Fabrication of modified carbon paste electrodes with

Journal of Electroanalytical Chemistry 809 (2018) 153–162

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Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem

Fabrication of modified carbon paste electrodes with Ni-doped Lewatit FO36 nano ion exchange resin for simultaneous determination of epinephrine, paracetamol and tryptophan

T

S. Bahmanzadeh, M. Noroozifar⁎ Analytical Research Laboratory, Department of Chemistry, University of Sistan and Baluchestan, Zahedan, P.O. Box 98135-674, Iran

A R T I C L E I N F O

A B S T R A C T

Keywords: Lewatit FO36 nano ion exchange resin Electrochemical sensor Epinephrine Paracetamol Tryptophan

A novel carbon paste electrode modified with Ni-doped Lewatit FO36 nano ion exchange resin (Ni-LFONRCPE) was fabricated and used as a sensitive electrochemical sensor for simultaneous determination of Epinephrine (EP), Paracetamol (PT) and Tryptophan (TRP). Cyclic voltammetry, electrochemical impedance spectroscopy, differential pulse voltammetry (DPV) and Chronoamperometry methods were employed to study the behavior of EP, AC and TRP on this modified electrode. DPVs peak currents of EP, PT and TRP increased linearly with their concentrations within the ranges of 7–560 μM, 5–580 μM and 4–560 μM with detection limits 0.45, 0.27 and 0.38 μM for EP, PT and TRP, respectively. The diffusion coefficient (D), electron transfer coefficient (α), and heterogeneous rate constant, for oxidation of EP, PT and TRP at the modified electrode surface were also determined. The Ni-LFONRCPE has been applied for the simultaneous determination of EP, PT and TRP in different real samples and the spiked recoveries were in the range of 96–100%.

1. Introduction Epinephrine (EP) is a hormone and a neurotransmitter in mammalian central nervous system which is released into the bloodstream while strong emotions such as fear or anger cause an increase in heart rate, blood pressure, and sugar metabolism. Epinephrine also finds use in medicine, where it is used to treat a number of conditions including: cardiac arrest, anaphylaxis, and superficial bleeding and has been used historically for bronchospasm and hypoglycemia [1,2]. Paracetamol (PT), also known as acetaminophen is one of the most commonly used medications in the world. It relieves pain, fever and is usually combined with other active ingredients in medicines for treatment of allergy, cough, colds, flu, sleeplessness and severe pain associated with arthritis and other chronic pain conditions [3–6]. Tryptophan (TRP) is one of the amino acids, which are the building blocks of protein. It is called an “essential” amino acid, though; the body cannot produce it and must be obtained from external sources (diet). Tryptophan can be found in many plant and animal proteins. It is needed for normal growth in infants and for nitrogen balance in adults. The body uses tryptophan to help make niacin and serotonin. Serotonin is thought to produce healthy sleep and a stable mood. L-tryptophan is used for insomnia, sleep apnea, depression, anxiety, facial pain, a severe form of premenstrual syndrome called premenstrual dysphonic disorder (PMDD),

⁎

[7–9]. These compounds are co-existing in real samples such as human urine and serum. So, the fast, simple and cheap determination methods for the simultaneous determination of EP, PT and TRP in biological fluids are great importance. There are many reports for the individual and simultaneous determination of EP, AC and TRP in literature using various analytical methods such as spectrophotometry [6,10–11] mass spectrometry [12–14], fluorometry [15,16], capillary zone electrophoresis [17,18], chromatography [19–23] and electrochemical sensors [24–28]. Among these methods, electroanalytical methods have attracted more attention because they are simple, sensitive, accurate and low cost tools for determination of bimolecular compounds. There are several reports in literature for individual or simultaneous determination of EP, PT and TRP. For example, Afkhami et al. was used graphene–CoFe2O4 nanocomposite modified carbon paste electrode for determination of AC in the presence of codeine [29], Ensafi et al. was used porous silicon/ palladium nanostructure for determination of AC in the presence of codeine [30], Ghica and Brett was used a carbon film electrode for determination of TRP [31], Ensafi et al. was used NiFe2O4 nanoparticles decorated with MWCNTs for determination of EP [32], Tavana et al. was used a novel ionic liquid modified carbon nanotubes paste electrode for simultaneous determination of EP and AC 33 [33], Keyvanfard et al. was used vinylferrocene-modified multiwall carbon nanotubes

Corresponding author. E-mail address: [email protected] (M. Noroozifar).

https://doi.org/10.1016/j.jelechem.2017.11.073 Received 19 June 2017; Received in revised form 27 November 2017; Accepted 28 November 2017 Available online 01 December 2017 1572-6657/ © 2017 Elsevier B.V. All rights reserved.


S. Bahmanzadeh, M. Noroozifar

purged with pure nitrogen gas (99.999%) before investigations. A series of electrolyte solutions including H3PO4 were prepared and pH adjusted using NaOH (0.1 M) in the range from 2.0 to 11.0. The electrolyte solutions were deoxygenated with nitrogen bubbling before each voltammetric experiment. Aqueous solutions were prepared with doubly distilled water (DDW), and all other chemicals used were of analytical reagent grade. All experiments were performed under nitrogen atmosphere at room temperature (RT). Urine and serum samples were obtained from the Omid Clinical Laboratory (Zahedan, Iran).

paste electrode for determination of TRP in the presence of cysteamine [34], Ensafi et al. was used a Modified Carbon Nanotubes Paste Electrode with N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide for simultaneous determination of ascorbic acid, AC, and TRP [35] and Nacetylcysteine and AC [36]. Carbon paste electrode (CPE), which is a mixture of carbon powder and a suitable liquid binder, has found widespread application due to being an easy to use substrate for a wide variety of chemical and biological modifications. CPE offer a lot of advantages such as fast response, low background current, simple polishing, uniform distribution of the catalyst into the paste, very low ohmic resistance and ease of fabrication and loading of organic and inorganic molecules as modifier [37–45]. Different modified CPE (MCPE) has been reported in the past years for the electrochemical analysis of biologically relevant molecules. Ion exchangers such as zeolites and resins can be adsorbed ionic compounds with positive or negative charges (cationic or anionic compounds) in their frameworks and the redox property of adsorbed ions can be studied by electrochemical methods. Wulcarius was explained application of a variety of zeolite modified electrodes with different electroactive compounds as modifiers when integrated in CPE for voltammetry determination of inorganic and organic compounds [46]. Among these reports, there are just a few reports for application of modified resins for voltammetry determination. For example, Agraz et al. was used a MCPE with amberlite IRC 718 chelating resin for voltammetric measurement of cadmium [47], Wen-Jian et al. was used a MCPE with a chelating resin DOULITE ES 467 for determination of copper [48], Yildiz et al. was used a resin MCPE for voltammetric determination of bisphenol A [49]. dos Santos et al. was used a graphitepolyurethane composite electrode nodified with a N,N′-ethylenebis (salicylideneiminato) copper(II) Schiff base for determination of dopamine [50], Dong et al. was used a MCPE with nanostructured resorcinol-formaldehyde resin for dye additive Sunset Yellow [51]. Lewatit®FO 36 nano ion exchange resin (LFONR) is a macroporous, monodispersed, polystyrene-based resin for the selective adsorption of oxoanions, such as arsenate or arsenite ions. It is a weakly basic ion exchange resin which is doped with a nano-scaled film of iron oxide covering the inner surfaces of the pores of the polymer bead. Oxoanions are bond by a specific, reversible reaction involving hydroxy-groups on the iron oxide surface. This resin is mostly used for removal of oxoanions such as arsenate or arsenite ions from water [52,53]. So, the LFONR can easily be exchanged with the ionic complexes (such as NiCl42 − in this study) that have been used as an electron transfer mediator for the electrooxidation proposes. In our best knowledge there is no any report for using a modified CPE with Ni-doped LFONR (Ni-LFONR) chelating resin. In this approach, we used the facility of absorbing of anions by LFONR to fabricate a new modified CPE with Ni-LFONR (Ni-LEONRCPE) for simultaneous and sensitive determination of EP, AC and TRP using differential pulse voltammetry (DPV). We also investigated the electrochemical performance of this modified electrode in phosphate electrolyte solution pH = 9, using different electrochemical techniques. The effects of some important parameters were optimized and the proposed modified electrode was used successfully for the simultaneous determination of EP, AC and TRP in real samples.

