Iron oxide (Fe2O3) nanoparticles modified carbon paste electrode as an advanced material for electrochemical investigation of paracetamol and dopamine

The electrochemical behavior of paracetamol (PA) and dopamine (DA) has been investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) using a selective and sensitive iron oxide (Fe2O3) nanoparticle modified carbon paste electrode (IOCPE).

Original Article

advanced material for electrochemical investigation of paracetamol

and dopamine

Department of Chemistry, School of Chemical Science, Kuvempu University, Shankaraghatta, 577451, Karnataka, India

a r t i c l e i n f o

Article history:

Received 10 April 2019

Received in revised form

22 July 2019

Accepted 28 July 2019

Available online 12 August 2019

Keywords:

Carbon paste electrode

Differential pulse voltammetry

Electrochemical impedance spectroscopy

Iron oxide nanoparticles

a b s t r a c t

The electrochemical behavior of paracetamol (PA) and dopamine (DA) has been investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) using a selective and sensitive iron oxide (Fe2O3) nanoparticle modified carbon paste electrode (IOCPE) The PA and DA showed an anodic peak potential at 0.458 V and 0.247 V and a cathodic peak potential at 0.088 V and 0.11 V (vs Ag/AgCl), respectively In the DPV mode, PA and DA gave linear responses over the con-centration range of 2e150mM (R2¼ 0.998) and 2e170 mM (R2 ¼ 0.989), respectively The limit of detection (LOD¼ 3 s/m) for PA and DA were found to be 1.16 and 0.79mM, respectively IOCPE possesses

an excellent electrocatalytic activity towards the determination of PA and DA The proposed method could be successfully validated for the simultaneous and individual determination of PA and DA present

in pharmaceutical and real samples

© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

1 Introduction

Paracetamol (PA) (N-acetyl-p-aminophenol or acetaminophen)

is one of the most widely used analgesic and antipyretic drugs[1]

PA releases the pain associated with headache, backache, arthritis

and postoperative effect, and it is commonly used for reducing

fever[2] PA having a pKavalue of 9.5, rapidly gets distributed after

oral administration and is easily excreted in urine PA does not

exhibit any harmful side effects, but in few cases, it leads to the

formation of liver damage and nephrotoxic metabolites [3] An

overdose of PA leads to hepatic toxicity, liver and kidney damage

and in some cases causes death[4] Dopamine (DA), another most

leading catecholamine-based neurotransmitter drug, is monitoring

the central nervous system (CNS) by arbitrating the multiple CNS

functions such as memory, learning, neuroendocrine secretion,

cognition and control of locomotion The difference in the

con-centration of the DA level may lead to severe causes such as

Par-kinson's disease, depression, schizophrenia and Huntington's

disease, HIV infection, epilepsy and senile dementia[5] So, it is

necessary to determine the drugs present in pharmaceutical

samples and human biologicalfluids (urine and blood) Therefore, the development of simple, rapid, sensitive, and precise analytical procedures for the detection and quantification of these drugs is of great importance[6]

Numerous methods are available for the determination of PA and DA such us spectrophotometry[7], TLC[8], HPLC[9,10], LC-MS

[11],flow-injection analysis[12], UV-Vis spectrometry [13], elec-trochemical methods [14], fluorimetry methods [15] and chem-iluminescence methods[16] The electrochemical techniques have received a remarkable consideration due to their unique qualities such as a simple pretreatment procedure, good sensitivity, better selectivity, less time-consumption and low cost [17] In recent years, the modification of the electrode surface fascinated signifi-cant attention because of its extremely enhanced sensitivities A literature survey reveals that PA and DA undergo electrochemical reactions at different electrodes, such as graphite electrodes (GE)

[18], polyurethane modified GE[19], glassy carbon electrodes (GCE)

[20], modified GCE [21], screen-printed electrodes [22], carbon paste electrodes (CPE) [23], modified CPE [24], carbon fiber mi-croelectrodes[25], carbon ionic liquid electrodes [26], platinum electrodes [27], gold electrodes [28] and boron doped diamond electrode (BDDE)[29]

Currently, metal nanoparticles, nanodiamonds, fullerenes, carbon nanotubes, etc., are being used in biomedical and sensor applications, since nanomaterials possess fundamental features

* Corresponding author Fax: þ9108282 256255.

