Investigation of Fiber Optic Sensor for Monitoring of Ammonia

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Absorbance, au 1.1 0.9 0.7 A B C D E F G H I Absorbance min. at 480nm when exposed to 18ppm ammonia The plots 6 and 7 shown above give a relative measurement of absorbance compared to the initial plot in DI water. Plot 8 shows plot of percentage change in absorbance as a function of wavelength for ammonia. This helps in understanding the effect of the interaction between the sensing region and the contaminant. Percentage change in absorbance is defined as 0.5 0.3 Absorbance min. at 540nm Absorbance min. shifted to 516nm when exposed to 2.25ppm ammonia A conta min ant A − A DIwater DIwater 400 600 800 1000 Wavelength, nm Fig. 6 Plot of Absorbance vs. Wavelength when sensor S1 was exposed to A: DI water; B: 2ppm; C: 4ppm; D: 6ppm; E: 8ppm; F: 10ppm; G: 12ppm; H: 14ppm; I: 16ppm solutions of ammonia. Hence the sensor developed can be used to detect ammonia to a concentration down to 18ppm. Another sensor with the same configuration was made but without the 0.1M HCl solution. This gives a uniform blue colored layer of Polyaniline in its Emeraldine base form. Such a sensor can be used to detect any acid that maybe present in water. In this case HCl was used as the contaminant. Fig. 7 shows the plot between absorbance and wavelength for various concentrations of HCl as contaminant. Plot A is obtained when the sensor is introduced into DI water and as concentration of HCl contaminant is added the absorbance minimum shifts from 430nm to 530 nm which belongs to green region of visible spectrum. The amount of HCl required to saturate the sensor can be seen from fig. 7 to be around 116ppm. This suggests that less amount of ammonia is required to saturate the sensor than HCl. It is speculated that the presence of gas permeable layer over the Polyaniline material is the cause of this variation. The + gas permeable layer is partially blocking some of the H 3 O ions from interacting with the Polyaniline material, hence increasing the selectivity of the sensor towards Ammonia. 1.1 A B C D E F G Where, A DIWater and conta ant A min are absorbance values of the 2 sensors when exposed to DI water and contaminant solution, respectively. Normalized Absorbance 0 .4 0 .2 0 .0 - 0 .2 - 0 .4 A B C D E F G H I 4 0 0 6 0 0 8 0 0 1 0 0 0 W a v e le n g th , n m P e a k a t 7 6 0 n m Fig. 8 Plot of %change in Absorbance vs. Wavelength when sensor S1was exposed to A: DI water; B: 2ppm; C: 4ppm; D: 6ppm; E: 8ppm; F: 10ppm; G: 12ppm; H: 14ppm; I: 16ppm solutions of ammonia. As was observed from fig. 8, the sensor starts saturating when exposed to 18ppm of ammonia and above and is completely saturated at a concentration of 30ppm. This plot shows that the maximum change of 0.15 in absorbance is obtained at the wavelength of 760nm. A similar plot for HCl was obtained as shown in fig. 9. 0.4 A B C D E F G Absorbance 0.9 % change in absorbance 0.2 0.0 0.7 -0.2 0.5 400 600 800 1000 Wavelength 400 600 800 1000 W avelength Fig. 7 Plot of Absorbance vs. Wavelength when sensor S2 was exposed to A: DI water; B: 58ppm; C: 116ppm; D: 174ppm; E: 232ppm; F: 290ppm; G: 348ppm solutions of HCl. Fig. 9 Plot of %change in Absorbance vs. Wavelength when sensor S2 was exposed to A: 58ppm; B: 116ppm; C: 174ppm; D: 232ppm; E: 290ppm; F: 348ppm; G: 408ppm solutions of HCl. 4 Copyright © 2008 by ASME