2.2. Instrumentation A computerized electrochemical SAMA500 analyzer (SAMA Research Center, Iran) was used for the electrochemical measurements. The electrochemical cell was set up with a common three-electrode system: saturated Ag/AgCl electrode as a reference electrode, a platinum electrode as an auxiliary electrode and different electrodes including carbon paste electrode (CPE) and modified CPEs as working electrodes. Electrochemical impedance measurements were performed in 10 mM [Fe (CN) 6]3 −/4 − prepared in 0.1 M KCl. EIS was performed over a frequency range of 0.1 Hz to 10 kHz with 0.02 V amplitude (rms). A Metrohm pH meter, model 744 was also used for pH measurements. Transmission electron microscopy (TEM) images were taken using a Philips CM120 transmission electron microscopy with 2.5 Å resolution. 2.3. Preparation of Ni –doped LFONR In a typical synthesis, the NiCl42 − solution of 0.1 M was prepared by dissolving the corresponding Nickel nitrate in saturated NaCl at RT. 1 g of LFONR resin was added to the resultant solution and mixed by shaking for 1 h at RT. Then, the Ni-LFONR was filtered and washed with distilled water and dried at RT. 2.4. Preparation of Ni-LFONR carbon paste electrode working electrodes A Ni-LFONR carbon paste electrode (Ni-LFONRCPE) was prepared by carefully hand mixing the 10 mg of Ni-LFONR and 190 mg graphite powder (5% m/m) and an appropriate amount of paraffin oil to obtain a uniform paste. This paste was packed into the end of the Teflon cylinder hole, and then polished on a smooth paper. Before each measurement, for the elimination of any memory effects, the electrode surface was easily and rapidly renewed, and a few potential cycles (vs. Ag/AgCl) within the range of −1 to 1.2 V were applied in the electrolyte solution to obtain a constant background current. The RSD% of this procedure was smaller than 5% which is acceptable. The electrode was kept in DDW at RT when not in use. The same method was used for preparation of Ni-LFONRCPE with different percent of 1, 3, 7, 10 and 20 of NiLFONRs. The same method was used for preparation of bare CPE (BCPE) and LFONRCPE. 2.5. Sample preparation Human urine and blood serum samples were obtained from the Clinical Laboratory, Zahedan, Iran. The samples were frozen at − 20 °C immediately after collection and were shipped. The urine and blood serum samples were diluted 5 times with PBS prior to measurement. For the analysis of EP and PT in tablets, five tablets were accurately weighed and ground to a fine powder. An amount of powder equivalent to the weight of one tablet was dissolved in DDW and then diluted with PBS to produce a solution of EP and PT with a concentration of 10 mM. DPV, in conjunction with standard addition technique, was used for the determination of the EP, PT and TRP contents of the sample. Measurements of the samples were carried out immediately after the preparation steps.

2. Experimental 2.1. Reagents and materials The Lewatit FO36 ion-exchange resin was purchased from Aldrich. The EP, PT and TRP were purchased from Sigma-Aldrich Company. Nickle Nitrate (Ni(NO3)2), sodium chloride (NaCl), graphite fine powder (G), paraffin oil were obtained from Merck Company and used as received. The stock solutions of EP, PT and TRP (0.001 M) were freshly prepared by dissolving each one in doubly distilled water 154



(B)

(A)

63 60

55

50

%T

45

40

(C)

35

30

25 23 4000 Name resin1 resin 2

3500

3000

2500

Description Sample 088 By Administrator Date Sunday, December 20 2015 Sample 089 By Administrator Date Sunday, December 20 2015

cm-1

2000

1500

1000

500 400

Fig. 1. (A) TEM images of Ni-LFONRCPE (B) LFONRCPE, (C) FT-IR spectra of LFONR (orange line) and Ni-LFONR (green line). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

3. Results and discussion

surface. Fig. 1C shows FT-IR of LFONRCPE and Ni-LFONRCPE. In the recorded spectra, the stretching vibrations at 3290 and 3170 cm− 1 are related to the presence of hydroxyl and amine groups in the LFONR. Other characteristic bands emerge at the wavelengths 1636 cm− 1 and 1478 cm− 1. These are connected with the presence of the NH deformation vibration of symmetric and asymmetric of COO– group. In addition, the band at 1031 cm− 1 and 1086 cm− 1 are referred to the stretching vibrations of CO group. These bands were also observed in the Ni bonded resin, because only a fraction of the functional groups on the polymer are involved in Ni bonded formation, however as can be seen in the Fig. 1C absorption of Ni to the matrix of resin causes a slight shift of various bands.

3.1. Morphological and FTIR characterization of the Ni-LFONRCPE The surface morphologies of LFONRCPE and Ni-LFONRCPE were investigated by TEM as shown in Fig. 1A, B. From our observations, it appears that Ni is uniformly dispersed in the porous structure of LFONR matrix. This structure contributes to an increase in the effective surface area of electrode and assists the Ni to immobilize, allowing the analytes to pass into the composite. As shown in the Fig. 1A, B, the diameter of pure LFONR has been changed from 50 in the pure resin to about 200 nm after Ni deposition; therefore, it can be concluded that the increase in diameter corresponds to the position of Ni onto LFONRCPE 155



50

100

A

B 50

I/ µA

I/µA

25

0

-25

-50 -1.5

c b

0

a

Fig. 2. (A) Cyclic voltammograms of (a) BCPE, (b) LFONRCPE and (c) Ni-LFONRCPE in the PBS electrolyte solution with pH 9, (B) cyclic voltammograms of (a) BCPE, (b) LFONRCPE and (c) Ni-LFONRCPE in 0.1 M KCl solution containing 1.0 mM [Fe(CN)6]3 −/4- and (C) Nyquist plots showing the step-wise modification of the BCPE (a), LFONRCPE (b) and (c) Ni-LFONRCPE. Electrochemical measurements were performed in 10 mM [Fe(CN)6]3 −/4 − prepared in 0.1 M KCl. EIS was analyzed over a frequency range of 0.1 Hz to 10 kHz (inset the typical Randles model used to fit the EIS results in the present work.