E-mail address: drarthoba@yahoo.co.in (Y Arthoba Nayaka).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

https://doi.org/10.1016/j.jsamd.2019.07.006

2468-2179/© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license

Journal of Science: Advanced Materials and Devices 4 (2019) 442e450

nanoparticles have a wide applicability in many industrial

pro-cesses including extended new electronic and optical devices,

information storage, magnetocaloric refrigeration, color imaging,

bioprocessing, ferrofluid technology or the manufacture of

mag-netic recording media[40]

The present work reports on the determination of PA and DA

simultaneously, using electrochemical techniques such as CV, DPV,

SWV and EIS The analytical applications of IOCPE have been tested

via the redox reaction of PA and DA present in biological (urine and

serum) and pharmaceutical samples The proposed modified

elec-trode IOCPE has got a low limit of detection, good sensitivity, better

selectivity and so it could be used for the estimation of PA and DA

present in pharmaceutical and real samples

2 Experimental

2.1 Apparatus

All the voltammetric experiments were carried out using the

Electrochemical Workstation (Model number: CH Instrument

660D, USA) The electrochemical experiments were performed

using a conventional three-electrode system The IOCPE, platinum

wire and silver/silver chloride were used as working, auxiliary and

reference electrode, respectively The Equiptronics EQ-611 pH

me-ter was used for the pH measurements All the electrochemical

studies were carried under lab temperature

2.2 Chemicals and reagents

The standard drugs Paracetamol (Acetaminophen) (99%) and

Dopamine hydrochloride (99%) have been procured from Sigma

Aldrich (USA and Germany, respectively), di-Potassium hydrogen

phosphate anhydrous (98%), Potassium hydrogen phosphate

(98%) and Potassium chloride purified (99%) were procured

from Merck (Mumbai, India) Silicon oil and Potassium ferricyanide

(III) (99%, A.R.) were obtained from Himedia (Mumbai, India)

Paracetamol tablets and Dopamine injection tubes have been

pur-chased from the local market (Shivamogga, India) PBS of 0.1 M was

prepared (lab temperature at 26± 2C) and the pH was adjusted

using NaOH and H3PO4 All the solutions were prepared using

doubly distilled water

2.3 Procedure

2.3.1 Preparation of iron oxide nanoparticles (ION's)

Iron oxide nanoparticles have been synthesized by a simple

precipitation method under laboratory condition using FeCl3.6H2O

and liquid ammonia The stoichiometric ratio of FeCl.6HO powder

through the center of the paste packed glass tube without any crack The exposed end of the electrode was mechanically polished and renewed using butter sheet to get a reproducible smooth and shiny working surface This operation has been repeated before start of each experiment The BCPE has been prepared in the same way without the addition of a modifier

3 Result and discussion 3.1 Characterization of the prepared ION's and IOCPE The prepared ION's sample has been characterized by a powder X-ray diffractometer (Cu-Ka, radiation atl¼ 1.5406 Å) to confirm the physical properties like structure, crystallinity, lattice planes etc.Fig 1(a) depicts the reflection planes (220), (311), (400), (422), (511), (440) corresponding to the 2qangles values of 30.26, 35.65, 43.32, 53.77, 57.32 and 62.98, respectively These values were well matches with standard JCPDS file no.: 39e1346 (volume-582.5, lattice-primitive, system-cubic, space group-P4132, cell parameter

a¼ 8.351) The sharp peak with the small FWHM (full width at half maximum) showed that the sample has got a good crystal-linity The DebyeeScherrer formula has been used for the calcu-lation of the crystallite size and was found to be 27 nm.Fig 1(b) represents the SEM image of synthesized iron oxide nanoparticles, which shows that the prepared nanoparticles were agglomerated The EDAX analysis has shown energy peaks of iron oxide nano-particles in the range 0.5e6.5 keV corresponding to iron and ox-ygen atoms of the prepared iron oxide nanoparticles (figure not shown) and has revealed that iron oxide has got a crystalline nature [43] Fig 1(c) represents the SEM (analysis of surface morphology) image of the prepared IOCPE

