A Compact System for Measurement of Absorbance of Light
In this work a compact device to measure absorbance based on light emitting diodes – LED - is proposed. Measurand is the concentration of specific chemical or biochemical components within the test fluid. The advantage of such a system lies in the use of low-cost standard optic-mechanical and electronic components that contribute to its compactness and robustness.
The proposed system measures absorbance (or transmittance) of monochromatic light inside a standardized cuvette of 10 mm light path within a temperature ranging from 25 to 40ºC (±0,2ºC). Some important features, such as stability, accuracy and precision of the measurement system are discussed. It is shown that the measurement stability is governed by the stability of the light source. An acceptable value is 0,002 units of absorbance per hour, which can be verified by measuring a dummy cuvette during a suitable long period. The accuracy and precision are estimated by means of traceable calibration standards throughout the desired spectrum of wavelengths. The wavelengths required for the target application of the proposed system are 340, 405, 505, 546, 600 and 700nm. Basic variables of influence are identified and a brief metrological analysis is presented in form of an uncertainty balance. First results obtained with the proposed system demonstrate uncertainties below 1,6 % relative to the measured value of absorbance.
KeywordsZinc Albumin Urea Tungsten Coupler
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- Bürmen, M.; Pernus, F.; Likar, B; LED light sources: a survey of quality-affecting factors and methods for their assessment – Measurement Science and Technology. 19 (2008) 122002Google Scholar
- Palma, A. J.; Ortigosa, J. M.; Lapresta-Fernández, A.; Fernández-Ramos, M. D.; Carvajal, M. A.; Capitán-Vallvey, L. F.; Portable light-emitting diode-based photometer with one-shot optochemical sensors for measurement in the Field – Review of Scientific Instruments 79, 103105 (2008)Google Scholar
- Belz, M.; Klein, F. A.; Eckhardt, H. S.; Klein, K. F.; Dinges, D.; Grattan, K. T. V.; Optical Detection Techniques and Light Delivery with UV LEDs and Optical Fibres – Third International Conference on Optical and Laser Diagnostics – Journal of Physics: Conference Series 85 (2007) 012034Google Scholar
- Gaião, E. N.; Medeiros, E. P.; Lyra, W. S.; Moreira, P. N. T.; Vasconcelos, P. C.; Silva, E. C.; Araújo, M. C. U.; Um fotômetro multi-LED microcontrolado, portátil e de baixo custo – Química Nova, vol. 28, No. 6, 1102–1105, 2005Google Scholar
- Weiwei, Y.; Aiyu, Z.; Baoshan, H.; Xinxia, C.; A portable biochemical detection device based on fiber optic sensor – Sensors and Actuators B 130 (2008) 21–24Google Scholar
- Yang, H.; Wei, X.; Liang, X.; Su, M.; Lu, X.; A SoC and LED based reconfigurable subminiature spectrometer for hand-held measurement applications – Measurement 41 (2008) 44–54Google Scholar
- Yeh, T.; Tseng, S.; A Low Cost LED Based Spectrometer – Journal of the Chinese Chemical Society, 2006, 53, 1067–1072Google Scholar
- Fonseca, A.; Junior, I. M. R.; A multichannel photometer based on an array of light emitting diodes for use in multivariate calibration – Analytica Quimica Acta 522 (2004) 223–229Google Scholar
- Hauser, P. C.; Rupasinghe, T. W. T.; Cates, N. E.; A multi-wavelength photometer based on light-emitting diodes – Talanta, Vol. 42, No. 4, pp. 605–612, 1995Google Scholar