A novel sensor fabrication using anionic surfactant sodium lauryl sulphate modified carbonnanotube and pencil graphite composite paste electrode (SLSMCNTPGCPE) is prepared and characterized using Field Emission Scanning Electron Microscope (FE-SEM) and Cyclic Voltammetry (CV).
Journal of Science: Advanced Materials and Devices (2020) 56e64 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article A surfactant enhanced novel pencil graphite and carbon nanotube composite paste material as an effective electrochemical sensor for determination of riboflavin Girish Tigari, J.G Manjunatha* Department of Chemistry, FMKMC College, Madikeri, Constituent College of Mangalore University, Karnataka, India a r t i c l e i n f o a b s t r a c t Article history: Received 11 September 2019 Received in revised form 25 October 2019 Accepted November 2019 Available online November 2019 A novel sensor fabrication using anionic surfactant sodium lauryl sulphate modified carbonnanotube and pencil graphite composite paste electrode (SLSMCNTPGCPE) is prepared and characterized using Field Emission Scanning Electron Microscope (FE-SEM) and Cyclic Voltammetry (CV) The devised SLSMCNTPGCPE is a responsive electrode material for the determination of Riboflavin (RF) as compared to carbon nanotube and pencil graphite composite paste electrode (CNTPGCPE) and bare pencil graphite paste electrode (BPGPE) The fabricated sensor shows a linear current response to a diverse concentration of RF in 0.2e0.8 mM and 1e5 mM with a low detection limit of 1.16 Â 10À8 M by applying differential pulse voltammetry (DPV) The stability, reproducibility, repeatability, interference and concurrent investigation with dopamine (DA) have been done with satisfactory outcomes The new sensor was applied for the RF estimation shows good recovery in B-complex pill and natural food supplement © 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/) Keywords: Sodium lauryl sulphate Carbon nanotubes Pencil graphite paste electrode Riboflavin Dopamine Introduction Vitamins and neurotransmitters are biologically active molecules and play a vital role in the humanoid biochemistry and metabolism RF (vitamin B2) is aqueous soluble and a principal component of flavoenzymes It assists the conversion of carbohydrates, fats, and proteins into energy and supports the body during anxiety [1e3] RF cannot be formed in the human body, so it has to be obtained from nutritional sources such as milk, eggs, green vegetables, tea, wine, liver, etc The lack of RF in the human body may lead to eye and skin disorders [4e6] Dopamine (DA) is a neurotransmitter molecule in the mammalian central nervous system and plays a substantial role in operating the central nervous, hormonal, renal and cardiac systems Abnormal levels of DA in the human brain cause brain diseases, such as Parkinson's and Schizophrenia [7e13] RF is determined using different analytical procedures such as high-performance liquid chromatography [14], spectrophotometry [15], Flow injection analysis [16], mass spectrometry [17], etc These analytical techniques are expensive and time-consuming Also, * Corresponding author E-mail address: manju1853@gmail.com (J.G Manjunatha) Peer review under responsibility of Vietnam National University, Hanoi some voltammetric methods for quantification of RF are reported in the previous literature such as: mercury drop electrode [18], ZnO/ Manganese hexacyanoferrate nanocomposite/glassy carbon electrode [19], Highly dispersed multiwalled carbon nanotubes coupled manganese salen nanostructure [20], pre-treated GC [21], Manganese (III) Tetraphenyl porphyrin Modified Carbon Paste Electrode [22], pencil graphite [23], Reduced graphene oxide [24], Poly (3methyl thiophene) Modified Glassy Carbon Electrode [25], etc Electroanalytical approaches are active and gifted analytical practices having a strong