CuCrO 4 Nanoparticles Composite Modiﬁed Carbon Paste Electrodes for Sensitive Detection of Paracetamol: A Cyclic Voltammetric Study

An electrochemical sensor containing carbon paste electrode (CPE) for paracetamol is developed and modified with the CuCrO 4 Nanocomposites. The synthesised CuCrO 4 Nanocomposites was discussed with X-Ray Diffraction studies. Experimental studies such as scan rate, concentration and pH was studied by using cyclic voltammetric method. The CuCrO 4 Nanocomposites modified CPE (CuCrO 4 Nanocomposites MCPE) exhibited excellent electrocatalytic response towards the oxidation of paracetamol (PC). Over potential for oxidation of PC was minimised which considerably enhance the current response on the CuCrO 4 Nanocomposites MCPE when compared with bare carbon paste electrode (BCPE). Scan rate study for PC discuss the process of the electrode. Linear calibration curve was obtained with the range of 2 μM to 14 μM having the detection limit and quantification limit value of PC is discussed with CuCrO 4 Nanocomposites MCPE. This study shows that electrochemical oxidation of PC at CuCrO 4 Nanocomposites MCPE is pH dependent process.


Introduction
Nanocomposites have wide applications in various fields [1] such as semiconductors [2], catalyst, pigment, drug [3] in the area of electronic and magnetic materials [4][5][6][7], and development of electrochemical sensors [8]. From the past two decades the influence of nanocomposites is immense on sensing applications and devices. Sensor is a transducer, which detects/sense some specific vicinities of substances. Numerous active materials have wide range of applications in the field of sensors. The material which includes metals, metal oxides, metal sulphides, metal chromates, composite nanoparticles and many more in their nano (10 -9 ) dimension. Different methods were discussed for the preparation of metal chromates those were wet chemical, micro emulsion, and sol-gel processes [9]. Ceramic and co-precipitation methods [10]. Electrochemical methods [11] have discussed a variety of applications and synthetic approaches of copper chromite nanocomposites [12]. In the present research work , the most significant stable Copper Chromate nanocomposites (CuCrO4 nanocomposites) is prepared through hydrothermal method, which is characterized through XRD. These CuCrO4 nanocomposites being used for the modification of CPE, which is CuCrO4 Nanocomposites MCPE was used as an electrochemical sensor for PC. Paracetamol (acetaminophen) (PC) is widely used as a pain reliever and a fever reducer. Many analytical techniques have been used for PC analysis including titrimetry [13][14], HPLC [15][16][17], fluorometry [18], Uv-visible spectrophotometric methods [19], colorimetry [20] and various modes of electrochemistry [21][22][23][24]. Since the results of above approaches are not accurate and the techniques involved are tedious and expensive, researchers have shown interest to detect the PC through nanocomposites modified carbon paste electrode. These modified electrodes are inexpensive and showed high sensitivity, minimum detection limit, high accuracy and response. These approaches are simple method to detect the PC through electrochemically. The electrochemical oxidation of PC at nanoparticles modified carbon paste electrode was reported in the earlier work [25]. Recently, the voltammetric behaviour of PC and some other drugs at various conducting polymers were studied [26]. Among all analytical methods, electrochemical methods are best.
Electrochemical approaches are effective to quantify the biomarker levels in the blood as they are economic, provide rapid diagnosis and cause less pain in patients. Various CuCrO4 composites show enhanced ionic-conductivity especially for O2 ions; thus, it is generally employed as fuel cells at high temperatures and oxygen sensors [27][28]. This composite also behaves as insulator at moderate temperatures, but it will turn into super ionic conductor at very high temperature. As of its good high hardness, biocompatibility and strength, hence it is frequently used as orthopaedic implants, such as dental implants and femoral head component in hip implants. As deliberated above, it is thermally and chemically firm, joint with its inimitable amphoteric characteristic, making it an idyllic candidate for catalyst. For instance, the decomposition of N2O2, hydrogenation of aromatic carboxylic acids, the isomerization of alkanes, and countless other reactions. CuCrO4 Nanocomposites is a familiar catalyst, holds both the common advantages of transition metal compound catalysts and its own unique merits.

