Amphoteric dissociation ion exchange medium and uses thereof and method for calibrating separation capacity thereof

An amphoteric dissociation ion exchange separation medium, wherein a surface of the amphoteric dissociation ion exchange separation medium is an amphoteric dissociation covalently-modified layer;

• the amphoteric dissociation covalently-modified layer has an isoelectric point (pIm) that is an environmental pH value at which a net charge on the surface of the amphoteric dissociation ion exchange separation medium is zero;
• wherein when the environmental pH value is lower than the pIm, the net charge on a surface of the amphoteric dissociation covalently-modified layer is positive and the amphoteric dissociation ion exchange separation medium acts as an anion exchanger;
• when the environmental pH value is higher than the pIm, the net charge on the surface of the amphoteric dissociation covalently-modified layer is negative and the amphoteric dissociation ion exchange separation medium acts as a cation exchanger;
• the amphoteric dissociation covalently-modified layer on the surface of the amphoteric dissociation ion exchange separation medium comprises both a group which dissociates to generate positive charges only, and a group which dissociates to generate negative charges only;
• wherein the group which dissociates to generate negative charges only is an aliphatic carboxyl group, and the group which dissociates to generate positive charges only is one or more groups selected from the group consisting of an aliphatic primary amine group, an aliphatic secondary amine group, an aliphatic tertiary amine group and an imidazolyl group;
• the amphoteric dissociation covalently-modified layer is derived from covalent modification of a surface of a separation medium substrate with an amphoteric dissociation group precursor;
• the surface of the separation medium substrate does not contain a long linear chain having a length of more than 9 carbon atoms, but contains a reactive group for covalently linking with the amphoteric dissociation group precursor to form the amphoteric dissociation covalently-modified layer;
• the reactive group is any one group selected from the group consisting of an aliphatic primary amine group, an aliphatic secondary amine group, an aliphatic carboxyl group and a thiol reactive group;
• wherein the thiol reactive group contains a small-size group that is substituted by a thiol to leave from the surface of the separation medium substrate;
• the amphoteric dissociation group precursor is a hydrophilic material having a molecular weight less than 500 Daltons and no hydrocarbon chains or hydrocarbon rings with more than 5 successive carbon atoms;
• wherein the amphoteric dissociation group precursor contains an alkylthiol group or an aliphatic primary amine group as a covalently-linking group and an aliphatic carboxyl group as the group which dissociates to generate negative charges only, and/or one or more groups selected from the group consisting of an aliphatic primary amine group, an aliphatic secondary amine group, an aliphatic tertiary amine group and an imidazolyl group as a group which dissociates to generate positive charges only;
• the amphoteric dissociation group precursor comprises a type A precursor, a type B precursor and a type C precursor, wherein the type A precursor is an amphoteric dissociation group precursor comprising only the group which dissociates to generate negative charge besides the covalently-linking group, the Type B precursor is an amphoteric dissociation group precursor comprising only the group which dissociates to generate positive charge besides the covalently-linking group, and the type C precursor is an amphoteric dissociation group precursor comprising the group which dissociates to generate negative charge and the group which dissociates to generate positive charge besides the covalently-linking group;
• wherein the type C precursor is selected from the group consisting of lysine, ornithine, histidine, N,N-dicarboxymethylethylenediamine, cysteine, 3-thiolhistidine, 3-thiol lysine and 3-thiol glutamic acid;
• the type A precursor is selected from the group consisting of glutamic acid, 3-thiol-1,5-glutaric acid, thioglycolic acid and tris-(carboxymethyl)-aminomethane;
• and the type B precursor is selected from the group consisting of mercaptoethylamine, 3-thiol-2-hydroxypropylamine, 2-mercaptoimidazole, diethylenetriamine, N,N-dimethylaminoethylenediamine and tetra-(aminomethyl)-methane.