Development and validation of stability-indicating TLC-densitometric method for determination of betaxolol with LC-ESI/MS analysis of degradation product.

The purpose of this work was to develop a sensitive stability indicating TLC-densitometric method for the determination of betaxolol (Bx) in pharmaceutical preparations and to study the stability of Bx in acidic solutions. The method was developed on TLC aluminium plates precoated with silica gel F254using the mobile phase chloroform-methanol-ammonia 25% (18 : 4: 0.2, v/v/v) which gives compact spots for Bx (R(f) approximately equal to 0.64) and its degradation product (R(f) approximately equal to 0.39). Densitometric analysis was carried out in UV at 280 nm. The developed method is highly sensitive (LOD = 66.6 ng/spot, LOQ = 200 ng/spot), precise (RSD = 2.73%) and accurate (mean recovery = 100.28% at 100% level). Bx was subjected to acidic and alkaline hydrolysis but degradation was observed only in acidic solutions. The degradation process was described with kinetic and thermodynamic parameters. Based on LC-ESI/MS analysis, it was found that Bx decomposes in acidic solution to produce ethoxyphenoxy-3-[(1-methylethyl)amino]propan-2-ol.