impact on human health and environmental monitoring The electrochemical methods are strongly recognized due to low cost, simple preparations, rapid analyzing time with the outstanding analytical performance [26e32] Pencil graphite is known to be a multipurpose tool for electroanalysis of bioactive molecules due to their sp2 hybridized carbon which shows characteristics like excellent electrical conductivity, adsorption, little background current, easy exterior modification and mechanical stability [33e35] Carbon nanotubes (CNTs) are frequently used in the fabrication of electrochemical sensors due to their excellent electronic properties, rapid renewal, extensive potential ranges, less residual noise with extreme stability [36e38] Surfactants (SDS, TX-100, CTAB), nanomaterials, stainless steel powder, ferrocene, etc can alter and regulate the characteristic properties of electrode surfaces, which leads to changes in the https://doi.org/10.1016/j.jsamd.2019.11.001 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 (http://creativecommons.org/licenses/by/4.0/) G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices (2020) 56e64 reaction rates and pathways Surfactant-modified electrodes have been extensively applied in the organic electroanalysis, including nutrition, medicinal, and bio-samples assessment [39e46] The present effort is the fabrication of a surfactant modified carbon nanotube and pencil graphite powder composite paste electrode for the electroanalysis of RF in the presence of DA Experimental 2.1 Apparatus The Electroanalytical experiments were carried out through CHI-6038E (electrochemical workstation - USA) It is assembled with a standard three-electrode arrangement with a computer for information storage and selection of analytical parameters The fabricated bare and chemically modified electrodes were executed as a working electrode, a saturated calomel electrode (SCE) and a platinum wire were executed as a reference electrode and counter electrode correspondingly Field emission scanning electron microscopy (FE-SEM) was obtained using the instrument operating at 5.00 kV (DST-PURSE Laboratory, Mangalore University) All current measurements were taken with background current All experiments were done at lab temperature 2.2 Reagents and chemicals RF (!99%) was purchased from Molychem, India DA (!99%) and CNTs were bought from Sigma Aldrich, US Silicone oil (!99%) was bought from Nice Chemicals, India 8B pencil is purchased from the local market Other chemicals are of assay !98.5%, A.R grade used as received The RF and DA standard solution of 2.5 mM was prepared just before the experiment with distilled water 25 mM SLS was prepared using distilled water The 0.1 M Phosphate buffer solutions (PBS) of different pH values were prepared by mixing the suitable quantity of 0.1 M Na2HPO4 and 0.1 M NaH2PO4 57 Result and Interpretations 3.1 FE-SEM and electrochemical characterization of BPGPE, CNTPGCPE, SLSMCNTPGCPE Fig 1(a), (b) and (c) depict the FE-SEM images of BPGPE, CNTPGCPE, and SLSMCNTPGCPE The BPGPE morphology appears flat whereas CNTPGCPE shows spheres and a fibrous morphology, therefore it was successfully modified with CNTs SLSMCNTPGCPE shows an agglomerated surface with white patches which indicates that the electrode surface is modified with SLS The three electrodes having different topographical properties show different electrochemistry with electroactive species An electroanalytical description of BPGPE, CNTPGCPE, SLSMCNTPGCPE for the standard mM K4[Fe(CN)6] in 0.1 M KCl is presented in Fig 1(d) The SLSMCNTPGCPE (curve c) senses K4[Fe(CN)6] oxidation at 0.268 V, and reduction at 0.204 V, with elevated current signals and a lesser DEp value (0.064V) But in case of BPGPE (Curve a) and CNTPGCPE (curve b) the DEp values are 0.173, 0.154 V, respectively, with lower current responses