Application of HPLC-DAD and spectrophotometric continuous wavelet transform methods for simultaneous determination of amoxicillin and diclofenac in their pure and capsule dosage forms Fathy M. Salama, Khalid A. Attia, Ahmed A. Abouserie, Ahmed El-Olemy and Ebrahim Abolmagd * Two methods have been developed and validated for simultaneous determination of amoxicillin sodium and diclofenac sodium in their pure and combined pharmaceutical dosage forms. The first method was HPLC- DAD; the chromatographic separation and resolution has been carried out using a reversed phase BDS Hypersil C18 column with a mobile phase consisting of methanol : acetonitrile : water : orthophosphoric acid (60 : 30 : 9 : 1 by volume), at a flow rate of 1 mL minute 1 and UV detection at 250 nm. The retention times were found to be 3.906 and 6.997 minutes for amoxicillin and diclofenac respectively. The second method was continuous wavelet transform (CWT), which is based on derivative calculation of spectrophotometric spectral data of both drugs in their binary mixture, and the zero crossing point for amoxicillin and diclofenac was found to be at 233 and 247 nm, respectively. The results obtained were statistically compared to reference methods and there were no significant differences between the proposed methods and the reference methods regarding the accuracy and precision. The method was validated according to ICH guidelines and the results were satisfactory. 1. Introduction Determination of two analytes simultaneously in one reaction system using the same procedures has become a useful and attractive feature in modern analytical chemistry. Such proce- dures are considered to be economic because they reduce the analyst's effort and time and reduce the cost of chemicals by estimating the two target analytes at the same time. This feature is realized in this article since the authors develop two tech- niques, namely, RP-HPLC and CWT, which is a signal process- ing technique based on derivative calculations used in chemical analysis for many purposes such as peak sharpening, determi- nation of end-points of potentiometric titration and to resolve spectral overlapping as discussed in this article. Both tech- niques are capable of simultaneous assessment of amoxicillin sodium and diclofenac sodium. The pharmaceutical combination of amoxicillin and diclo- fenac till now has only one chemometric-PLS method for their simultaneous determination; neither HPLC, spectrophoto- metric nor spectrourimetric methods or any other analytical techniques have been developed for their simultaneous quan- titative determination. So the novelty of this work is to develop methods that provide high accuracy and precision and are at the same time economic. Cost reduction is the main advantage of these methods since the developed methods have the properties of being very simple without the need for any complicated procedures. In the area of research and development and in drug manufacturing, the HPLC method is considered the most appli- cable method for selective quantitative simultaneous determi- nation of amoxicillin and diclofenac and it is recommended for routine analysis of their pharmaceutical preparations. The environmental safety in the present work is of great importance considering the absence of hazardous reactions, reuxing and toxic reagents. Continuous wavelet transform (CWT) is a new, simple, rapid and selective signal processing method for the determination of components having overlapping spectra in binary mixtures. It has the advantages of de-noising, smoothing and a wider range of application. 1–3 CWT is similar to Fourier transform with the advantage of having many basic functions called wavelets while the basic functions in Fourier transform are the trigonometric functions (sine and cosine). A wavelet transform is the representation of a function by wavelets. A wavelet is dened as a number of scaled and dilated functions J a,b (l) derived from a basic function J (l). Therefore the basic function is oen called a mother wavelet since it gives birth to a family of wavelets. 4 Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Al-Azhar University, 11751, Nasr City, Cairo, Egypt. E-mail: Eb.Abolmagd@yahoo.com; Tel: +20 1284955570 Cite this: Anal. Methods, 2018, 10, 2588 Received 21st March 2018 Accepted 26th April 2018 DOI: 10.1039/c8ay00621k rsc.li/methods 2588 | Anal. Methods, 2018, 10, 2588–2594 This journal is © The Royal Society of Chemistry 2018 Analytical Methods PAPER