Journal
of Ravishankar University–B, 34 (1), 80-86 (2021)
|
Assessment of Cymoxanil in Soil, Water,
and Vegetable Samples
Ajay
Kumar Sahua*, Manish Kumar Raia *, Joyce Raib,
Yaman Kumar Sahua, Deepak Kumar Sahua, Kalpana Wani, Jyoti
Goswamia and Chhaya Bhatta
aSchool of Studies in chemistry Pt. Ravishankar
Shukla University Raipur (Chhattisgarh), 492010, India.
bChhattisgarh Council of Science and Technology,
Vigyan Bhawan Vidhan Sabha Road Daldal Seoni, Raipur (Chhattisgarh) 492014,
India.
*Corresponding Author: mkjkchem@gmail.com, ajaykumar.as50@gmail.com
[Received: 20 March 2021; Revised: 25 June 2021; Accepted: 28 June
2021]
Abstract. The present work describes a newly developed method
for the spectrophotometric determination of cymoxanil in soil, water and
vegetable samples. The detection of the target chemical substance is based on
the reaction of cyanide released from the hydrolysed product of cymoxanil with
potassium iodide-potassium iodate to form a blue-coloured complex in the
presence of starch solution. This complex is water-soluble and shows maximum
absorbance at 580 nm. For this complex, Beer's law is obeyed over the
concentration range of 2-50 μg mL−1 with molar absorptivity 1.2×105
L mol-1cm-1 and Sandell’s sensitivity 1.0×10-3
µg cm-2. The reproducibility was assessed by carrying out seven days
replicate analysis of a solution containing 10 µgmL-1 of cymoxanil
in a final solution of a volume of 10 mL. The standard deviation and relative
standard deviation for the absorbance value were found to be ± 2.9×10-3
and 1.6% respectively. The proposed method is free from the interference of
other toxicants. The analytical parameters were optimized and the method was
applied to the determination of cymoxanil in water, soil, and vegetable
samples.
Keywords: Spectrophotometric,
Cymoxanil, Potassium iodide-potassium iodate and Blue-coloured
complex.
Introduction
Pesticides are used
worldwide for the control of insects, microorganisms, fungi, and other harmful
pests to protect agricultural products. According to a U.S. Environmental
Protection Agency (EPA) report, world pesticide expenditure at the producer
level was $55921 million in 2012. (Shin et al 2018). The increasing vegetable
intake could
significantly increase pesticide exposure and health risk in humans. The
current problems in food safety and phytosanitary barriers demand rigorous
control in correctly identifying and quantifying residues of pesticides present
in vegetables and fruits as well as the absence of banned pesticides for
certain crops (Zhao et al, 2014) India is produced about 109 million tons of
vegetables and it is the second-largest producer after China and account
for13.4% of world production. Surveys carried out by institutions spread during
the country indicate that 50-70% of vegetables are contaminated with pesticide
residues (Nirmal et al, 2017).
Cymoxanil-based
fungicides have been in use for over 25 years. Today, cymoxanil is registered
in over 50 countries and used on over 10 million hectares worldwide for 17
different crops. (Morrica et al, 2004) Cymoxanil,
1-(2-cyano-2-methoxyiminoacetyl)-3-ethyl urea, is a fungicidal
cyanooxime effective against plant diseases caused by fungi belonging to the
Perenosporales. In practice, it is mainly used against downy mildew of vine (Plasmopara
Viticola) and potato blight (Phytophthora infestans). Cymoxanil is
applied as a seed treatment to cut potato seed pieces or as a foliar
application to the plants to control late blight (Phytophthora infectans). As
well as in cucumber, tomatoes, sugar beets and grapes. So, cymoxanil is a frequently used fungicide
and it has been detected in drinking water. (Tellier
et al, 2008, Rao et al, 2020, Bavol et al, 2016). Long-term consumption of food containing pesticide
residues will inevitably cause great damage to the human body. Excessive intake
of cymoxanil by humans will have serious consequences such as the decline of
body immunity, the increase of burden on the liver, gastrointestinal diseases,
and even cancer. Therefore, there is a crucial need for suitable analytical
methods that could quickly detect cymoxanil residue in various foods. (Mi et
al, 2021). Because of the highly toxic and widely used cymoxanil, many
instrumental systems have been described for the detection or determination of
cymoxanil fungicides such as ultrahigh-performance liquid chromatography
coupled with electrospray ionization quadrupole Orbitrap high-resolution mass
spectrometry (UHPLC/ESI Q-Orbit rap) (Wang et al, 2016), High-performance
liquid chromatography (Liu et al, 2016, Balayiannis et al, 2014), Liquid
chromatography-tandem mass spectrometry (Holmes et al, 2015), quick, easy,
cheap, effective, rugged and safe method (QuEChERS) (Chen et al, 2020). High-performance
liquid chromatography equipped utilizing ultraviolet detector lamp (HPLC-UV) (Rao
et al. 2020). Some of these techniques suffer from poor sensitivity, analyses
are limited to laboratory facilities and expensive due to its analytical cost
and instability of colour or longer time required for colour development. To
overcome these drawbacks a rapid and sensitive method has been developed for
the determination of cymoxanil. UV-Visible spectrophotometry is considered the
most convenient analytical technique, because of its inherent simplicity, low
cost, and wide accessibility most in laboratories.