So, SLSMCNTPGCPE exhibits higher electrochemical amplification with a small DEp value as compared to CNTPGCPE and BPGPE SLSMCNTPGCPE might deliver a conducting track through the surfactant layer for quicker electron transfer kinetics Hence, SLSMCNTPGCPE acts as an electron exchange negotiator The effective surface area of SLSMCNTPGCPE, CNTPGCPE, BPGPE can be calculated by using the Randles-Sevcik equation [50] Ip ¼ 2.69 Â 105 n3/2 A D1/2 C0y1/2 where Ip is the anodic/cathodic peak current in A, Co is the concentration of electroactive species (mol cmÀ3), n is the number of electrons interchanged, D is the coefficient of diffusion (cm2/s), y is the potential scan rate (V/s), A is the effective surface area (cm2) The surface area is found to be extremely large for SLSMCNTPGCPE (0.04 cm2) as compared to CNTPGCPE (0.025 cm2), BPGPE (0.016 cm2) 2.3 Preparation of pencil graphite powder 3.2 Optimization of the quantity of carbon nanotubes and SLS The acid-treated pencil graphite, polymer, and surfactant modified pencil graphite are previously reported for electroanalysis of electroactive species The present effort of sensor fabrication provides advantages like less impurity electrode, easy surface renewal as like carbon paste, simple procedure, easy activation approach, low cost with good sensitivity and selectivity The 8B pencil lead is cut into small pieces and crushed in an agate mortar to a fine pencil powder and the obtained powder is stirred with N H2SO4 (1:5 ratio) for 30 min, kept 12 h for digestion at 30 C and then washed with dilute acid followed by distilled water The washed product is dried in the oven at 60 C [47e49] The amount of carbon nanotubes used for the preparation of CNTPGCPE effects the electrochemical response of RF (0.1 mM) So, it was optimized by varying the magnitude of carbon nanotubes from mg to 25 mg using CV in 0.1 M PBS of pH 6.5 at a sweep rate of 0.1 V/s as shown in Fig 2(a) The highest electrochemical activity for RF (0.1 mM) is obtained at the 15 mg carbon nanotube amount, so it is an optimized carbon nanotube amount for electrode fabrication throughout the experiment The surfactant amount optimization is an essential parameter in electroanalysis The surfactant optimization from to 20 mL at CNTPGCPE for the detection of RF (0.1 mM) was performed using CV in 0.1 M PBS of pH 6.5 at a sweep rate of 0.1 V/s as shown in Fig (b) The elevated current is reached at 10 mL SLS because at 10 mL SLS the critical aggregation concentration was reached At any further increase in the amount of SLS, the cathodic peak current decreases 2.4 Development sodium lauryl sulphate modified carbon nanotube and pencil graphite composite paste electrode The carbon nanotube and pencil graphite composite electrode was equipped by hand mixing of 55% pencil graphite powder, 15% carbon nanotube, 30% silicone oil in a mortar and grounded well for 20 to get an homogenous paste; the obtained paste was filled into a hollow tube of Teflon and it was smoothed out by a tissue paper The electrical connection was provided through a wire of copper joined to the end of the tube The surface modification of the electrode was done by immobilization 10 mL SLS surfactant on the carbon nanotube and pencil graphite composite paste electrode 3.3 Electroanalysis of RF at different electrodes The electrocatalytic behavior of RF (0.1 mM) at BPGPE, CNTPGCPE and SLSMCNTPGCPE was investigated in 0.1 M PBS of pH 6.5 at a sweep rate of 0.1 V/s and is presented in Fig 3(a) At BPGPE (curve a) the cyclic voltammogram for 0.1 mM RF reveals poor oxidation and reduction responses at À0.445 V and À0.579 V, respectively, with quasi-reversible behavior The electrocatalytic 58 G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices (2020) 56e64 Fig FE-SEM Depiction of (a) BPGPE (b) CNTPGCPE (c) SLSMCNTPGCPE (d) Electrochemical performance of BPGPE (curve