Abstract: A comparison of the results obtained by applying three spectrophotometric methods ( at fixed wavelength , second-derivative and multicomponent analysis ) to the determination of gamma-oryzanol in rice bran oil is reported . At fixed wavelength the results are more accurate when using isopropyl alcohol , rather than n-heptane , to dilute the oil samples , because the absorption bands of gamma-oryzanol are red-shifted and the absorbance , measured at lambda ( max ) =327 nm , is less affected by the interference of the oil "matrix" ( lambda ( max ) =314 nm in n-heptane ) . However , to obtain accurate results also in oils with a low content of gamma-oryzanol , it is necessary to perform the analysis using second-derivative ( ( 2 ) D330 . 365 ) or multicomponent ( lambda=310-360 nm ) methods .
The first one fully removes the interference of oil matrix whilst the second , which needs a specific computational program to process the spectrophotometric data , furnishes evidence the presence of some unexpected interference in the analysis and/or standards which are not representative of the analysed samples , from the square root of the sum of the squared differences at each point between the linear combination of the standards and the unknown spectra ( RMS error ) . Finally , some aspects of the chemical , spectroscopic ( UV , IR ) and thermoanalytical ( TG , DSC ) behaviour of gamma-oryzanol and the values of the parameters which enable "computation" of its UV spectra are reported .
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