A Molecularly Imprinted Polymeric Sensor Based on Poly(methyldopa) for Electrochemical Quantification of Formoterol in Raw Material and Pharmaceutical Dosage Form

doi:10.21203/rs.3.rs-4200502/v1

Catechol amine-derived polymers, which include dopamine and its natural analogues, reveal desirable adhesion characteristics, great biocompatibility, and an achievable antifouling surface, by manipulating electro-polymerization procedures. Methyldopa, a synthesised substitute for dopamine which featuring several phenolic, amine, and carboxylic functional groups, a highly specific and selective molecular imprinted polymer (MIP) was utilized. The significant advancements in polymers with molecular imprints, have stimulated the addition of novel molecules as functional monomers to achieve extra precise and more selective electrochemical determination and quantification for the template analyte formoterol fumarate dihydrate (FFD), which utilized as long-acting beta2-agonist in the controlling of asthma and chronic obstructive pulmonary disease (COPD). A polymethyldopa polymer (PMD), was electro-grafted onto pencil graphite electrode (PGE) in the existence of FFD as a template, by UV spectroscopy, the interaction between poly methyldopa (PMD) and template (FFD) has been evaluated. Cyclic voltammetry was applied for electropolymerization of the MIP by scanning potential window over the range of -0.1 to 0.8 voltage versus the reference electrode Ag/AgCl in phosphate buffer at pH equal to 6.5. Indirect method was employed to measure formoterol, where a redox probe (ferrocyanide/ferricyanide) was utilized to detect the binding of FFD to the 3D binding cavities in MIP, by applying the differential pulse voltammetry. The sensor's voltammetric response was steady over a linearity range of 2×10 ^-10 M – 1 ×10 ^-9 M of FFD with a detection limit of 1.7×10 ^-11 M. The International Council for Harmonization’s (ICH) requirements were followed in the validation of the created method, The sensor’s powerful analyte selectivity and sensitivity make it suitable for quantitative evaluation of FFD in the pharmaceutical dosage formulas.

Mussel-inspired polymers

Poly (methyldopa)

Formoterol

Molecularly-imprinted polymers

electrochemical sensors

Under aerobic and alkaline pH conditions, Catecholamines have a tendency to be spontaneously oxidised and polymerized by self-assembly, forming a polymeric thin film [1-4] , However, the self-polymerization method requires increasing concentration of monomer and a lengthy time of deposition , also alkaline-labile substrate materials are incompatible with it , an alternate polymerization procedure is operating electro-chemical polymerization techniques such as cyclic voltammetry, the rate of deposition was accelerated at neutral or slightly acidic phase . Dopamine and its substitutes have been shown in numerous investigations to have the capacity to serve as active functional monomers for fabricating electro-polymerized polymer with molecular imprinting (MIP) [5-7 ], poly(methyldopa) (PMD) has lately attracted interest from the analytical chemistry discipline, owing to having an extra carboxylic group in its structure [8-10], several strategies have been applied for modification of electrochemical sensors with MIPs for increasing selective analysis of various analyte in their dosage form [11-12] including electro-polymerization, as the electro –active monomers are polymerized when the analyte drug is existing on the electrode cover upon a specified current or voltage is applied [13-14] which is straightforward accurate, precise, cost effective and analytically quick technique, with no necessity for UV exposure or heating or polymerization initiators, such performance is essentially based on the molecular interaction that happen among the template analyte molecules and the functional monomer. As well as by adjusting the variables related to the number of voltammetric cycles and the scan rate applied, the thickness of polymeric film and its uniformity and well-adherence properties can be regulated in the experiment .

Formoterol fumarate dihydrate (FFD) is chemically known as N-[2-Hydroxy-5-[(1RS)-1-hydroxy-2-[[(1RS)-2-(4-methoxy-phenyl)-1-methylethyl] amino ethyl phenyl] formamide I-butenedioate dihydrate [15] as shown in Figure [1].

