Optimisation and validation of liquid chromatographic and partial least-squares-1 methods for simultaneous determination of enalapril maleate and nitrendipine in pharmaceutical preparations

Simultaneous determination of enalapril maleate (ENA) and nitrendipine (NIT) in pharmaceutical preparations was performed using liquid chromatography (LC) and the partial least-squares-1 (PLS-1) method. In LC, the separation was achieved on a C8 column and the optimum mobile phase for good separation in a gradient elution programme was found to be acetonitrile-water (φ _r = 81: 19) and optimum flow-rate, temperature, injection volume, and detection wavelength were set at 1.0 mL min⁻¹, 25°C, 10 μL, and 210 nm, respectively. Dienogest was selected as an internal standard. In the spectrophotometry, a PLS-1 chemometric method was used. The absorbance data matrix related to the concentration data matrix was established by measurement of absorbances in their zero order spectra with an increment of Δλ = 1 nm in the 220–290 nm range for ENA and with Δλ = 1 nm in the 230–290 nm range for NIT in the PLS-1 method. Following this step, calibration was established by using this data matrix to predict the unknown concentrations of ENA and NIT in their binary mixture. These optimised methods were validated and successfully applied to a pharmaceutical preparation in tablet form and the results were subjected to comparison.