The short shelf life of Milk has always been a problem. Some small business milk producers utilize various adulterations to increase the shelf life, potentially risking the health of end-users [1]. These adulterations may include the addition of hypochlorite [2]. As a result of the bleach solution's contact with the milk components, chemical reactions occur [3]. The determination of bleach solution adulteration in milk by the present methods in Iran were not applicable for this aim due to the fast reaction of ClO - anions with milk compounds and the low residual concentration of it in the milk received by the end-users. Then, the determination of bleach adulteration in milk is by a developed method critically important. Paired emitter- detector diodes (PEDD) based on photometers provide low fabrication cost, low power consumption, ease of miniaturization and a high signal-noise ratio response in a large wavelength range [4]. This paper reports on developing a cheap but efficient paired emitter- detector diode (PEDD)-based photometer. The photometer consists of a white light-emitting diode (LED) as the emitter diode, an RGB LED as the detector diode and a multimeter for recoding the signal. The developed PEDD-based photometer was used for the determination of liquid bleach adulteration in cow milk samples. N, N-Diethyl-p-phenylenediamine sulfate aqueous solution (pH=6.0) was used as a probe to monitor the presence of residual active chlorine in milk. Finally, the calibration curve for determining sodium hypochlorite by using the developed method covered a linear dynamic range, 0.5 to 20.0 ppm, with a detection limit of 0.14 ppm and quantification limit of 0.46 ppm. Real sample analysis results showed that some pasteurized milk products.
