Herbal formulations have played a pivotal role in healthcare for thousands of years, bridging the gap between traditional remedies and modern therapeutics. Globally, herbal medicines are widely used across Asia, particularly in countries such as India and China; Africa; and South America. According to the World Health Organization (WHO), nearly 80% of the world’s population relies on herbal medicines for primary healthcare needs, largely due to their accessibility, cultural acceptance, and favorable safety profile compared to synthetic drugs. In recent decades, the rise of phytopharmaceuticals standardization and scientific validation has transformed herbal medicine from a folkloric practice into an evidence-based therapeutic discipline. Phytopharmaceuticals integrate traditional botanical knowledge with modern pharmaceutical science, offering safer, sustainable, and cost-effective options for the prevention and management of chronic diseases.^1,2

Despite this progress, quality control remains a major challenge in the herbal medicine sector. The chemical composition of herbal formulations can vary widely depending on plant source, harvesting season, storage conditions, and extraction methods. Unlike synthetic pharmaceuticals that usually contain a single pure active ingredient, herbal preparations often include dozens or even hundreds of phytochemicals. This complexity makes robust analytical methods essential to ensure batch-to-batch consistency, safety, and efficacy.³

Among medicinal plants, cinnamon (Cinnamomum zeylanicum Blume, also known as C. verum) is one of the most widely used culinary spices and medicinal agents. Obtained from the dried inner bark of C. zeylanicum, native to Sri Lanka and southern India, cinnamon has been used in Ayurveda, Unani, and traditional Chinese medicine to treat ailments ranging from digestive to respiratory disorders.⁴ Modern pharmacological research supports its antioxidant, antiinflammatory, antidiabetic, and antimicrobial activities.⁵

Cinnamon contains three major bioactive constituents: cinnamaldehyde, cinnamic acid, and eugenol.

Because herbal formulations often contain multiple bioactives with synergistic or antagonistic effects, multicomponent analysis is critical for quality assurance. However, most reported analytical methods focus on quantifying a single marker compound, which may not adequately reflect product quality or therapeutic potential. Previous UV spectrophotometric studies have shown that simultaneous estimation of flavonoids, alkaloids, and phenolic compounds in polyherbal mixtures is feasible, with acceptable accuracy and precision. Binary and ternary mixtures of phytochemicals have also been resolved using simultaneous equation and absorbance ratio methods, establishing UV spectroscopy as a cost-effective alternative to high-performance liquid chromatography (HPLC) for quality control.^9,10

Pharmacopoeial guidelines reinforce the need for herbal standardization. The Indian Pharmacopoeia and United States Pharmacopeia include monographs for cinnamon bark, cinnamon oil, and clove oil, specifying tests for identification, assay of active components, and impurity limits. Similarly, WHO monographs on Cinnamomum species and Syzygium aromaticum (clove) provide global reference standards.^11,12,13 Incorporating such standards into routine UV-based assays enhances both regulatory compliance and global acceptability.

Nevertheless, multicomponent UV analysis faces challenges, including overlapping absorption spectra, matrix interferences from pigments and tannins, and variability in extraction efficiency.¹⁴ Advanced chromatographic methods such as HPLC, gas chromatography–mass spectrometry (GC–MS), and LC–MS are widely used for cinnamaldehyde, cinnamic acid, and eugenol quantification, offering high sensitivity and specificity. However, these techniques involve high instrumentation cost, demand skilled operators, require longer analysis times, and consume large volumes of organic solvents—factors that limit their accessibility for small- and medium-scale herbal manufacturers.⁵

Alternative UV-based approaches, such as chemometric-assisted spectrophotometry and derivative spectrophotometry, have been reported to resolve overlapping spectra with improved selectivity. Yet, these methods often require specialized software, advanced mathematical treatment, and greater analyst expertise. By contrast, the simultaneous equation method provides a simple, rapid, and cost-effective alternative while maintaining compliance with International Council for Harmonization (ICH) Q2(R1) validation guidelines. This makes it particularly suitable for industries that lack access to sophisticated chromatographic systems.¹⁵

Overall, UV–Visible (UV–Vis) spectrophotometry represents an attractive tool for herbal quality control due to its low cost, simplicity, rapid analysis, minimal solvent use, and compatibility with mathematical methods such as the simultaneous equation approach.¹⁶ Despite these advantages, no published study has yet reported a UV spectrophotometric method for the simultaneous estimation of cinnamaldehyde, cinnamic acid, and eugenol in a single run within complex herbal formulations. To address this gap, the present study introduces a validated UV spectrophotometric method using the simultaneous equation approach. This method eliminates the need for chromatographic separation, reduces analysis time and cost, aligns with ICH Q2(R1) validation requirements, and provides a practical tool for quality control in small- and medium-scale herbal industries. By bridging the gap between sophisticated chromatographic assays and routine spectrophotometric testing, this work contributes to the democratization of herbal quality control and supports the global standardization of phytopharmaceuticals.

