For the separation, removal, isolation, purification, characterisation, identification or quantification of fibrinogen or a protein that is a fibrinogen 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; Y is O, S or NR.sub.2; 0 Z is O, S or NR.sub.3; R.sub.2 and R.sub.3 are each H, alkyl, hydroxyalkyl, benzyl or &bgr;-phenylethyl; n is 0 to 6; A is a support matrix, optionally linked to the triazine ring by a spacer; R.sub.7 is a group bearing a positive charge at neutral pH; W is an optional linker; V is an aromatic group; and R.sub.8 and R.sub.9 are each H, OH, alkyl, alkoxy, amino, NH.sub.2, acyloxy, acylamino, CO.sub.2H, sulphonic acid, carbamoyl, sulphamoyl, alkylsulphonyl or halogen or a cyclic structure such as a morpholino group, or R.sub.8 and R.sub.9 are linked to form such a cyclic structure.