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Abstract
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Portable spectrophotometers are of importance in many fields, such as environmental and clinical applications. A cheap, simple, and portable device operated with some ordinary small batteries seems to be a suitable alternative for commercial spectrophotometers. In the design of these spectrometers, compromises are made in the selection of the optoelectronic components to allow for reduced size and cost [1]. Over the last decades, the electronic industries have offered a great variety of devices that are of considerable advantages when applied in chemical instrumentations. These devices could help to overcome the challenges in devising portable colorimeters. Among them, Light emitting diodes (LEDs) received a great interest in the analytical applications and are used as light sources in portable and miniaturized absorption devices. The LEDs are available for almost all the wavelength ranges employed in the analytical spectrophotometers. Since these sources emit light of relatively narrow band widths (20-100 nm) they have been utilized as a monochromatic light source. Another challenge in the development of portable analytical devices is to reduce detector size. Hence, light-dependent resistors, LDR (small, cheap and accessible device) could be a good choice for fabrication of portable colorimeters [2].
In this work, a simple and portable multi-color Light emitting diode based photocolorimeter for determination of nitrite ions in river water has been used. The photocolorimeter designed employs two red–green–blue (RGB) LEDs as light source and two LDRs as detector. The emission wavelengths and the spectral band width of each emitter are: red, 625 and 25 nm; green, 525 and 40; and blue, 465 and 30 nm respectively. A programmable microcontroller sequentially turns the emitters on, receives the signals followed by calculating the absorbance and displaying it on a liquid–crystal display. For determination of nitrite, p-nitroaniline and naphth-1-ol were used as diazotizatio
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