Functionalized Fe3O4 Magnetic Nanoparticle Potentiometric Detection Strategy versus Classical Potentiometric Strategy for Determination of Chlorpheniramine Maleate and Pseudoephedrine HCl

Nanosized adsorbents when used in potentiometric methods of analysis usually show better performance rather than the traditional potentiometric approach; this is attributed to the high specific surface area of the nanomaterial used in addition to the lack of internal diffusion resistance, thus improving their adsorption capacity. In the presented work, a rapid and sensitive potentiometric determination of chlorpheniramine maleate (CPM) and pseudoephedrine hydrochloride (PSE) in pure form, in pharmaceutical preparation, and in biological fluid was developed based on functionalized magnetic nanoparticles (Fe3O4). This strategy was compared with the classical potentiometric strategy. Three types of sensors were constructed using phosphotungstic acid (PTA), β-cyclodextrin (β-CD), and β-cyclodextrin-conjugated Fe3O4 magnetic nanoparticles for the potentiometric determination of each of CPM and PSE. The prepared sensors were characterized in regards to their composition, life duration, working pH range, and response time. The sensors have demonstrated promising selectivity to CPM and PSE in the presence of pharmaceutical formulation excipients, plasma matrix, and a diversity of both organic and inorganic interfering materials. The developed sensors have displayed good responses. Statistical comparison of the achieved results with a reported method has revealed no significant difference regarding both accuracy and precision.

CPM, PSE, and IBF are coformulated drugs in a single dosage from which is utilized for treating the symptoms cough and common cold.
Analytical methods involving molecular host-guest approaches have attracted tremendous concern due to their high selectivity. Cyclodextrins as ionophoric polymers are extensively recognized to compose stable inclusion complexes with a variety of organic, inorganic, and biological guest molecules in their lipophilic cavities while demonstrating high molecular selectivity as well as enantioselectivity [24,25].
Functionalized magnetite nanoparticles have the ability to be widely dispersed in the analyte solution and intensely stimulate the chemical reaction between their functional groups and the target analyte, and this is attributed to their considerably lower diffusion layer thickness in contrast to their bulk counterparts. Magnetic nanoparticles are among the particles that were actively examined, where based on their interesting magnetic properties, they are evolving as possibly useful tools for a wide variety of applications [26] due to, for example, their successful usage as a new approach in potentiometric analysis of drugs in different pharmaceutical preparations [27].
In view of the previously mentioned points of view, we aimed to develop a new potentiometric approach utilizing magnetic nanoparticles for the rapid and sensitive quantification of CPM and PSE in their bulk powder, pharmaceutical dosage form, and plasma samples without interference from IBF. e proposed study has demonstrated certain encouraging improvements to the use of β-cyclodextrin. e achieved results were compared to the classical potentiometric methods.

Experimental
2.1. Apparatus. Potential measurements were carried out using a Jenway digital ion analyzer model 3505 (Jenway, UK) with Ag/AgCl double junction reference electrode (Aldrich, USA). e pH adjustment was performed utilizing a Jenway pH glass electrode (Jenway, UK). Imaging of Iron oxide magnetite nanoparticles was performed with the aid of a JEOL JEM-2100 high-resolution transmission electron microscope where the accelerating voltage was adjusted to 200 kV.    [28,29]. In addition, imaging was performed to confirm the size and shape as demonstrated in Figure 2.

Standard Solutions
e stock solutions of both CPM and PSE were prepared separately in the concentration of (10 −2 M) using distilled water as a solvent.
Both the stock and working solutions were stable for at least one month when kept in a refrigerator at 4°C.

Precipitation of the Ion Exchanger.
Two aliquots of 10 mL of (10 −2 M) aqueous standard CPM and PSE solutions were transferred in two different beakers followed by the addition of 10 mL of aqueous (10 −2 M) of PTA solution on each beaker. e two prepared solutions were mixed well for 5 minutes. e obtained precipitates were filtered through Whatman filter papers and then washed several times using cold distilled water till the precipitate is chloride-free as indicated when tested by AgNO 3 solution. e precipitate is then dried at room temperature and ground to be in the form of fine powder. Elemental analysis (carbon, hydrogen, and nitrogen) was performed to check both the formation and purity of the ion-associates as well as the chemical composition of the precipitates as abridged in Table 1. 1, 2, 4, and 5). For the preparation of sensors 1 and 4, 10 mg of the ion exchangers (CPM-PT and PSE-PT) was separately mixed in glass Petri dishes (5 cm diameter) with 0.35 ml of DBP and 0.19 g PVC. While for the preparation of sensors 2 and 5, the following materials were thoroughly mixed with each other: 0.19 g PVC with 0.35 ml DBP and 0.04 g β-CD. Subsequently, the obtained mixtures were dissolved in 5 ml THF in Petri dishes (5 cm diameter) and homogenized carefully.

