An inexpensive portable ratiometer for absorbance measurements

Abstract

This paper describes the construction and testing of a low cost dual beam spectrometer for the determination of chemical concentration in coloured liquids. The principle of operation is based on the partial extinction of light by chemical absorption. The spectrometer incorporates an optical bridge system which consists of a pulsed high intensity LED, two general purpose photodiodes and two 4-quadrant multiplier based PSDs. These components ensure that the signal-tonoise is maximized at minimum cost. The range of absorbance measurements which can be made with the present system may be extended using high intensity yellow, green and blue LEDs.

Laser-based double beam absorption detection for aggregation immunoassays using gold nanoparticles

“…The output current of each photodiode is converted to voltage by the operational amplifier to produce voltage outputs as transmittances. Campbell et al [4] obtained the ratio of the photodiode signals from an AD633JN 4-quadrant multiplier device, which operates in a divider mode. In our experiments we used Excel software to eliminate direct current (DC) noise contributions and to correct for intensity differences between the signal and reference channels.…”

“…The electronic circuit of the double beam detector was constructed following Campbell et al [4] with slight modifications. Briefly, the detector circuit consists of signal and reference photodiodes.…”

“…Due to the relatively low intensity of lamps at single wavelength their signal to noise ratio (S/N) is often shot noise limited. There have been several attempts to construct dual beam spectrometers using pulsed high intensity LEDs [4] and vertical-cavity surface-emitting lasers [5] in UV-VIS and atomic absorption spectrometry [6,7]. The use of a laser beam enhances the optical properties of a conventional lamp-based light source such as collimation and focusing power.…”