Simultaneous determination of clobutinol together with some anti-inflammatory drugs in urine by HPLC

An isocratic high performance liquid chromatography method is described for simultaneous determination of clobutinol hydrochloride together with some anti-inflammatory drugs, such as diclofenac, meloxicam, and nimesulide in urine. For the development and optimization of the system, three different buffers containing ammonium acetate, tetraethylammonium hydrogen sulfate (THAS), and tetrabutylammonium hydrogen sulfate (THBS) were investigated, because it has been proven that different salts added in the mobile phases considerably affect solute retention and selectivity. The effect of salt content in the aqueous portion of the mobile phase together with pH over a wide range, was investigated. A response surface method based on non-linear multiple regression analysis was employed to illustrate the changes in k' values as a function of a range of pH values and different salts contents. On the basis of the chromatographic behavior of clobutinol together with the other drugs determined, optimum chromatographic conditions were achieved with good peak symmetry, reasonable retention time, and noticeable separation. The intra- and inter-day accuracy and precision at low, medium, and high concentration(s) for the compounds were in the range %error 5.40-11.50 and %RSD 1.76-5.06, respectively.