Quaternary Ammonium Salts Immobilized on Silica Gel: Exchange Properties and Application as Potentiometric Sensor for Perchlorate Ions.
Ammonium chlorides immobilized on silica gel, SA(+)/Cl(-) and SE(+)/Cl(-), were obtained from silica previously modified with 3-aminopropyltriethoxysilane and N-[3-(trimethoxysilyl)-propyl]ethylenediamine, respectively. Both materials showed potential use as an anion exchanger: they are thermically stable (up to 413 K), achieve equilibrium rapidly in the presence of suitable exchanger ions, and are easily recovered. The exchange capacities observed for SA(+)/Cl(-) and SE(+)/Cl(-) are 0.70 and 1.19 mmol Cl(-) g(-1), respectively. Through the exchange isotherms and competitive Cl(-)-X(-) exchange (X(-)=F(-), Br(-), I(-), N(3)(-), NO(3)(-), SCN(-), ClO(4)(-)) it was observed that: (i) SE(+)/Cl(-) exchanges the counterion Cl(-) more easily than SA(+)/Cl(-); (ii) SA(+)/Cl(-) presents higher selectivity than SE(+)/Cl(-); and (iii) SA(+)/Cl(-) presents high affinity for ClO(4)(-). Because of these two latter properties presented by the SA(+)/Cl(-), the derivative SA(+)/ClO(4)(-) was used as a potentiometric sensor for this anion, prepared from the supported material on a mixture of graphite powder with epoxy resin. The electrode showed a nernstian behavior and a limit of response of 0.13 mmol L(-1). Potentiometric selectivity coefficients, K(pot)(A, B), were obtained for some interfering anions, and the following interference order was observed: F(-) > SCN(-) > NO(3)(-) > Br(-) > Cl(-) > CH(3)COO(-). The electrode showed fast and stable responses and was useful for approximately 200 measures. Copyright 2001 Academic Press.
de Campos
Elvio A.
EA
Departamento de Química, Universidade Estadual de Maringá, Av. Colombo 5790, Maringá-PR, 87020-900, Brazil
da Silva Alfaya
Antonio A.
AA
Ferrari
Rosilene T.
RT
Costa
Creusa Maieru M.
CM