Characteristics of the Fiber Laser Sensor System Based on Etched-Bragg Grating Sensing Probe for Determination of the Low Nitrate Concentration in Water.

Thanh Pham,Huy Bui,Huu Le,Van Pham

doi:10.3390/s17010007

Thanh Pham, Huy Bui + Show 2 more

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https://doi.org/10.3390/s17010007

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Abstract

The necessity of environmental protection has stimulated the development of many kinds of methods allowing the determination of different pollutants in the natural environment, including methods for determining nitrate in source water. In this paper, the characteristics of an etched fiber Bragg grating (e-FBG) sensing probe—which integrated in fiber laser structure—are studied by numerical simulation and experiment. The proposed sensor is demonstrated for determination of the low nitrate concentration in a water environment. Experimental results show that this sensor could determine nitrate in water samples at a low concentration range of 0–80 ppm with good repeatability, rapid response, and average sensitivity of 3.5 × 10−3 nm/ppm with the detection limit of 3 ppm. The e-FBG sensing probe integrated in fiber laser demonstrates many advantages, such as a high resolution for wavelength shift identification, high optical signal-to-noise ratio (OSNR of 40 dB), narrow bandwidth of 0.02 nm that enhanced accuracy and precision of wavelength peak measurement, and capability for optical remote sensing. The obtained results suggested that the proposed e-FBG sensor has a large potential for the determination of low nitrate concentrations in water in outdoor field work.

Highlights

Nitrate (NO3 − ) is considered to be one of the important substances to measure in water, because of its potential environmental and human health implications
Nitrates are not directly toxic to human health, but their possible reduction to nitrites and a reaction of nitrites with secondary or tertiary amines present in the body can result in the formation of carcinogenic N-nitrosamines
The Bragg wavelength shifted to the shorter wavelength range due time wavelength shifted shorter wavelength range to to theprogressed, reduction ofthe theBragg cladding diameter, since to thethe fundamental mode is less confined in thedue fiber the reduction of the cladding diameter, since the fundamental mode is less confined in the fiber core core region, leading to a higher evanescent field, and to a more efficient interaction with the region, leading to a higher andand a more of efficient the surrounding medium

Summary

Introduction

Nitrate (NO3 − ) is considered to be one of the important substances to measure in water, because of its potential environmental and human health implications. Nitrates are not directly toxic to human health, but their possible reduction to nitrites and a reaction of nitrites with secondary or tertiary amines present in the body can result in the formation of carcinogenic N-nitrosamines. The nitrite oxidizes iron in the hemoglobin of the red blood cells to form methemoglobin, which lacks the oxygen-carrying ability of hemoglobin. This creates a condition known as methmoglobinemia, wherein blood iron in hemoglobin (Fe+2 ) is reduced to its oxidized form Fe+3. Different methods, including ultraviolet-visible spectroscopy (UV-VIS), electrophoresis, electrochemical detection, chromatography, mass spectroscopy, Sensors 2017, 17, 7; doi:10.3390/s17010007 www.mdpi.com/journal/sensors

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