a), CNTPGCPE (curve b) SLSMCNTPGCPE (curve c) for mM K4[Fe (CN)6] in 0.1 M KCl at sweep rate of 0.1 V/s Fig (a) Calibration of carbon nanotube weight for the preparation of CNTPGCPE for reduction of RF (0.1 mM) (b) Effect SLS quantity for RF (0.1 mM) electroanalysis Fig (a) Cyclic voltammetric output of RF (0.1 mM) at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) in 0.1 M PBS of pH 6.5, sweep rate of 0.1 V/s (b) Cyclic voltammetric behavior in the presence of RF (curve b) and absence of RF (curve a) at SLSMCNTPGCPE, under optimal conditions G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices (2020) 56e64 59 activity of RF was increased at CNTPGCPE (curve b) with quasireversible behavior The anodic and cathodic potential for RF at CNTPGCPE were detected at - 0.464 V and À0.577 V, respectively, with elevated current responses The current sensitivity obtained at CNTPGCPE was two times higher than that at BPGPE The SLSMCNTPGCPE (curve c) creates further enhancement in the current signal for 0.1 mM RF with anodic and cathodic detection potentials of À0.467 V and À0.678 V, respectively The current produced at SLSMCNTPGCPE for 0.1 mM RF is four times higher than the current signal produced at CNTPGCPE The results show that the electrochemical response is amplified at each step of modification The CV analysis in the presence and absence of RF was performed at the optimal condition as shown in Fig 3(b) In the absence of RF (curve a) the characterized CV portrays no peak at SLSMCNTPGCPE But under parallel conditions in the presence of RF (0.1 mM), the sharp oxidation and reduction were observed at À0.467 V and À0.678 V, respective;y, with an excellent current response (curve b) of 0.1 V/s A plot of Ipc vs pH (Fig 5(b)) confirms that the reduction peak current was maximum at pH 6.5 At a further increase and decrease in pH, the reduction peak current values decrease and so a pH value of 6.5 was preferred to complete the electrochemical experiments Meanwhile, at this pH, a swift electron transfer reaction will occur The basic pH is not appropriate for an estimate of RF since it may be influenced by the creation of unstable lumiflavin molecules with irradiation of light A plot of Epc vs pH (Fig 5(c)) demonstrates the impact of pH on the cathodic peak potential of 0.1 mM RF over the range of 5.5e7.5 The plot shows that the electrocatalytic peak is lifted towards a more negative potential with an increase in pH according to the equation Epc (V) ¼ À0.0574 pH-0.31 The slope value of 0.0574 is close to the accepted value 0.059 which indicates that the electrons and protons involved in the electrochemical reaction are in the ratio 1:1 So the sequence of reduction/oxidation of RF comprises two electrons and two protons as revealed in Scheme 3.4 Influence of potential sweep rate 3.6 Linearity, limit of detection and quantification The impact of the potential scan rate on the RF oxidation/ reduction was analyzed to identify the electrode kinetics By altering the sweep rate from 0.1 to 0.3 V/s in 0.1 M PBS of pH 6.5, the voltammograms are found as in Fig 4(a) As the sweep rate increases the peak current also increases and the anodic potential shifts to the more positive side and the cathodic peak potential shifts to the more negative side with a significant change in DEp values It shows that the RF process is quasi-reversible The potential fluctuations were due to the kinetic limitation of diffusion layers, which is formed at the upper current density The plot of Ipc vs v1/2 (Fig 4(b)) is found to be linear and it is stated by the linear regression equation Ipc (A) ẳ 2.49 105ỵ3.39 104 v1/2 (V/s)1/2 with a value for the correlation coefficient of 0.99 This discloses that the process is diffusion rather than adsorption-controlled, so it is the ideal instance for a quantitative assessment For the quantitative estimate of