The solubility of the fumarate salt of formoterol in water is 1.16 ± 0.02 mg/mL, soluble in methanol, ethanol and acetonitrile. Formoterol used as long-acting beta2-agonist in the controlling of asthma and chronic obstructive pulmonary disease (COPD). It has similar properties to those of salbutamol, Formoterol fumarate dihydrate is direct acting sympathomimetic, primarily β-adrenoceptor stimulating action that is specific to β2 receptor (β2 agonist). It has rapid onset of action (2-3 minutes) and has prolonged duration of action up to 12 hrs, it is utilized in cases when treating reversible airway obstruction, such as chronic asthma or certain COPD patients, requires consistent long acting beta2 agonist treatment. It can be purchased as a single-entity or in various formulations combined with inhaled corticosteroids [15-16]. Literature survey revealed several UV spectrophotometry methods for determination of FFD with other drugs combination [17-20], several chromatographic methods including: UPLC [21], HPTLC [22-24] and HPLC [25-31] for simultaneous quantitation of FFD with other drugs combination, and voltammetric method based on square wave and differential pulse of formoterol in aqueous solution using 0.5 M sulphuric acid over the linear range 8×10 ^-6-6×10^-5M [32].

In the current contribution, we investigate methyldopa’s potential as an electro-active monomer in the process of creating electro-polymerized (MIP) electrode for the purpose of quantitavely determination of formoterol fumarate in different matrices for the first time. Initially, the screening of the interaction between FFD and various functional monomers was performed using UV spectrophotometry measurements to evaluate the plausible molecular interactions between the functional monomer complex and the template, to find out which template monomer had the maximum interaction, the functional monomers o-phenylenediamine, dopamine, and methyldopa were evaluated in order to polymer preparation and hence higher sensitivity. Additionally, a variety of electrochemical factors were thoroughly assessed to determine the ideal conditions for boosting the suggested methyldopa electro-grafting method’s sensitivity. Finally, the differential pulse voltammetry (DPV) was implemented for indirect quantitative estimation of FFD using redox probe in raw powder and pharmaceutical dosage form, which have benefits for the quality control laboratories to routinely practice it.

Instruments

PalmSens4 potentiostat were be conducted for the electrochemical experiment and operated with PSTrace 5.0 software (PalmSens, Netherlands), The 0.9 mm diameter pencil graphite electrode (PGE, HB, Rotring, Germany) that serves as the working electrodes, platinum counter electrode, and Ag/AgCl reference electrode for the electrochemical operating cell. For spectrophotometric measurements, a Shimadzu EPMA-1610, Tokyo, Japan, double beam UV-visible spectrophotometer was used. The chemical configuration of the surface was determined using an X-ray photoelectron spectrometer (XPS); (K-Alpha, ThermoFisher Scientific, WI, USA, X-ray photoelectron spectrometer).

Materials and reagents:

Pure FFD were kindly supplied by Novartis Company Cairo, Egypt. The certified purities were 99.5% ±1.26, according to the reported method [25].

Glacial acetic acid, methanol, dopamine hydrochloride, o-phenylenediamine, methyldopa, potassium ferrocyanide, K₄[Fe (CN)₆], and potassium ferrocyanide, K₃ [Fe (CN)₆] were all premium analytical grade chemicals and reagents that had been purchased from Sigma-Aldrich (Darmstadt, Germany). Double-distilled water was gotten from a new human power1 water purifying system (Human Corporation in Seoul, South Korea).

Phosphate buffer (0.1 M) was prepared comprising the pH range from 5.5 to 8.5 as a supportive electrolyte used for electro-polymerization procedure.

Pharmaceutical dosage form (Flutiform^® inhaler): batch number 9h053fc It is manufactured by Fisons Limited, United Kingdom, marketing authorization holder: Napp Pharmaceuticals Ltd. (I.A.C. of Mundipharma), Cambridge, United Kingdom. Each metered dose (ex-valve) contains 5.0 µg of (FFD) Formoterol Fumarate Dihydrate and 50.0 µg of drug full name (FP) Fluticasone Propionate.

Procedure

The methyldopa electro –polymerization process

First, the PGE’s bar surface was cleaned from any contaminants by washing it in a methanol and water mixture (1:1v/v). Next, it was dried under a nitrogen stream, then it was connected as working electrode and immersed in sodium phosphate buffer with pH equal to 6.5 containing 5×10^-3 M of FFD and 5×10^-3 M of methyldopa, nitrogen gas was used to purge the solution from oxygen for about fifteen minutes, then ten voltammetric cycles were applied to begin the electro-polymerization process between potential windows from -0.1 v to 0.8 V using a scan rate of 130 mV/s versus the Ag/AgCl reference electrode.

Subsequently, the formed template was eluted, the modified electrode, or PMD/PGE, was gently stirred for 20 minutes with a solution of methanol in addition to glacial acetic acid with the ratio (4:1) v/v while being washed .

