum electrode (6.2) into the test sample and start the titration with the 0,01 N sodium thiosulfate standard solution (5.8) while stirring at high speed. 9.3.6In a parallel blank test, not more than 0,1 ml of the 0,01 N thiosulfate solution shall be used. 9.3.7Most titration equipment evaluates the equivalent point automatically; otherwise determine the end-point graphically using the point of inflection method. NOTE Typical end-point titration curves are shown in Figure A.1. 10 Calculationand expression of results 10.1 Calculation Calculate the peroxide value (PV), in milliequivalents of active oxygen per kilogram, using Formula (2): (V-Vo)c(Na2S203)f ×1000 (2) m where is the factor for the 0,01 N sodium thiosulfate standard solution, determined by Equation (1); f 5 nal organizaonfe sandardallonghts reserved Copyright Intern Not for Resale ISO 27107:2008(E) m is the mass, in grams, of the test portion; V is the volume, in millilitres, of the O,o1 N sodium thiosulfate standard solution used for the determination; Vo is the volume, in millilitres, of the O,o1 N sodium thiosulfate standard solution used for the blanktest Report the result of the determination to one decimal place. 11Precision 11.1 Interlaboratory test Details of an interlaboratory test on the precision of the method are summarized in Annex B. It is possible that the values derived from this interlaboratory test are not applicable to concentration ranges and matrices other than those given. 11.2 Repeatability The absolute difference between two independent single test results, obtained with this same method on interval of time, will, in not more than 5 % of cases, exceed the repeatability limits, r, given in Table B.1 and Table B.2. 11.3 Reproducibility The absolute difference between two single test results, obtained with this same method on identical test 12 Test report The test report shall specify: a) allinformation necessary for the complete identification of the sample; b) the sampling method used, if known; c) the test method used, with reference to this International Standard; (p the mass(es) of the test portion(s); e) all operating details not specified in this International Standard or regarded as optional, together with details of any incidents that may have influenced the test result(s); the test result(s) obtained, or, if the repeatability has been checked, the final quoted result obtained. @ ISO 2008 - All rights reserved onal Organization for Standardizatior Not for Resale ISO27107:2008(E) Annex A (informative) Examplesofpotentiometrictitrationcurves U,mV PV = 3,2 PV = 7,5 PV = 11,4 PV = 16,7 PV = 26,0 150 y 125 100 75 EP1 EP1 EP1 EP1 EP 50 25 0 -25 -50 0,0 5,0 7,5 10,0 12,5 2,5 V, ml Key EP1 titration end-point PV peroxide value U potential difference A volume FigureA.1Pot