Here, the maximum change is observed at 610nm but saturation is achieved much later unlike in case of ammonia which emphasizes the assumption that the gas permeable layer + is blocking O ions. Figure 10 and 11 show percentage H 3 change in absorbance as a function of concentration. It can be seen that sensor which is exposed to ammonia saturates at a concentration of 30ppm for ammonia and in case of HCl the saturation is not reached even at 400ppm. Two different test runs were performed for the ammonia sensor as shown in Fig.11; the second test was done 24 hours later from the first one. Normalized Absorbance for hcl Normalized Absorbance for Ammonia 0 -0.05 -0.1 -0.15 -0.2 -0.25 -0.3 Fig. 10 Plot of normalized change in absorbance as a function of concentration for HCl. 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 200 400 600 Fig. 11 Plot of normalized change in absorbance as a function of concentration for Ammonia. 8. Conclusion y = -0.0005x - 0.0803 R² = 0.9266 Concentration R² = 0.9834 R² = 0.9794 610nm Linear (610nm) First run Second run Poly. (First run) Poly. (Second run) 0 10 20 30 40 50 Concentration (ppm) Two different sensors are developed one each for ammonia and HCl, respectively. The sensor was saturated by ammonia with a concentration as small as 30ppm whereas in case of HCl the saturation was not reached even at 400ppm suggesting that the gas permeable layer on Polyaniline is blocking all the ions. Ammonia and HCl could be detected to a concentration as low as 2ppm and 58ppm, respectively. Further work needs to be done to determine the minimum concentration that can be detected by bending the fiber cable. 9. References 1. M. A. El-Sherif, “An Apparatus and a Method Comprising an Optical Fiber Modulator, Coupler, Switch, Sensor, and Distribution System,” U.S. Patent 5 060 307, Oct. 22, 1991. 2. J. Yuan, “Development of Smart Structures Utilizing Chromogenic Materials for Optical Fiber Sensor,” M.S. thesis, Drexel Univ., Philadelphia,PA, 1997. 3. M. A. El-Sherif, “On-Fiber sensor and modulator,” IEEE Trans. Instrum. Meas., vol. 38, pp. 595–598, Apr. 1989. 4. M. A. El-Sherif and J. Yuan, “Development of a novel class of fiber optic sensors for environmental field measurements,” in International Conference on Agropoles and Agro-industrial Technological Parks, Barretos, Sao Paulo, Brazil, Nov. 15–21, 1999. 5. A. D. Kersey, “A review of recent developments in fiber optic sensor technology,” Opt. Fiber Technol., vol. 2, pp. 291–317, 1996. 6. T. G. Giallorenzi, J. A. Bucaro, A. Dandrige, G. H. Sigel, J. H. Cole Jr, and S. C. Rashleigh, “Optical fiber sensor technology,” J. Quantum Electron., vol. QE-18-4, pp. 626–665, 1982. 7. R. Narayanaswamy, “Current developments in optical biochemical sensors,” Biosens. Bioelectron., vol. 6, pp. 467–475, 1991. 8. Xiaojing Liu and Weihong Tan, “A Fiber-Optic Evanescent Wave DNA Biosensor Based on Novel Molecular Beacons”, Anal. Chem. 1999, 71, 5054- 5059. 9. M. A. El-Sherif, J. Yuan, and A. G. MacDiarmid, “Fiber optic sensors and smart fabrics,” J. Intell. Mater. Syst. Structures, vol. II, no. 5, pp. 407–414, May 2000. 10. Jaroslav Stejskal, Irina Sapurina, “Polyaniline: Thin Films and Colloidal Dispersions”, Pure and Applied Chemistry, Vol.77, No.5, pp. 815-826, 2005. 11. Jianming Yuan and Mahmoud A. El-Sherif, “Fiber- Optic Chemical Sensor Using Polyaniline as Modified Cladding Material”, IEEE Sensors Journal, Vol. 3, No. 1, February 2003. 12. Zhe Jin, Yongxuan Su, Yixiang Duan, “An improved optical pH sensor based on Polyaniline”, Sensors and Actuators B 71 (2000) 118-122. 13. Stejskal J.; Sapurina I.; Prokes J.; Zemek J., “In-Situ Polymerized Polyaniline films”, Synthetic Metal, Vol.105, No.3, Sep. 1999, pp.195-202 5 Copyright © 2008 by ASME
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Investigation of Fiber Optic Sensor for Monitoring of Ammonia

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