For the separation, removal, isolation, purification, characterisation, identification or quantification of plasminogen or a protein that is a plasminogen analogue, an affinity adsorbent is used that is a compound of formula (II) wherein one X is N and the other is N, C--Cl or C--CN; A is a support matrix, optionally linked to the triazine ring by a spacer; Z is O, S or N--R and R is H, C.sub.1-6 alkyl, C.sub.1-6 hydroxyalkyl, benzyl or &bgr;-phenylethyl; B is an optionally substituted hydrocarbon linkage containing from 1 to 10 carbon atoms; D is H, OH or a primary amino, secondary amino, tertiary amino, quaternary ammonium, imidazole, guanidino or amidino group; or B-D is --CHCOOH--(CH.sub.2).sub.3-4--NH.sub.2; and q is 2 to 6.