| http://www.w3.org/ns/prov#value | - For instance the chelate-forming groups may have the general formula ##STR1## wherein n is 2 or 3, m is an integer 1, 2, 3 or higher, generally lower than 1000, e.g. lower than 100 or lower than 50 such as 1-50, or 2-6, and R1, R2 and R3, which may be equal or different, each represents a hydrogen atom or a group --CH2 --COOH or --CH2 --CH2 --COOH. The carboxymethyl and the carboxyethyl groups may
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