Optimization of light source wavelength for ammonia detection in water

TELKOMNIKA Telecommunication Computing Electronics and Control
Vol. 20, No. 5, October 2022, pp. 1132~1138
ISSN: 1693-6930, DOI: 10.12928/TELKOMNIKA.v20i5.24079  1132
Journal homepage: http://telkomnika.uad.ac.id
Optimization of light source wavelength for ammonia detection
in water
Nurfatihah Che Abd Rashid1
, Noran Azizan Cholan1
, Kim Gaik Tay 1
, Afiqah Yaacob1
,
Nazrah Ilyana Sulaiman1,2
, Khairulanwar Mokhiri3
, Nor Hafizah Ngajikin1
1
Faculty of Electrical and Electronic Engineering, Universiti Tun Hussein Onn Malaysia
Batu Pahat, Johor, Malaysia
2
Malaysia Marine and Heavy Engineering Sdn Bhd (MMHE), PLO3 Jalan Pekeliling, P.O. Box 77, 81700 Pasir Gudang, Johor,
Malaysia
3
Mass Rapid Transit Corporation Sdn. Bhd. (MRT), MRT Sungai Buloh Depot, Jalan Sungai Buloh, U 4, 47810 Petaling Jaya, Selangor,
Malaysia
Article Info ABSTRACT
Article history:
Received Apr 21, 2021
Revised Jul 31, 2022
Accepted Aug 08, 2022
Optimization of light source wavelength for ammonia detection in surface
water is presented in this work. For the ammonia detection, the surface water
sample is mixed with sodium chloride and nessler reagent, whereas the
sensor head consists of unclad plastic optical fiber. The unclad region has a
length of 1 cm and the cladding is removed by immersing it in acetone
solution. Experimental results indicate that the output light intensity of the
sensor has linear relationship with the ammonia concentration. At the
wavelength of 510 nm, the output light increases linearly as the ammonia
concentration varies from 0.07 mg/L to 8.97 mg/L. At the same wavelength,
the proposed sensor achieves the sensitivity of 0.0139 (mg/L)-1
, accuracy of
99.59% and resolution of 0.72 µg/L. The analysis of light source wavelength
reveals that a wavelength range from 450 nm to 580 nm produces the
optimized performances. Within this wavelength range, the proposed sensor
achieves sensitivity of higher than 0.01 (mg/L)-1
, accuracy of higher than
99% and resolution of less than 1 µg/L.
Keywords:
Ammonia detection
Optical sensor
Plastic optical fiber
This is an open access article under the CC BY-SA license.
Corresponding Author:
Noran Azizan Cholan
Faculty of Electrical and Electronic Engineering, Universiti Tun Hussein Onn Malaysia
86400 Parit Raja, Batu Pahat, Johor Malaysia
Email: noran@uthm.edu.my
1. INTRODUCTION
Ammonia has been widely used in various industrial processes, agricultural activity, and a variety of
biological systems [1]. Ammonia molecules are a nutrient required for life, but excess ammonia will cause
toxic effect on the health of plants, animals as well as human beings. Consuming water with presence of
ammonia will corrode the lining of the mouth, esophagus, and stomach. Furthermore, excess ammonia level
may affect aquatic life. Previous studies have found that lethal ammonia concentration for a variety of fish
species ranges from 0.2 mg/L to 2.0 mg/L [2]. However, the ammonia tolerance varies between fish species
and physiological status. To avoid the environmental risk, the Food and Agriculture Organization (FAO) has
advised that the ammonia levels in water should be lower than 1 mg/L. Thus, it is essential to control the
concentration of ammonia in water to prevent environmental pollution.
Recently, a variety of sensing techniques for measuring ammonia concentration in water have been
suggested, such as electro-chemical method [3], metal oxide semiconductor detectors [4], a ratiometric
fluorescence sensor [5], and fiber optic based sensors [2], [6]–[11]. The electrochemical method has high