-50

-0.5

0.5

-100 -1.2

1.5

-0.2

0.8

E/v

E/V 0.60

Z (K )

0.40

0.20

0.00 0.00

C

0.20

0.40

0.60

0.80

1.00

Z' (K )

electrons involved in reaction (n = 2), surface area of the electrode (0.364 cm2) and surface electroactive species concentration (mol cm− 2), respectively. Also, F is Faraday's constant (96,485 C mol− 1), R is gas constant (8.314 J mol− 1 K− 1), T is the temperature (298 K) and ν is the scan rate (V s− 1). By using the mean slope of both anodic and cathodic currents versus scan rate, the Γ for this electrode is estimated to be about 2.7 × 10− 7 mol cm− 2. Faradaic electrochemical impedance spectroscopy was performed for the CPE, LFONRCPE and Ni-LFONRCPE electrodes in the presence of Ferro/Ferricynaide redox couple. Fig. 2C shows the Nyquist plots for these three electrodes and the Randles equivalent circuit was used as an equivalent circuit for fitting the EIS data using the NOVA software. The results were illustrated in Table 1. It consisted of solution resistance Rs (88 Ω in this work), charge transfer resistance Rct, double layer capacitance Cdl and Warburg impedance ZW (inset in Fig. 2C). Nyquist diagram showed in case of bare CPE depressed semicircle with charge transfer resistance 415 Ω. After modification with LFONR for LFONRCPE, the charge transfer resistance increased to 428 Ω. Significantly lower charge transfer resistance was obtained for NiLFONRCPE (345 Ω) in comparison with CPE and LFONRCPE. As expected, the charge transfer resistance decreased to a lower value in the presence of Ni for Ni-LFONRCPE electrode.

3.2. Electrochemical characterization of the electrodes The electrochemical behaviors of BCPE, LFONRCPE and NiLFONRCPE electrodes were investigated in electrolyte solution (pH 9.0) and in 1.0 mM K3Fe(CN)6 solution by using cyclic voltammetry method (CV). As shown in the Fig. 2A, B, there is an increase in the current for Ni-LFONRCPE, Ni improved the current for the modified electrode compared to BCPE and LFONRCPE. As was expected, deposition of Ni caused an increase in the electroactive area and an improvement of the conductivity of composite electrode [54]. According to the Randles–Sevcik equation [54]:

Ip = 2.69 × 105n3/2AD1/2C0 ν1/2

(1)

where Ip is the peak current (A), n is the number of electrons transferred (n = 1 for Fe(CN)63 −/4 − redox), A the effective area (cm2), D is the diffusion coefficient of 1.0 mM K3Fe(CN)6 and 0.1 M KCl (7.6 × 10− 6 cm·s− 1), v is the scan rate (V s− 1) and C corresponds to the bulk concentration of the probe (mol·cm− 3), the apparent electrode surface area of GPE, LFONRCPE and Ni-LFONRCPE are calculated as 0.093, 0.158 and 0.364 cm2, respectively. Therefore, the results indicated that the presence of Ni greatly improved the effective area of the electrode and contribute to an increase in the conductivity of the sensor. An approximate amount of the electroactive species can be calculated by Sharp et al. method for Ni-LFONRCPE [54]. From the linear part of the plot and the following equation, the electrode surface coverage (Γ) can be determined using following equation;

n2F 2AΓν IP = 4RT

Table 1 The equivalent circuit elements of CPE, LFONRCPE and Ni-LFONRCPE.

(2)

where Ip, n, A and Γ impart the peak current (A), the number of 156

Electrode

Rct/Ω

Cdl/(μF)

CPE LFONRCPE Ni-LFONRCPE

615 428 345

38 44 74



represented in Fig. 4C, shows that increasing the pH shifts the anodic potential towards negative values, where, red stands for analytes; Ox stands for the corresponding products; and m and n are the number of protons and electrons involved in the reaction. Following equations show the relationship between Ep and pH:

TRP 100 µA

PT EP

TRP: E p = −0.056pH + 1.1309

(3)

PT: E p = −0.057pH + 0.8075

(4)

EP: E p = −0.057pH + 0.5175

(5)

As anticipated, these equations advocate compromising of theore2.303mRT m tical slope of − nF of 0.059 n V and raising of pH. These results express the equality in the number of protons and electrons that are involved in the processes of EP, PT and TRP. Based on the results in Section 3.3 about roles of each material in Ni-LFONRCPE and pH effect in this section the following electrochemical mechanism can be proposed for the mediated oxidation processes of EP, PT and TRP on the surface of Ni(II)-LFONRCPE. The overall reaction scheme can be represented by an initial electrochemical step (Eq. (6)) followed by a chemical reaction step (Eq. (7)) as follow;

(

-1

-0.5

0

0.5

1

1.5

E/V Fig. 3. Cyclic voltammograms of 150 μM of EP, PT and TRP in 0.1 M phosphate electrolyte solution (pH 9.0) with scan rate of 50 mV s− 1 at (a) BCPE, (b) LFONRCPE and (c) Ni-LFONRCPE.

2(Ni(II)-LFONRCPE -2e

( )

)

2(Ni(III)-LFONRCPE

2(Ni(III)-LFONRCPE + EP(red)

(6) +

2(Ni(II)-LFONRCPE + EP (ox) + 2H

(7)

Based on these equations, the redox transition of Ni(II) complex species (NiCl42 − in this case) in Ni-LFONRCPE are first oxidized to Ni (III) complex species at the electrode surface and then the Ni(III) complex species in Ni-LFONRCPE, undergoes a catalytic reduction by the analytes in the solution (EP, PT and TRP in this case) and back to the Ni(II) complex species. The Ni(II) complex in Ni-LFONRCPE can be electrochemically re-oxidized to produce an enhancement of the oxidation current. This mechanism was called EC mechanism [54].

3.3. Electrochemical behavior of EP, PT and TRP at different electrodes Fig. 3 shows the CV of a mixture of 150 μM EP, PT and TRP at the surface of CPE, LFONRCPE and Ni-LFONRCPE a 0.1 M phosphate electrolyte solution with pH 9 at a scan rate of 50 mV s− 1. As can be seen, the oxidation peaks of EP, PT and TRP on the surface of CPE, LFONRCPE are not detectable, but adding of Ni to the composition of the LFONRCPE electrode boosts the splitting of oxidation peaks and caused a significant enhancement in the kinetics of anodic peak current of EP, PT and TRP at anodic peak potential at 0.126, 0.490 and 0.803 V, respectively. This result specified that the sensitivity of well distinct voltammetric signals in three anodic peak currents is related to their oxidation and remarkable enough to apply for accurate, sensitive and simultaneous determination of EP, PT and TRP in different samples. The effect of Ni-LFONR % (m/m) in modified CPE was studied for different percent of 1, 2, 3, 5, 7, 10 and 20%. The anodic currents for EP, PT and TRP were increased with increasing of Ni-LFONR from 1 until 3% and then were constant until 7%. The modified CPE with 10 and 20% of NiLFONR were not stable and the modified paste dropped out into PBS solution. A 5% of Ni-LFONR in CPE was selected as optimum percent.