RF, the more responsive DPV technique was executed The effect of change in RF concentration vs oxidation peak current was obtained at SLSMCNTPGCPE using 0.1 M PBS of pH 6.5 as presented in Fig 6(a) and (b) These figures indicate that, under optimal conditions, the change in concentration of RF is directly proportional to the oxidation peak current values in the concentration domain 0.2e0.8 mM and 1e5 mM We considered the fine linear range 1e5 mM The linearity is described by an equation as Ipc(A) ẳ 8.60 106 ỵ 0.733 (M) and LOD and LOQ were calculated as 3sd/m and 10sd/m [51], respectively Here, ‘sd’ is the standard deviation of the buffer solution current values (5 replicates) and ‘m’ is the slope of the calibration graph The LOD and LOQ were found to be 1.16 Â 10À8 M and 3.87 Â 10À8 M (±0.065), respectively Table [52e56] depicts the comparison of the established electrode with previously reported electrodes The SLSMCNTPGCPE yields higher detection values as compared to modified glassy carbon with PdeCuNPS, MBeSO3HeMSM [52,53], detection values that are near to those of GCE/ AuNPS@PDA-RGO [54] and a smaller detection limit value as compared to that of SnO2/RGO/GCE, CreSnO2/GCE [55,56] Comparatively, the fabricated sensors provide advantages such as low cost, non-toxic nature, simple sensor development with good biosensing ability 3.5 Effect of pH pH is a key factor that affects the electrocatalytic sensing phenomena and is helpful in the prediction of biomolecular reaction pathways Fig 5(a) illustrates the cyclic voltammograms of 0.1 mM RF at various pH ranging from 5.5 to 7.5 of 0.1 M PBS at a sweep rate Fig (a) Cyclic voltammograms of RF (0.1 mM) at SLSMCNTPGCPE with different potential sweep rates, i.e 0.1e0.3 V/s in 0.1 M PBS of pH 6.5 (b) Graphical plot of (v)1/2 vs Ipc 60 G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices (2020) 56e64 Fig (a) Cyclic voltammetric characterization of RF (0.1 mM) at various pH from 5.5 to 7.5 at SLSMCNTPGCPE with a potential scan rate of 0.1 V/s (b) Plot of cathodic peak current vs pH (c) Plot of cathodic peak potential vs pH Scheme The Electron transfer mechanism of RF Fig (a) Differential voltammetric curves for RF from a to m i.e., 0.2e5 mM at a sweep rate of 0.05 V/s in 0.1 M PBS of pH 6.5 (b) Standard calibration plot for the concentration of RF vs the oxidation peak current G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices (2020) 56e64 61 Table Comparison of the proposed electrochemical sensor with previously reported sensor for voltammetric quantization of RF Working Electrode Modifier Method of analysis Linear range (mM) LOD (M) Reference Porous carbon Glassy carbon Glassy carbon Glassy carbon Glassy carbon CNTPGCPE PdeCuNPS MBeSO3HeMSM AuNPs@PDA-RGO SnO2/RGO Cr/SnO2 nanoparticle SLS DPV DPV DPV SWV LSV DPV 0.02 to 0.010e15 & 15e50 0.02e60.0 0.1e150 0.2e100 0.2e0.8 & 1e5 7.6 Â 10À12 5.0 Â 10À9 9.0 Â 10À9 34 Â 10À9 107 Â 10À9 11.6 Â 10À9 [52] [53] [54] [55] [56] Present work PdeCuNPS - palladium-copper nanoparticles, DPV- differential pulse voltammetry, MBeSO3HeMSM- Methylene blue incorporated mesoporous silica microsphere, AuNPs@PDA-RGO- gold nanoparticle/polydopamine/reduced graphene oxide, SnO2/RGO- reduced graphene oxide, SWV-square wave voltammetry, LSV- linear sweep voltammetry both B-complex tablets and natural food supplements, which shows the practicability of the developed sensor Table Estimate of RF in the B-complex pill and in the natural food supplement Sample Added (mM) Detected (mM) Recovery (%) RSD B-complex pill 1.0 3.0 1.0 3.0 0.95 3.023 0.96 2.91 95.0 100.7% 96.0 97.0% 1.25% 3.8 Determination, repeatability and stability of the devised sensor 2.0% Repeatability for the detection of 0.1 mM RF was assessed through CV in 0.1 M PBS (pH 6.5) with sweep rate 0.1 V/s at SLSMCNTPGCPE The fabricated electrode yields an admirable repeatability