Afterwards, the electrode was undergone three consecutive washes with water, then it was subjected to electrochemical characterisation by operating CV in KCl solution (0.1M) containing an equimolar amount of (5 mM) of [Fe (CN) ₆]^-3/-4 redox probe. Following that, the PMD/PGE electrode was immersed in FFD working solutions, then back to redox probe solution for electrochemical quantitative measurements of FFD after drug rebinding. by plotting the normalized decrease in the redox probe's current peak after FFD drug rebinding versus the corresponding template (FFD) concentrations in the range of 2×10^-10 M to 1×10^-9 M The calibration curve was designed, also X-ray photoelectron spectrometer (XPS) was employed to characterise the surface chemical configuration of the prepared electrodes. The electrochemical characterization was accompanied by utilizing 0.1 M KCl solution with an equimolar concentration of (5 mM) of [Fe (CN) ₆]^3−/4− redox probe.

Application to pharmaceutical formulation:

Flutiform inhaler labelled to contain 5 µg of FFD per one actuation, by taking four actuations in 25-mL volumetric flask, and make further dilution, we reach the final concentration 1×10^-9M, Subsequently, the previously described electrochemical measurements were carried out, and drug concentrations were quantitively estimated using the regression equation that was previously computed.

As MIPs become increasingly significant as efficient adsorption particles, there is a scope to use novel functional monomers with extra functional groups to increase their binding capacity to a given template, so increase the selective determination of various analyte in different matrices as dosage form and biological samples, so the electro-polymerization of methyldopa as functional sensing and efficient MIP recognizing material have been implemented. Electro-polymerization, proceed via applying a specific current or voltage which causes the electroactive monomers to be polymerized instantaneously on the PGE electrode surface in the occurrence of the template FFD analyte, and has the advantage of being simple, highly reliable without requiring a variety of polymerization initiators. Another benefit is that experimental conditions such as the number of applied voltammetric cycles and the scan rate could be adjusted to control the thickness of the polymeric film, resulting in thin, consistent, and extremely adherent films, [33-35].

The conducting of UV spectrophotometric evaluation is an efficient, fast, and economical tool for screening template–monomer complexes [36], it was observed that the FFD/methyldopa combination ʼs absorption spectrum has a marked hyperchromic shift. As the functionality of Polymers imprinted with molecules were mostly dependent on the molecular interactions of analyte molecules and functional monomers created a strongest interaction with the template drug. The FFD/methyldopa ʼs UV spectrum represents the creation of a complex with methyldopa characterized by increasing of binding capacity and its stability, as shown in Figure [2].

Methyldopa electro-polymerization on PGE surface

Dopamine and its analogues were electro-polymerized in several reported investigations to create polymeric films that worked well as MIPs for the target analyte. We had investigated the electro-polymerization of methyldopa, as a functional monomer, used to fabricate electrochemical sensors of polymers imprinted with molecules, a novel technique was operated and adjusted for methyldopa electro-polymerization via cyclic voltammetric approach, measurements were accomplished on PGEs for their availability, besides being easier to use, more affordable, more cost effective and environmentally friendly than other carbon electrodes [37]

The voltammogram of methyldopa electro-polymerization was recorded after 10 cycles of applying a voltage range of -0.1 to 0.8 V at a scan rate of 130 mV/s, can be observed in Figure [3].

Firstly, molecules of methyldopa were undergone intramolecular oxidation, cyclization, and consequent polymerization to produce a structure resembling melanin. This is indicated by the rapid decline of anodic peak current following the first cycle, which suggests a high rate of electro-polymerization process, that was accomplished without destroying the polymer’s distinct phenolic and carboxylic efficient groups which accountable for additional binding with molecules of FFD [38] Thereafter, as the number of voltammetric cycles increased that the peak current was gradually decreased till it was reduced showing that a PMD polymeric layer had completely covered the PGE surface, and this hinders the electron transfer, PMD/PGEs were formed by electro-polymerization with FFD acting as a template molecule.