3.5. The effect of scan rate on the electrochemical oxidation of EP, PT and TRP The cyclic voltammograms of Ni-LFONRCPE in the presence of EP, PT and TRP at various scans were recorded at optimum condition (Fig. 1SA).The anodic current upgrades by increasing of scan rate and a potential shift to positive value. These results demonstrate that at higher scan rates the progresses of the reaction between the Ni and EP, PT and TRP are opposed by kinetic limitation. Fig. 1SB represents the plot of anodic peak currents of Ni-LFONRCPE versus square root of scan rates. Plotting the peak current against ν1/2 the might lead to the conclusion that there is a linear relationship between these two parameters at the scan rates of 5 to 230 mV s− 1 for EP, PT and TRP which indicates the existence of a diffusion-controlled mechanism. The relationship of peak current versus the square root of scan rates (mV s− 1)1/2 can be represented by the following equations:

3.4. Influence of pH on the simultaneous oxidation of EP, PT and TRP The oxidation peaks of EP, PT and TRP in a combination of these analytes in different pH was explored (Fig. 4A, B, C). Results showed that pH solution has a powerful impact on the oxidation peaks. The anodic peak currents of EP, PT and TRP increased due to increasing pH till pH value of 9 and then decreased for pH values more than 9. Then, pH = 9 was opted as an ideal pH for simultaneous determination of EP, PT and TRP. Results show that increasing the pH, from 1 to 11, the anodic peak potentials decrease for the oxidation of EP, PT and TRP linearly Fig. 4. These outcomes suggest that protons are involved in the electrode processes and oxidation reactions of EP, PT and TRP. Also, result

TRP: Ip(ox) = 27.76 v1/2–21.00

R2 = 0.9887

PT: Ip(ox) = 25.98 v1/2–45.08

R2 = 0.9878

EP: Ip(ox) = 14.87 v1/2–16.53

R2 = 0.9880

(8) (9) (10)

implies the electroThe allegiance between currents and ν chemical activity of the Ni that is immobilized on the surface of the electrode. 1/2

157


S. Bahmanzadeh, M. Noroozifar 1 TRP: E = -0.0563pH + 1.1309 R² = 0.9998

0.8

150

(B) 0.6

(e)

E/V

I/ µA

100

(d) (c) (b) (a)

50

Fig. 4. (A) pH effect on peak currents of analytes at pHs (a) 3, (b) 5, (c) 7, (d) 9 & (e) 11, (B) influence of pH values on the current response of (a) EP, (b) PT, (c) TRP, at the Ni-LFONRCPE and (C) Variation of Ep versus the various electrolyte pH values: 3, 5, 7, 9 and 11 for (a) EP, (b) PT, (c) TRP.

PT:E = -0.0565pH + 0.8075 R² = 0.9954

0.4

0.2

0

0 EP:E = -0.0565pH+ 0.5175 R² = 0.9985

-50

-0.2

-1

-0.6

-0.2

0.2

0.6

1

2

4

6

8

10

12

pH

E /V 100

I/µA

80

(c)

60

(b)

40 (a)

20 0 2

4

6

8

10

12

pH 5SC). From the resulting slope and Cottrell equation the mean value of the Ds for EP, PT and TRP were found to be 4.0 × 10− 6, 2.7 × 10− 5and 8.1 × 10− 5 cm2 s− 1, respectively. There are some reports for Ds of EP, PT and TRP in literature. A comparison study was shown in Table 2. Based on this Table, the D for the EP, PT and TRP are the range of these analytes in literature [55–67]. Chronoamperometry can be used to evaluate the catalytic rate constants for the electrochemical reactions of EP, PT and TRP on the active sites of the NiLFONRCPE, Kh, according to the Galus equation [35]:

Ks was calculated by using following equation [55]:

ks = 1.11 ×

1 D2

(Ep − Ep/2

)−1/2

ν1/2

(11)

where, D, Ep, Ep/2, ν represent for diffusion coefficient, potential for maximum current peak, potential for half of the maximum current peak and scan rate for the EP, PT and TRP at a low scan rate. The Ks were calculated to be 1.6 × 10− 4, 1.6 × 10− 3, 2.4 × 10− 3 cm·s− 1. Tafel plots for EP, PT and TRP for the sharply rising part of the voltammogram at the scan rate of 5 mV s− 1 is shown in the Fig. 2S. Kinetic parameters α (cathodic charge transfer coefficient) and (1 − α) (anodic charge transfer coefficient) can be determine by using the slope of the plots. The slope of the linear part is identical to 2.3RT/αnαF and 2.3RT/((1 − α)nαF) for the cathodic and anodic peaks, while the evaluated values for the anodic charge transfer coefficients are 0.75, 0.96 and 0.96 for EP, PT and TRP, respectively.

IC 1 1 1 1 = γ 2 π 2 = π 2 (kh C0 t ) 2 IL

where IC and IL are the current in the presence and absence of analyte at Ni-LFONRCPE, and t is the time elapsed (s). The catalytic rate constant can be calculating from the slope of plot IC vs. t1/2 for given conIL centrations of EP, PT and TRP. The average values of Kh for EP, PT and 4 4 TRP were found to be 2.9 × 10 , 4.9 × 10 and 5.4 × 104 M− 1 s− 1, respectively.

3.6. Chronoamperometric measurements Figs. 3SA, 4SA and 5SA were shown the chronoamperometric measurements of EP, PT and TRP at Ni-LFONRCPE at different concentration by setting the potential of working electrode at 0.088, 0.752 and 0.937 respectively. For an electroactive material (EP, PT and TRP in this case) with a diffusion coefficient of D, the current observed for the electrochemical reaction at the mass transport limited condition is described by the Cottrell equation [54].

I = nFAD1/2Cb π−1/2t−1/2

(13)

3.7. Interference study The interference studies for the electrooxidation of EP, PT and TRP in a mixture were also investigated with intermolecular effect method by DPV. In this method, the concentration of one species was changed and the others were kept constant. The results for interference studies of the EP, PT and TRP were shown in Fig. 6S. In a certain range of concentrations, one analyte has no interference if it causes relative error lower or equal to ± 5 (%). Examination of Fig. 5SA shows that the peak current of EP increased with increasing EP concentration, whereas the concentrations of PT and TRP remained constant. Similar studies for PT and TRP was studied and the results for PT were shown in Fig. 5SB and C. Based on this figure, the Ip for PT increased with increasing

(12) -1/2

Under diffusion control, a plot of I vs. t is linear and the value of D can be obtained from the slope. Experimental plots of I vs. t− 1/2 were employed, with the best fits for different concentrations of EP, PT and TRP (Fig. 3SB, 4SB and 5SB). The slopes of the resulting straight lines were then plotted vs. EP, PT and TRP concentration (Figs. 3SC, 4SC and 158



more than 150. Also, the determination of EP, PT and TRP were studied in presence of various foreign species such as glucose, fructose, lactose, sucrose, maltose, ascorbic acid, dopamine, and Ca2 +, Mg2 +, NH4+, ClO4−, F−, Cl−, Br−. The tolerance limits was taken as the maximum concentration of the foreign compounds, which caused an approximately ±5% relative error in the determination of EP, PT and TRP. The results were shown in Table 1S.

Table 2 The comparison study for the diffusion coefficient of EP, PT and TRP using Ni-LFONRCPE with literature. Analyte

D/cm2 s− 1

Ref.

