Adsorption of ochratoxin A on octadecyldimethyl benzyl ammonium exchanged-clinoptilolite-heulandite tuff

Abstract

The in vitro adsorption of ochratoxin A (OCHRA) by clinoptilolite-heulandite rich tuff modified with different amounts - 20, 50 and 100 μmol M+/g of octadecyldimethyl benzyl ammonium (ODMBA) ion was investigated. The organo-zeolites were denoted as OZ-2, OZ-5 and OZ-10. The maximal amount of ODMBA in organo-zeolites 100 μmol M+/g was equal to external cation exchange capacity of starting material. Adsorption of OCHRA by unmodified zeolitic tuff was 40% at pH 3 and 3% at pH 7 and 9. OCHRA adsorption on organo-zeolites increased as the levels of ODMBA increased. At low coverage of zeolitic surface with ODMBA-organo-zeolite OZ-2, adsorption of OCHRA was lower at pH 7 and 9 than at pH 3. The decreased adsorption of OCHRA at pH 7 and 9 may be induced by the presence of anionic form of OCHRA which probably led to repulsion between the OCHRA and uncovered negative zeolitic surface. At higher coverage of the zeolitic surface, organo-zeolites OZ-5 and OZ-10, adsorption of OCHRA was pH independent. OCHRA adsorption on OZ-2 and OZ-10 showed non linear type of isotherm at pH 3, 7 and 9. Adsorption of OCHRA by OZ-5 followed a non linear type of isotherm at pH 7 and 9, while at pH 3 the adsorption was best represented by an S-shaped isotherm. Adsorption of OCHRA on organo-zeolites is dependent on the amount of organic cation at the surface, as well as on their surface concentration - arrangement of alkyl chains at the surface. At low surface concentration of ODMBA, adsorption of OCHRA may be dependent on the form of OCHRA in solution. © 2003 Elsevier Science B.V. All rights reserved.