Fabrication of PVC-Based Membrane Sensors (Sensors
e Petri dishes were left overnight at room temperature after being covered with filter papers in order to permit for solvent evaporation. Master membranes were formed with a thickness of about 0.1 mm. Disks of about ≈10 mm diameter were cut from the master membranes, with the aid of a cork borer. e disks were then pasted utilizing THF to interchangeable PVC tips that were clipped into the end of the electrodes glass bodies. Equal separate volumes of (10 −2 M) CPM or PSE and (10 −2 M) KCl were mixed well where the obtained solution was considered to be the internal reference solution. However, the internal reference electrode was formed through the immersion of an Ag/AgCl wire (1 mm diameter) in the internal reference solution. Each formed electrode (sensor) was preconditioned by being dipped in (10 −2 M) CPM and PSE solutions for 24 h. e electrochemical cell for the potential measurements could be represented as follows: Ag/AgCl (internal reference electrode)/1.0 × 10 −2 M CPM or PSE solutions, 1.0 × 10 −2 M KCl (internal reference solution)//PVC membrane//test solution (pH 4-8) and (pH 4-7) for CPM and PSE, respectively//Ag/AgCl double junction reference electrode. e electrodes were usually kept in deionized water in between the measurements. e fabrications of the four ISE electrodes (sensors 1, 2, 4, and 5) are described in Table 2.

Coating of Nanoparticles with β-CD and Fabrication of Functionalized Fe 3 O 4 Nanoparticles Membrane Sensors (Sensors 3 and 6).
Coating of nanoparticles with β-CD, as ionophoric polymer, was achieved through the addition of 0.04 mg β-CD which is dissolved in 0.35 mL DBP as a plasticizer. e components were carefully mixed with 5 mL THF until the mixture is completely homogenous. en, 1 mL of the nanoparticles solution was added, followed by sonication for 15 minutes, and finally, the mixture was left to allow for the evaporation of THF.

Journal of Analytical Methods in Chemistry
For the fabrication of the functionalized Fe 3 O 4 nanoparticles membrane sensors, the same procedure for the preparation of sensors (2 and 5) was repeated as explained in Section 2.4.2.
However, in order to allow for the formation of the inclusion complex between the nanoparticles' functional groups and CPM and PSE, 0.1 mL of the final magnetic fluid was added to the inner solution (which is composed of equal volumes of (10 −2 M) CPM or PSE and (10 −2 M) KCl) of the membrane electrode of the prepared sensors. e internal reference electrode was formed through the immersion of a Ag/AgCl wire (1 mm diameter) in the internal reference solution.
e designed sensors (3 and 6) were preconditioned by being dipped in (10 −2 M) CPM and PSE solutions for 24 hours. e induced membrane potential was measured while applying a magnetic field with the aid of a magnetic stirrer, during the time of sample measurement [26]. e calibration curves were constructed by plotting E (mV) against the corresponding negative concentration logarithm of CPM or PSE.

Sensors Calibration.
e conditioned sensors were calibrated through their immersion in about 50 mL of the working standard solutions equivalent to 1 × 10 −8 -1 × 10 −3 M and 1 × 10 −9 -1 × 10 −3 M for CPM and PSE, respectively. e sensors were in conjunction with the Ag/AgCl reference electrode and were permitted to equilibrate with constant stirring utilizing a magnetic stirrer throughout the whole process. e sensors were usually washed with distilled water in between the measurements. e electrode potential of each sensor was recorded after being stabilized to ±2 mV and was plotted against the corresponding negative logarithmic concentration of CPM and PSE. Consequently, the constructed calibration curves were then utilized for the measurement of unknown samples.

Effect of pH.
As the developed potentials of the six fabricated sensors is influenced by the pH, the effect of pH was examined within the range of 2-10 utilizing the solutions of CPM and PSE in a concentration equivalent to 10 −4 M and 10 −3 M, respectively. Both dilute sodium hydroxide and hydrochloric acid solutions were used for pH adjustment to the required value. e acquired potential for each pH value was recorded.