EP

2.37 × 10− 7 7.13 × 10− 5 7.70 × 10− 6 1.50 × 10− 6 3.50 × 10− 6 3.42 × 10− 6 4.00 × 10− 6 2.26 × 10− 5 6.60 × 10− 6 3.55 × 10− 6 3.61 × 10− 6 2.70 × 10− 5 1.00 × 10− 5 1.63 × 10− 4 5.10 × 10− 4 8.10 × 10− 5

[55] [56] [57] [58] [59] [60] This work [61] [62] [63] [64] This work [65] [66] [67] This work

PT

TRP

3.8. Calibration curve, limit of detection Fig. 5A represents the calibration graphs and curves (see Fig. 5B–D) for standard solution of EP, PT and TRP in phosphate electrolyte solution (pH 9) using DPV technique. The plot of peak current vs. concentration was linear in the range of 7–560 μM for EP according to the equation: ΔI = 0.066C + 0.508 with a correlation coefficient of 0.9954, 5–580 for PT according to the equation ΔI = 0.110C + 0.867 with a correlation coefficient of 0.9994 and 4–560 μM for TRP according to the equation ΔI = 0.078C + 0.424 with a correlation coefficient of 0.9970. Detection limits (LOD) of 0.45, 0.27 and 0.38 μM for EP, PT and TRP were estimated based on 3Sbk/m, where Sbk is the standard deviation of the blank signal (obtained based on 10 measurements on the blank solution) and m is the slope of the calibration curve. Also, the limit of quantification (LOQ) of the proposed method was calculated based on LOQ = 10Sbk/m. The calculated LOQ for EP, PT and TRP are 1.5, 0.9 and 1.3 μM, respectively. A comparison study of the Ni-LFONRCPE with others modified electrode in literature for the simultaneous determination of EP, PT and TRP was shown in Table 3. Based on Table 3, the Ni-LFONRCPE seems

concentration of PT while the concentrations of the other two compounds are constant. The TRP was shown the similar results too. It was found that EP, PT and TRP had no interference in simultaneous determination of one another in the linear ranges of EP, PT and TRP. The interference of dopamine (DA) and ascorbic acid (AA) on the simultaneous determination of EP, PT and TRP has been also investigated. The DPVs of EP, PT and TRP in different concentration of DA and AA were shown in Fig. 7S. Based on the results, the DA has serious interference on the signal EP with tolerance limit 1 (see Table 1S) but the interference of AA on the EP, PT and TRP was happened in tolerance limit

Fig. 5. (A) DPVs of the mixtures of EP, PT and TRP at the Ni-LFONRCPE electrode in 0.1 M phosphate electrolyte solution (pH 9.0). Concentrations within the ranges of 7–560 μM, 5–580 μM and 4–560 μM, Calibration curves of EP, PT and TRP in the linear ranges and (B), (C) and (D) are the plots of calibration curves for EP, PT and TRP, respectively.

50

60 40

D

C

B

40

40

30 20

20 10

10

0

0

0 200

400

0

600

200

400

600

0

200

400

600

80

PT

A

70

60

TRP 50

I/µA

0

EP

40

30

20

10

0 -0.2

0

0.2

0.4

0.6

0.8

E/V

159

1



Table 3 Comparison study of the Ni-LFONRCPE with others modified electrode in literature for the individual and simultaneous determination of EP, PT and TRP. Modifiers

Method

N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide N-(3,4-Dihydroxyphenethyl)-3,5-dinitrobenzamide modified-multiwall carbon nanotubes 8,9-Dihydroxy-7-methyl-12H-benzothiazolo[2,3-b] quinazolin-12-one Vinylferrocene-modified multiwall carbon Ionic liquid and CNTPE Multiwall carbon nanotubes NiFe2O4–MWCNTs Porous silicon/palladium nanostructure Graphene and CoFe2O4 Poly-Trypan Blue Modified GCE NiO–CuO 3,4-Dihydroxycinnamic acid Received in revised form 12 October 2012 (3,4DHCA) Graphene oxide (GO) and 2-(5-ethyl-2,4dihydroxyphenyl)-5,7-dimethyl-4H-pyrido [2,3-d][1,3]thiazine-4-one (EDDPT) AuNPs@Fe3O4 Ionic liquid-ZnO nanoparticle 8,9-Dihydroxy-7-methyl-12H-benzothiazolo [2,3-b] quinazolin-12-one Ni-LFORCPE

pH

EP

PT

TRP

Ref.

Linear range/ μM

Detection limit/μM

Linear range/ μM

Detection limit/μM

Linear range/ μM

Detection limit/μM

CV SWV

7.0 7.0

– –

– –

15.0–270.0 0.6–452

10.0 0.3

– 0.7–270.0

– 0.4

[36] [35]

SWV

7.0

–

–

3.0–600.0

0.9

10–700

5.0

[68]

SWV DPV DPV DPV DPV SWV CV SWV SWV

7.0 7.0 7.0 6.0 5.0 7.0 3.0 8.0 6.0

– 0.3–450.0 up to 100 0.9–800 – – – – –

– 0.09 0.9 0.09 – – – – –

– 1.0–600.0 – – 1.0–700.0 0.03–12 0.2–530.0 4–400 2–400

– 0.50 – – 0.4 0.025 0.1 1.33 0.1

5.0–1000.0 – – – – – 1.0–345.0 0.3–40 5–500

1.0 – – – – – 0.8 0.1 0.096

[34] [33] [31] [32] [30] [29] [69] [70] [64]

DPV

7.0

1.5–600.0

0.65

–

–

–

–

[57]

DPV CV SWV

5.5 7.0 7.0

– – –

– – –

0.1–70 0.1–550 5.0–500

0.045 0.07 1.0

– – 10–800

– – 4.0

[71] [72] [73]

DPV

9

7–560

0.45

5–580

0.27

4–560

0.38

This work

Table 4 Determination of EP, PT and TRP in human serum and urine samples using Ni-LFONRCPE (n = 3). Sample

Added (μM)

Serum

EP 10 50 80 100 10 50 80 100

Urine

Found (μM) PT 10 50 80 100 10 50 80 100

TRP 10 50 80 100 10 50 80 100

EP 10.0 49.3 80.0 98.5 10.0 50.5 80.2 99.5

Recovery (%) PT 10.1 51.0 79.4 100.0 10.0 51.0 78.8 100.4

TRP 9.8 49.2 80.4 98.5 10.1 49.5 80.1 100.2

A

EP 100.0 101.4 100.0 101.5 100.0 99.0 99.8 100.5

RSD (%) PT 99.0 98.0 100.8 100.0 100.0 98.0 101.5 99.6

TRP 102.0 101.6 99.5 101.5 99.0 101.0 99.9 99.8

EP 2.9 1.3 2.5 2.1 2.1 2.4 1.4 1.9

PT 1.5 2.4 1.8 2.0 1.9 1.6 2.5 1.8

TRP 1.7 1.6 1.7 1.7 2.2 1.8 1.8 1.7

B

110.00

PT 100.00

TRP I/ µA

25 µA

90.00

80.00

EP 70.00

-1

-0.5

0

0.5

60.00

1

1

E/V

2

3

4

5

6

7

8

9

10

Days

Fig. 6. (A) A typical CVs of the Ni-LFONRCPE sensor for simultaneous determination of EP, PT and TRP in different days and (B) plot of the oxidation peak currents of analytes for one sensor during different days.