TELKOMNIKA Telecommun Comput El Control 
Optimization of light source wavelength for ammonia detection in water (Nurfatihah Che Abd Rashid)
1133
selectivity and low detection limit. However, this method lacks in term of the lifetime, miniaturization, and
stability of the reference electrodes [5]. On the other hand, metal oxide semiconductor detector has low
detection limit with fast response time, but has low sensitivity and lack in selectivity [1]. Ratiometric
fluorescence technique meanwhile has great advantages regarding high sensitivity and selectivity with low
detection limit [5]. Nonetheless, this method has complex acquisition and data manipulation due to the use of
fluorescence ratio [12]. Fiber optic based sensor, on the other hand, is widely known for its immunity to
electromagnetic interference, small in size, and ruggedness. Furthermore, fiber optic sensor has low loss, low
dispersion, ultrawide bandwidth, high dynamic range, durability, upgradability, and low cost [9].
The basic operating principle of the fiber optic sensor is that the light signal travelling through an
optical fiber changes when it is subjected to chemical or physical stimulus [13]. Such mechanism allows the
fiber optic sensor to find applications in detecting properties such as temperature [14], [15], liquid level [16], [17],
refractive index [18]–[20], uric acid concentration [21], [22] and ammonia concentration [2], [6]–[11].
For ammonia detection in water, many methods have engineered the fiber such that a part of the cladding of
the fiber sensor is removed through chemical etching, tapering or a combination of etching and tapering.
In order to enhance the sensor sensitivity and selectivity in detecting ammonia concentration, additional coating
material such as tin dioxide [2], oxazine 170 perchlorate [6]–[8], sol-gel silica [9], [10] and zinc oxide [11] were
deposited on the modified cladding. However, such developments [2], [6]–[11] have limitations in that they
lack analysis of the light wavelength for the optimized performances for ammonia detection in water. In this
work, the light source wavelength is analysed experimentally for the optimized performances with respect to
the sensitivity, accuracy and resolution.
2. EXPERIMENT
2.1. Experimental setup
The ammonia concentration in surface water samples is detected using clad modified fiber optic
sensor where the cladding of the optical fiber is removed using etching method. The optical fiber used is a
15 cm long plastic optical fiber (POF) with polymethyl methacrylate (PMMA) core. The POF has a diameter
core of 980 µm and diameter cladding of 20 µm thick. The refractive index of the core and cladding are
1.492 and 1.417, respectively. The sensing region of the fiber is prepared based on chemical etching
technique using acetone, de-ionized water, and sandpaper. No additional coating is deposited on the modified
cladding surface. The sensor head of the POF is prepared by removing 1 cm of the middle fiber jacket using a
fiber stripper. The cladding of the sensor head is then removed by immersing the optical fiber sensing region
in acetone solution for 10 seconds. Reaction between acetone and the cladding forms a milky white foam on
the outer fiber surface. To neutralize this reaction towards acetone, the fiber is then dipped in de-ionized
water. The milky white foam on the outer fiber surface is then removed using 2000 grit sandpaper and
cleaned again using de-ionized water. The unclad part of the fiber (sensing region) is then tested using FIS
fiber optic continuity tester as shown in Figure 1(a). The test is conducted to ensure perfection on the sensor
head. The POF is then connected to ocean optics deuterium halogen (DH)-mini light source, and ocean optics
HR4000CGUV-VIS spectrometer for measurement as shown in Figure 1(b).
(a) (b)
Figure 1. Experimental setup of fiber optic sensor that consists of (a) unclad POF as sensor head and (b) light
source and spectrometer

