Three simple, reliable methods were developed for the simultaneous determination of a mixture of Ambroxol HCl (A) and Guaifenesin (G) in presence of the oxidative degradate (AD) of A and guaicol (GD), the impurity of G . The first method is an isocratic HPLC method, where separation of the four components A, AD, G and GD was achieved on C18 column using water: methanol (80: 20, v/v, containing 1% triethylamine, pH 2.9) with a flow rate of 1.5 ml/min and UV detection at 220nm. A linear relationship in the range of 5-80 �µg.ml-1 and 10-150 �µg.ml-1 was obtained for A and G, respectively. The second method was a TLC-spectrodensitometric method, where the drugs together with AD and GD were applied on silica gel 60F254 plates and a mobile phase consisted of chloroform: methanol: ethyl acetate: acetic acid (70: 8: 12:10, by volume) was used for separation. Densitometric evaluation of the separated zones was performed at 270 nm. The regression analysis for the calibration plots showed good correlation over the range 1-7 �µg/ band and 2-10 �µg/band for A and G, respectively. The third method was a multivariate spectrophotometric calibration method where principal component regression (PCR) and partial least squares (PLS) methods were used for the determination of the four components A, AD, G, and GD. The three methods were applied to pharmaceutical dosage forms containing either ambroxol alone (drops, capsules and tablets) or A together with G (syrup). Model update of multivariate calibration was used to determine A and G in syrup dosage form due to interfering additives. Results for the three methods were statistically compared with those obtained by applying reference reported methods for the drugs and showed that the proposed methods are accurate, precise, and can be easily applied.
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