Chromatographic Conditions for Drug Analysis
The chromatographic methods used for drug analysis were modifications of published methods (31,32). Drug quantification was performed with HPLC with ultraviolet (UV) detection (Agilent HPLC system 1100/1200 series; Agilent, USA). A RP Agilent Eclipse XDB C18 column (250 mm × 4.6 mm, 5-μm particle size) was used for both drugs. For montelukast, the mobile phase was composed of ammonium acetate buffer pH 5.5 and methanol (solvents A and B, respectively) delivered at a flow rate of 1 mL min−1, on a linear gradient. The selected gradient started with 10% of solvent B, which was increased to 50% within 2 min, and 90% within 4 min; at 11.30 min, the initial conditions of analysis were re-established. Injection volume was 100 μL. Analysis was performed at 20°C and the detection wavelength was 284 nm. Elution time for montelukast was 8.9 min. For analysis of mesalazine, the mobile phase was composed of 0.05% TFA/water and methanol (95:5), delivered at a flow rate of 1 mL min−1. Injection volume was 20 μL. Analysis was performed at 40°C and the detection wavelength was 304 nm. Elution time for mesalazine was 4.6 min.