Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The chromatographic behaviors of some basic solutes were evaluated on stationary phases based on poly(methyloctylsiloxane) immobilized onto silica (PMOS-SiO(2)). The test solutes present both hydrophobic and hydrophilic properties. Evaluations of the pH effect used 80: 20 v/v methanol/buffered mobile phase over the pH range of 5-11.5 with inorganic buffers such as borate, carbonate and phosphate and with organic buffers such as citrate, tricine and triethylamine. Evaluations in acidic mobile phases used 50: 50 v/v and 30: 70 v/v methanol/buffer (pH 2.5; 20 mmol/L) mobile phases. The buffer concentration effect used 65:35 v/v methanol/phosphate (pH 7; 20 and 100 mmol/L) mobile phases. The results are compared with those obtained with two chemically bonded stationary phases. The immobilized phases show greater contributions from an ion-exchange mechanism than do the commercial phases. The results indicate that the silanol activity of PMOS-SiO(2) stationary phases can be adequately evaluated by using appropriate basic probes and mobile phases having different pH, using different buffers.341011411148Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)