In
this study, we aimed to establish a simple, sensitive, effective, and accurate
method for the determination of cymoxanil. The method is based on the hydrolysis
of cymoxanil and bromination reaction followed by reaction with KI and KIO3
and starch. Herein, the determination of cymoxanil in various environmental and
vegetable samples using UV-Visible spectrophotometer. Firstly we have collected
samples and performed hydrolysis of cymoxanil using sodium hydroxide and
further its reaction with bromine water, KI and KIO3, and starch to obtain
a blue colour complex.
Material and Methods
Equipments
UV-Visible absorption
spectrum was performed on double beam spectrophotometer make Cary -60 UV-Visible
Spectrophotometer (Agilent technologies) with accuracy and quartz glass are used for all
spectral measurements with 10 mm matched silica gel. Digital pH meter model pH700 EUTECH was used for pH measurements. A REMI C-854/4 clinical centrifuge having a maximum
speed of 3600 rev min-1 and a maximum centrifugal force of 1850 g
with fixed swing-out rotors was used for centrifugation.
Reagents
All
reagents used were of Analytical Reagent grade and Double Distilled water was
used during the experiment.
Standard solution of cymoxanil- Cymoxanil (Isagro). A stock
solution of 1 ppm cymoxanil is prepared in double-distilled water. Working
standard solution was prepared by proper dilution of stock.
Sodium hydroxide- Sodium
hydroxide (Loba Chemie) aqueous solution of 5 M concentration was prepared.
Bromine Water – A Saturated solution of bromine in water was prepared. This
solution was prepared daily.
Formic Acid- 90% solution was prepared.
Potassium iodide-Potassium iodate mixture: prepared by
mixing 0.1 mol L-1 Potassium iodide and 0.2 mol L-1Potassium
iodate in a 5:1 ratio (Nirmal et al, 2014).
Starch solution- A 100 mg amount of soluble
starch was made into a paste with a few drops of hot water and diluted to 100
ml using nearly boiling water. (Patel et al, 2014).
Procedure for determination of cymoxanil in soil, water and vegetable
samples
The standard stock
solution was prepared in ethanol at the concentration of 100µg mL-1
of cymoxanil. Working standard solutions were prepared by suitable dilution of
stock solution in ethanol with different concentration level (2µgmL-1,
5µgmL-1, 10µgmL-1, 15µgmL-1, 20µgmL-1,
25µgmL-1, 30µgmL-1, 35µgmL-1, 40µgmL-1,
45µgmL-1,50µgmL-1) respectively to form calibration curve
solution. Recovery was assessed by analysing environmental samples spiked with
cymoxanil at a concentration of 40µg mL-1. The method was validated based
on previous work regarding the performance of spectrophotometric methods and
their explanation of results. The analysis included, develop and validate a
method, linear calibration curve, collection of original samples, and
preparation of synthetic samples, reproducibility, and recovery. An aliquot of
different concentration levels (2µg-50µgmL-1) of cymoxanil solution
was placed in a 25 mL calibrated volumetric flask, then 1 mL bromine water was
added and shaken gently for 2 minute. After that 0.5 mL of formic was added to
remove excess bromine water, and then 1 mL of a mixture of potassium iodide and
potassium iodate solution was added to liberate iodine. Then 1 drop of starch
solution was added. A blue colour dye was found and their absorption maxima were
found at λmax 580 nm. The proposed reaction scheme is shown in (Figure 1).
Sample Preparation
Sample preparation for determination of
cymoxanil
Samples were
collected from Meghnath farmhouse and Girwar farmhouse situated in village
Sukhari which is on the bank of Shivanth River in Rajnandgaon district,
Chhattisgarh where cymoxanil was sprayed. Collected samples were chopped into
fine pieces and Samples were spiked with a known amount of cymoxanil and kept
for 5-6 hours and dipped in ethanol solution for some time. After some time
these samples were crushed and shaken for 5-10 minutes and then filtered and
centrifuged for 10 minutes. After centrifugation transparent layer was
separated and then analysed as given the above-mentioned procedure. (Khatoon et
al, 2017).
Results and Discussions
Reaction Mechanism
Cymoxanil was hydrolysed with a basic
medium (OH-) and it was dissociated into 1-ethyl-5-methoxyimino-2,
4-dioxoimidazolidine, and cyanide were released (Teller et al, 2008). The
bromination of hydrogen cyanide was carried out forming cyanogen bromide (Sahu
et al, 2020). The cyanogen bromide was reacted with a mixture of potassium
iodide and potassium iodate in presence of formic acid releasing iodine. This
iodine further reacts with starch forming a blue coloured complex.
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|
| Spectral Characteristics
The absorption spectrum of
cymoxanil with starch is observed in the maximum absorbance wavelength peak
(λmax) at 580nm as shown in (Figure 2).
