6 mm, 5 ��m) column despite with the mobile phase containing a gradient mixture of solvent A (90:10 v/v mixture of 0.02 M KH2PO4, pH adjusted to 3.2 with orthophosphoric acid and methanol) and B (10:90 v/v mixture of 0.02 M KH2PO4 buffer of pH 3.2 and methanol). The gradient program (time (min)/%B) was set 0/0, 50/40, 52/0, and 60/0. The mobile phases were filtered through nylon 0.45 ��m membrane filters and degassed. The flow rate of the mobile phase was 0.8 mL/min. The column temperature was maintained at 25��C, and the eluted compounds were monitored at the wavelength of 273 nm. The sample injection volume was 10 ��l. Preparation of standard solution Milli-Q water and acetonitrile in the ratio of 20:80 v/v were used as diluent.

A standard stock solution of guaifenesin was prepared by dissolving an appropriate amount of drug in diluent having a concentration of 0.24 mg/mL. The working standard solution containing 12 ��g/mL was prepared from the above stock solution. Preparation of sample solution Tablet powder equivalent to 600 mg of guaifenesin was dissolved in diluent with sonication for 10 min to give a solution containing 2.4 mg/mL drug. This solution was centrifuged at 4000 rpm for 10 min. RESULTS AND DISCUSSION Method development and optimization The aim of the study was to separate all known and unknown degradation products from guaifenesin and their simultaneous determination in pharmaceutical tablet forms. Various attempts were made to separate all degradation products with different pH of the mobile phase buffer and composition of methanol in the mobile phase using C-18 and C-8 stationary phase columns.

To ensure great resolution between all known and unknown degradation compounds, the C-18 stationary phase with an end-capping was used. In this case, the optimized mobile phase was constituted by solvent A (90:10 v/v mixture of 0.02 M KH2PO4, pH adjusted to 3.2 with orthophosphoric acid and methanol) and B (10:90 v/v mixture of 0.02 M KH2PO4 buffer of pH 3.2 and methanol). The gradient program (time (min)/%B) was set 0/0, 50/40, 52/0, and 60/0. The flow rate of the mobile phase was 0.8 mL/min. The column temperature was maintained at 25��C, and the eluted compounds were monitored at the wavelength of 273 nm. Validation of the method The proposed method was validated as per ICH guidelines.

[13�C15] The following validation characteristics were addressed: Specificity, accuracy, precision, limit of detection and quantification, linearity, range, and robustness. System suitability System suitability shall be checked for the conformance of suitability and reproducibility of chromatographic system for analysis. System suitability was determined Dacomitinib before sample analysis from duplicate injections of the standard solution containing 12 ��g/mL of guaifenesin. The acceptance criteria were USP tailing factor not more than 2.0 and the area similarity ratio between 0.9 and 1.