A simple, accurate and sensitive method for the quantitative determination of Bromoquat, Decylamine, Didecylamine and Decylaminoquat which are an alkyl, Polyalkyl amines impurities of Colesevelam Hydrochloride tablet. The method has been developed and validated by LCMS (liquid chromatography mass spectrometry). The chromatographic separation of impurities was achieved on C-18 column, the mobile phase was pumped at 1.0 ml minute-1 by using gradient pump mode, the mixture contains aqueous trifluroacetic acid (1.0 ml Lit.-1) buffer, acetonitile and methanol as mobile phase -A and with acetonitrile mobile phase-B .The peaks were Scanned and quantified in ESI (Electro spray ionization) positive ion and SIM (selected ion monitoring) mode respectively. The method was validated and the chromatographic resolution between the impurities was found to be greater than 2. The responses were determined and (correlation coefficient) regression r values were obtained greater than 0.998 for all components. The method was capable of detecting impurities 0.02 % with respect to sample concentration of 3000ppm.