Application of monolithic columns in pharmaceutical analysis. Determination of indomethacin and its degradation products.

Comparison of HPLC methods using conventional particle-based and monolithic columns for determination of indomethacin and its two degradation products, viz. 5-methoxy-2-methylindoleacetic acid and 4-chlorobenzoic acid, was carried out. Ketoprofen was used as an internal standard for data evaluation throughout the study. Conventional separation was based on analytical column Zorbax SB-Phenyl (75x4.6 mm; 3.5 microm particles) used with a mobile phase composition of acetonitrile and phosphoric acid 0.2% (50:50, v/v) and isocratic flow at 0.6 mL/min. Three different lengths of Chromolith columns RP-18e (25x4.6 mm, 50x4.6 mm, and 100x3 mm) were tested with respect to the validation parameters peak asymmetry, resolution, height equivalent to a theoretical plate, repeatability, and after optimisation compared to values obtained using a conventional Zorbax column. The developed methods were used to determine all three compounds in a pharmaceutical formulation--Indobene gel. Chromatographic parameters were comparable to those of a conventional particle-based column. The analysis time was shortened as expected (retention times were lowered by a factor of two). Moreover, the repeatability of peak areas and retention times obtained with a 50 mm monolithic column was greatly improved (RSD values were lower than 0.40%).