Temperature-responsive chromatography, in which the characteristics of the stationary phase can be controlled by varying the column temperature with only an aqueous eluent, was applied to the analysis of psychoactive drugs. Temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm)-based copolymers were synthesized with n-butyl methacrylate (BMA) and N-acryloyl L-phenylalanine methyl ester (Phe-OMe) as a comonomer. These polymers were grafted onto aminopropyl silica and used as the stationary phase. Seven psychoactive drugs could be separated simultaneously by the column, including BMA. Among the seven drugs, for triazolam, which has a triazole ring in its structure, the order of elution changed on changing the column temperature. The phenomenon could be explained by NH-π interactions between the NH groups of PNIPAAm and π electrons of the triazole ring. The conformational changes of PNIPAAm altered the degree of exposure of the NH groups and would affect the elution order of the analytes. To enhance the molecular recognition ability for the triazole ring, the column containing Phe-OMe was used. Noticeable changes in the retention factors occurred due to the additional π-π interactions between the phenyl moieties of Phe-OMe and the triazole ring. The effects of the π-π interactions were also altered by the changes in column temperature. This chromatographic system, which needs no toxic organic solvent, offers an effective way to determine the causes of addiction in medical institutions.

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