d¼0:963l

3.2 Electrochemical behavior of [Fe(CN)6]3/4couple The electrochemical behavior of IOCPE has been monitored through the redox process of [Fe(CN)6]3/4couple.Fig 2shows the cyclic voltammograms obtained a) in the absence of analyte at IOCPE; b) at BCPE and c) at IOCPE in 1 mM K3[Fe(CN)6] containing 0.1 M KCl solution In the forward scan (positive scan) Fe[(CN)6] 3-was electrochemically oxidized from Fe[(CN)6]4-(anodic process) and in the reverse scan (negative scan) this Fe[(CN)6]3-has been reduced back to Fe[(CN)6]4-(cathodic process) The obtained vol-tammogram of [Fe(CN)6]3/4couple shows a peak to peak sepa-ration potential (DE) of 309 mV and 136 mV, at BCPE and IOCPE,

respectively The value of DEp has been decreased at IOCPE

compared to BCPE and it clearly indicated the more-reversible

charge-transfer process at IOCPE than that of BCPE Also the peak

currents for [Fe(CN)6]3/4couple have been enhanced at IOCPE

compared to BCPE The decrease inDEpvalue with the increase in

peak current suggested that the IOCPE has got an increased surface

area compared to BCPE This may be due to the presence of iron

oxide nanoparticles that enhance the electron transfer rate The

surface area of BCPE and IOCPE have been calculated by the

Randles-Sevcik equation using 1 mM K3[Fe(CN)6] in 0.1 M KCl

so-lution at different scan rate[44]

Ip¼2:69  105

whereIpandnrefer to the peak current (mA) and scan rate (V s1),A

is the active surface area of electrode (cm2),DoandC0* represent the diffusion co-efficient (cm2 s1) and bulk concentration of

K3[Fe(CN)6] (mol cm3), respectively The diffusion co-efficient for

1 mM K3[Fe(CN)6] in 0.1 M KCl can be obtained by plotting Ipavs.n1/

2(n¼ 1, Do¼ 7.6  106cm2s1)[9] On substituting the above values, the effective surface areas of BCPE and IOCPE were found to

be 0.116 cm2and 0.1786 cm2, respectively

3.3 Effect of modifier (ION's) concentration The effect of the modifier concentration was studied by cyclic voltammetry using the 1 mM PA in PBS (pH 7.0) and plotting the graph of current vs potential (Fig 3 - supplementary) The 4-wt% of ION's in carbon paste electrode demonstrates a good redox behavior of PA compared to other compositions The resistive electrochemical signal was observed for more than 4-wt% of the modifier This may be an indication that the saturation point of iron oxide nanoparticles has been attained and, hence, this electrode composition has been selected for further electrochemical studies 3.4 Electrochemical characterization of IOCPE

Electrochemical impedance spectroscopy (EIS) is an efficient method to analyze the interfacial properties of surface modified electrodes and it provides valuable information regarding the impedance change at the electrode surface EIS uses the frequency sweep of very minute AC voltage modulated over DC bias to extract the equivalent circuit The circuit has been obtained by plotting the

Fig 1 Characterization of the prepared ION's: (a) X-ray diffraction spectrum; (b) SEM image of the iron oxide nanoparticles; (c) SEM image of the prepared IOCPE.

Fig 2 Cyclic voltammograms of: (a) blank at IOCPE; (b) BCPE; (c) IOCPE in 1 mM

K 3 [Fe(CN) 6 ] containing 0.1 M KCl (at scan rate 100 mV s1).

M.M Vinay, Y Arthoba Nayaka / Journal of Science: Advanced Materials and Devices 4 (2019) 442e450 444

redox reaction of the probe on the electrode surface This indicated

that the presence of mediator ION's on CPE played a significant role

in increasing the charge transfer capability[46e48]

3.5 Voltammetric behaviors of PA and DA at BCPE and IOCPE

The BCPE and IOCPE electrodes were used for the investigation

of the PA signal by cyclic voltammetry The curve a inFig 5depicts

the cyclic voltammogram (CV) of a blank solution at IOCPE and

curve b and c shows the cyclic voltammograms (CVs') in presence of

1 mM PA in PBS (pH 7.0) at BCPE and IOCPE, respectively at a scan

rate 100 mV s1(Fig 5) At IOCPE, PA exhibits the quasi-reversible

redox behavior with an anodic (Epa) and cathodic peak potential

(Epc) of 45 and 8.8 mV, respectively The significant enhancement of

the anodic (Ipa) and cathodic peak currents (Ipc) provides a clear

evidence for the catalytic effect of IOCPE towards the redox

behavior of PA[44,49] After 120 days, the same procedure has been

performed for the determination of PA and DA using the same

IOCPE The curves e and f show CVs' for blank solution and 1 mM

DA at BCPE, respectively, and curve d and g represents the redox

behavior of 1 mM PA and 1 mM DA at IOCPE, respectively in PBS (pH

7.0) at scan rate 100 mV s1(Fig 5) The results have shown that

even after long storage, the working electrode IOCPE has retained

its good sensitivity and stability for the determination of PA and DA

3.6 Effect of scan rate and pH

The influence of the scan rate on the peak currents (Ip) of PA at

IOCPE was investigated by cyclic voltammetry.Fig 6(a) shows the

voltammetric response of 1 mM PA at IOCPE at different scan rates

of 50e350 mV s1 The redox peak current increases linearly with increasing scan rate and the reduction peak shifts towards a more negative potential whereas the oxidation peak shifts towards a more positive potential which indicates to the diffusion-controlled kinetics of the electron transfer reaction at the electrode surface Linear regression equations were obtained from the graph Ipaand

Ipc vs n1/2 (square root of scan rate) as follows; Ipa ¼ 11.11 

106þ 6.892n1/2, (R2¼ 0.999; N ¼ 12); Ipc¼ 22.85  106- 5.516n1/

2, (R2 ¼ 0.9977; N ¼ 12) for the anodic and cathodic process, respectively, which indicates that the reaction of PA at IOCPE is diffusion controlled[49] The linear relationship between log Ipavs logncan be obtained as follows; log Ipa¼ 5.383 þ 0.572 logn(mV

s1), (R2¼ 0.9993; N ¼ 12) The slope value 0.57 is very close to the theoretical value of 0.5 and confirms that the reaction at the elec-trode surface is diffusion controlled[50,51] For comparison, the scan rate from 50 to 250 mV s1was performed for PA and DA individually using a long-stored working electrode (IOCPE) The redox peak currents of both PA and DA were obtained and found to

be increased linearly with increase in scan rate (Fig 6(b) and (c)) The linear correlation equations have been given by:

Ipa¼ 28.07  106þ (4.87  106) v1/2, (R2¼ 0.9965; N ¼ 9);

Ipc¼ 27.85  106þ 3.503  106v1/2, (R2¼ 0.9993; N ¼ 9) for PA and Ipa¼ 5.8  106þ (3.21  106) v1/2, (R2¼ 0.9937; N ¼ 9);

Ipc¼ 14.49  106þ 2.56  106v1/2, (R2¼ 0.9984; N ¼ 9) for DA The plots of log Ipa vs log n for PA and DA as follows; log

