1.1 These test methods measure the amount of toluene-2,6-diisocyanate (2,6-TDI) isomer or toluene-2,4-diisocyanate (2,4-TDI) isomer in mixtures of the 2,4- and 2,6-isomers of toluenediisocyanate (TDI). Two different test methods are provided to give accurate results over the broad range of isomer concentrations possible.