Comparative study between univariate spectrophotometry and multivariate calibration as analytical tools for simultaneous quantitation of Moexipril and Hydrochlorothiazide Shereen M. Tawakkol a , M. Farouk b , Omar Abd Elaziz b , A. Hemdan c,⇑ , Mostafa A. Shehata d a Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Helwan University, Cairo, Egypt b Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt c Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Ahram Canadian University, 6th of October, Egypt d Pharmaceutical Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Cairo, Egypt highlights  Comparison between univariate spectrophotometry and multivariate calibration.  The reported methods need sophisticated and expensive instruments and reagents.  First chemometric methods done for this combination.  The good recovery and accuracy makes it applicable in quality control laboratories. graphical abstract Zero order absorption spectra of 30 lg/mL MOX (......), and 10 lg/mL HCTZ (—) showing severe overlapping. article info Article history: Received 5 February 2014 Received in revised form 20 March 2014 Accepted 5 May 2014 Available online 5 June 2014 Keywords: Moexipril Hydrochlorothiazide Extended ratio subtraction method PCR PLSs abstract Three simple, accurate, reproducible, and selective methods have been developed and subsequently validated for the simultaneous determination of Moexipril (MOX) and Hydrochlorothiazide (HCTZ) in pharmaceutical dosage form. The first method is the new extended ratio subtraction method (EXRSM) coupled to ratio subtraction method (RSM) for determination of both drugs in commercial dosage form. The second and third methods are multivariate calibration which include Principal Component Regression (PCR) and Partial Least Squares (PLSs). A detailed validation of the methods was performed following the ICH guidelines and the standard curves were found to be linear in the range of 10–60 and 2–30 for MOX and HCTZ in EXRSM method, respectively, with well accepted mean correlation coefficient for each analyte. The intra-day and inter-day precision and accuracy results were well within the acceptable limits. Ó 2014 Elsevier B.V. All rights reserved. Introduction Moexipril (3S)-2-[(2S)-2-[[(1S)-1-(Ethoxycarbonyl)-3-phenyl- propyl]amino]-1-oxopropyl]-1,2,3,4-tetrahydro-6,7-dimethoxy-3- http://dx.doi.org/10.1016/j.saa.2014.05.061 1386-1425/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Present address: Ahram Canadian University, 4th Industrial Region, 6th October, Egypt. Tel.: +20 1221620730; fax: +20 (2) 38334379. E-mail address: hemmdan@yahoo.com (A. Hemdan). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 300–306 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa