Alkylphosphonic acids are decomposition byproducts of chemical warfare agents. Analysis of phosphonic acid in water is regulated by Environmental Protection Agency (EPA). All phosphonic acids are polar acidic compounds. Analysis for retention and separation of methylphosphonic, ethylphosphonic, ethyl methylphosphonic and isopropyl methylphosphonic acids was developed using Primesep SB reversed-phase anion-exchange column. Method is compatible with LC/MS and can be used for quantitation of phosphonic acid in water.