160



to provide a favorable alternative for the simultaneous determination of EP, AC and TRP with better or satisfactory results than those described in the literature [29–36,57,64,68–73].

of epinephrine at a gold electrode, Electrochim. Acta 45 (2000) 2889–2895. [2] P. Kalimuthu, S. Abraham, Simultaneous determination of epinephrine, uric acid and xanthine in the presence of ascorbic acid using an ultrathin polymer film of 5amino-1,3,4-thiadiazole-2-thiol modified electrode, Anal. Chim. Acta 647 (2009) 97–103. [3] S. Samanta, R. Srivastava, Simultaneous determination of epinephrene and paracetamol at copper-cobalt oxide spinel decorated nanocrystalline zeolite modified electrodes, J. Colloid Interface Sci. 475 (2016) 126–135. [4] A. Kannan, R. Sevvel, Electrochemical nucleation and growth of Cu onto Au nanoparticles supported on a Si (111) wafer electrode, J. Electroanal. Chem. 791 (2017) 8–16. [5] M. Tefera, A. Geto, M. Tessema, Sh. Admassie, Simultaneous determination of caffeine and paracetamol by square wave voltammetry at poly(4-amino-3-hydroxynaphthalene sulfonic acid)-modified glassy carbon electrode, Food Chem. 210 (2016) 156–162. [6] S. Glavanovic, M. Glavanovic, V. Tomisic, Simultaneous quantitative determination of paracetamol and tramadol in tablet formulation using UV spectrophotometry and chemometric methods, Spectrochim. Acta A Mol. Biomol. Spectrosc. 157 (2016) 258–264. [7] H. Zeinali, H. Bagheri, Z.M. Khoshhesab, H. Khoshsafar, A. Hajian, Nanomolar simultaneous determination of tryptophan and melatonin by a new ionic liquid carbon paste electrode modified with SnO2-Co3O4@rGO nanocomposite materials, Mater. Sci. Eng. C 71 (2017) 386–394. [8] W. Setyaningsih, I.E. Saputro, C.A. Carrera, M. Palma, C.G. Barroso, Multiresponse optimization of a UPLC method for the simultaneous determination of tryptophan and 15 tryptophan-derived compounds using a box-Behnken design with a desirability function, Food Chem. 225 (2017) 1–9. [9] Y. Haldorai, S. Yeon, Y.S. Huh, Y.K. Han, Electrochemical determination of tryptophan using a glassy carbon electrode modified with flower-like structured nanocomposite consisting of reduced graphene oxide and SnO, Sensors Actuators B Chem. 239 (2017) 1221–1230. [10] J. Ren, M. Zhao, J. Wang, C. Cui, B. Yang, Spectrophotometric method for determination of tryptophan in protein hydrolysates, Food Technol. Biotechnol. 45 (4) (2007) 360–366. [11] M. Utrera, M. Estévez, Analysis of tryptophan oxidation by fluorescence spectroscopy: effect of metal-catalyzed oxidation and selected phenolic compounds, Food Chem. 135 (2012) 88–93. [12] B. Williamson, L. Benson, A. Tomlinson, A. Mayeno, G. Gleich, S. Naylor, On-line HPLC-tandem mass spectrometry analysis of contaminants of L-tryptophan associated with the onset of the eosinophilia-myalgia syndrome, Toxicol. Lett. 92 (1997) 139–148. [13] X. Qiua, D. Loub, D. Sua, Simultaneous determination of acetaminophen and dihydrocodeine in human plasma by UPLC–MS/MS: its pharmacokinetic application, J. Chromatogr. B 992 (2015) 91–95. [14] D. Tonoli, E. Varesio, G. Hopfgartner, Quantification of acetaminophen and two of its metabolites in human plasma by ultra-high performance liquid chromatography–low and high resolution tandem mass spectrometry, J. Chromatogr. B 904 (2012) 42–50. [15] M.K. Gaitonde, A fluorimetric method for the determination of tryptophan in animal tissues, Biochemist 139 (1974) 625–631. [16] J. Zhao, H. Chen, P. Ni, B. Xu, X. Luo, Simultaneous determination of urinary tryptophan, tryptophan-related metabolites and creatinine by high performance liquid chromatography with ultraviolet and fluorimetric detection, J. Chromatogr. B 879 (2011) 2720–2725. [17] B.J. de Kort, G.J. de Jong, G.W. Somsen, Native fluorescence detection of biomolecular and pharmaceutical compounds in capillary electrophoresis: detector designs, performance and applications: a review, Anal. Chim. Acta 766 (2013) 13–33. [18] N. Nuchtavorn, W. Suntornsuk, Recent applications of microchip electrophoresis to biomedical analysis, J. Pharm. Biomed. Anal. 113 (2015) 72–96. [19] M.F. Dario, T.B. Freire, C.A.S. de Oliveira Pinto, M.S.A. Prado, A.R. Baby, M.V.R. Velasco, Tryptophan and kynurenine determination in human hair by liquid chromatography, J. Chromatogr. B. 1065 (2017) 59–62. [20] J. Zhao, P. Gao, Optimization of Zn2 +-containing mobile phase for simultaneous determination of kynurenine, kynurenic acid and tryptophan in human plasma by high performance liquid chromatography, J. Chromatogr. B 878 (2010) 603–608. [21] C. Wong, C. Strachan-Mills, S. Burman, Facile method of quantification for oxidized tryptophan degradants of monoclonal antibody by mixed mode ultra performance liquid chromatography, J. Chromatogr. A 1270 (2012) 153–161. [22] V.P. Hanko, J.S. Rohrer, Direct determination of tryptophan using high-performance anion-exchange chromatography with integrated pulsed amperometric detection, Anal. Biochemist 308 (2002) 204–209. [23] R.R. Taylor, K.L. Hoffman, B. Schniedewind, C. Clavijo, Comparison of the quantification of acetaminophen in plasma, cerebrospinal fluid and dried blood spots using high-performance liquid chromatography–tandem mass spectrometry, J. Pharm. Biomed. Anal. 83 (2013) 1–9. [24] M. Noroozifar, M. Khorasani-Motlagh, R. Akbari, M. Bemanadi-Parizi, Simultaneous and sensitive determination of a quaternary mixture of AA, DA, UA and Trp using a modified GCE by iron ion-doped natrolite zeolite-multiwall carbon nanotube, Biosens. Bioelectron. 28 (2011) 56–63. [25] M. Noroozifar, M. Khorasani-Motlagh, A. Taheri, Preparation of silver hexacyanoferrate nanoparticles and its application for the simultaneous determination of ascorbic acid, dopamine and uric acid, Talanta 80 (2010) 1657–1664. [26] M. Tertis, A. Florea, R. Sandulescu, Carbon based electrodes modified with horseradish peroxidase immobilized in conducting polymers for acetaminophen analysis,