Apparatus and Reagents
Cyclic voltammetry was achieved in CHI-660c potentiostat an analytical system model (Electrochemical workstation, USA). The conventional three electrode electrochemical cell consist of a saturated calomel electrode (SCE) which act as reference electrode while platinum wire as a counter electrode and bare Carbon Paste Electrode CuCrO4 composites modified Carbon Paste Electrode as working electrode. A digital pH meter MK VI (Systronics) employed for the pH measurements. All potentials were given against SCE at 25±0.5°C. PC was procured from Himedia and the stock solution of PC (2.5 mM), and they were prepared in doubly distilled water. Graphite powder was bought from Lobo and silicon oil (as binder) was bought from sigma Aldrich. All chemicals were of AR grade. For buffer solution preparation, the chemicals were bought from Merck. 0.2M PBS was prepared by adding standard stock solutions NaH2PO4·H2O (0.2M) and Na2HPO4, (0.2M). All the solutions were prepared freshly prior to be analysis.

Preparation of bare carbon paste electrode (BCPE)
BCPE was prepared by adding graphite powder (70%) and silicone oil (30%) and hand mixing this mixture in a agate mortar for 45mins till to get a uniform paste. Then paste is poured to Poly Vinyl Chloride tube cavity and made smooth on a rubbing paper. A copper wire was used at the end of tube for the electrical connection.

Preparation of Copper (II) Chromate nanoparticles (CuCrO4 NPs)
The CuCrO4 NPs were prepared through hydrothermal approach. For that, the copper chloride (CuCl2) and potassium chromate (K2CrO4) taken in the ration 1:1 and dissolved in deionized water (50 mL). Then, 0.7 g NaOH was added and sonicated for 3 hrs consequently, later mixture was poured to Teflon-autoclave and maintained at 210 °C for 20hrs. Final products were parted using centrifugation and allowed for drying at 60 °C. Further, centrifugation removes powders from solution and washed with deionised water and methanol and dried at 100 °C for 24 hrs to obtain CuCrO4 NPs.

Preparation of CuCrO4 NPs composite MCPE
The CuCrO4 NPs MCPE were synthesized by adding 30% silicon oil and 70% graphite powder and different amounts of CuCrO4 NPs from 2mg to 8mg in an agate mortar till it results a uniform paste. Resulted paste was crammed firmly to electrode cavity and then refined the surface by tissue paper.

The XRD pattern of Carbon/ CuCrO4 NPs
The XRD patterns of Carbon/ CuCrO4 powders are presented in Fig. 1  NPs composite MCPE the electroactive surface area was found to be maximum (i.e., 0.03522 cm 2 ) when compared to BCPE (i.e., 0.02829 cm 2 ).

Effect of scan rate on peak current of PC
The scan rate effect for 10µM PC in 0.2 M PBS was examined by cyclic voltammetry at CuCrO4 NPs composite MCPE depicted in Fig. 5. The changed scan rate displays a reflective effect on the redox Ipeak, shows that the redox Ipeak regularly enhances with increment in the scan rate i.e., from 0.05 to 0.5V/s and proportional to each other according to Randles Sevcik eqn. The Epa changed partly towards positive direction while Eca towards negative direction. The graph of log Ipa of PC v/s logυ was plotted for CuCrO4 NPs composite MCPE and the slope obtained was 0.55 therefore the electrode process was controlled by diffusion [32] as shown in Fig.6. From the graph, it shows a good linearity between anodic Ipeak and scan rates. It showed an excellent linearity for CuCrO4 NPs composite MCPE i.e., (log Ipa) = 0.55940(logυ) + 4.8669 with (r 2 = 0.9991).

Effect of solution pH
PC is an easily oxidizable electroactive drug. The CV studies were carried out to examine the supporting electrolyte effect on electrochemical oxidation of PC at CuCrO4 NPs composite MCPE. The Fig.9 (Fig.10). The results afford from linear equation with the slope of 43mV/pH (r 2 = 0.998) at CuCrO4 NPs composite MCPE [37]. All this indicates that during electrochemical reaction of PC, the process of electrode where, exchange of electron is considerably affected by protons and electrons. From the slope, it is confirmed that the number of exchanged electrons and protons were same. This study exposes that electrochemical oxidation of PC at CuCrO4 NPs composite MCPE was pH dependent process and CuCrO4 NPs composite MCPE represents good enhancement of redox Ipeak and minimize the over potential.