Spectroscopic analysis of intrinsic optical signature of dissolved ions in water

• Main Author: Ng, Yong Shen.
• Other Authors: Masoud Ghandehari
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Environmental engineering::Water supply
• Online Access: http://hdl.handle.net/10356/16026
• Institution: Nanyang Technological University

In this report, the aim is to detail the procedures in researching and experimenting with the method of infrared spectroscopy and finally to fabricate an optical fiber sensor for the spectroscopic measurement of dissolved chlorides. The infrared region is separated further into three regions and we will only be focusing on the near infrared regions. It is important to understand the principles of the infrared spectroscopy and the absorbance of the different substance to perform accurate experiments. The initial experiments involves the trying out of different cuvettes and the parameters used on the spectrophotometer. It is a long process as there are quite a number of variables that needs to be considered such as the slit width of the light source, the pathlength of the cuvette and also the type of materials to use. Finally a do-it-yourself (DIY) cuvette was fashioned out of microscope slides and a thin sheet of rubber from the laboratory gloves to achieve the desired pathlength. The experiments were conducted using deionised water, sodium chloride solutions of varying concentrations and pH buffer solutions of pH ranging from 10 to 13. Repeated experiments were done to ensure that the results are conclusive and viable. After this, the optical fiber sensor was fabricated with fiber that was developed using step-index multimode low OH plastic clad silica (PCS) fibers purchased from Thor Labs Inc. with 600 µm core diameter, 630µm cladding diameter, and 1,030 µm buffer diameter. This is because it can transmit with very little O-H absorption. A collimator is attached to one end of the optical fiber via a SMA connector to concentrate the light source into the optical fiber itself. The optical fiber sensor is then attached to a Perspex holder and put through a Perspex mould that contains the sample. It can be concluded that the project has achieved its aim in the fabrication of the optical fiber sensor, however due to the time constraint and limited access to the laboratory facilities, the results obtained did not show the essential spectrums and therefore more tests and troubleshooting needs to be done for it to successfully measure the dissolved chlorides. This optical fiber sensor can be further developed as it is not costly, able to withstand rough handling and can be used in situ for outdoor monitoring and detection. It could be then used to detect the presence of chlorides in groundwater and this is especially for people who live near the coast and needs to dig wells to obtain freshwater. The test can help in ensuring that the location selected has freshwater not contaminated or mixed with the seawater. Another area of use could be the detection of chlorides in the water used for cement mixing. It is important as the chlorides will react with the steel used as reinforcement and results in the rusting and corrosive of the steel and this may cause the failure of the concrete structure and leading to the loss of property and even lives.