Voltammetric Determination of Adrenaline Using a Poly(1-Methylpyrrole)

Modified Glassy Carbon Electrode

Mehmet Aslanoglu,* Aysegul Kutluay, Serpil Karabulut and Sultan Abbasoglu

Department of Chemistry, University of Harran, Sanliurfa 63510, Turkey

A voltammetric method using a poly(1-methylpyrrole) modified glassy carbon electrode was devel-

oped for the quantification of adrenaline. The modified electrode exhibited stable and sensitive current re-

sponses towards adrenaline. Compared with a bare GCE, the modified electrode exhibits a remarkable

shift of the oxidation potentials of adrenaline in the cathodic direction and a drastic enhancement of the

anodic current response. The separation between anodic and cathodic peak potentials (�Ep) for adrenaline

is 30 mV in 0.1 M phosphate buffer solution (PBS) at pH 4.0 at modified glassy carbon electrodes. The lin-

ear current response was obtained in the range of 7.5 � 10-7 to 2.0 � 10-4 M with a detection limit of 1.68 �

10-7 M for adrenaline by square wave voltammetry. The poly(1-methypyrrole)/GCE was also effective to

simultaneously determine adrenaline, ascorbic acid and uric acid in a mixture and resolved the overlap-

ping anodic peaks of these three species into three well-defined voltammetric peaks in cyclic voltam-

metry. The modified electrode has been successfully applied for the determination of adrenaline in

pharmaceuticals. The proposed method showed excellent stability and reproducibility.

Keywords: Modified electrodes; 1-Methylpyrrole; Adrenaline; Ascorbic acid; Uric acid.

INTRODUCTION

Adrenaline, a sympathomimetic drug, is widely used

for the treatment of hypertension, cardiac arrest, myocar-

dial infarction and cardiac surgery in clinics.1 It is a chemi-

cal mediator for conveying the nerve pulse to efferent or-

gans. Adrenaline is also used to stimulate heartbeat and to

treat emphysema, bronchitis, bronchial asthma and other

allergic conditions, as well as in the treatment of the eye

disease, glaucoma.2 Therefore, sensitive determination of

adrenaline has an important significance to medicine and

life science. Several methods have been reported for the de-

termination of adrenaline such as high performance liquid

chromatography,3-5 fluorometry,6-8 chemiluminescence,9,10

capillary electrophoresis11 and spectrophotometry.12 How-

ever, such methods are quite complicated since some of

these methods need derivatization or combination with

various detection methods. They also have low sensitivity

and specificity.

Electrochemical methods have been useful for the de-

termination of electroactive species in pharmaceuticals and

body fluids due to their simplicity and low cost. However,

in electrochemical detection of adrenaline, voltammetric

methods may suffer from low sensitivity and selectivity

that leads to an inactive overpotential due to the irrevers-

ibility of its voltammetric behavior.1 Another problem in

monitoring adrenaline with electrochemical methods is the

coexistence of ascorbic acid and uric acid. The presence of

ascorbic acid and uric acid with adrenaline possessing oxi-

dation peak potentials close to those of adrenaline results in

the voltammetric response of adrenaline being almost over-

lapped by that of ascorbic acid or uric acid at conventional

electrodes. A number of articles have appeared in the litera-

ture regarding these problems.13-17 In these articles, electro-

chemically modified electrodes show good electrocatalytic

activity and stability towards the detection of electroactive

species.18-20 Poly(osmium oxide/hexacyanoruthenate) film

is a good example of the determination of adrenaline which

shows electrocatalytic activity for monitoring adrenaline.21

Yao et al. also described a poly(erichrome black T) film-

modified GCE, which exhibited good activity for the detec-

tion of adrenaline.1 In this study, we report cyclic voltam-

metric behaviour of adrenaline at a bare and a poly(1-meth-

ylpyrrole) modified GCE. The modified electrode was

found to be electrocatalytically active towards the oxida-

tion of adrenaline. Furthermore, it has been shown that the

oxidation peak potential of adrenaline could be well sepa-

794 Journal of the Chinese Chemical Society, 2008, 55, 794-800

* Corresponding author. Tel: +90-4143440020 ext. 1264; E-mail: maslanoglu@harran.edu.tr

rated from than that of ascorbic acid and uric acid at the

poly(1-methylpyrrole) modified GCE.

EXPERIMENTAL

Chemicals and Apparatus

Adrenaline obtained from Fluka (Germany) was used

as received. 1-Methylpyrrole, ascorbic acid and uric acid

were purchased from Fluka (Germany). Solutions of 1-

methylpyrrole were prepared in 0.2 M KCl at pH 7.4. All

other reagents were of analytical grade or equivalent and

obtained from Merck or Fluka. Solutions of adrenaline,

ascorbic acid and uric acid were prepared in 0.1 M phos-

phate buffer solution (PBS) at pH 4.0. Adrenaline injec-

tions (Drogsan Co., Turkey) containing 0.5 mg/mL were

purchased from the local pharmacy. Aqueous solutions

were prepared with doubly distilled water. Oxygen-free ni-

trogen was bubbled through the cell prior to each experi-

ment. All experiments were carried out at approx. 25 �C.

Electrochemical experiments were performed using

an EcoChemie Autolab PGSTAT 12 potentiostat/galvano-

stat (Utrect, The Netherlands) with the electrochemical

software package 4.9 or an Epsilon potentiostat (Bioana-

lytical Systems, Lafayette, USA) with the electrochemical

software 1.6.70_XP. A three-electrode system was used: a

bare or poly(1-methylpyrrole) modified glassy carbon

electrode as working electrode [3 mm in diameter (Bioana-

lytical Systems, Lafayette, USA)], a Pt wire counter elec-

trode and an Ag/AgCl reference electrode.

Preparation of Modified Glassy Carbon Electrodes

Prior to electrochemical modification, the bare GCE

was polished with 0.05 µm alumina slurry on a polishing

pad. Then it was rinsed with water and sonicated with 1+1

HNO3 and acetone, and water for 10 min, respectively. Af-

ter being cleaned, the electrode was activated by 5 cyclic

sweepings from -0.6 to +0.8 V in PBS at pH 7.2. Then, the

electrode was immersed in a solution of 10 mM 1-methyl-

pyrrole dissolved in 0.2 M KCl at pH 7.4 and was condi-

tioned by cyclic sweepings from -1.5 to +2.0 V for 10

scans. Afterwards, the modified electrode was electroacti-

vated by cyclic voltammetry from -0.6 to +0.8 V at 50 mV/s

in 0.1 M PBS at pH 4.0. 10 mM 1-methylpyrrole was found

to be an optimum concentration for the electropolymeriza-

tion. The double layer charging current is higher above

10-12 cyclic scans in electropolymerization. Fig. 1 shows

cyclic voltammograms of the poly(1-methylpyrrole)/GCE

in the range of -0.6 V to 0.8 V at various scan rates in 0.1 M

PBS at pH 4.0. A pair of redox peaks, which are clearer at

high scan rates, was obtained in each voltammogram. The

anodic peak current (Ipa) was proportional to the scan rates

over the range of 50-250 mV/s. Therefore, a surface con-

trolled process played a more important role in the electro-

chemical process. Images of Scanning Electron Micros-

copy (SEM) of the poly(1-methylpyyrole)/GCE are also

shown in Fig. 2. These images indicate that significant

modification of the glassy carbon electrode surface mor-

phology is observed.

RESULTS AND DISCUSSION

Voltammetric behaviour of adrenaline at bare and

poly(1-methylpyrrole) modified electrodes

Fig. 3 shows the cyclic voltammograms of adrenaline

at bare GCE and poly(1-methylpyrrole)/GCE in 0.1 M PBS

at pH 4.0. At a bare glassy carbon electrode, no consider-

able cyclic voltammetric peaks were observed. However, at

the poly(1-methylpyrrole) modified GCE, a well-defined

redox wave of adrenaline was obtained, with the oxidation

and the reduction peak potentials at 0.389 and 0.359 V, re-

spectively. The separation of peak potentials was 30 mV.

This suggested that the number of electrons in the reaction

was two. It has also been shown that the poly(1-methylpyr-

role)/GCE has accelerated the electron transfer rate of

adrenaline. Compared with a bare glassy carbon electrode,

the electrochemical response of adrenaline has greatly been

increased on the poly(1-methylpyrrole)/GCE. Intensive in-

crease in peak current is observed owing to the improve-

ment in the reversibility of the electron transfer process and

A Modified Electrode for the Quantification of Adrenaline J. Chin. Chem. Soc., Vol. 55, No. 4, 2008 795

Fig. 1. Cyclic voltammograms of poly(1-methylpyr-

role)/GCE in 0.1 M PBS at pH 4.0. Scan rates

increasing from 50 to 250 mV/s. Equilibrium

time: 5 s.

the larger real area of the polymer film. This suggests an ef-

ficient oxidation reaction toward adrenaline at the poly(1-

methylpyrrole) modified glassy carbon electrode.

The effect of scan rate on the electrochemical re-

sponse of adrenaline at poly(1-methylpyrrole)/GCE was

carried out to investigate the electrochemical process of

adrenaline at the modified electrode (Fig. 4). The anodic

peak current (Ipa) was proportional to the scan rate (v) over

the range of 25-150 mV/s. The results indicated that the

electrochemical oxidation of adrenaline at poly(1-methyl-

pyrrole)/GCE is a surface-controlled process.22

In addition, the effect of the pH value of the PBS

buffer solution on peak potential of adrenaline at poly(1-

methylpyrrole)/GCE was also investigated. The anodic

peak potential of adrenaline shifted in the negative direc-

tion with increasing pH. This shows that the redox couple

796 J. Chin. Chem. Soc., Vol. 55, No. 4, 2008 Aslanoglu et al.

Fig. 2. SEM images of poly(1-methylpyrrole)/GCE.

Fig. 3. Cyclic voltammograms of 2.0 � 10-5 M adrena-

line at (a) bare GCE and (b) poly(1-methylpyr-

role)/GCE in 0.1 M PBS at pH 4.0. Equilibrium

time: 5 s, scan rate: 50 mV/s.

Fig. 4. Cyclic voltammograms of 9.0 � 10-5 M adrena-

line in 0.1 M PBS at pH 4.0. Scan rates increas-

ing from 25 to 150 mV/s. Equilibrium time: 5 s.

of adrenaline includes proton transfer in the electrochemi-

cal processes. The slope of the plot of the peak potential vs.

pH value of the solution was approx. 59.0 mV/pH (Fig. 5).

This indicated that the proportion of the electrons and pro-

tons involved in the reactions is 1:1. Since equal numbers

of electrons and protons should be involved in the electrode

reaction, the number of hydrogen ions involved in the

whole electrode reaction is 2.

The electrochemical behaviour of adrenaline at poly-

(1-methylpyrrole)/GCE might be represented as follows:

peak (1) results from the oxidation of adrenaline, which is a

two-electron process to produce adrenalinequinone (reac-

tion 1). Peak (2) appears by the reduction of adrenaline-

quinone to adrenaline (reaction 1). Peak (3) corresponds to

formation of leucoadrenalinechrome resulting from the

ring closure of adrenalinequinone which contains an elec-

tron-deficient ring (reaction 2). The behaviour of adrena-

line at poly(1-methylpyrrole)/GCE is an electrochemical-

chemical (EC) process.22 The proposed electrochemical re-

actions of adrenaline at the modified electrode are given in

Scheme I.

Calibration Equation for the Determination of

Adrenaline

Determination of the concentration of adrenaline at

poly(1-methylpyrrole)/GCE was performed at pH 4.0. Cy-

clic voltammograms of various concentrations of adrena-

line at poly(1-methylpyrrole)/GCE are given in Fig. 6. The

anodic peak currents were plotted against the bulk concen-

tration of adrenaline after the background subtraction. The

response of anodic peak currents of adrenaline at poly(1-

methylpyrrole) was linear with the concentration of adren-

aline in the range of 1.0 � 10-6 ~ 5.0 � 10-4 M. The linear re-

gression equation was Ipa (�A) = 0.99207 + 0.25786 C

(�M) with a correlation coefficient of 0.9988. The detec-

tion limit was 5.6 � 10-7 M (S/N = 3). Determination of

adrenaline was also carried out using square wave voltam-

metry. Fig. 7 shows the square wave voltammograms of

various concentrations of adrenaline at poly(1-methylpyr-

role)/GCE. The response of the anodic peak currents of

adrenaline was linear with the concentration of adrenaline

in the range of 7.5 � 10-7 M to 2.0 � 10-4 M. The linear re-

gression equation was Ipa (�A) = 4.12480 + 6.45644 C

(�M) with a correlation coefficient of 0.9980. The detec-

tion limit was 1.68 � 10-7 M (S/N = 3). These results indi-

cated that pulse voltammetric methods are more sensitive

for the detection of species.

