recommended medthod of analysis for determination of anisidine value of fish oil
international association of fish meal manufacturers
general
The anisidine value is a measure of the alpha-beta unsaturated aldehydes of fats and oil. The Anisidine method replaces the former benzidine method due to the toxic benzidine. notice that the two method gives different values. applicable to marine body oils.
Principle
the anisidine value is defined as 100 times the contribution of the extinction of 1gram oil in 100ml solvent and anisidine reagents, read at 350nm
the oil is dissolved in iso-octane and treated with p-anisidine in acetic-acid solution. the extinction is measured, corrected for blank, and multiplied by 100.
reagents
All reagents shall be of analytical reagent grade.
para anisidine p.a.
2,2,4, Trimethylpentane (iso-octane) 99%
acetic-acid 100% p.a.
anisidine reagent 0.25% W/v. dissolve 0.25g para-anisidine in 100ml acetic-acid
apparatus
volumetric flask 25ml
test-tubes 10ml glass stoppered.
pipettes 1ml and 5ml.
spectrophotometer.
method
weigh 0.5-4g oil accurately into a 25 ml volumetric flask.
dissolve and make up to volume with iso-octane and mix.
measure the absorbance of the fat solution against pure iso-octane at 350nm in a one cm glass cell. pipette 5ml of the fat solution into a test-tube A and 5ml iso-octane into a test-tube B. Add 1ml anisidine reagent into test-tube A and B. stopper the tubes, shake vigorously and leave in a dark place for exactly 10 min.
measure the absorbance of the content of tube A against tube B at 350nm in a one cm glass cell.
calculation
anisidine value
ea is the net absorbance of the fat-solution.
eb is the net absorbance of the fat-anisidine-solution.
w is weight of sample.
repentability
the different between the results of two determinations carried out simultaneously or in rapid succesion by the same analyst should not differ by more than 0.5 in a sample with av between 1-20.