The developed UV spectrophotometric method successfully resolved cinnamaldehyde, cinnamic acid, and eugenol using the simultaneous equation approach. The regression data confirmed excellent linearity (R² > 0.999) for each analyte, while recovery values of 98–102% demonstrated compliance with ICH Q2(R1) guidelines for accuracy. Precision studies yielded low %RSD values (<2.0%), confirming reproducibility, and the LOD/LOQ values indicated high analytical sensitivity.

Traditionally, quantification of these phytoconstituents has relied on HPLC or GC–MS. Although these techniques provide excellent selectivity and sensitivity, they require sophisticated instrumentation, extended analysis times, higher costs, and trained personnel.¹⁷ Such constraints limit accessibility, particularly for small- and medium-scale herbal manufacturers in resource-limited settings. The present method bridges this gap by employing a simple, rapid, and cost-effective UV spectrophotometric technique in combination with a simultaneous equation strategy.¹⁸

The choice of λmax 290 nm for cinnamaldehyde, 270 nm for cinnamic acid, and 280 nm for eugenol was based on their respective absorption maxima in methanol. This selection maximized sensitivity for each analyte while minimizing spectral interference. Despite partial overlap of the absorption spectra, the simultaneous equation method enabled precise resolution without the need for chromatographic separation. This is particularly advantageous for routine quality control laboratories where rapid turnaround time is essential. Calibration curves showed excellent proportionality between absorbance and concentration over the tested ranges (2–12 μg/mL for cinnamaldehyde, 2–10 μg/mL for cinnamic acid, and 1–8 μg/mL for eugenol), with correlation coefficients exceeding 0.999. The detection limits (0.127 μg/mL for cinnamaldehyde, 0.108 μg/mL for cinnamic acid, and 0.090 μg/mL for eugenol) and quantification limits (0.385, 0.328, and 0.274 μg/mL, respectively) were sufficiently low to allow quantification even in formulations with minimal active content.

Accuracy was confirmed by recovery values ranging from 98.5–101.2% and intraday and interday precision studies yielded %RSD values well below the ICH Q2(R1) acceptance criterion of 2%. Robustness testing further demonstrated negligible variability when deliberate changes were introduced in wavelength (±1 nm) and solvent composition (±2% methanol). Together, these findings confirm that the method is reliable, reproducible, and resistant to minor analytical variations. In addition, the method requires minimal sample preparation—simple methanolic extraction—thus avoiding analyte loss and reducing analysis time compared with multistep chromatographic procedures. To the best of our knowledge, no prior UV spectrophotometric method has been reported for the simultaneous estimation of cinnamaldehyde, cinnamic acid, and eugenol. Previous reports have focused on single analytes or relied exclusively on chromatographic techniques.^17,18

Solvent consumption was approximately 3 mL of methanol per sample, and the Analytical Eco-Scale score was calculated as 87, which falls under the category of “excellent green analysis.” This confirms the ecofriendly nature of the method compared with solvent- and energy-intensive chromatographic approaches.¹⁹ As with most equation-based UV methods, selectivity is inherently constrained when analytes exhibit highly overlapping spectra or when the sample matrix is strongly colored or contains UV-absorbing impurities. In such cases, derivative or chemometric UV techniques—or chromatographic separation—may be required.²⁰

Therefore, this study fills an important methodological gap by providing a validated, simple, and economical UV method for the simultaneous estimation of three bioactive phytoconstituents. The method holds promise for routine quality control of polyherbal formulations, particularly those developed for metabolic, antiinflammatory, and antimicrobial applications.

A validated, rapid, and cost-effective UV spectrophotometric method was successfully developed for the simultaneous quantification of cinnamaldehyde, cinnamic acid, and eugenol in a cinnamon-based herbal formulation. The method exhibited excellent linearity, accuracy, precision, and robustness in accordance with ICH Q2(R1) guidelines,¹⁷ confirming its reliability for analytical applications. Unlike sophisticated chromatographic methods such as HPLC or GC–MS, which are resource-intensive and time-consuming, the proposed UV approach offers simplicity, shorter analysis time, minimal sample preparation, and lower operational cost without compromising performance.

The method was rigorously validated for specificity, linear dynamic range, LOD, and LOQ, with all results falling within the acceptable limits prescribed by regulatory guidelines. Owing to these attributes, this technique represents a practical and efficient alternative for routine quality control, batch-to-batch consistency assessment, and stability testing of herbal formulations containing cinnamon. Its application in the herbal and phytopharmaceuticals industry holds particular promise, especially for small- and medium-scale enterprises, where reliable yet affordable analytical methods are critically needed.