A homologous series of eight 2,4,6_trichlorophenyl alkyl ethers (TCPEsl was synthesized to provide a retention index (RI) reference system for routine analysis by high-resolution gas chromatography (HRGC) with electroncapture (ECD) or mass spectrometric (MS) detection. The chemical structure of the RI markers was chosen in order to mimic to some extent the molecular interaction between the GC system and important families of environmental contaminants such as halogenated, low-volatile compounds. Owing to the three chlorine atoms in the TCPEs, a good signal is obtained with ECD. With MS detection the different TCPEs give a common strong signal due to the 2,4,6&chlorophenol fragment. This allows the monitoring of all the TCPBs with a unique single ion monitoring (SIM) trace. A reference scale of retention indices was set (RI T8IiJ with absolute rounded values for the TCPEs (e.g., RI-T2 -1400, RI-T4 = 1600). The retention indices of the TCPEs referred to n-alkanes were also calculated (stationary phase: 5% diphenyl-95% dimethylpolysiloxane). In addition to their use as RI markers, the TCPEs can be used as single or multiple internal standards and as test substances to ascertain possible discrimination phenomena in the GC part (injection block and column) of a GC-MS system.