A Modified Electrode for the Quantification of Adrenaline J. Chin. Chem. Soc., Vol. 55, No. 4, 2008 797

Scheme I Proposed adrenaline reactions at poly(1-methylpyrrole)/GCE in 0.1 M PBS at pH 4.0

Fig. 5. A plot of oxidation peak potential of adrenaline

vs. solution pH.

Reproducibility and Stability of Poly(1-methylpyr-

role)/GCE

The relative standard deviation (RSD) of 6 successive

scans was 2.3% for 5.0 � 10-5 M. This indicated that the

reproducibility of the poly(1-methylpyrrole) modified

GCE was excellent. However, the modified electrode should

be well treated to maintain its reproducibility. It was found

that 20 cycles of scanning in 0.1 M PBS in the potential

range 0.0~0.8 V could regenerate clean background CV

curves and the modified electrode was ready for the next

experiment or storage in 0.1 M PBS. Also, the current re-

sponse decreased only by 5% over a week for storage in 0.1

M PBS.

Detection of Adrenaline in the Presence of Ascorbic

Acid and Uric Acid

Ascorbic acid coexists in samples and can be easily

oxidized at a potential rather close to that of adrenaline us-

ing a conventional electrode resulting in electrochemical

response of adrenaline being overlapped by that of ascorbic

acid always interfering with the measurement of adrena-

line.1 In this work, it was found that this problem could be

eliminated using poly(1-methylpyrrole)/GCE. The cyclic

voltammograms of the mixture of adrenaline and ascorbic

acid at bare GCE and the modified electrode are given in

Fig. 8. Compared to the bare GCE, two well-defined cyclic

voltammetric peaks were obtained at poly(1-methylpyr-

role)/GCE. The two peaks observed at 0.170 V and 0.393 V

in CV correspond to the oxidation of ascorbic acid and

adrenaline, respectively. Fig. 9 represents the CV record-

ings at various concentrations of adrenaline where concen-

tration of ascorbic acid was kept constant. In the presence

of ascorbic acid, the anodic peak current of adrenaline in-

creased linearly with the increase in its concentration.

Overall facility of the poly(1-methylpyrrole)/GCE for si-

798 J. Chin. Chem. Soc., Vol. 55, No. 4, 2008 Aslanoglu et al.

Fig. 6. Cyclic voltammograms of increasing concen-

trations of adrenaline at poly(1-methylpyrrole)/

GCE in 0.1 M PBS at pH 4.0. Adrenaline con-

centrations: (a) 1.0 � 10-5 M (b) 2.5 � 10-5 M (c)

4.0 � 10-5 M (d) 5.0 � 10-5 M (e) 6.0 � 10-5 M (f)

7.0 � 10-5 M (g) 8.0 � 10-5 M. Equilibrium time:

5 s, scan rate: 50 mV/s.

Fig. 7. Square wave voltammograms of increasing con-

centrations of adrenaline at poly(1-methylpyr-

role)/GCE in 0.1 M PBS at pH 4.0. Adrenaline

concentrations: (a) 7.5 � 10-7 M (b) 1.5 � 10-6 M

(c) 2.0 � 10-6 M (d) 4.0 � 10-6 M (e) 5.0 � 10-6 M

(f) 7.0 � 10-6 M. Equilibrium time: 5 s., fre-

quency: 10 Hz, step potential: 20 mV, ampli-

tude: 25 mV.

Fig. 8. Cyclic voltammograms of the mixture of 1.5 �

10-4 M ascorbic acid and 4.0 � 10-5 M adrena-

line at (a) bare GCE and (b) poly(1-methylpyr-

role)/GCE in 0.1 M PBS at pH 4.0. Equilibrium

time: 5 s, scan rate: 50 mV/s.

multaneous determination of ascorbic acid and adrenaline

was demonstrated by simultaneously changing the concen-

tration of ascorbic acid and adrenaline. Fig. 10 depicts the

cyclic voltammograms that were obtained for adrenaline

and ascorbic acid coexisting at various concentrations.

