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The multi-component preparation Co-Diovan® is indicated for the hypertension treatment in patients whose blood pressure is not adequately controlled by monotherapy. Its active ingredients are valsartan and hydrochlorothiazide. The reversed-phase high performance liquid chromatographic method (RP-HPLC) for the determination of valsartan and hydrochlorothiazide, as well as their impurities level, was developed and described in this paper. As the investigated substances were structurally different with extremely different lipophilicity and polarity, isocratic elution was not possible, so an optimal gradient mode was settled on. The chromatograms were recorded using the Agilent 1100 Series chromatographic system with DAD detector. Separations were performed on a Hypersil 120-5 ODS column (250 mm×4.6 mm; 5 µm particle size) at 25°C column temperature. The gradient high performance liquid chromatographic system was developed, and the following mobile phases were used: A) mixture acetonitrile-water (10:90 V/V); pH of the mobile phase was adjusted to 2.5 with 85% orthophosphoric acid, and B) mixture acetonitrile-water (90:10 V/V); pH of the mobile phase was adjusted to 2.5 with 85% orthophosphoric acid. Injection volume was 50 µL, flow rate 1 mL min-1 and UV detection was performed at 256 nm. Methyl parahydroxybenzoate was used as an internal standard and acetonitrile-water (40:60 V/V) as a solvent. Afterwards, the developed method was subjected to the method validation. The investigated validation parameters (selectivity, linearity, precision, accuracy, LOQ, and LOD) proved the suitability of the method for the simultaneous determination of valsartan, hydrochlorothiazide, and their impurities in appropriate tablets. [ABSTRACT FROM AUTHOR]

Pramipexole is a dopamine D2-agonist/antiparkinsonian agent in which BI-II 546 CL, BI-II 751 xx and 2-amino benzothiazole are commonly found as impurities. Due to the lack of analytical data on pramipexole and its related substances in bulk drug and pharmaceuticals, we aim at the optimization and characterisation of the chromatographic behaviour of pramipexole and its related substances employing experimental design. The analysis was performed using a C18 column with mobile phases containing different ratios of acetonitrile and water phase (aqueous triethylamine/ortophosporic acid). The detection was performed at 262 nm for pramipexole, BI-II 751 xx and 2-aminobenzthiazole and at 326 nm for BI-II 546 CL. To define the influence of chromatographic parameters on separation, a central composite design was chosen. The content of acetonitrile, TEA and pH of the water phase were identified as the factors with important influences on retention. Using an appropriate mathematical model, we were able to predict retention under different conditions. [ABSTRACT FROM AUTHOR]