Sensors Selectivity.
e interference which foreign ions might perform on the response of each fabricated sensor to its primary ion was evaluated using the potentiometric selectivity coefficient-log K pot. (primary ion, interferent). e selectivity coefficients were calculated through measurement of the developed potentials from 10 −3 M aqueous of each of CPM and PSE solution and then for 10 −3 M aqueous interferent solution. For calculating the potentiometric selectivity, the following equation was used: where E D is the potential measured in 10 −3 M of drug solution for CPM or PSE, E M is the potential measured in 10 −3 M interferent solution, Z D and Z M are the charges of CPM or PSE and interfering ion, respectively, and 2.303RT/Z D F represents the slope of the investigated sensor (mV/concentration decade).

Application to Pharmaceutical Dosage Forms.
Ten Sinlerg ® tablets were accurately weighted, powdered, and mixed well. e weight equivalent to one tablet was transferred into a 50 mL volumetric flask, and the volume was completed using distilled water. en, further dilution with the same solvent was carried out to achieve a concentration of 10 and 150 μg/mL of CPM and PSE, respectively (IBF is sparingly soluble in water). e fabricated sensors (3 and 6) were dipped in the solution and were kept under constant stirring using a magnetic stirrer throughout the whole process. e sensors were in conjunction with the Ag/AgCl reference electrode.

Determination of CPM and PSE in Spiked Human
Plasma. One milliliter of the working standard solutions of CPM and PSE equivalent to 10 −5 , 10 −6 , and 10 −7 M was added individually into a set of stoppered tubes comprising 9 mL of human plasma, and then the tubes were shaken for 1 min. e fabricated sensors (3 and 6) were dipped in the plasma solutions and were kept under constant stirring using a magnetic stirrer throughout the whole process. e sensors were in conjunction with the Ag/AgCl reference electrode. e acquired potential values were measured, and the concentrations of CPM and PSE were calculated from the corresponding previously computed regression equations.

Results and Discussion
Magnetite Fe 3 O 4 nanoparticle is currently one of the most widespread magnetic nanoparticles which are extensively utilized in several applications. Based on the specific properties of nanoparticles, including their extreme small size, large surface area to volume ratio, and non-existence of internal diffusion resistance, this has led to providing improved kinetics for adsorbing contaminants from aqueous  [30]. Besides, the insertion of β-CD on the surface of magnetic nanoparticles was expected to enhance both their stability and dispersion in aqueous solutions, thus leading to increase in their surface areas and consequently improving their adsorption capacities [31][32][33]. e magnetic nanoparticles utilized in the presented study were manufactured by a classical coprecipitation method using β-CD as ionophoric polymer [34]. rough the inclusion of the prepared magnetic fluids into the inner solution of the membrane electrode, this would allow for the prompt and symmetric dispersion of the ion exchangerfunctionalized magnetic nanoparticles in the solution [26,35]. When a magnetic field is applied, the magnetic nanoparticles will be aggregated to the inner side of the polymeric membrane while the adsorbed ionophore and plasticizer on the nanoparticles will dissolve on the surface of the membrane resulting in a substantial potentiometric response [26,35] (Figure 3). e introduced work is devoted to evaluate the possibility of quantitative analysis of CPM and PSE by using ion selective electrode (ISE) sensors by means of PTA as ion exchanger, β-CD that forms host-guest inclusion complexes, and β-CD-conjugated Fe 3 O 4 magnetic nanoparticles. A comparative study was held between traditional potentiometric strategy and potentiometric detection strategy based on functionalized Fe 3 O 4 magnetic nanoparticles showing their advantages. e performance characteristics of the fabricated sensors were assessed in accordance with the IUPAC recommendations [36].

Sensors Fabrication.
Generally, the solubility product of PTA ionic exchangers is low and it has suitable grain size. CPM and PSE were found to react as a monovalent cation, and they formed 3 : 1 ion association complex with PTA which was confirmed both by elemental analysis (Table 1) as well as by the achieved Nernstian slopes.

Sensors Performance Characteristics and Response Time.
e electrochemical performance characteristics of the examined CPM and PSE sensors were assessed in accordance with the IUPAC recommendations [36] where the obtained results are abridged in Table 3. Typical calibration plots are demonstrated in Figure 4. As the electrodes responds mainly to the activity of the analytes (as cations) rather than their concentration, the slopes of the calibration plots have displayed a deviation from the ideal Nernstian slope (60 mV). e slopes of the calibration plots were 54.60, 55.10, 53.70, and 55.00 mV/concentration decade for sensors (1, 2, 4, and 5), respectively. However, Fe 3 O 4 electrodes have exhibited the nearest value to the ideal Nernstian slope with the values of 58.17 and 57.79 mV/concentration for sensors (3 and 6), respectively. e investigated Fe 3 O 4 electrodes have demonstrated constant potential values in between different measurements where the slopes of the calibration curves were not altered by more than ±2 mV/decade throughout the stability periods of the developed sensors. Additionally, the slopes were not changed significantly but revealed a gradual decrease in sensitivity. e examined Fe 3 O 4 electrodes have displayed a fast response time. e time desired by the electrodes to accomplish ±1 mV values of the equilibrium potential after increasing the analytes concentration to 10-folds was about 5-10 s.