for distinct measurements with the relative standard deviation (RSD) of 1.81% The stability of the proposed sensor for the electrochemical detection of 0.1 mM RF was investigated by 30 uninterrupted cycles It has been noticed that 95% of the primary current signal was retained even after 30 cycles, so the established sensor has a high stability Natural food supplement RSD-relative standard deviation 3.7 Analytical applicability The devised SLSMCNTPGCPE was applied to estimate the amount of RF in the B-complex pill and in a natural food supplement solution, using the DPV technique at optimal conditions A suitable quantity of the B-complex powder and food supplement to a standard solution of a concentration of 1.0 Â 10À4 M was prepared using distilled water The determination of RF was performed using the standard addition method in a 0.1 M PBS solution The recoveries in the B-complex pill and food supplement were about 95e100.7% The estimates and recovery assessments are tabulated in Table So, the electrochemical sensor offers good recovery in 3.9 Electrochemical behavior DA (0.1 mM) and sweep rate effects The electrochemical enhancement of DA (0.1 mM) behavior was inspected by CV at SLSMCNTPGCPE, CNTPGCPE and BPGPE in 0.1 M PBS of pH 6.5 as shown in Fig 7(a) The DA detection using SLSMCNTPGCPE (curve c) was achieved with oxidation and Fig (a) Cyclic voltammetry of DA (0.1 mM) at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) (b) Scan rate studies of DA from 0.1 to 0.3 V/s in 0.1 M PBS of pH 6.5 at SLSMCNTPGCPE (c) a Plot Ipc vs (v)1/2 62 G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices (2020) 56e64 reduction potentials of 0.231 V and 0.165 V, respectively, with a swift current response Whereas in CNTPGCPE (curve b), DA was characterized at 0.221 V and 0.118 V with less current as compared to SLSMCNTPGCPE At BPGPE (curve a) the DA voltammetric sensing was very poor with oxidation and reduction potentials of 0.230 V and 0.139 V, respectively So, the cyclic voltammetric sensing of DA was enhanced at SLSMCNTPGCPE The scan rate effect from 0.1 V/s e 0.3 V/s on DA oxidation/ reduction was studied using CV in 0.1 M PBS of pH 6.5 displayed in Fig 7(b) The graphical plot of Ipc vs v1/2 (Fig 7(c)) gives a straight line and it is expressed using a linear equation as Ipc(A) ẳ 3.16 105ỵ1.48 10À4 v1/2(V/s)1/2, R ¼ 0.99 This illuminates that the electrochemical DA interaction with the electrode surface was diffusion controlled 3.9.1 Instantaneous analysis of RF in the presence of DA using CV and DPV The electrochemical separation of RF (0.1 mM) and DA (0.1 mM) at SLSMCNTPGCPE is achieved using CV in 0.1 M PBS of pH 6.5, with a 0.1 V/s scan rate as displayed in Fig (a) At BPGPE (curve a) RF oxidation and reduction peaks were detected at À0.473 V and À0.576 V, respectively, with a low current value But after bulk modification with CNT i.e CNTPGCPE (curve b) the RF oxidation and reduction peaks appeared at À0.490, À0.608 V and DA anodic and cathodic potential peaks were detected at 0.165 V and 0.037 V, respectively, with an improved current response as compared to BPGPE However, a clear separation and current enhancement was achieved at SLSMCNTPGCPE (curve c), the RF anodic and cathodic peaks were characterized at À0.377 V, À0.699 V and DA characteristic oxidation and reduction potentials appeared at 0.247 V and - 0.017 V, respectively, with enriched current signals So, the electrochemical separation is amended at SLSMCNTPGCPE The concurrent study of RF and DA at different electrodes using DPV were performed as depicted in Fig 8(b) At SLSMCNTPGCPE (curve c) the RF and DA detection potentials were at À0.536 and 0.080 V with a peak separation of 0.456 V and with high current responses in contrast to CNTPGCPE and BPGPE The RF and DA separation at CNTPGCPE (curve b) were characterized at the potentials À0.536 and 0.063 