Ipa¼ 4.744 þ 0.417 logn(mV s1), (R2¼ 0.9917; N ¼ 9) and log

Ipa¼ 5.237 þ 0.41 logn(mV s1), (R2¼ 0.9903; N ¼ 9), respec-tively The slope values for PA and DA have been found to be 0.417 and 0.41, respectively and these confirmed that the redox processes

of PA and DA at IOCPE were diffusion controlled[42,50,51] The CVs' were performed in the scan rate from 50 to 225 mV s1for deter-mination of the number of electrons transferred and the electron transfer coefficients in PA and DA The linear regression equations (Epa and Epc vs log n) for PA and DA are as follows: Epa (PA)¼ 0.3438 þ 0.08 logn(R2¼ 0.9948); Epc(PA)¼ 0.2512e0.09 log

v (R2¼ 0.9927) and Epa(DA)¼ 0.254 þ 0.061 log v (R2¼ 0.9969); Epc (DA)¼ 0.2431e0.078 log v (R2 ¼ 0.9927) According to Laviron's equation, the slopes of line obtained from the above linear regression equations have been found to be 2.303RT/(1-a)nF and2.303RT/anF, where R is the gas constant (8.314 J K1mol1),

T is the temperature (298 K), F is Faraday's constant (96,485 C), n andaare the electron-transfer number and electron-transfer

co-efficient, respectively The transfer number and

electron-Fig 4 Nyquist plots of 5 mM K 3 [Fe(CN) 6 ] containing 0.1 M KCl at: (a) BCPE; (b) IOCPE

(frequency range from 0.1 to 10 3 kHz, inset: Randle's equivalent circuit).

1 mM DA at (f) BCPE; (g) IOCPE at scan rate of 100 mV s1((d), (e), (f) and (g) obtained

at IOCPE after 120 days).

transfer coefficients for PA and DA have been found to be 1.7 (z2),

1.9 (z2) and 0.43, 0.51 respectively

The square wave voltammetric method (frequency 15 Hz;

amplitude 25 mV) has been employed to investigate the effect of

pH on the electrochemical behavior of PA (20mM) and DA (50mM)

in 0.1 M PBS.Fig 7shows the variation of peak currents at different

pH and the inset plot shows the variations of the peak potentials

with pH The shift in the peak potentials towards the negative side

with increase in pH indicates the involvement of protons in the

reaction The increase in the peak current with the increase in pH

(from 4.0 to 6.0) in case of PA is attributed to the formation of

p-benzoquinone The maximum peak current obtained at pH 7.0 is

due to the formation of N-acetyl-p-quinone-imine which exists in

unprotonated stable form[52,53] At higher pH values (above 8.0)

the peak current is found to decrease which is due to the

dimer-ization of N-acetyl-p-benzoquinone-imine[54] The above results

clearly indicated that at pH 7.0 a good electrostatic interaction

exists between unprotonated PA and IOCPE which, in turn, is

responsible for the fast electron transfer reaction Hence PBS of pH 7.0 has been selected as an appropriate standard electrolytic me-dium for further studies[55] The square wave peak potential for PA has a linear relationship with pH (from 4.0 to 8.0) and the corre-sponding regression equation has been given by the following equation: Ep(V)¼ 0.739e0.050 pH (R2¼ 0.9993) Further from pH 4.0 to 6.0, the square wave peak potential of DA is found to be shifted towards the negative side and at pH 7.0 a rapid increase in the peak current was observed Above pH 8.0, the peak potential again shifted towards the negative side with a decrease in peak current that may be due to self-polymerization of DA into poly-dopamine in an alkaline medium[56] The corresponding linear regression equation for DA is as follows: Ep(V)¼ 0.562e0.0558 pH (R2¼ 0.9993) The slope value for PA and DA were found to be 50 and 55 mV pH1respectively These values are nearly equal to the theoretical value of 59 mV pH1which is in good agreement with the Nernst equation These results indicated that the electro-chemical redox process of PA and DA at IOCPE involves two protons and two electrons transfer reactions[52,57] The probable redox reaction mechanisms of PA and DA are shown in (Scheme 1 -Supplementary)

