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Tkach & al./ Appl. J. Envir. Eng. Sci. 6 N°3(2020) 284-290
284
The theoretical description for the imidaclopride and thiaclopride
simultaneous determination, assisted by a squaraine dye –
vanadium(III) oxyhydroxide composite
Volodymyr V. Tkach1,2, Marta V. Kushnir1, Yana G. Ivanushko3, Andrii V.
Bocharov3, Sílvio C. De Oliveira2, Petro I. Yagodynets´1, Zholt O. Kormosh4,
Lucinda Vaz dos Reis5
1Chernivtsi National University, 58000, Kotsyubyns´ky Str. 2, Chernivtsi, Ukraine
2 Universidade Federal de Mato Grosso do Sul, Av. Sen. Felinto. Müller, 1555, C/P. 549, 79074-460, Campo
Grande, MS, Brazil
3Bukovinian State Medical University, 58000, Teatral´na Sq. 9, Chernivtsi, Ukraine
4East Ukrainian National University, 43000, Voli Ave., 13, Lutsk, Ukraine
5Universidade de Trás-os-Montes e Alto Douro, Quinta de Prados, 5001-801, Folhadela, Vila Real, Portugal
Corresponding author. E-mail : vovovlademir@mail.ru
Received 28 Jan 2020, Revised 09 Sep 2020, Accepted 16 Sep 2020
Abstract
The simultaneous electrochemical determination of two insecticides thiaclopride and imidaclopride by
an electrode, modified by a squaraine dye – VO(OH) hybrid composite, has been evaluated from the
mathematical point of view. The correspondent model has been developed and analyzed by means of
linear stability theory and bifurcation analysis. It was shown that the squaraine dye – VO(OH)
composite may be an efficient electrode modifier for thiaclopride and imidaclopride determination,
despite of the hybridity of the reduction mechanism in the last case. On the other hand, the oscillatory
behavior for this system will be caused only by DEL influences of the electrochemical stage.
Keywords: thiaclopride, imidaclopride, hybrid composites, electrochemical sensors, stable steady-
state
Introduction
Thiaclopride and imidaclopride (Fig. 1) [1 – 4] are insecticides of neonicotinoid class – the most
widely used since 1990. Both of the formulations have been introduced and used by Bayer®
corporation. They are used in rice, cotton, potato plantations. Also they are widely used in gardens, in
order to control the soil insects.
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N
NO2
N
Cl N
N
H
N
N
Cl N
S
N
Fig. 1. Thiaclopride and imidaclopride
Nevertheless, both of them are highly toxic not only to parasite insects, but also to culture insects like
honey bees. Also it is toxic to birds, reason why both of these substances were banned in France in
2018 [5]. In 2019, the European Union has decided to ban their use elsewhere within the European
territory [6]. Also, in 2018, Turkey has restricted their application, having banned it in some types of
crops [7]. Nevertheless, in other countries it is still widely used [8 – 10]. Thus, the development of an
efficient method for its quantification is really actual [11 – 18], and the electrochemical methods
would give it an interesting service [15 -18].
As both thiaclopride and imidaclopride contain the accepting groups, in order to detect both pesticides
electrochemically, it is preferable to use a cathodic electrochemical reduction. Anodic oxidation is also
possible, but with relatively strong oxidants.
For the cathodic reduction, a vanadium (III) oxyhydroxide [19 – 21], alone or in the composite with a
conducting polymer, squaraine dye, conjugated heterocyclic derivative or carbon material, may be
used. In this composite, the inorganic nanoparticles will implement the role of the active substance,
interacting with two pesticides, and the organic conjugated system will act as a stabilizer of the
inorganic phase and as an electronic transfer mediator.
Nevertheless, the use of novel electrode modifiers with novel analytes may be
impeded by:
- the indecision concerning the exact mechanism of electrochemical reaction;
- necessity of determination of the parameter region, correspondent to the most efficient active
substance and mediating action;
- the presence of electrochemical instabilities, accompanying the electrochemical oxidation of
organic molecules (including electrochemical polymerization of heterocyclic compounds)
[22 - 25].
The mentioned problems may only be solved by means of an analysis of a mathematical model,
capable to describe adequately the neotame electrochemical determination Moreover, it is also capable
compare the behavior of this system with that for the similar ones without any experimental essay.
So, the goal of this work is the mechanistic theoretic analysis of the thiaclopride and imidaclopride
simultaneous electrochemical determination, assisted by VO(OH) – Squaraine dye composite. In order
to achieve it, we realize the specific goals:
- suggestion of the mechanism of the reaction consequence, leading to the appearance of
analytical signal;
- development of the balance equation mathematical model, correspondent to the
electroanalytical system;
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- analysis and interpretation of the model in terms of the electroanalytical use of the system;
- the seek for the possibility of electrochemical instabilities and for the factor, causing them;
- the comparison of the mentioned system´s behavior with the similar ones [26 – 28].