Electrochemical characterisation for the process of electro-polymerization

Satisfactory results were obtained when measuring 5 ×10^-3 M of FFD in sodium phosphate buffer pH equal to 6.5 by applying voltage over ten cycles utilizing a scan rate of 130 mV/s, subsequently ,eluting with a methanol/glacial acetic acid's mix with a ratio of 4:1 for about 20 min in order to extract the template medication leaving behind three-dimensional channels inside the matrix of polymer ,that have function as active pathways for the probe's transmission, The peak value of the current has obviously reduced at the FFD/PGE surface when the electro-polymerization procedure has finished and prior to template removal. This reflects the PMD coating that insulates the entire PGE surface, preventing electron transmission. Consequently, the probe solution’s redox peaks were successfully established upon rebinding with FFD molecules these channels were blocked with notable decline of [Fe (CN) ₆]^-3/-4 signal. These outcomes demonstrated how the imprinted cavity that was created could adsorb the analyte during the rebinding procedure as presented at Figure [4].

X-ray photoelectron spectrometer (XPS) survey

Following adherent film deposition on the electrode surface, the characteristics of the film’s chemical and electronic features were examined, Figure [5] show the PMD/PGE film’s XPS survey spectrum with three distinctive O1s, N1s and C1s peaks , indicating presence of oxygen, carbon and nitrogen comprising group, The successful electro-polymerization of PMD film attaching to the PGE electrode was indicated by the appearance of the N1s peak, at binding energies of 533.18 eV, 285.97 eV, and 401.16 eV, the three peaks were detected.

Condition optimization for measurements of FFD electrochemically using PMD/PGEs

An examination into enhancing the sensitivity of the sensor led to an exploration of optimized experimental conditions. Intentional adjustments were made to various experimental parameters, such as the number of cycles, scan rate, and pH buffer range, and through a single variable optimization research that employing a one-variable-at-a-time approach. The objective was to improve measured outcomes while saving time.

Initiate by the elution of the template medication from the cross-linking polymer without altering its structure, a suitable elution solvent was acclaimed, the solvent were mixed with either an acid or a basic in order to disrupt the electrostatic bonds between the polymer and template, aiming for optimal signal sensitivity and efficient template removal. A mix of methanol and glacial acetic acid was chosen, considering the high solubility of FFD in methanol and the ability of acetic acid to disrupt the hydrogen bond formed between PMD and FFD [39]. An extraction time of 20 minutes proved efficient for template removal, and a methanol to acetic acid ratio of 4:1 was identified as satisfactory for achieving reproducible and consistent sensor outcomes.

Effect of scan rate:

During an investigation into the current response, the scan rate of CV measurements for a 5 ×10 ^-3M FFD in a sodium phosphate buffer solution was systematically altered, ranging from 70 to 150 mV/s. Notably, the most significant reduction in current response after the washing process and subsequent drug rebinding occurred at a scan rate of 130 mV/s. This finding highlights the sensitivity of the system to changes in the scan rate and underscores the importance of optimizing this parameter for the desired outcomes in the experiment.

Effect of pH

The pH of the sodium phosphate buffer solution was investigated alongside CV measurements of 5 ×10 ^-3M FFD across a range of diverse pH values, ranging from 5.5 to 8.5. The analysis revealed that the most distinct peak formation and consistently reproducible current responses were achieved at a pH of 6.5. This pH value appears to be optimal for obtaining reliable and well-defined outcomes in the CV measurements of the FFD system.

Number of cycles

The impact of varying the number of cycles on the current response was examined, revealing that the optimal current response was achieved when increasing the number of cycles to ten. Subsequent increases in the number of cycles resulted in a decline in the current response, indicating that further cycles did not contribute to an improvement in sensitivity. The optimization studies played a crucial role in enhancing the sensor's sensitivity, culminating in a maximum response to FFD, as depicted in Figure [6].

The analytical performance for FFD quantitatively assay by using PMD/PGEs

Differential pulse voltammetry (DPV) was employed instead of CV due to its ability to enhance current sensitivity. This improvement arises from the differentiation between the pulse application and the subsequent decrease in charging current. Optimal signal resolution and a reproducible current response were achieved by using a step potential of 0.01 V, an E pulse of 0.2 V, and a t pulse of 0.02 s, with a scan rate of 0.1 V/s. Subsequently, the current peak responses from DPV measurements were recorded for the redox probe after multiple FFD rebinding events within a concentration range spanning from 2×10^-10 M to 1×10^-9M. This data is visually presented in Figure [7].

The calibration plot, accompanied by the computed regression equation, is illustrated in Figure [8].

These figures depict the relationship between the concentration of the template (FFD) and the diminishing signal of the redox probe, providing a comprehensive view of the concentration-dependent response.

