Abstract: ClO₄^--field effect transistor sensor takes perchlorate-cetylpyridinium as an active material. The C10₄^--ISEFY showed Nernstian response in 1.0×10°～6.2×10^-5 mol/L ClO₄^- solution over a pH range of 4～10 with cationic slope of 55 mV/pC featuring quick response, good reproducibility and precision. The selectivity coefficients of nearly 20 chemical compounds were determined by means of distinctive solution method, only a few ions interfered such as I^-, MnO₄^-, SCN^-, etc. Applying the C1O₄^--ISEFT determination, the content of raw material employed in the compounding of propantheline bromide could be identified. The content of benzalkonium bromide was 97.6% and standard deviation 0.57%. Analysis of drug with C1O₄^--ISEFT gave satisfatory results.