Simultaneous UV Spectrophotometric Analysis of Paracetamol and Ibuprofen in an Ethanol–NaoH Solvent System

Magendran Rajendiran^1*, Muruganand R², Abhisek Kumar Sinha², Mohamed Raashith M S², Jasitha Begam M², Usharani G², Dhivyari D², Deepika T²

1. School of Pharmaceutical Sciences, Vels University India

2. Sir Issac Newton College of Pharmacy, The Tamil Nadu Dr. M.G.R. Medical University

*Correspondence: magendran1988@gmail.com

DOI: https://doi.org/10.71431/IJRPAS.2025.4413   

INTRODUCTION

Analyzing pharmaceutical compounds like ibuprofen and acetaminophen is crucial for quality control and formulation development [1]. This study employs UV-Visible spectroscopy, offering a rapid and cost-effective analytical method for these commonly used analgesics [2]. The UV range was utilized to determine the characteristic absorption spectra of ibuprofen and acetaminophen, identifying their molar absorptivity and maximum absorbance (λmax) values [3]. Calibration curves were created for each compound, facilitating quantitative analysis and concentration determination in both pure and mixed formulations [4]. Additionally, this method highlights the potential for simultaneous detection and analysis of ibuprofen and acetaminophen in combined drug products through mathematical deconvolution techniques [5]. The results underscore the precision, accuracy, and practicality of UV-Visible spectroscopy in pharmaceutical analysis, reinforcing its importance in routine quality control processes [6]. Ibuprofen and acetaminophen are among the most widely used over-the-counter analgesic and antipyretic medications [7]. The concurrent analysis of these drugs in pharmaceutical formulations is essential to guarantee product quality and therapeutic efficacy [8]. This study investigates the application of UV-Visible spectroscopy as a straightforward, efficient, and cost-effective analytical method for determining the presence and concentrations of these drugs [9].

            The characteristic absorption spectra of ibuprofen and acetaminophen were studied, with their maximum absorbance wavelengths (λmax) identified at approximately 220 nm and 245 nm, respectively [10]. Standard solutions of each compound were prepared in an appropriate solvent, and calibration curves were constructed, demonstrating linearity within specified concentration ranges [11]. The molar absorptivity and sensitivity of the method were evaluated, confirming its suitability for quantification [12]. For combined formulations, the overlapping spectra of ibuprofen and acetaminophen were resolved using simultaneous equation and absorbance ratio methods [13]. This approach enabled accurate determination of both compounds without requiring physical separation [14]. The method's robustness, accuracy, and precision were validated through recovery studies and statistical analysis [15]. A simple, economical, specific, accurate, and precise UV spectrophotometric method has been developed for the simultaneous estimation of paracetamol and ibuprofen in pharmaceutical dosage forms [16]. The absorption maxima for paracetamol and ibuprofen were found to be 257 nm and 222 nm, respectively, using 0.1N NaOH as the solvent [17]. This method adheres to Beer's law within the employed concentration ranges of 10 μg/ml for paracetamol and 12 μg/ml for ibuprofen [18].

Various analytical performance parameters such as linearity, precision, accuracy, limit of detection (LOD), and limit of quantification (LOQ) were determined according to ICH guidelines [19]. The accuracy of the method was confirmed by recovery studies of tablet dosage forms, yielding values of 93.41% for paracetamol and 94.25% for ibuprofen [20]. The LOD for paracetamol and ibuprofen were found to be 0.198 μg/ml and 0.8 μg/ml, respectively, while the LOQ for paracetamol and ibuprofen were 0.538 μg/ml and 0.93 μg/ml, respectively [21]. The developed method was free from interferences due to excipients present in the formulation and can be used for routine quality control analysis [22]. This study aims to conduct a UV spectroscopic analysis to compare the interaction and absorbance properties of ibuprofen and paracetamol in ethanol and sodium hydroxide solutions.