All spectral measurements carried out against reagent blank which is double
distilled water shows negligible absorption at this wavelength. In the
calibration curve, the colour system obeys Beer’s law in the range of 2 to
50µgmL-1 shown in (Figure 3)
of cymoxanil in 10mL of final solution at 580nm. The molar absorptivity and
Sandell’s sensitivity were found to be 1.25×105 L moL-1 Cm-1
and
1.0×10-3 µg cm-2 % respectively. All
parameters and statistical data are shown in (Table I) |
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Table I. Optical Characteristics
and statistical data of the reaction of cymoxanil with starch reagent
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Parameters
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Values
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Volume of dye
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1mL
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Λmax (nm)
|
580
|
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Beer’s law limit (µgmL-1)
|
2-50
|
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Molar absorptivity (L mol-1 cm-1)
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1.25×105
|
|
Limit of detection (µgmL-1)
|
0.084
|
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Limit of Quantification (µgmL-1)
|
0.250
|
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Sandell’s sensitivity (µg cm-2)
|
1.0×10-3
|
|
Standard deviation (µgmL-1)
|
2.9×10-3
|
|
Relative Standard deviation (%)
|
1.6
|
|
Correlation coefficient (R2)
|
0.972
|
|
Intercept
|
284.38
|
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Slope
|
0.01132x
|
|
Table
II. Tolerance limit of foreign species and ions
on the determination of cymoxanil
|
|
Species
|
Tolerance limit in µgL-1
|
|
Dicholorovos
|
350
|
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Thiochloprid
|
350
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Monocrotophos
|
400
|
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Cypermethrin
|
500
|
|
Acetamethrin
|
550
|
|
Bifenthrin
|
250
|
|
Fe
++
|
50
|
|
Zn
++
|
800
|
|
Ca++
|
150
|
|
SO42-
|
600
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Accuracy
It was checked by
the repeat analysis of a working standard solution containing a solution of
2µgmL-1 of cymoxanil in 10mL final solution over 7 days traces. The
standard deviation and relative standard deviation for the absorbance value
were found to be 2.9×10-3 and 1.6% respectively.
Interference studies of foreign
species and ions
Different types of foreign ions and species that
could be potentially associated with the sample matrix were studied in terms of
their effect on the determination of cymoxanil at a concentration of 5.0 µg mL-1.
The results showed that most of the foreign ions and species tested did not
interfere with their concentrations. The tolerance limit was taken as the
concentration causing an error of ±2% in the determination of the pesticide.
The tolerance limit for the foreign ions and species studied is shown in (Table II).
Application
The proposed method was
significant for the determination of the cymoxanil in soil, water vegetables,
and Fruits samples. To ensure the authenticity of the method, different
samples of soil, water, vegetables, and fruits were taken. In these samples
known amount of cymoxanil was added and examined by the proposed method. (Table
III).
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Table
III. Determination
of cymoxanil in different environmental and agricultural samples
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|
Sample
|
Cymoxanil in original found* in µg
|
Cymoxanil added in µg/mL
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Total Found
|
Difference (µg/mL)
|
Recovery (%±RSD)
|
|
Water**
|
2.4
|
2
|
4.4
|
1.9
|
95.20 ± 0.23
|
|
Cabbage***
|
1.80
|
2
|
3.77
|
0.90
|
96.50 ± 0.35
|
|
Paddy***
|
2.81
|
2
|
4.2
|
1.90
|
97.00 ± 0.20
|
|
Potato***
|
2.60
|
2
|
4.52
|
1.91
|
97.36 ± 0.13
|
|
Beans***
|
3.41
|
2
|
5.0
|
1.88
|
96.40 ± 0.22
|
|
Tomato***
|
0.96
|
2
|
2.96
|
1.94
|
96.70 ± 0.25
|
|
Brinjal***
|
1.74
|
2
|
3.68
|
1.90
|
96.60 ± 0.16
|
|
Soil***
|
3.6
|
2
|
5.52
|
1.92
|
97.10 ± 0.12
|
|
*Mean of three
replicate analyses.
**Water sample
50mL after treatment 50mL of aliquot was analysed.
***Sample 5g
(Taken from the agricultural field, 10mL aliquot was analysed after treatment
as described in the currently proposed method).
|
Stability Studies
Standard
stock solutions and working standard solutions were stored in the refrigerator
at 4°C and analysed daily for 7 days. No variation in the concentration of both
analytes was observed even on the 7th day, which indicates the
stability of both analytes.
Conclusion
Based on the literature
survey reported analytical methods are expensive and sophisticated. So we have
developed a low-cost and simple method for the detection of cymoxanil in
environmental and agricultural samples by spectrophotometry. We have studied
this method for analysis of cymoxanil in the UV-Visible range and found
absorbance maxima at 580nm. The achievement of the proposed method is mainly
its simplicity, sensitivity, and higher stability of the coloured system and
this gives more advantage of flexibility in performance on any reported instruments.
Therefore is proposed method is successfully applied for the determination of
cymoxanil in various environmental samples.
Acknowledgment
Authors are thankful to
the Head, School of Studies in Chemistry Pt. Ravishankar Shukla University
Raipur and Director-General Chhattisgarh Council of science and technology for
providing laboratory facilities and financial assistance.
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