The test procedures to assure ASTM biodiesel quality are not being widely implemented because of the lengthy procedures and laboratory equipment requirements. A critical need in the increasingly emerging biodiesel industry right now is a reliable, affordable and rapid test method for determining the blends of biodiesel in diesel fuel. As an effort to explore a reliable and rapid method, a spectrophotometer was used to scan the blends of #2 fossil diesel and biodiesel for spectrums in the wavelength range of 190-1100 nm.

The shape of the spectrum curve was found to be different for different biodiesel feedstock where as relative absorbance and characteristic peaks of absorbance curve was attenuated with increasing amount of diesel in the blend. Shape characteristics were fed into neural network to predict the biodiesel feedstock and blend level in biodiesel-diesel mixture.

http://asae.frymulti.com/abstract.asp?aid=19829&t=2

how spectrophotometer works

There are two major classes of devices: (1) single beam and (2) double beam. A double beam spectrophotometer compares the light intensity between two light paths, one path containing a reference sample and the other the test sample.

Wikipedia File:Spetrophotometer-en.svg

In short, the sequence of events in a spectrophotometer is as follows:

1. The light source shines into a monochromator.
2. A particular output wavelength is selected and beamed at the sample.
3. The sample absorbs light.

intensity of that particular wavelength (I vs nm) is recorded.

It successfully applied to determination of low concentration of cationic surfactants in the domestic sewage and Xian city moat.