A method for quantifying target functional groups immobilized on a solid support comprising: contacting the target functional groups with an amount of a selective compound, wherein an amount of the selective compound binds to the target functional groups and an amount of the selective compound does not bind to the target functional groups; obtaining a byproduct having an amount of the unbound selective compound; adding an indicator to the byproduct which binds to unbound selective compound in the byproduct to provide a measurable result; measuring the measurable result; determining from the measured result an amount of unbound selective compound in the byproduct; determining an amount of selective compound immobilized on the solid support from the amount of unbound selective compound; and determining from the amount of the immobilized selective compound an amount of the target functional groups immobilized on the solid support, wherein a) the target functional groups immobilized on the solid support comprise aldehydic functional groups and wherein the aldehydic functional groups are immobilized on the solid support by a reaction which adds the aldehydic functional groups to amino groups present on the solid support, and wherein the selective compound selectively reacts with the immobilized aldehydic functional groups and comprises an amino functional group, and wherein the indicator comprises a solution comprising 2,4,6-trinitrobenzene sulfonic acid (TNBSA); or b) the target functional groups immobilized on the solid support comprise amino functional groups, and wherein the selective compound comprises an aldehydic compound which selectively reacts with immobilized amino functional groups on the solid support, and wherein the indicator comprises 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole, 4-Amino-5-hydrazino-1,2,4-triazole-3-thiol (Purpald). contacting the target functional groups with an amount of a selective compound, wherein an amount of the selective compound binds to the target functional groups and an amount of the selective compound does not bind to the target functional groups; obtaining a byproduct having an amount of the unbound selective compound; adding an indicator to the byproduct which binds to unbound selective compound in the byproduct to provide a measurable result; measuring the measurable result; determining from the measured result an amount of unbound selective compound in the byproduct; determining an amount of selective compound immobilized on the solid support from the amount of unbound selective compound; and determining from the amount of the immobilized selective compound an amount of the target functional groups immobilized on the solid support, wherein a) the target functional groups immobilized on the solid support comprise aldehydic functional groups and wherein the aldehydic functional groups are immobilized on the solid support by a reaction which adds the aldehydic functional groups to amino groups present on the solid support, and wherein the selective compound selectively reacts with the immobilized aldehydic functional groups and comprises an amino functional group, and wherein the indicator comprises a solution comprising 2,4,6-trinitrobenzene sulfonic acid (TNBSA); or b) the target functional groups immobilized on the solid support comprise amino functional groups, and wherein the selective compound comprises an aldehydic compound which selectively reacts with immobilized amino functional groups on the solid support, and wherein the indicator comprises 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole, 4-Amino-5-hydrazino-1,2,4-triazole-3-thiol (Purpald). a) the target functional groups immobilized on the solid support comprise aldehydic functional groups and wherein the aldehydic functional groups are immobilized on the solid support by a reaction which adds the aldehydic functional groups to amino groups present on the solid support, and wherein the selective compound selectively reacts with the immobilized aldehydic functional groups and comprises an amino functional group, and wherein the indicator comprises a solution comprising 2,4,6-trinitrobenzene sulfonic acid (TNBSA); or b) the target functional groups immobilized on the solid support comprise amino functional groups, and wherein the selective compound comprises an aldehydic compound which selectively reacts with immobilized amino functional groups on the solid support, and wherein the indicator comprises 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole, 4-Amino-5-hydrazino-1,2,4-triazole-3-thiol (Purpald).