3.7 Effect of concentration The DPV method has been employed for the electrochemical detection of PA at IOCPE.Fig 8shows the differential pulse vol-tammograms (DPVs') for different concentration of PA (1mMe14mM) in 0.1 M PBS at pH 7.0 The oxidation peak current is directly proportional to the concentration of PA and increases lin-early with the increase in concentration The linear regression equation for PA is as follows: Ip(mA) ¼ 7.65  107 -2.19 102C(mM) and the correlation coefficient R2¼ 0.9994 The limit of detection (LOD) can be detected by using the formula LOD¼ 3 s/m where s indicates the standard deviation of the first five runs and where m indicates the slope obtained from a linear graph (concentration vs current) and where LOD has been found to

be equal to 0.904 The IOCPE has shown an enhanced performance for the electrochemical determination of PA After 120 days, the above experimental procedure has been repeated for the analysis of

PA and DA using the same IOCPE Fig 9(a) shows DPVs' of PA keeping the concentration of DA at a constant value andFig 9(b) represents DPVs' of DA keeping the concentration of PA at a con-stant value.Fig 9(c) shows DPVs' for the simultaneous estimation

Fig 6 (a) CV's of 1 mM PA at different scan rate from 50 to 350 mV s1in 0.1 M PBS at

pH 7.0; (inset: linearity plot of current vs scan rate and log current vs log scan rate) (b)

and (c) CV's of individual scan rates of 1 mM PA and 1 mM DA, respectively at different

scan rate from 50 to 250 mV s1(a to i) in 0.1 M PBS (pH 7.0) at long stored IOCPE

(inset: linearity plot of PA and DA from log peak current vs log scan rate).

Fig 7 Effect of pH (from 4.0 to 9.0) on SWV's of 20mM PA and 50mM DA: (frequency

15 Hz; amplitude 25 mV; inset: linearity plot of pH vs potential).

M.M Vinay, Y Arthoba Nayaka / Journal of Science: Advanced Materials and Devices 4 (2019) 442e450 446

of PA and DA The concentration of PA has been varied from 2 to

150mM keeping the DA concentration at 15mM where the

regres-sion equation is given by: Ipa(PA)¼ 7.74  107þ 1.7  102C(mM)

with correlation coefficient R2¼ 0.9982 Similarly, the DA

concen-tration has been varied from 2 to 170mM keeping PA at 14mM

where the corresponding regression equation is as follows: Ipa

(DA)¼ 1.45  106þ 2.49  102C(mM) with correlation coefficient

R2 ¼ 0.989 From the regression equations, the LOD values have

been calculated as 1.16 and 0.79 mM (S/N¼3) for PA and DA,

respectively It was observed that the change in concentration of

one species does not alter the peak potential and current of the

other species Further, the concentrations of both PA and DA have

been varied from 1 to 170mM and they exhibited well- separated

peaks with the following regression equations: 9.35  107 þ

1.367  102 C(mM) (R2 ¼ 0.9924) for PA and

1.44 106þ 1.81  102C(mM) (R2¼ 0.9786) for DA From the

above equations, the LOD values were found to be 1.44 and 1.09mM

and these values are in good agreement with the individual

determination of PA and DA The above results show that the

modified electrode IOCPE exhibited good and acceptable LOD and

LR values compared to other modified electrodes reported in

literature (Table 1 - Supplementary)

3.8 Interference, stability and repeatability

In order to estimate the optionality of IOCPE, the effect of

interference has been studied via the DPV technique by adding a

known concentration of important interfering organic

com-pounds like glucose, vitamin-c, cysteine, methionine, tyrosine

and inorganic species Naþ, Kþ, Ca2þ, Mg2þ, Cl, SO4  into the

analytical solution containing 20mM PA and 20mM DA The

ob-tained results showed that interfering compounds have no effect

on the peak current and peak potential of PA and DA The percent

recovery of both analyte PA and DA in presence of interfering

substance has been calculated and the obtained RSD value is 1.2%

In sensor applications, long-lasting stability was the most

important criterion So, the stability of the prepared modified

Fig 8 DPV plots at IOCPE of different concentration from 1 to 14mM (a to l) obtained

at IOCPE in 0.1 M PBS at pH 7.0; (inset: linearity graph of current vs concentration).

