This article reports a fast and simple liquid chromatographic method for determination of ascorbic acid, phenylephrine, paracetamol and caffeine. Salicylic acid was used as internal standard. The analytes were successfully separated in less than 5 min by isocratic elution using monolithic column, Onyx Monolithic C18 (100 Â 4.6 mm), with mobile phase composed of acetonitrile and phosphate buffer (pH 6.50) (10 : 90, v/v) at a flow rate of 1.0 mL min À1 and 25 C, sample volume was 10 mL. Detection was observed at two wavelengths 210 nm (phenylephrine, paracetamol and salicylic acid) and 235 nm (ascorbic acid and caffeine). The optimized method was applied for the determination of the analytes in pharmaceutical formulation Coldrex tablets (Smithkline Beecham Consumer Healthcare, United Kingdom) commonly used in virosis treatment.

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This work describes a comparison of three types of commercial high-performance liquid chromatography silica monolithic columns with different inner diameters and generations of monolithic sorbent: a "classic" monolithic column, the first generation (Onyx™ monolithic C(18), 100 mm × 4.6 mm, Phenomenex); a "narrow" monolithic column for fast separation at lower flow rates (Chromolith® Performance RP-18e, 100 mm × 3 mm, Merck); and a recently introduced "high-resolution" monolithic column, the next generation (Chromolith® HighResolution RP-18e, 100 mm × 4.6 mm, Merck). Separation efficiency (number of theoretical plates, height equivalent to a theoretical plate and van Deemter curves), working pressure, the symmetry factor and resolution were critical aspects of the comparison in the case of the separation of ascorbic acid, paracetamol and caffeine. The separations were performed under isocratic conditions with a mobile phase consisting of 10:90 (v/v) acetonitrile-phosphoric acid (pH 2.80). Detailed comparison of the newest-generation monolithic column (Chromolith® HighResolution) with the previously introduced monolithic sorbents was performed and proved the advantages of the Chromolith® HighResolution column.

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