Stability and reproducibility of the sensor

The intra-batch and inter-batch reproducibility of the fabricated PMD/PGE sensor were analyzed by evaluating FFD at three concentration levels (2 ×10^-10, 4 ×10^-10and 6 ×10^-10M) manipulating three different electrodes within the same day (intra-batch analysis). The same protocol was strictly adhered to ensure consistency.

For intra-batch analysis, the estimated RSD% values are presented in Table (1), demonstrating that they were within the permissible range of less than 2%. This indicates that the suggested method is precise and yields consistent results within the same day.

Table (1) Assay validation parameters of the proposed DPV method for the quantitatively determination of formoterol fumarate dihydrate in pure powder form

Parameters (DPV)	FFD
Linearity range (M)	2×10^-10 M to 1×10^-9 M
Slope	1E+08
Standard error of slope	5E+05
Intercept	0.8275
Standard error of intercept	33E-05
Correlation coefficient	0.9999
Accuracy (mean ± SD)	101.42 %±1.08
Repeatability ^a(RSD)%	1.026
Intermediate precision^b(RSD)%	1.260
LOD^c	1.7×10^-11M
LOQ^d	5.18×10^-11M

^(a) Intraday precision; average of three different concentrations of three replicate each (n=9) repeated three times within the same day.

^(b) Interday precision (n=9) : average of three different concentrations of three replicate each (n=9) repeated on three successive days.

^(c)LOD (Limit of Detection): 3.3 (SD of residual) / slope

^(d)LOQ (Limit of Quantitation):10 (SD of residual) / slope

To evaluate inter-batch reproducibility over three repeated days, the RSD% values, also presented in Table (1), remained within the acceptable range of less than 2%. This further confirms the precision and reproducibility of the method over different experimental days.

Accuracy was evaluated by estimating the recovery percentages for four different concentrations (3×10^-10, 5×10^-10, 7×10^-10and 9×10^-10M) falling within the linearity range, as detailed in Table (1). The acceptable recovery percentages obtained affirm the accuracy of the proposed method for FFD analysis.

Selectivity of the proposed sensor

The selectivity of the proposed sensor was investigated by evaluating the change in differential pulse voltammetry (DPV) current of the redox probe when measuring 1×10^-9 M of FFD with the existence of dissimilar interfering drugs at different concentrations. These interfering drugs included salbutamol, a structurally comparable drug used to treat symptoms of asthma and COPD, as well as fluticasone, a co-administered drug with FFD. Additionally, acetaminophen, a commonly co-administered analgesic medication anticipated to be present in-patient plasma, was also assessed. The data provided at Table (2), revealed that the influence of interfering drugs at the FFD peak was insignificant, this observation underscores the high identification, and enhanced fabricated MIP sensor's selectivity and sensitivity. The sensor has a minimal interference from structurally similar and co-administered medicine, highlighting its specificity for FFD assessment.

Table 2: The evaluation of selectivity analysis of the fabricated sensor towards formoterol fumarate in the existence of some interfering drugs

Interfering medicines	Concentration(M)	∆I for 1.0×10^-9M FFD estimation at 0.11 V	% relative error in current
Salbutamol	1×10^-9	0.304	4.10
	5×10^-10	0.289	3.89
Fluticasone	1×10^-9	0.217	2.50
	5×10^-10	0.198	2.28
paracetamol	1×10^-9	0.076	1.62
	5×10^-10	0.043	0.90

Dosage form analysis

The fabricated PMD/PGEs were employed for the quantification of FFD in its marketed dosage form, Flutiform®. Three separate samples were analyzed, and the measurements yielded an acceptable average recovery percentage with an RSD percentage of less than 2.0, as detailed in Table (3). This indicates the precision and consistency of the sensor in quantifying FFD in the pharmaceutical formulation.

Table 3: Estimation of FFD in Flutiform® inhaler pharmaceutical dosage form by DPV method

Preparation

Claimed Concentration

FFD (Recovery %±SD^*)

Flutiform ^® Inhaler

B.N 9h053fc

1×10^-9 M

100.67%± 1.16

*Average of three determinations

Furthermore, standard addition techniques were implemented, and the results, depicted in Table (4), demonstrated appropriate recovery percentages. These findings underscore the heightened affinity for recognition of the MIP sensor toward FFD. The use of standard addition techniques further validates the accuracy and reliability of the sensor for quantifying FFD in complex matrices such as pharmaceutical formulations.

