Organic analysis by ion chromatography 1. Determination of aromatic amines and aromatic diisocyanates by cation-exchange chromatography with amperometric detection

A method has been developed for the simultaneous determination of a range of aromatic amines using cation-exchange chromatography performed on a standard ion chromatography column using d.c. amperometric detection. The analytes separated were 2,4- and 2,6-toluenediamine (2,4- and 2,6-TDA), aniline, o-toluidine, benzidine, p-chloroaniline, 4,4′-diaminodiphenyl (4,4′-DDP), m-nitroaniline and 1-naphthylamine. A Dionex CS12 column was used with gradient elution from an initial eluent of 5% CH3CN+35 mM H2SO4 to 27% CH3CN+35 mM H2SO4 (at 35 min). Detection limits in the range 2.6–22.6 μg/l were observed for all analytes except m-nitroaniline, for which the detection limit was 201 μg/l. Linear calibrations and good precision were observed and the method was applied to the determination of benzidine, p-chloroaniline and 1-naphthylamine in wastewater samples. Further, the separation was also used (after some modification of the eluent conditions) for the determination of 2,4- and 2,6-toluene diisocyanate (2,4- and 2,6-TDI) and 4,4′-methylenediphenyl diisocyanate (4,4′-MDI) after their hydrolysis to 2,4-TDA, 2,6-TDA and 4,4′-DDP. Detection limits for 2,6- and 2,4-TDI and 4,4′-MDI were 3.8, 8.2, and 11.2 μg/l, respectively. The method was applied to the determination of diisocyanates in air.