Tris(2-chloroethyl)amine isomerization and subsequent spectrophotometric determination using sulfonephthaleins

In a polar environment, tris(2-chloroethyl)amine molecule undergoes isomerization when forming N,N-bis(2-chloroethyl)aziridinium cation as a reactive intermediate. New methods were developed to spectrophotometrically determine tris(2-chloroethyl)amine in the form of aziridinium cation extraction using 4 sulfonephthaleins—bromothymol blue, thymol blue, bromoxylenol blue, and bromocresol green. The developed methods, reflecting potent electrophilic properties of the analyte, are based on the formation of extractable ion pairs between the aziridinium cation and a quinoid anion form of a sulfonephthalein. Chloroform was used as the solvent for extraction from the water phase. The conditions of the methods were optimised by determining the suitable pH (8.5) of a buffer and the concentration of sulfonephthaleins as reagents. The dependence of the reaction time in the water phase was found to be 10 min. The composition of the ion pairs was found to be 1:1 by in all cases and the conditional extraction constant of the complexes were calculated. The detection and determination limits of separate procedures were ascertained. Best results (detection limit 3.5 µg ml^?1 and determination limit 11.6 µg ml^?1) were obtained using bromothymol blue. The methods were empirically compared with a group spectrophotometric method to determine alkyl halides using the alkalized water–ethanol solution of thymolphthalein. Relatively low interferences of other nitrogen mustards and sulfur mustard were recorded. The interaction mechanism—ion association—was validated.