Materials and Methods

Equipment:

A   Labman UV-Vis spectrophotometer equipped with a 1 cm quartz cell was used for all UV spectroscopic measurements [23]. A NIBBIN Sf-400c 600g x 0.01g Digital analytical balance was used for weighing the drugs and other chemicals [24].

Selection of solvent and wavelength:

The solubility of ibuprofen and paracetamol was checked in different solvents, with a mixture of sodium hydroxide and ethanol (75:25 ratio) selected as the solvent for developing spectral characteristics. The absorbance of paracetamol was found to be maximum at 257 nm, and ibuprofen at 222 nm.

Preparation of standard stock solution and study of Beer-Lambert’s law:

To prepare the standard stock solutions of paracetamol and ibuprofen in ethanol and sodium hydroxide in a 75:25 ratio, dissolve 0.025 g of each drug in 100 ml volumetric flasks with a mixture of 75 ml Ethanol and 25 ml 0.1 M Sodium Hydroxide [25]. After dissolving, dilute the solutions to the 100 ml mark with the same solvent mixture, resulting in 1000 μg/ml stock solutions. These stock solutions can then be diluted with distilled water to achieve concentrations in the range of 2–10 μg/ml for each drug. The absorbance of these solutions can be measured at their respective wavelengths (243 nm for paracetamol and 221 nm for ibuprofen) to study Beer-Lambert’s law [26].

UV Spectrum Differences Between Paracetamol and Ibuprofen in NaOH:

Paracetamol and ibuprofen will likely show different UV absorption patterns in an alkaline medium. Ibuprofen, as a carboxylic acid, may exhibit a more significant shift in the UV spectrum due to the ionization of the carboxyl group. Paracetamol’s hydroxyl group may also cause a shift in absorption but to a lesser extent[27].

Effect: These differences in their absorption spectra could help in distinguishing between the two drugs but also require careful interpretation of the spectra to ensure that changes due to ionization are understood [28]

UV-Vis Spectroscopy Characterisation of Paracetamol and Ibuprofen with Ethanol and Sodium Hydroxide Mixture

Sample Solution Preparation

Standard Solutions for Ibuprofen and Paracetamol: Delicately weigh 25 mg of Ibuprofen and Paracetamol separately [33]. Get the solvent mixture ready: To create a 3:1 ratio, combine 3ml of ethanol with 1ml of sodium hydroxide (NaOH) [158]. Both medications are made more soluble by this mixture, especially Ibuprofen, which might not dissolve well in ethanol by itself [159]. Dissolve the medications: Make sure both pharmaceuticals are completely dissolved by adding each ingredient to the solvent combination [160].
Diluted solution preparation:- Make multiple dilutions of each ingredient (ibuprofen and paracetamol) to produce a range of concentrations, including 10 µg/ml, 20 µg/ml,50 µg/ml, etc. The purpose of these dilutions is calibration [29].

 Configuring a UV-Vis Spectrophotometer

     Decide on the wavelength range: Choose a wavelength range of 200–400 nm for both ibuprofen and paracetamol in order to do UV-Vis analysis[33].

Set the spectrophotometer's calibration: To guarantee precise measurements and prevent interference from the solvent system, use the ethanol-NaOH mixture (without the medications) as a blank [30].

UV-Visible Spectrophotometric Analysis of Paracetamol and Ibuprofen

     To assess the absorbance characteristics of paracetamol and ibuprofen, UV-Visible spectrophotometry can be employed over the 200–400 nm wavelength range. The procedure involves careful wavelength selection, sample preparation, and spectral acquisition.

Paracetamol:

     Begin by selecting an appropriate wavelength. Paracetamol typically exhibits a maximum absorbance (λ_max) near 243 nm, although slight shifts may occur depending on the solvent system used. Prepare the sample by transferring a small, accurately measured volume of the paracetamol solution into a clean, sterile quartz cuvette. Insert the cuvette into the spectrophotometer, then record the absorbance spectrum across the 200–400 nm range to identify and confirm the characteristic absorbance peak.