 ISSN: 1693-6930
TELKOMNIKA Telecommun Comput El Control, Vol. 20, No. 5, October 2022: 1132-1138
1134
2.2. Sample preparation
The detection of ammonia in this work is based on the reaction of surface water sample with two
reagents: sodium chloride (NaCl) and nessler (K2HgI4). The surface water samples are collected in the area of
Batu Pahat, Johor, Malaysia. The sample of the surface water collected is shown in Figure 2(a). The water
sample used for measurement is prepared by mixing 1 mL of surface water sample with 9 mL of sodium
chloride reagent as shown in Figure 2(b). Then, 4 drops of nessler reagent are added into the mixture.
The addition of nessler reagent causes a brown precipitate in the sample as shown in Figure 2(c).
The refractive index and concentration of each sample is measured using Atago refractometer and Hanna
instrument ammonia high range portable photometer (HI96733), respectively. The concentrations obtained are
0.07 mg/L, 2.63 mg/L, 6.93 mg/L, and 8.97 mg/L. Such concentrations act as the reference for the result
analysis. For the measurement, 1.5 mL of the sample is added into a cuvette as shown in Figure 1(b). The light
intensity of each sample is observed and recorded using OceanView software installed in a computer.
Each water sample is tested 3 times and the average value of each concentration is obtained subsequently.
(a) (b) (c)
Figure 2. Preparation of water sample for testing: (a) water sample only, (b) water sample with sodium
chloride reagent, and (c) water sample with sodium chloride and nessler reagent
3. RESULTS AND DISCUSSION
Table 1 shows the refractive index of the sample against the ammonia concentration. Based on
Table 1, it is evident that the refractive index of the sample increases when the ammonia concentration in the
sample increases. Meanwhile, Figure 3 illustrates the spectrum of light intensity against wavelength with
different concentrations of ammonia. Based on Figure 3, it is found that the light intensity increases as the
ammonia concentration in the sample increases. This condition is related to the increase of refractive index
with the ammonia concentration shown in Table 1. As the refractive index of the sample increases, the
refractive index difference between the sample and fiber core reduces. Consequently, the light loss is
reduced, causing the output light intensity of the sensor becomes higher [23], [24].
Table 1. Refractive index of water sample
Concentration (mg/L) Refractive index
0.07 1.3322
2.63 1.3330
6.93 1.3340
8.97 1.3348
For the case of study, the change of light intensity towards different ammonia concentrations at the
wavelength of 510 nm is presented in Figure 4. The graph is obtained based on the data obtained from Figure 3.
Based on the data shown in Figure 4, it is found that the output light intensity has linear relationship with the
ammonia concentration. The sensitivity of the sensor is 0.0139 (mg/L)-1
, which is obtained based on the slope
of the linear graph [23]. On the other hand, the sensor shows accuracy of 99.59%. The accuracy of the sensor
is calculated using the (1) [21].
𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = 1 − |(𝑐_𝑟𝑒𝑎𝑙 − 𝑐_𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑)/𝑐_𝑟𝑒𝑎𝑙 | (1)
Where 𝑐_𝑟𝑒𝑎𝑙 is the real ammonia concentration measured by a commercial hanna instrument ammonia high
range portable photometer (HI96733) and 𝑐_𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 is the measured concentration obtained from the
linear fit equation in Figure 4. Meanwhile, the sensor has resolution of 0.72 µg/L, which is calculated using
the following the (2) [25].

1135
𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 =
𝑛
𝑆
(2)
Where 𝑛 is the smallest scale that can be measured by detector and 𝑆 is the sensitivity of the sensor. In order
to determine the best wavelength range for ammonia detection, the sensitivity, accuracy and resolution of the
fiber optic sensor is calculated for every 10 nm wavelength from 400 nm to 900 nm. The data obtained is
presented in Figure 5.
Figure 3. Light intensity as function of wavelength for different ammonia concentration
Figure 4. Light intensity as function of ammonia concentration at wavelength of 510 nm
Figure 5(a) plots the sensor sensitivity as a function of wavelength. It can be seen that the sensitivity is
higher than 0.01 (mg/L)-1
at a wavelength range from 440 nm to 580 nm. At wavelength ranges from 400 nm to
430 nm and 590 nm to 900 nm, the sensor has sensitivity of less than 0.01 (mg/L)-1
. As for the accuracy as
illustrated in Figure 5(b), the accuracy of the system is higher than 99% when the wavelength is between 450 nm
and 900 nm. Whereas the sensor possesses less than 99% accuracy as the wavelength spans from 400 nm to
440 nm. On a different note, the sensor has resolution of less than 2 µg/L at a wavelength range from 430 nm
to 900 nm as shown in Figure 5(c). Resolution of higher than 2 µg/L is recorded when the wavelength spans
from 400 nm to 420 nm. All in all, based on the findings in Figure 5, the best wavelength range for the
optimized performances with respect to the sensitivity, accuracy and resolution is from 450 nm to 580 nm.
Within this wavelength range, the sensor produces high sensitivity, accuracy and resolution.

