Estimation of Total Carbonyl Content in Oxidized Oil by 2, 4-Dinitrophenylhydrazine

Abstract

The measurement of carbonyl value by 2, 4-dinitrophenylhydrazine (in alkaline solution) is generally practiced for the estimation of an oxidative stage of oil processing. This paper deals the estimation method of carbonyl compounds.1) In the case of measurement of the total carbonyl value of an oxidized oil, an approximate value can be obtained by reading the extinction only at 440mμ and calculation is as follows;Total carbonyl value (m eq/kg) =E/0.584×W ×103E : Extinction at 440mμ W : Weight of oil (mg) 2) When this method was applied to the high peroxide oil, the carbonyl value was biased to be overestimated. The peroxide may have a substantial influence on the carbonyl value, probably because hydroperoxide reacts with 2, 4-DNPH.3) It is undesirable to dilute the sample with solvent after color developing, because there occurs the shift of absorption maximum and the subsequent change of extinction.4) Some of carbonyl radicals that exist in oxidized glyceride molecules seem to be difficult to react with 2, 4-DNPH rather than hydroxylamine or hydrazine.5) What ever kind of unit is applied as the total carbonyl value, it is reasonable to understand that the number obtained is not an accurate value of carbonyl contents, but a tentative measure indicating an oxidative stage of oil.