A method for evaluating antibodies, comprising the steps of: a) providing a first and second antibody sample each comprising a plurality of antibodies comprising at least one acceptor glutamine residue in a constant region, wherein the first and second antibody-containing samples differ from one another with respect to antibody sequence, wherein substantially all of the antibody present in the first sample is of the same sequence and substantially all of the antibody present in the second sample is of the same sequence; b) (i) reacting each of said first and second antibody sample with a lysine-based linker comprising a reactive group, in the presence of a transglutaminase (TGase), under conditions sufficient such that antibodies in such first and second antibody samples are conjugated to a lysine-based linker comprising the reactive group, wherein said lysine-based linker is a linker comprising a NH- n- moiety, where n is a substituted or unsubstituted carbon chain, wherein any carbon of the chain is optionally substituted by a O, N or S atom of an ether, ester, thioether, thioester, amine, alkyamine, amide or alkylamide, the substituent is selected from alkyl group, aryl group, alkyl aryl group, carboxylic acid, amide group and hydroxy group, and n, the length of the carbon chain, is an integer selected from the range of 2 to 20; and said reactive group is a maleimide, a haloacetamide, an o -phosphene aromatic ester, azide, fulminate, sulfonate ester, alkyne, cyanide, aldehyde, 1,2,4,5-tetrazine, norbonene and strained alkene; and (ii) further reacting the resulting antibody of step (i) with a compound comprising: (a) a reactive group (R') that reacts with reactive group on the lysine based linker, and (b) a moiety-of-interest, whereby a first and a second antibody each conjugated to a lysine-based linker comprising a moiety-of-interest is obtained; and c) evaluating antibodies from said first and second antibody sample obtained in step (b) for a characteristic of interest. a) providing a first and second antibody sample each comprising a plurality of antibodies comprising at least one acceptor glutamine residue in a constant region, wherein the first and second antibody-containing samples differ from one another with respect to antibody sequence, wherein substantially all of the antibody present in the first sample is of the same sequence and substantially all of the antibody present in the second sample is of the same sequence; b) (i) reacting each of said first and second antibody sample with a lysine-based linker comprising a reactive group, in the presence of a transglutaminase (TGase), under conditions sufficient such that antibodies in such first and second antibody samples are conjugated to a lysine-based linker comprising the reactive group, wherein said lysine-based linker is a linker comprising a NH- n- moiety, where n is a substituted or unsubstituted carbon chain, wherein any carbon of the chain is optionally substituted by a O, N or S atom of an ether, ester, thioether, thioester, amine, alkyamine, amide or alkylamide, the substituent is selected from alkyl group, aryl group, alkyl aryl group, carboxylic acid, amide group and hydroxy group, and n, the length of the carbon chain, is an integer selected from the range of 2 to 20; and said reactive group is a maleimide, a haloacetamide, an o -phosphene aromatic ester, azide, fulminate, sulfonate ester, alkyne, cyanide, aldehyde, 1,2,4,5-tetrazine, norbonene and strained alkene; and (ii) further reacting the resulting antibody of step (i) with a compound comprising: (a) a reactive group (R') that reacts with reactive group on the lysine based linker, and (b) a moiety-of-interest, whereby a first and a second antibody each conjugated to a lysine-based linker comprising a moiety-of-interest is obtained; and (i) reacting each of said first and second antibody sample with a lysine-based linker comprising a reactive group, in the presence of a transglutaminase (TGase), under conditions sufficient such that antibodies in such first and second antibody samples are conjugated to a lysine-based linker comprising the reactive group, wherein said lysine-based linker is a linker comprising a NH- n- moiety, where n is a substituted or unsubstituted carbon chain, wherein any carbon of the chain is optionally substituted by a O, N or S atom of an ether, ester, thioether, thioester, amine, alkyamine, amide or alkylamide, the substituent is selected from alkyl group, aryl group, alkyl aryl group, carboxylic acid, amide group and hydroxy group, and n, the length of the carbon chain, is an integer selected from the range of 2 to 20; and said reactive group is a maleimide, a haloacetamide, an o -phosphene aromatic ester, azide, fulminate, sulfonate ester, alkyne, cyanide, aldehyde, 1,2,4,5-tetrazine, norbonene and strained alkene; and (ii) further reacting the resulting antibody of step (i) with a compound comprising: (a) a reactive group (R') that reacts with reactive group on the lysine based linker, and (b) a moiety-of-interest, whereby a first and a second antibody each conjugated to a lysine-based linker comprising a moiety-of-interest is obtained; and c) evaluating antibodies from said first and second antibody sample obtained in step (b) for a characteristic of interest.