A very simple photometer based on paired-emitter-detector diodes

According to the concept of paired-emitter-detector diode (PEDD)-based photometry, a light emitting diode (LED) used as a light source together with a second LED serving as a light detector comprises a novel kind of a photometric device. It has been found that coupling of PEDD with an ordinary multimeter used simultaneously as a power supply of LED-emitter and as an instrument measuring the signal generated by LED-detector allows form a complete, extremely simple, and low-cost photometer. Owing to these advantages such photometer is especially useful for student teaching, although it could be used also for more advanced analytical applications. This paper reports on the set of experiments with a use of the developed photometer demonstrating its practical utility, including determination of selected dyes in the ppm concentration range, pH detection with the use of acid-base-indicators, enzymatic detection of urea, and finally bioassays for evaluation of urease and alkaline phosphatase activities.