3.9. Reproducibility, repeatability and stability of the sensor The reproducibility of the sensor was evaluated by using CV technique. 5 different independent electrodes were prepared with the same composition and the peak current of sensor was recorded. A typical CVs of the Ni-LFONRCPE sensor for simultaneous determination of EP, PT and TRP in different days was shown in Fig. 6A. Based on this figure, the calculated relative standard deviations of 10 measurements for the sensor were calculated 2.8%. The long term stability of the sensor was investigated by recording CVs of the modified sensor in a period of 2 months. During this time, the sensor was used extensively (at least 4 h per day) and its response was recorded twice a week. The Ipa values EP, PT and TRP were retained at 93.2%, 93.2% and 89.7% respectively (see Fig. 6B). Also, the stability and repeatability of the Ni-LFONRCPE were investigated by DPV technique for 10 successive simultaneous determinations of EP, PT and TRP and the results were shown in Fig. 8S. Based on this figure, the relative standard deviations of the results were calculated as 1.6, 1.5 and 1.4 (%) for EP, PT and TRP, respectively. So, the electrooxidation current responses of EP, PT and TRP on the NiLFONRCPE have an excellent stability, repeatability and reproducibility. 3.10. Analytical applications For assessment of the analytical applicability and verifying the accuracy of the proposed sensor, it was used for the simultaneous determination of EP, AC and TRP in biological samples such as water, serum and urine. The results are summarized in Table 4, showing satisfactory agreement with the recovery in the range of 96.7–100.8%, showing that the proposed electrode could be efficiently applied to routine detection with good accuracy. So the proposed method is suitable for the routine detection in commercial pharmaceutical samples. Also, the Ni-LFONRCPE was used for simultaneous determination of EP, PT and TRP in the real samples such as Tablet, human urine and injection solution of these analytes and the accuracy of the proposed method were checked using HPLC methods [74–76]. The results were shown in Table 2S. Based on this Table, the Ni-LRORCPE is capable for determination of EP, PT and TRP in real samples with good selectivity and accuracy. 4. Conclusion In this work, a chelating resin, Ni-LFONR, was used for modification of CPE and then the proposed modified electrode, Ni-LFONRCPE was used for the simultaneous determination of EP, AC and TRP. Our results were shown that the Ni-LFONR not only improves the selectivity but also increased the electrochemical catalytic activities towards the oxidation of EP, AC and TRP in the individual and simultaneous determination. Under optimum conditions, the calibration curve were liner up to 590, 570 and 550 μM with a detection limits 0.3, 0.2 and 0.16 μM for EP, AC and TRP, respectively. The preparation method for modifier and modified electrode is very simple, cheap and the proposed modified electrode is very stable. Also, the proposed modified electrode can be applied to determination of trace amounts of EP, AC and TRP in human urine and serum samples with satisfactory results. Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jelechem.2017.11.073. References [1] S.H. Kim, J.W. Lee, I.H. Yeo, Spectroelectrochemical and electrochemical behavior

161



376–387. [53] S.K. Maji, Y.-H. Kao, C.-W. Liu, Arsenic removal from real arsenic-bearing groundwater by adsorption on iron-oxide-coated natural rock (IOCNR), Desalination 280 (2011) 72–79. [54] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Fundamentals and Applications, Wiley, New York, 2001. [55] M. Noroozifar, M. Khorasani-Motlagh, H. Tavakoli, Preparation of tetraheptylammonium iodide-iodine graphite-multiwall carbon nanotube paste electrode: electrocatalytic determination of ascorbic acid in pharmaceuticals and foods, Anal. Sci. 27 (2011) 929–935. [56] L.V. Silva, C.B. Lopes, W.C. Silva, Y.G. Paiva, Electropolymerization of ferulic acid on multi-walled carbon nanotubes modified glassy carbon electrode as a versatile platform for NADH, dopamine and epinephrine separate detection, Microchem. J. 133 (2017) 460–467. [57] A.C. Anithaa, K. Asokan, C. Sekar, Voltammetric determination of epinephrine and xanthine based on sodium dodecyl sulphate assisted tungsten trioxide nanoparticles, Electrochim. Acta 237 (2017) 44–53. [58] M. Dehghan Tezerjani, A. Benvidi, Epinephrine electrochemical sensor based on a carbon paste electrode modified with hydroquinone derivative and graphene oxide nano sheets: simultaneous determination of epinephrine, acetaminophen and dopamine, Measurement 101 (2017) 183–189. [59] T.D. Thanha, J. Balamurugana, Ng.T. Tuana, Enhanced electrocatalytic performance of an ultrafine AuPt nanoalloy framework embedded in graphene towards epinephrine sensing, J. Biosens. Bioelectron. 89 (2017) 750–757. [60] M. Zohreh, S.M. Ghoreishi, M. Behpour, Applied electrochemical biosensor based on covalently self assembled monolayer at gold surface for determination of epinephrine in the presence of Ascorbic acid, Arab. J. Chem. 10 (2017) S657–S664. [61] M. Mazloum-Ardakani, H. Beitollahi, M.K. Amini, Simultaneous determination of epinephrine and uric acid at a gold electrode modified by a 2-(2,3-dihydroxy phenyl)-1, 3-dithiane self-assembled monolayer, Sensors Actuators B Chem. 222 (2016) 270–279. [62] X.K. Yeyu, W.Q. Zhang, T. Zhang, Ex-situ decoration of ordered mesoporous carbon with palladium nanoparticles via polyoxometalates and for sensitive detection of acetaminophen in pharmaceutical products, J. Colloid Interface Sci. 505 (2017) 615–621. [63] W. Zhu, H. Huang, X. Gao, H. Ma, Electrochemical behavior and voltammetric determination of acetaminophen based on glassy carbon electrodes modified with poly(4-aminobenzoic acid)/electrochemically reduced graphene oxide composite films, Mater. Sci. Eng. C. 69 (2016) 1–11. [64] N. Soltani, N. Tavakkoli, N. Ahmadi, Simultaneous determination of acetaminophen, dopamine and ascorbic acid using a PbS nanoparticles Schiff basemodified carbon paste electrode, C. R. Chim. 18 (2015) 438–448. [65] M. Keyvanfard, R. Shakeri, Highly selective and sensitive voltammetric sensor based on modified multiwall carbon nanotube paste electrode for simultaneous determination of ascorbic acid acetaminophen and tryptophan, Mater. Sci. Eng. C. 33 (2013) 811–816. [66] S.M. Ghoreishi, M. Behpour, F.S. Ghoreishi, S. Mousavi, Voltammetric determination of tryptophan in the presence of uric acid and dopamine using carbon paste electrode modified with multi-walled carbon nanotubes, Arab. J. Chem. 10 (2017) S1546–S1552. [67] F. Yang, Q. Xie, H. Zhang, S. Yu, X. Zhang, Y. Shen, Simultaneous determination of ascorbic acid, uric acid, tryptophan and adenine using carbon-supported NiCoO2 nanoparticles, Sens. Actuators B. Chem. 210 (2015) 232–240. [68] B. Kaur, T. Pandiyan, Bi. Satpati, R. Srivastava, Simultaneous and sensitive determination of ascorbic acid, dopamine, uric acid, and tryptophan with silver nanoparticles-decorated reduced graphene oxide modified electrode, Colloids Surf. B Biointerfaces 111 (2013) 97–106. [69] M. Asnaashariisfahani, H. Karimi-Maleh, Novel 8,9-dihydroxy-7-methyl-12H-benzothiazolo[2,3-b]quinazolin-12-one multiwalled carbon nanotubes paste electrode for simultaneous determination of ascorbic acid, acetaminophen and tryptophan, Anal. Methods 4 (2012) 3275–3282. [70] M. Taei, M. Jamshidi, A voltammetric sensor for simultaneous determination of ascorbic acid noradrenaline, acetaminophen and tryptophan, Microchem J. 130 (2017) 108–115. [71] B. Liu, X. Ouyang, Electrochemical preparation of nickel and copper oxides-decorated graphene composite for simultaneous determination of dopamine acetaminophen and tryptophan, Talanta 146 (2016) 114–121. [72] E. Haghshenas, T. Madrakian, A novel electrochemical sensor based on magneto Au nanoparticles/carbon paste electrode for voltammetric determination of acetaminophen in real samples, Mater. Sci. Eng. C 57 (2015) 205–214. [73] J. Raoof, N. Teymoori, Synergistic signal amplification based on ionic liquid-ZnO nanoparticle carbon paste electrode for sensitive voltammetric determination of acetaminophen in the presence of NADH, J. Mol. Liq. 219 (2016) 15–20. [74] H. Karimi-Maleh, M. Moazampour, A sensitive nanocomposite-based electrochemical sensor for voltammetric simultaneous determination of isoproterenol acetaminophen and tryptophan, Measurement 51 (2014) 91–99. [75] H.X. Zhao, H. Mu, Y.H. Bai, H. Yu, Y.M. Hu, A rapid method for the determination of dopamine in porcine muscle by pre-column derivatization and HPLC with fluorescence detection, J. Pharm. Anal. 1 (2011) 208–212. [76] M.L. Altun, N. Erk, The rapid quantitative analysis of phenprobamate and acetaminophen by RP-LC and compensation technique, J. Pharm. Biomed. Anal. 25 (2001) 85–92.