This indicates that the poly(1-methylpyrrole)/GCE enables

the simultaneous determination of adrenaline and ascorbic

acid. Fig. 11 displays cyclic voltammograms of the simul-

taneously increasing concentrations of ascorbic acid, ad-

renaline and uric acid. The anodic peak responses of all

species increase linearly with their concentrations indicat-

ing that the voltammetric responses of ascorbic acid, adren-

aline and uric acid are independent of each other. It is also

remarkable that excess amounts of ascorbic acid and uric

acid do not interfere with the determination of adrenaline.

It is therefore possible to determine adrenaline in the pres-

ence of ascorbic acid and uric acid at poly(1-methylpyr-

role) modified GCE.

Analytical Applications

The proposed method was utilized for the determina-

tion of adrenaline in drug samples. Adrenaline injections

(0.5 mg/mL) were analysed using the proposed method.

Adrenaline samples were diluted with 0.1 M PBS. The in-

jections were analysed by the standard addition method.

The data obtained at poly(1-methylpyrrole)/GCE are in

close agreement with the claimed value in adrenaline injec-

tions. The average recovery of 97.5% with an RSD of 1.7%

was obtained employing the proposed method for the six

different determinations. The data are also in good agree-

A Modified Electrode for the Quantification of Adrenaline J. Chin. Chem. Soc., Vol. 55, No. 4, 2008 799

Fig. 9. Cyclic voltammograms of the increasing con-

centrations of adrenaline in the presence of 1.5

� 10-4 M ascorbic acid at poly(1-methylpyr-

role)/GCE in 0.1 M PBS at pH 4.0. Adrenaline

concentrations: (a) 4.0 � 10-5 M (b) 6.0 � 10-5 M

(c) 8.0 � 10-5 M (d) 1.0 � 10-4 M. Equilibrium

time: 5 s, scan rate: 50 mV/s.

Fig. 10. Cyclic voltammograms of the increasing con-

centrations of ascorbic acid and adrenaline at

poly(1-methylpyrrole)/GCE in 0.1 M PBS at

pH 4.0. Ascorbic acid concentrations: 3.0 �

10-4 M (b) 4.5 � 10-4 M (c) 5.5 � 10-4 M (d) 6.5

� 10-4 M (e) 7.5 � 10-4 M. Adrenaline concen-

trations: (a) 7.50 � 10-5 M (b) 1.25 � 10-4 M (c)

1.5 � 10-4 M (d) 1.75 � 10-4 M (e) 2.0 � 10-4 M.

Equilibrium time: 5 s, scan rate: 50 mV/s.

Fig. 11. Cyclic voltammograms of the increasing con-

centrations of ascorbic acid, adrenaline and

uric acid at poly(1-methylpyrrole)/GCE in 0.1

M PBS at pH 4.0. Ascorbic acid concentra-

tions: (a) 5.0 � 10-5 M (b) 7.5 � 10-5 M (c) 1.0 �

10-4 M. Adrenaline concentrations: (a) 3.5 �

10-5 M (b) 5.0 � 10-5 M (c) 7.5 � 10-5 M. Uric

acid concentrations: (a) 1.25 � 10-4 M (b) 2.5 �

10-4 M (c) 5.0 � 10-4 M. Equilibrium time: 5 s,

scan rate: 50 mV/s.

ment with certified values obtained by the reported HPLC

method with an average recovery of 96.9%.23 However, the

data obtained by the proposed method are comparable with

the two previous studies using electrodeposition film of

erichrome black T (recoveries between 94.8% and 97.6%)

and caffeic acid (recoveries between 94.7% and 102.4%).1,2

The results indicated that the proposed method could easily

be used for the determination of adrenaline in pharmaceu-

ticals.

CONCLUSIONS

This study has indicated that poly(1-methylpyrrole)

modified glassy carbon electrode exhibits electrocatalytic

activity to the oxidation of adrenaline and provides voltam-

metric monitoring of adrenaline in the presence of ascorbic

acid and uric acid. Compared with a bare GCE, the modi-

fied electrode exhibits a distinct shift of the oxidation po-

tential of adrenaline in the cathodic direction and a marked

enhancement of the anodic current response. The modified

electrode has successfully been applied for the determina-

tion of adrenaline in pharmaceutical preparations. The

poly(1-methylpyrrole) modified electrode has good sensi-

tivity and reproducibility.

ACKNOWLEDGEMENTS

The authors appreciate the financial support from the

Scientific and Technological Research Council of Turkey

for a grant (Project No. 106T404).

Received January 16, 2008.

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