A process for the assay of 2-haloethylphosphonic acid, containing such impurites as esters thereof, 2-hydroxyethylphosphonic acid, vinylphosphonic acid, and/or phosphoric acid, is described. The process comprises: 1. neutralizing an aqueous solution of a sample of 2-haloethylphosphonic acid to a pH in the range of about 8.5-9.6, preferably about 9.3. 2. boiling the neutralized solution for about one-half hour, 3. titrating the thus obtained solution with an alkali to a pH in the range of about 8.5-9.6 preferably about 9.3. A preferred indicator, for the neutralization (1) and the titration (3), is Thymol Blue indicator, and a preferred alkali for said neutralization and titration is sodium hydroxide. The percent of 2-haloethylphosphonic acid in the sample can be computed from the amount of alkali consumed in the titration.
