A dual-wavelength method using the BDJ detector and its application to iron concentration measurement

A new and uncomplicated method for absorption detection is presented that requires no optical instrument such as a spectrophotometer or colorimeter. it makes use of a two-wavelength light source and a BDJ (buried double p-n junction) detector operating as wavelength-sensitive device. The intensity-insensitive photocurrent ratio r(dual) = I-2/I-1 is used as the detector response and is related to the absorbing species. A reference curve r(dual)(C) obtained by calibration serves to determine concentrations of the component. It has been theoretically shown and experimentally verified that the curve r(dual)(C) becomes linear at low concentrations. Through an investigation in the case of iron concentration measurements, the suggested method has proved to be sensitive and reliable.