Effect of pH.
In order to optimize the experimental conditions to allow for the quantitative analysis with the ion selective electrodes, the effect of pH on the response of the examined electrodes was investigated using 1 × 10 −4 and 1 × 10 −3 M solutions of CPM and PSE. e potential-pH profile for sensors (1, 2, and 3) has demonstrated that the responses were fairly constant within the pH range 4-8, whereas the responses of the sensors (4, 5, and 6) were constant within the pH range 4-7. e effect of pH on the responses of the developed electrodes is illustrated in Figure 5.

Sensors Selectivity.
e potentiometric selectivity coefficients of the investigated sensors in the presence of coformulated drug (IBF), excipients present in the pharmaceutical formulations in addition to some inorganic cations such as K + , Na + , and Ca 2+ which are normally present in biological fluids, are all demonstrated in Table 4. e obtained results have revealed that the Fe 3 O 4 sensors (3 and 6) exhibited higher selectivity than the classical sensors (1, 2, 4, and 5) for the quantitative analysis of CPM and PSE. e proposed method was validated according to ICH guidelines, and it was found to be linear within the ranges from 10 −8 to 10 −2 with correlation coefficient close to one. e method displayed good accuracy and precision, where the accuracy was found to be between 99.45 and 101.85 and precision was less than 2. e calculated LOD was found to be 5 × 10 −8 for sensor 3 and 4 × 10 −9 for sensor 6 which indicates the sensitivity of the proposed method. Due to these obtained promising results, the method was applied for the estimation of CPM and PSE both in pharmaceutical formulation and human plasma.

Potentiometric Determination of CPM and PSE in
Pharmaceutical Formulation. Due to the higher selectivity of the Fe 3 O 4 sensors (3 and 6), they were applied for the quantitative determination of CPM and PSE in tablet dosage form, where the recovery% ± S.D. was found to be 102.26 ± 1.204 and 101.09 ± 1.106 for CPM and PSE, respectively. e obtained results were compared by using the reported method and verified the ability of the proposed sensors to be applied for the potentiometric estimation of the target drugs with no interference from IBF as a coformulated drug or from the commonly used excipients (Table 5). investigation with high accuracy and precision as abridged in Table 6. e response time of the Fe 3 O 4 sensors was instant (within 5 s), so the sensors were quickly moved between the biological samples and the deionized water in between the measurements in order to prevent the sensing components from adherence on the surface of certain matrix components. It was obvious that the proposed Fe 3 O 4 sensors could be utilized effectively for in vitro studies. A core benefit of these sensors is their ability to directly determine the target drugs in human plasma samples without the need for any prior treatment or extraction.

Potentiometric Determination of CPM and PSE in Spiked
As final conclusion, electrodes based on functionalized Fe 3 O 4 magnetic nanoparticles (sensors 3 and 6) were found to be superior over classical electrodes (sensors 1, 2, 4, and 5) regarding sensitivity (lower LOD), selectivity, response time, and stability.

Statistical Analysis
Statistical comparison was performed between the six fabricated sensors and a reported method [23] for the analysis of CPM and PSE. As the calculated t and F values were found to be less than the theoretical values, it was concluded that there was no significant difference as demonstrated in Table 7. One-way ANOVA was also done to ascertain the absence of significant difference between the obtained results of the different proposed sensors (Table 8).

Conclusion
is work presented a comparative study between potentiometric detection strategy based on functionalized Fe 3 O 4 magnetic nanoparticles versus classical potentiometric strategy for the quantitative estimation of CPM and PSE. e     e Fe 3 O 4 sensors were effectively applied for the analysis of CPM and PSE in both pharmaceutical formulation and spiked human plasma. No interference was observed from coformulated drugs, additives commonly used in dosage form and inorganic substances. e proposed sensors introduced certain advantages as being accurate and do not require drug pretreatment or separation steps which offers a cost-effective method of analysis allowing this method to be used in CPM and PSE routine analysis in quality control laboratories.

Data Availability
All the data are included in the manuscript in the form of provided tables and figures.