An affinity ligand-matrix conjugate of the structure Z-Spacer-[NX-A]m-NY-A-NK2 is useful for the isolation, separation, purification, characterization, identification or quantification of endotoxins in an aqueous system, wherein m is an integer of at least one; each A independently represents an optionally substituted linear, branched or cyclic saturated hydrocarbon chain containing 1 to 6 carbon atoms; each X independently represents hydrogen or alkyl; Y is X or A-NX2; and Z is a support matrix attached to the ligand through an optional spacer arm (Spacer).