 ISSN: 1693-6930
1136
(a) (b)
(c)
Figure 5. Performance analysis for light source wavelength range (400 nm – 900 nm) in terms of
(a) sensitivity, (b) accuracy, and (c) resolution
4. CONCLUSION
In conclusion, optimization of light source wavelength for ammonia detection in the surface water is
experimentally demonstrated in this work. The ammonia content in the water is detected by unclad plastic
optical fiber with the presence of sodium chloride and nessler reagent. Based on experimental results, it is
found that the output light intensity has linear relationship with the ammonia concentration. Experimental
results suggest that the wavelength range that produces the optimized performances spans from 450 nm to
580 nm. Within this wavelength range, the proposed sensor achieves sensitivity of higher than 0.01 (mg/L)-1
,
accuracy of higher than 99% and resolution of less than 1 µg/L.
ACKNOWLEDGEMENTS
This work was supported in part by the Ministry of Higher Education Malaysia (MOHE) under
Fundamental Research Grant Scheme (FRGS) FRGS/1/2018/TK04/UTHM/02/13 Vot K095 and by the
Universiti Tun Hussein Onn Malaysia (UTHM) under Post-Graduate Research Grant (GPPS) Vot H620.
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BIOGRAPHIES OF AUTHORS
Nurfatihah Che Abd Rashid received her B.E and M.E in Electrical Engineering
from Universiti Teknologi Malaysia (UTM) in 2015 and 2019 respectively. She has involved
in research on spectrophotometric detection for uric acid and soil nutrient applications. She is
currently pursuing a PhD degree in Faculty of Electrical and Electronic Engineering,
Universiti Tun Hussein Onn Malaysia (UTHM). She can be contacted at email:
nurfatihahcar@gmail.com.
Noran Azizan Cholan was born on 31st August 1979 in Segamat, Johor,
Malaysia. He received his bachelor degree in Electronics Engineering from Universiti Tenaga
Nasional Malaysia in 2002. Afterwards in 2004, he obtained his master degree in Electronics-
Telecommunications Engineering form Universiti Teknologi Malaysia. In 2010, he enrolled as
a PhD student in Universiti Putra Malaysia. During his PhD study in 2012, he went to Swansea
University, UK and The Hong Kong Polytechnic University, Hong Kong for research
attachment. He completed his PhD in 2014 before serving as a senior lecturer in Universiti Tun
Hussein Onn Malaysia. As of now, he has been authors/co-authors for 25 journal and 16
conference proceeding papers. His research interests include lasers, amplifiers, optics
modeling, microwave optics and optical sensors. He can be contacted at email:
noran@uthm.edu.my.

 ISSN: 1693-6930
1138
Kim Gaik Tay is an Associate Professor of Applied Mathematics in the Faculty
of Electrical and Electronic Engineering at Universiti Tun Hussein Onn Malaysia. Her
research interests include Nonlinear Waves, Optical Solitons, Fiber Optics Parametric
Amplifier (FOPA), Numerical Methods, Forecasting, Breast Cancer Classification and Dorsal
Hand Vein Pattern Recognition using machine learning and deep learning techniques. She
completed her Bachelor’s, Master and Ph.D. degrees in Applied Mathematics at Universiti
Teknologi Malaysia. She is currently a member of the International Association of Engineers
(IAENG) and Persatuan Sains Matematik Malaysia (PERSAMA). She can be contacted at
email: tay@uthm.edu.my.
Afiqah Yaacob received her Bachelor degree from Universiti Teknologi Mara
(UiTM). Currently, she is pursuing her Masters degree in Faculty of Electrical and Electronic
Engineering, Universiti Tun Hussein Onn Malaysia (UTHM) in the field of spectrophotometer
application. She can be contacted at email: chandanputeri@gmail.com.
Nazrah Ilyana Sulaiman received her Bachelor Degree in Electrical and
Electronic Engineering from Universiti Teknologi Malaysia (UTM). Currently, she is pursuing
a part-time Masters degree in Faculty of Electrical and Electronic Engineering, Universiti Tun
Hussein Onn Malaysia (UTHM) in the field of Optical Sensor application. Presently working
at Malaysia Marine and Heavy Engineering (MMHE) as Mechanical Completion -
Instrumentation Engineer, specialised in Field engineering, construction, installation, pre
commissioning, Hook-Up & Commissioning and Start-Up of Topside platforms. She has
completed a various Greenfield and Brownfield projects including onshore and offshore
phases in Oil and Gas upstream industry with major clients namely PETRONAS ,
EXXONMOBIL, SHELL, TECHNIP, CHEVRON & AKER SOLUTIONS. She can be
contacted at email: nazrahi.sulaiman@mmhe.com.my.
Khairulanwar Mokhiri received his Diploma in Electronic Engineering
(Communication) from Politeknik Ibrahim Sultan (PIS) in 2014 and B.E in Electronic
Engineering from Universiti Tun Hussein Onn Malaysia (UTHM) in 2019. He has involved in
research on development of Ammonia spectrophotometer. Currently, he is working with Rapid
Rail Sdn Bhd as a Quality Assurance Engineer for MRT Kajang Line. He can be contacted at
email: khairulanwarmokhiri@gmail.com.
Nor Hafizah Ngajikin received her B.E and M.E in Electronic Engineering from
Universiti Teknologi Malaysia (UTM) in 2001 and 2003 respectively. She was awarded a
Ph.D from UTM for her work on MEMS Fabry-Perot optical tunable filter. From 2004 – 2017,
she served as a senior lecturer and researcher at Lightwave Communication Research Group
(LCRG), UTM. She is currently a lecturer at Universiti Tun Hussein Onn Malaysia. Her
research interest includes an optical devices and sensors for biomedical applications. She can
be contacted at email: norhafizah@uthm.edu.my.

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