System And Its Modeling
The mechanism for VO(OH)-assisted thiaclopride and imidaclopride electrochemical determination
will be similar. Nevertheless, if thiaclopride reduction is realized by a non-hybridic mechanism, for
imidaclopride two scenarios are possible. Either way, the resultant vanadium (IV) oxide is
cathodically reduced, regenerating VO(OH).
Therefore, the electroanalytical process will be schematically exposed as on the Fig. 2:
N
NO2
N
Cl N
N
H
N
NH2
N
Cl N
N
H
NH
NH2
CH3
N
Cl N
HNH2
N
N
Cl N
S
CN
NH2
C
H2
NH2
N
Cl N
S
VO(OH)
VO2
+
Fig. 2. Scheme of the electroanalytical process
Thus, the electrochemical behavior of this system may be described by a trivariant equation set,
composed by the variables:
n – imidaclopride concentration in the pre-surface layer;
s – thiaclopride concentration in the pre-surface layer;
v – tetravalent vanadium surface coverage degree.
To simplify the modeling, we suppose that the reactor is intensively stirred, so we can neglect the
convection flow. Also we assume that the background electrolyte is in excess, so we can neglect the
migration flow. The diffusion layer is supposed to be of a constant thickness, equal to δ, and the
concentration profile in it is supposed to be linear.
It is possible to show that the electroanalytical process will be described by the three-dimensional
equation set, exposed as
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287
(1)
in which N and S are diffusion coefficients for imidaclopride and thiaclopride, n0 and s0 are their bulk
concentrations, V is the maximal surface concentration of vanadium dioxide and r are correspondent
reaction rates, which may be calculated as (2 – 5): (2)
(3)
(4)
(5)
n which the parameters k are the correspondent rate constants, F is the Faraday number, R is the
universal gas constant and T is the absolute temperature. Herein, the elementary electrochemical act
involves one electron transfer, regenerating the trivalent vanadium.
Comparing to the similar systems involving ionic compounds and VO(OH) [26 – 28], in this system
(5<pH≤7), this system will be more stable. The oscillatory and monotonic instabilities will be less
capable to realize, as the pyridinic nitrogen of both thiaclopride and imidaclopride in fact won’t be
involved in DEL formation and rearrangement, as shown below.
Results And Discussion
In order to describe the behavior of the system with thiaclopride and imidaclopride electrochemical
determination, assisted by a composite VO(OH) – Squaraine Dye, we analyze the equation set (1) by
means of linear stability theory and bifurcation analysis. The steady-state Jacobian matrix members
will be exposed as:
(6)
in which:
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
(15)
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Contrarily to the similar systems [26 – 28], the oscillatory behavior in this system, despite of
remaining possible, is of less probability. It is explained by the absence of DEL influences of chemical
stages, present in the similar systems. Thus, the unique main-diagonal element, which may be possible
(and, consequently, responsible to the positive callback, causing the Hopf bifurcation), is
if j<0, describing the cyclic DEL capacitance changes during the
electrochemical stage. This factor is common for the great majority of the electroanalytical systems
and is realized in sufficient manner to cause significant oscillations far beyond the detection limit. The
oscillations are expected to be frequent and of small amplitude.
Yet if the mentioned element is negative, the steady-state stability is warranted. Really, applying the
Routh-Hurwitz criterion to the Jacobian matrix and introducing new variables, having it rewritten as
(16):
(16)
and opening the brackets and applying the condition Det J<0, salient from the criterion, we obtain the
steady-state stability requirement (17):
++ (17)
which is readily satisfied in the case of the negativity of j. It defines the vast parameter region of the
steady-state stability. From the electroanalytical point of view, it is correspondent to the linear
dependence between the electrochemical parameter and the pesticides’ concentrations, describing an
efficient diffusion-controlled electroanalytical process, even more stable than in similar systems [26 –
28].
The monotonic instability, correspondent to the detection limit, from the electroanalytical point of
view, is also probable, if the destabilizing and stabilizing influences are equal. Its conditions will be
described as: ++ (18)
This system describes the case, in which the pH, chosen for the pesticide determination is mildly
acidic up to neutral. If the pH is a bit lower, or if an alkyl halide is present to quaternize the pyridinic
nitrogen atom, this model won’t be adequately correspondent to that case. The chemical stage
reactions will be calculated as: (19)
(20)
(21)
and the model will become more or less similar to that described in [26 – 28].
Conclusions
From the system with the electrochemical determination of thiaclopride and imidaclopride on a
VO(OH) – squaraine dye composite it was possible to conclude that:
- contrarily to the similar systems involving vanadium (III) oxyhydroxide, squaraine dye and
basic nitrogen compounds, this system will be more readily stable and electroanalytically
efficient;
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- the linear dependence between the electrochemical parameter and concentration of the
pesticides is realized in a broad topological parameter region. The electroanalytical process
is diffusion-controlled;
- the oscillatory behavior in this system is less probable than in the similar systems, being
caused uniquely and exclusively by the DEL influences of the electrochemical stage.
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