pharmaceuticals Article Quantification and Classification of Diclofenac Sodium Content in Dispersed Commercially Available Tablets by Attenuated Total Reflection Infrared Spectroscopy and Multivariate Data Analysis Eirini Siozou 1, Vasilios Sakkas 1,* and Nikolaos Kourkoumelis 2 1 Laboratory of Analytical Chemistry, Department of Chemistry, University of Ioannina, 45 110 Ioannina, Greece; [email protected] 2 Department of Medical Physics, School of Health Sciences, University of Ioannina, 45 110 Ioannina, Greece; [email protected] * Correspondence: [email protected]; Tel.: +30-26510-08303; Fax: +30-26510-08795 Abstract: A new methodology, based on Fourier transform infrared spectroscopy equipped with an attenuated total reflectance accessory (ATR FT-IR), was developed for the determination of diclofenac sodium (DS) in dispersed commercially available tablets using chemometric tools such as partial least squares (PLS) coupled with discriminant analysis (PLS-DA). The results of PLS-DA depicted a perfect classification of the tablets into three different groups based on their DS concentrations, while the developed model with PLS had a sufficiently low root mean square error (RMSE) for the prediction of the samples’ concentration (~5%) and therefore can be practically used for any tablet with an Citation: Siozou, E.; Sakkas, V.; Kourkoumelis, N. Quantification and unknown concentration of DS. Comparison with ultraviolet/visible (UV/Vis) spectrophotometry as Classification of Diclofenac Sodium the reference method revealed no significant difference between the two methods. The proposed Content in Dispersed Commercially methodology exhibited satisfactory results in terms of both accuracy and precision while being rapid, Available Tablets by Attenuated Total simple and of low cost. Reflection Infrared Spectroscopy and Multivariate Data Analysis. Keywords: diclofenac sodium; ATR spectroscopy; Fourier transform infrared; quantitative analysis; Pharmaceuticals 2021, 14, 440. chemometrics https://doi.org/10.3390/ph14050440 Academic Editors: Luisa Barreiros and Marcela Segundo 1. Introduction Non-steroidal anti-inflammatory drugs (NSAIDs) are a broad family of compounds Received: 16 March 2021 which are commonly used for the treatment of inflammation and pain. Diclofenac Accepted: 3 May 2021 ([2-(2,6-dichloroanilino)phenyl]acetic acid) is one of the most widely used NSAIDs com- Published: 7 May 2021 monly used for the treatment of rheumatoid arthritis, osteoarthritis, ankylosing spondylitis, and musculoskeletal and sports injuries, as well as for the relief of dysmenorrhea and Publisher’s Note: MDPI stays neutral postoperative pain [1–6]. It is typically found as sodium or potassium salt and it is available with regard to jurisdictional claims in in a variety of drug formulations including tablets, capsules, ophthalmic drops, suppos- published maps and institutional affil- iations. itories, and ointments, depending on the site of application. Diclofenac sodium (DS) (Figure1) is primarily used for its anti-inflammatory properties and acts at a slower pace than potassium salt which is readily absorbed by the body and provides instant relief [7]. Quality control of dosage forms plays a major role in pharmaceutical industries, since the products must meet certain criteria set by pharmacopoeias and other authorities; other- Copyright: © 2021 by the authors. wise, they may be substandard and/or even pose a threat to public health. Therefore, the Licensee MDPI, Basel, Switzerland. development of sensitive and reliable methods for the determination of active ingredients This article is an open access article in dosage forms is crucial. The official method for the determination of DS proposed by the distributed under the terms and conditions of the Creative Commons European Pharmacopoeia (Ph.Eur.) and the United States Pharmacopoeia (USP) includes Attribution (CC BY) license (https:// the dispersion of the standard compound in anhydrous acetic acid followed by titration creativecommons.org/licenses/by/ with perchloric acid and potentiometric determination of the endpoint [8,9], while for the 4.0/). Pharmaceuticals 2021, 14, 440. https://doi.org/10.3390/ph14050440 https://www.mdpi.com/journal/pharmaceuticals Pharmaceuticals 2021, 14, x FOR PEER REVIEW 2 of 11 (USP) includes the dispersion of the standard compound in anhydrous acetic acid fol- Pharmaceuticals 2021, 14, 440 2 of 11 lowed by titration with perchloric acid and potentiometric determination of the endpoint [8,9], while for the determination of DS in slow-release tablets, the USP proposes its dis- persiondetermination in a methanol of DS– inwater slow-release mixture tablets,(70:30) theand USP subsequent proposes analysis its dispersion in a liqu in aid methanol– chro- matographwater