V with less current as compared to SLSMCNTPGCPE At BPGPE (curve a) minor separations were detected at À0.540 and 0.072 V with poor current sensitivity 3.9.2 Determination of RF in the presence of DA using DPV The feasibility of RF (0.1 mMe0.110 mM) determination in the presence of DA was analyzed by using DPV technique in 0.1 M PBS of pH 6.5 at a sweep rate of 0.05 V/s in the potential domain À1.0 to 0.4 V as demonstrated in Fig (a) The RF concentration was varied from 0.1 mM to 0.110 mM while the DA concentration was kept constant as 0.1 mM For each successive addition of RF, there is a rise in current values without affecting much to the DA peak So, it may be concluded that SLSMCNTPGCPE is the dominant electrochemical sensor for the estimate of RF in the presence of DA The plot of the concentration variation of RF from 100 mM to 110 mM against the peak current (Fig 9(b)) gives a straight line It follows the linear regression equation Ipc(A) ¼ 8.14 106 ỵ 0.21 (M) with a coefcient of correlation of 0.99 It underlines the feasibility of RF determination in the presence of DA Fig (a) CV concurrent analysis of RF and DA at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) at sweep rate of 0.1 V/s in 0.1 M PBS of pH 6.5 (b) Instantaneous separation of RF and DA at BPGPE (curve a), CNTPGCPE (curve b) and SLSMCNTPGCPE (curve c) at a 0.05 V/s sweep rate in 0.1 M PBS of pH 6.5 using DPV Fig (a) Differential pulse voltammograms for RF concentration variations from a to f i.e., 0.1 mMe0.110 mM in the presence of DA at a scan rate of 0.05 V/s in 0.1 M PBS of pH 6.5 (b) Calibration graph for RF (0.1 mMe0.110 mM) in the presence of 0.1 mM DA G Tigari, J.G Manjunatha / Journal of Science: Advanced Materials and Devices (2020) 56e64 3.9.3 Anti-interference ability analysis The effects of diverse species that can have interference with the 0.1 mM RF electroanalysis, such as folic acid, ascorbic acid, biotin, pyridoxine, alanine, glycine, estriol, tartrazine (0.1 mM) were evaluated at optimal conditions using the DPV technique The results showed that there was no significant effect on peak potential and peak current value of 0.1 mM RF So, the proposed sensor has an excellent selectivity with low interference effects (below ±3%) Conclusion The established electrode is a low cost and an active sensor for the determination of RF in the presence of DA The projected sensor offers a low detection limit, good linearity, comparable with previous sensores reported in literature The presented sensing strategy was applied to pharmaceutical and food samples with an excellent recovery So, the demonstrated sensor can be applied to routine analysis of RF in real samples Moreover, the electrode exhibits a high stability, low interference effects, good repeatability and is eco-friendly From these discussions, we conclude that the devised sensor is the best alternative for the electrochemical quantification of RF in the presence of DA Declaration of Competing Interest The authors declare no conflict of interest Acknowledgements We gratefully acknowledge the financial support from the VGST, Bangalore under Research Project No KSTePS/VGSTKFIST(L1)2016e2017/GRD-559/2017-18/126/333, 21/11/2017 References [1] P Xu, C Qiao, S Yang, L Liu, M Wang, J Zhang, Fast determination of vitamin B2 based on molecularly imprinted electrochemical sensor, Eng (2012) 129e134 [2] B Kaur, R Srivastava, Metallosilicate 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N Lavanya, S Radhakrishnan, C Sekar, M Navaneethan, Y Hayakawa, Fabrication of Cr doped SnO2 nanoparticles-based biosensor for the selective determination of riboflavin in pharmaceuticals, Analyst... 2.3 Preparation of pencil graphite powder 3.2 Optimization of the quantity of carbon nanotubes and SLS The acid-treated pencil graphite, polymer, and surfactant modified pencil graphite are previously