Fig 9 DPV's plots at IOCPE after 120 days; (a) variation of PA under fixed concen-tration of 15mM DA (from a to m; 2, 4, 6, 10, 20, 30, 40, 50, 60, 80, 110, 150mM respectively); (b) variation of DA under fixed concentration of 14mM PA (from a to j; 2,

4, 6, 10, 30, 50, 50, 80, 120, 170mM respectively); (c) variation of both PA and DA (from

a to m; 1, 2, 4, 7, 11, 16, 22 30, 50, 80, 120, 170mM respectively) in 0.1 M PBS at pH 7.0: (all inset: linearity graph of current vs concentration).

electrode has been evaluated by CV in the presence of 1 mM PA.

Even after being stored at the lab temperature (25± 1C) for 120

days, the peak potential of PA remained almost constant in the

applied potential range0.2e0.8 V but the current response was

slight decreased of its preliminary value Further repeatability of

IOCPE towards the estimation of PA and DA has been analyzed by

preparing four different electrodes under the same experimental

condition with the RSD value found to be equal to 2.4% These

results have shown that the prepared electrode has good stability,

reproducibility and could be used for determination of PA and DA

3.9 Real sample analysis

3.9.1 Determination of PA and DA in pharmaceutical samples

The analytical applicability of the prepared IOCPE has been

tested by determining PA present in tablets Dolo (Dolo-650, IP

650 mg) and Oromol (Oromol-650, IP 650 mg), and DA present in

an injected sample (Dopamine hydrochloride, U S P 200 mg) The

Dolo and Oromol tablets were weighed separately and powdered

using a mortar A known amount of Dolo (0.5 g) and Oromol (0.5 g)

tablets was dissolved separately in 100 ml of PBS of pH 7.0 and

sonicated for 15 min andfiltered Similarly, the Dopamine

hydro-chloride injection sample (5 ml injection containing 200 mg

Dopamine hydrochloride) was also dissolved in 100 ml of 0.1 M PBS

The concentration of the so prepared tablets and of the injection

sample solutions has been studied using the DPV technique within

the adjusted calibration range as shown in Fig 9(C) Also, the

concentration of PA present in a synthetic serum sample has been

determined The obtained DPV results indicate the applicability of

IOCPE for the estimation of PA and DA present in pharmaceutical

samples and PA in serum samples (Tables 2 and 3)

4 Conclusion

The prepared ION's and IOCPE have been characterized by SEM,

EDAX, XRD techniques The surface area and impedance of IOCPE

have been studied by CV and EIS The ION's present in the carbon

paste enhances the good electron transfer ability, sensitivity and

selectivity towards the determination of redox behavior of PA In

the DPV mode, PA gave the linear response over the concentration

range 3.0e14mM with a LOD value of 0.904mM Similarly, the

ef-fects of scan rate, pH, concentration, interference, stability and

reproducibility of the IOCPE (long stored electrode for 120 days)

have been analyzed for PA and DA simultaneously In the DPV

mode, PA and DA gave linear responses over the concentration

range 2e150 mM (R2 ¼ 0.998) and 2e170 mM (R2 ¼ 0.989),

respectively The LOD values of PA and DA were found to be 1.16 and 0.79mM, respectively The results have shown that IOCPE possesses the good stability, better sensitivity, selectivity, reproducibility, wide linear concentration range and low limit of detection towards the determination of PA and DA So, the proposed method can be successfully validated for the individual and simultaneous deter-mination of PA and DA present in pharmaceutical and real samples Acknowledgements

The authors are grateful to acknowledge the UGC-BSR (Univer-sity Grant Commission-Basic Scientific Research; UGC letter No F.25-1/2013-14 (BSR)/7-229/2009/dated: 30-07-2014), SERB (DST), New Delhi, India for providingfinancial support and instrument facility

Appendix A Supplementary data Supplementary data to this article can be found online at

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Table 2

Analytical application of PA and DA in pharmaceutical sample (standard addition method, n ¼ 3).

Table 3

Analytical application of PA alone in real sample (standard addition method, n ¼ 3).

Analyte Spiked (mM) Found (mM) % Recovery

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