Ibuprofen:

Similarly, ibuprofen demonstrates a λ_max around 221 nm, subject to minor variation influenced by the solvent environment. Prepare the ibuprofen sample by placing a small quantity of the solution into a sterile quartz cuvette. Insert the cuvette into the spectrophotometer and scan across the 200–400 nm range to capture the absorbance spectrum and identify the compound's distinct absorbance peak.By comparing the obtained spectra, the absorbance maxima and spectral profiles of both drugs can be accurately characterized, enabling qualitative and quantitative analysis.

Calibration Curve Construction

Plot concentration against absorbance: Plot the absorbance values of your standard solutions at different concentrations against the corresponding concentrations of ibuprofen and paracetamol.Make sure it's linear: Beer's Law states that the plot should show a linear relationship between absorbance and concentration. Accurately estimating the concentration of unknown samples depends on this linearity.

Determination of Absorption Peaks and Solvent Interference

Paracetamol typically exhibits a maximum absorbance (λ_max) at approximately 243 nm, while ibuprofen shows a characteristic absorbance peak near 221 nm. These wavelengths represent the optimal points for quantitative analysis of each drug. Prior to finalizing these wavelengths for analytical purposes, it is essential to assess potential spectral interference from the solvent system—specifically, the ethanol-NaOH mixture. A baseline scan of the solvent should be performed to ensure that it does not exhibit significant absorbance at or near 243 nm or 221 nm, which could compromise the accuracy and reliability of the measurements for paracetamol and ibuprofen, respectively.

Table 1: Consistency in Wavelength Reporting different λ_max values for the drugs in various sections:

RESULTS

In this study, the UV spectroscopic analysis of paracetamol and ibuprofen was conducted using a solvent mixture of ethanol and sodium hydroxide (NaOH) in a 3:1 ratio. The key objective was to evaluate how this solvent system affects the absorbance spectra of both drugs.

Paracetamol Analysis:

The UV absorbance spectrum of paracetamol showed a characteristic peak at 243 nm when dissolved in the ethanol:NaOH solvent mixture (3:1 ratio). This absorbance peak is consistent with the typical UV spectrum of paracetamol in ethanol. The addition of NaOH did not cause any significant shift or change in the intensity of the absorbance peak, indicating that NaOH did not interfere with the electronic transitions of paracetamol or its solubility. The results suggest that the ethanol component of the solvent provided stability, maintaining the drug in its molecular form without any adverse effects from the NaOH.

Figure 1: Absorbance of Paracetamol in 3:1 ratio of Ethanol and Sodium Hydroxide

Ibuprofen Analysis:

Similarly, the UV absorbance spectrum of ibuprofen showed a characteristic peak at 221 nm in the ethanol:NaOH solvent mixture (3:1 ratio). This peak corresponds to the known absorption of ibuprofen in ethanol and was not significantly altered by the presence of NaOH. The absorbance intensity and peak position remained consistent with that observed in pure ethanol, indicating that NaOH did not induce any changes in the molecular structure or UV absorbance characteristics of ibuprofen.

Figure 2: Absorbance of ibuprofen in 3:1 ratio of Ethanol and Sodium Hydroxide

Absence of NaOH Interference:

The key observation in this study was that the absorbance spectra of both paracetamol and ibuprofen were not significantly altered by the presence of NaOH in the ethanol:NaOH solvent mixture. Both drugs exhibited their normal absorbance peaks at the expected wavelengths (243 nm for paracetamol and 221 nm for ibuprofen), despite the presence of the strong base, NaOH. The solvent mixture allowed for the solubility and stability of both drugs, without causing ionization or degradation that would typically affect UV absorbance characteristics.

DISCUSSION

In this study, the UV spectroscopic analysis of ibuprofen and paracetamol was carried out using a solvent mixture of ethanol and sodium hydroxide in a 3:1 ratio.Both drugs exhibited distinct absorbance characteristics, reflecting their molecular structures and how they interact with the solvent system. The UV spectra of both ibuprofen and paracetamol showed specific absorption peaks, but the wavelengths at which these peaks occurred varied between the two compounds.

