Chemical Education Journal (CEJ), Vol. 7, No. 2 /Registration No. 7-18/Received October 27, 2003.
URL = http://www.juen.ac.jp/scien/cssj/cejrnlE.html


Application of A Low-Cost Four-LED Based Photometer for Environmental Analysis1)

Wing Hong Chan,Yuen Kit Cheng, Martin M. F. Choi*, Albert W. M. Lee, Man Shing Wong, and Wai Yeung Wong

Department of Chemistry, Hong Kong Baptist University, 224 Waterloo Road, Kowloon Tong, Hong Kong SAR, P. R. China

Dan Xiao

School of Chemical Engineering, Sichuan University, Chengdu 610065, P. R. China

* Corresponding should be addressed to M. M. F. Choi.
E-mail: mfchoi@hkbu.edu.hk

1) Presented at the Tenth Asian Chemical Congress, Hanoi, Vietnam on 21-24 October 2003.


Abstract: In this article, a four-LED based photometer, in which four LEDs are used as light sources, are demonstrated to be an useful instrument for water and air pollutants analyses. This photometer is applicable to various spectrophotometric methods for the determination of chemical species exhibiting absorption maxima of the coloured complexes in the visible light spectrum. The target analytes are absorbed and reacted with colorimetric reagents in specially designed passive samplers and the absorbances of the resulting compounds are subsequently measured by the photometer. The concentrations of the analytes are calculated from calibration curves based on the Beer-Lambert law. Four experiments have been developed for the environmental analysis: (1) Analysis of airborne formaldehyde: This experiment makes use of a passive sampler to collect formaldehyde in indoor air. The sampler consists of two large surface gas-permeable diffusion membranes that regulate the permeation rate of the gas. After diffusion, the formaldehyde is analysed by a colorimetric method using 3-methyl-2-benzothiazolinone hydrazone hydrochloride and the red-LED based photometer. (2) Analysis of nitrogen dioxide: Nitrogen dioxide (NO2) in air is collected by an absorbent reagent in the passive sampler. When NO2 and absorbent reagent are brought together, a pink colour azo dye is developed. The absorbance of the dye is directly proportional to the concentration of NO2 which is subsequently analysed by the green-LED based photometer. (3) Determination of copper in water sample: This experiment describes the formation of a blue complex between Cu(II) ions and oxalic acid bis(cyclohexylidene hydrazide) and the concentration of Cu(II) is then determined by the yellow-LED based photometer. (4) Determination of iron content in commercial minerals tablet: In this experiment, Fe(III) in a commercial iron tablet is extracted with nitric acid. The digested sample then reacts with potassium thiocyanate to form a blood red complex solution. A blue-LED based photometer is employed to determine the iron content in the tablet. The proposed four LED-based photometer possesses the advantages of low cost, durability, and long-term optical stability.


BODY OF PAPER

Abstract
1. Introduction
2. Principle
3. Experimental
4. Results and Discussion
5. Conclusion
Acknowledgements
References


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