Sensors 13 (2013) 4841–4854. [27] T. Thomas, R.J. Mascarenhas, O.J.D. Souza, Pristine multi-walled carbon nanotubes/SDS modified carbon paste electrode as an amperometric sensor for epinephrine, Talanta 125 (2014) 352–360. [28] H. Bagheri, A. Afkhami, Y. Panahi, Facile stripping voltammetric determination of haloperidol using a high performance magnetite/carbon nanotube paste electrode in pharmaceutical and biological samples, Mater. Sci. Eng. C 37 (2014) 264–270. [29] A. Afkhami, H. Khoshsafar, H. Bagheri, T. Madrakian, Facile simultaneous electrochemical determination of codeine and acetaminophen in pharmaceutical samples and biological fluids by graphene–CoFe2O4 nancomposite modified carbon paste electrode, Sensors Actuators B Chem. 203 (2014) 909–918. [30] A.A. Ensafi, N. Ahmadi, B. Rezaei, A new electrochemical sensor for the simultaneous determination of acetaminophen and codeine based on porous silicon/palladium nanostructure, Talanta 134 (2015) 745–753. [31] M.E. Ghica, C.M.A. Brett, Simple and efficient epinephrine sensor based on carbon nanotube modified carbon film electrodes, Anal. Lett. 46 (2013) 1379–1393. [32] A.A. Ensafi, F. Saeid, B. Rezaei, A.R. Allafchian, NiFe2O4 nanoparticles decorated with MWCNTs as a selective and sensitive electrochemical sensor for the determination of epinephrine using differential pulse voltammetry, Anal. Methods 6 (2014) 6885–6892. [33] T. Tavana, M.A. Khalilzadeh, H. Karimi-Maleh, Ali A. Ensafi, H. Beitollahi, D. Zareyee, Sensitive voltammetric determination of epinephrine in the presence of acetaminophen at a novel ionic liquid modified carbon nanotubes paste electrode, J. Mol. Liq. 168 (2012) 69–74. [34] M. Keyvanfard, A.A. Ensafi, H. Karimi-Maleh, A new strategy for simultaneous determination of cysteamine in the presence of high concentration of tryptophan using vinylferrocene-modified multiwall carbon nanotubes paste electrode, J. Solid State Electrochem. 16 (2012) 2949–2955. [35] A. Ensafi, H. Karimi-Maleh, S. Mallakpour, Simultaneous determination of ascorbic acid, acetaminophen, and tryptophan by square wave voltammetry using N(3,4dihydroxyphenethyl)-3,5-dinitrobenzamide-modified carbon nanotubes paste electrode, Electroanalysis 24 (2012) 666–675. [36] A.A. Ensafi, H. Karimi-Maleh, S. Mallakpour, M. Hatami, Simultaneous determination of N-acetylcysteine and acetaminophen by voltammetric method using N(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide modified multiwall carbon nanotubes paste electrode, Sensors Actuators B Chem. 155 (2011) 464–472. [37] H. Beitollahi, M.A. Taher, Fabrication of a nanostructure-based electrochemical sensor for simultaneous determination of epinephrine and tryptophan, Measurement 51 (2014) 156–163. [38] T. Alizadeh, Preparation of magnetic TNT-imprinted polymer nanoparticles and their accumulation onto magnetic carbon paste electrode for TNT determination, J. Biosens. Bioelectron. 61 (2014) 532–540. [39] B. Haghighi, M. Khosravi, A. Barati, Mater. Sci. Eng. C 40 (2014) 204–211. [40] J.G. Manjunathaa, M. Deraman, N.H. Basri, Sodium dodecyl sulfate modified carbon nanotubes paste electrode as a novel sensor for the simultaneous determination of dopamine, ascorbic acid, and uric acid, C. R. Chim. 17 (2014) 465–476. [41] W. Sun, Y. Wangb, S. Gongb, Application of poly(acridine orange) and graphene modified carbon/ionic liquid paste electrode for the sensitive electrochemical detection of rutin, Electrochim. Acta 109 (2013) 298–304. [42] S. Nouacer, S. Hazourli, C. Despas, M. Hebrant, Sorption of polluting metal ions on a palm tree frond sawdust studied by the means of modified carbon paste electrodes, Talanta 144 (2015) 318–323. [43] S. Mukdasai, U. Crowley, M. Pravda, X. He, Electrodeposition of palladium nanoparticles on porous graphitized carbon monolith modified carbon paste electrode for simultaneous enhanced determination of ascorbic acid and uric acid, Sensors Actuators B Chem. 218 (2015) 280–288. [44] A. Ourari, H. Nora, C. Noureddine, Elaboration of new electrodes with carbon paste containing polystyrene functionalized by pentadentate nickel(II)-Schiff base complex – application to the electrooxidation reaction of methanol and its aliphatic analogs, Electrochim. Acta 170 (2015) 311–320. [45] A. Soleymanpour, M. Ghasemian, Chemically modified carbon paste sensor for the potentiometric determination of carvedilol in pharmaceutical and biological media, Measurement 59 (2015) 14–20. [46] A. Wulcarius, Zeolite-modified electrodes: analytical applications and prospects, Electroanalysis 8 (1996) 971–986. [47] R. Agraz, M. Term Sevilla, J.M. Pinilla, L. Hernandez, Voltammetric determination of cadmium on a carbon paste electrode modified with a chelating resin, Electroanalysis 3 (1991) 393–397. [48] Q. Wen-Jian, L. Zhi-Hong, W. Meng, J. Tongji, The Chelating-resin Modified Electrode and Its Application in the Detection of Copper in Human Samples, 12 Medical University, 1992, pp. 80–84. [49] G. Yildiz, S. Ikikardesler, F. Bildik, F. Senkal, The voltammetric determination of bisphenol a content of polycarbonate utensils using a resin modified carbon paste electrode, Curr. Phys. Chem. 7 (2017) 47–56. [50] S.X. dos Santos, É.T.G. Cavalheiro, Using of a graphite-polyurethane composite electrode modified with a Schiff Base as a bio-inspired sensor in the dopamine determination, J. Braz. Chem. Soc. 25 (2014) 1071–1077. [51] D. Sun, C. Xu, J. Long, T. Ge, Determination of sunset yellow using a carbon paste electrode modified with a nanostructured resorcinol-formaldehyde resin, Microchim. Acta 182 (2015) 2601–2606. [52] D. Kołodynska, M. Kowalczyk, Z. Hubicki, V. Shvets, Vl. Golub, Effect of accompanying ions and ethylenediaminedisuccinic acid on heavy metals sorption using hybrid materials Lewatit FO 36 and Purolite Arsen Xnp, Chem. Eng. J. 276 (2015)

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