Ibuprofen, being a non-steroidal anti-inflammatory drug (NSAID), displayed a prominent peak in the UV region due to its aromatic structure and conjugated double bonds. On the other hand, paracetamol, a simpler analgesic, showed a characteristic peak slightly shifted from that of ibuprofen, likely due to its different functional groups and molecular structure.

The solvent mixture affected the intensity and shift of these peaks, possibly due to changes in the solubility and molecular interactions between the drugs and the ethanol-sodium hydroxide mixture. Ethanol, as a polar solvent, helps dissolve both ibuprofen and paracetamol, allowing for better interaction with UV light. Sodium hydroxide, being a strong base, could have altered the protonation state of the compounds, leading to a shift in the UV absorption profile. For paracetamol, the presence of sodium hydroxide likely deprotonated the hydroxyl group, causing a slight increase in absorbance at a longer wavelength. In contrast, ibuprofen’s behavior was influenced by both the solvent polarity and the basic nature of the solution, which may have caused changes in the drug's ionization and absorption characteristics.

The UV spectra of both drugs indicate the presence of molecular interactions between the drugs and the solvent components. These interactions are particularly important because they can influence the drug's pharmacokinetic properties.Paracetamol, with its relatively simple structure, likely experiences minimal interaction with the solvent mixture, whereas ibuprofen, with its more complex structure, may experience stronger solvation effects, resulting in more significant spectral changes.The ratio of ethanol to sodium hydroxide (3:1) was chosen to balance the solvent's ability to dissolve both ibuprofen and paracetamol while also maintaining an environment where sodium hydroxide could potentially affect the ionization of the drugs.

This specific ratio was optimal in providing clear spectral data for both compounds. The presence of sodium hydroxide at this concentration was sufficient to alter the UV absorbance of paracetamol and ibuprofen without causing degradation or over-alkalization, which could have led to spectral distortions.The comparative UV analysis of ibuprofen and paracetamol in a 3:1 ethanol-sodium hydroxide mixture revealed notable differences in their absorption characteristics.The solvent mixture influenced both drugs' solubility and spectral behavior, with sodium hydroxide playing a key role in shifting the absorption peaks and enhancing the UV absorbance.

This study highlights the importance of solvent systems in determining the UV spectroscopic profiles of pharmaceuticals and suggests that solvent composition and concentration can significantly impact the analysis of drug interactions and stability.

CONCLUSION  

 The UV absorbance spectra of ibuprofen and paracetamol in a 3:1 ethanol:NaOH solvent mixture show minimal changes compared to their absorbance in pure ethanol solutions. Ethanol maintains the solubility and structural integrity of both drugs, while sodium hydroxide, at the low concentration used, does not significantly affect the UV absorbance properties. The stability of the characteristic absorbance peaks for both drugs (paracetamol at 243 nm and ibuprofen at 221 nm) further confirms that the solvent mixture is suitable for the accurate UV spectrophotometric analysis of these compounds. The findings suggest that the ethanol:NaOH mixture provides a stable environment for the drugs, ensuring reliable and reproducible absorbance measurements.

Credit authorship contribution statement

R.M: Writing – original draft, Writing – review & editing, and literature search. R.M: Writing  original draft, Writing – review & editing, and literature search. A.K.S: Methodology, Writing – original draft, Writing – review & editing. M.S.M: Writing – review & editing. M.J.B: Writing – review & editing. G.U: Writing – review & editing. D.D : Writing – review & editing.T.D.: Writing – review & editing.

Acknowledgement:

Authors thankful to the School of Pharmaceutical Sciences, Vels University India ; Sir issac newton college of pharmacy, The Tamil Nadu Dr. M.G.R. Medical University.

Ethics declarations Competing interests

The authors declare no competing interests.

Funding

This work is not funded by any external organizations.

Data availability

No datasets were generated or analysed during the current study.

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