mixture with a (70:30)UV detector, and subsequent using methanol analysis and inphosphate a liquid buffer chromatograph (pH 2.5) as with mobile a UV phasedetector, components using methanol [10]. In recent and phosphate decades, bufferseveral (pH analytical 2.5) as mobilemethods phase have components been devel- [10]. opedIn recentfor the decades, determination several of analytical diclofenac methods in drug have products, been developed including for spectrophot the determinationometric of [7,11diclofenac–16], spectroscopic in drug products, [17–21], including fluorimetric spectrophotometric [22], potentiometric [7,11 –[2216],–27], spectroscopic and chromato- [17–21], graphicfluorimetric methods [22 [28], potentiometric–34]. [22–27], and chromatographic methods [28–34]. Figure 1. Structure of diclofenac sodium molecule. Figure 1. Structure of diclofenac sodium molecule. Spectroscopic methods have the advantages of a relatively low cost and rapid sample analysis.Spectroscopic Attenuated methods total have reflectance the advantages infrared of spectroscopy a relatively low with cost Fourier and rapid transformation sample analysis.(ATR FT-IR)Attenuated is not t consideredotal reflectance as a quantitativeinfrared spectroscopy technique with by many. Fourier However, transformation ATR FT-IR (ATRhas FT been-IR) used is not before considered as a quantitative as a quantitative technique technique for the by analysis many. of However, NSAIDs asATR an accurate,FT-IR hassensitive, been used and before low-cost as a quantitative technique. technique for the analysis of NSAIDs as an accurate, sensitive,Van and Overbeke low-cost et technique. al. used ATR FT-IR to quantify ketoprofen in pharmaceutical formu- lationsVan Overbeke such as capsules et al. used and ATR injection FT-IR ampoules, to quantify in combination ketoprofen in with pharmaceutical partial least-squares for- mulations(PLS) analysis such as [35 capsules]. Similarly, and Boyerinjection et al.ampoules, proposed in an combination analytical method with partial without least prior- squaressample (PLS) treatment analysis for [35]. the Similarly, determination Boyer of et niflumical. proposed acid an in aanalytical pharmaceutical method gelwithout by ATR FT-IR and PLS calibration with a root mean square error of prediction (RMSEP) equal to prior sample treatment for the determination of niflumic acid in a pharmaceutical gel by 0.2 for the validation set [36]. Lawson et al. examined the potential use of ATR FT-IR to ATR FT-IR and PLS calibration with a root mean square error of prediction (RMSEP) equal provide rapid quantitative analyses of suspect counterfeit tablet formulations containing to 0.2 for the validation set [36]. Lawson et al. examined the potential use of ATR FT-IR to paracetamol [37]. Sensitive methods based on ATR FT-IR spectroscopy were developed provide rapid quantitative analyses of suspect counterfeit tablet formulations containing by Hassib et al. for the quantitative assessment of four NSAIDs, namely, etodolac, tolfe- paracetamol [37]. Sensitive methods based on ATR FT-IR spectroscopy were developed namic acid, bumadizone, and diacerein, by peak profiling using normal or derivative by Hassib et al. for the quantitative assessment of four NSAIDs, namely, etodolac, tolfen- spectroscopy [38]. amic acid, bumadizone, and diacerein, by peak profiling using normal or derivative spec- PLS combined with ATR FT-IR was proposed by Silva et al. for the simultaneous troscopy [38]. determination of the antibiotics sulphamethoxazole and trimethoprim in raw material PLS combined with ATR FT-IR was proposed by Silva et al. for the simultaneous powder mixtures [39]. Kandhro et al. developed a reliable analytical method for the determination of the antibiotics sulphamethoxazole and trimethoprim in raw material quantitative assessment of cefixime in orally administered pharmaceutical formulations powderbased mixtures on ATR FT-IR[39]. Kandhro spectroscopy. et al. developed Standards a were reliable prepared analytical in aqueous method medium for the quan- ranging titativefrom assessment 350 to 6000 of mg/kg cefiximeand in PLS orally regression administered was applied pharmaceutical in the range formulations 1485–887 cm based−1 [40 ]. on Furthermore,ATR FT-IR spectroscopy. ATR FT-IR has Standards also been were used prepared for the determination in aqueous medium of polymorphs ranging in from dosage −1 350forms. to 6000 Salari mg/kg and and Young PLS investigatedregression was the applied feasibility in the of ATRrange FT-IR 1485 for–887 the cm qualitative [40]. Fur- and thermore,quantitative ATR analysisFT-IR has of also mixtures been used of three for knownthe determinat polymorphsion of of polymorphs ganciclovir, in an dosage antiviral forms.compound. Salari