Table 4: Application of standard addition technique for the estimation of FFD in pharmaceutical dosage form by the proposed DPV method

pharmaceutical preparation	Added concentration (M)	Taken concentration (M)	Recovery % of FFD
Flutiform ^® Inhaler B.N 9h053fc	2×10^-10	5×10^-10	99.00
	3×10^-10	5×10^-10	101.33
	4×10^-10	5×10^-10	101.71
	5×10^-10	5×10^-10	100.52
Mean			100.62
SD			1.19
RSD%			1.18

Finally, a statistical investigation employing the student t-test and F-test was computed to compare the results gained from the proposed technique and those from a reported HPLC method [25]. With a p-value set at 0.05, it has been found that the computed student t-test and F-test outcomes were lower than their corresponding tabulated ones, indicating a lack of disagreement between the projected and reported process and highlighting the reliability of the fabricated MIP sensor in the quantification of the template (FFD), as illustrated in Table (5).

Table 5: Statistical analysis of the results obtained by the proposed DPV methods and the reported HPLC method for the determination of FFD.

Parameters	Proposed DPV method	Reported method ^b (FFD)
Mean R%	101.62%	99.5%
SD	0.45	1.26
n	5	5
Variance	0.205	1.60
Student’s t- test ^a	1.75 (2.01)^a
F –test ^a	1.09 (6.38)^a

^aTabulated values of t-test and F-test were obtained at P=0.05

^bReported RP-HPLC method using C18 column, acetonitrile: 0.01 m ammonium

Dihydrogen o-rtho phosphate buffer (80:20) v/v as a mobile phase and UV detection at 215 nm [25]

Moreover, the results underwent statistical evaluation using a one-way ANOVA test, revealing no discernible difference between the suggested technique and the reported one, as demonstrated in Table (6). This further supports the consistency and agreement between the proposed MIP sensor method and the established HPLC method for the quantification of FFD.

Table 6: Results of One -way ANOVA for comparison of the proposed DPV method for the estimation of FFD and the reported method [25]

	Source of variation	DF	Sum of squares	Mean square	F -value	P -value	F crit.

FFD	Between groups	1	9.12	9.12	4.63	0.00013	5.32
	Within groups Total	8 9	1.575 10.69	0.196

Electrochemical sensors are highly advantageous due to their simplicity, convenience, eco-friendliness, reduced reagent consumption, and cost-effectiveness. They offer a rapid analysis, producing accurate, precise, and reliable results. The proposed MIP sensor represents a novel approach by introducing methyldopa, which forms a stable complex with FFD, to fabricate an MIP film through a straightforward electro-polymerization process. This innovative sensor was validated by examining UV spectral changes in various complexes, providing confirmation without the need for expensive instrumentation. The sensor's chemical composition was defined using XPS. The suggested sensor demonstrated the capability to assess FFD in both bulk form and pharmaceutical dosage form without interference. Its sensitivity in recognizing low concentrations in the sub-micro molar range is particularly noteworthy, making it a valuable tool for potential applications in pharmacokinetics research. Furthermore, the sensor exhibited excellent selectivity, enabling the analysis of FFD in the presence of structurally similar and commonly co-administered drugs such as salbutamol and the frequently co-administered painkiller paracetamol. This selectivity positions the sensor as a promising platform for FFD sensing in pharmaceutical formulations and raw materials. Overall, the developed electrochemical sensor presents a versatile and efficient solution for FFD analysis, holding significant promise for various applications in the pharmaceutical field.

Credit authorship contribution statement

Hamees Abdelaty: Conceptualization, Methodology, Software, Data curation, Validation, Writing – original draft, Writing – review & editing. Maha Hegazy: Conceptualization, Visualization, Methodology, Investigation, Data curation, Supervision, Writing – review & editing. Amr Beket: Conceptualization, Visualization, Methodology, Investigation, Writing – review & editing. Samah Sabry: Visualization, Investigation, Supervision, Writing – review & editing. Shereen A. Boltia: Conceptualization, Visualization, Methodology, Investigation, Data curation, Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work presented in this paper.

Data availability

Data will be made available on request.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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No competing interests reported.

A Molecularly Imprinted Polymeric Sensor Based on Poly(methyldopa) for Electrochemical Quantification of Formoterol in Raw Material and Pharmaceutical Dosage Form

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Version 1

Abstract

Figures

Introduction

Experimental

Results And Discussion

Method validation

Conclusion

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References

Additional Declarations

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Version 1