Abstract: A method for analyzing protein(s) in a sample using an immunoassay kit includes creating protein-reducing and/or protein-denaturing conditions by contacting the sample with a reducing and/or denaturing agent provided in the immunoassay kit, to provide a partially or fully denatured protein population. One or both of a presence and an amount of one or more protein-associated analytes are determined under the created protein-reducing and/or protein-denaturing conditions by contacting the partially or fully denatured protein population with one or more specific antibodies or binding fragments thereof provided in the immunoassay kit. The one or more specific antibodies or binding fragments thereof include one or more chemically-introduced non-disulfide cross-links between at least one heavy chain or binding fragment thereof and at least one light chain or binding fragment thereof.

Abstract: An elution buffer for eluting one or more predetermined analytes from one or more analyte-specific antibodies or fragments thereof or for eluting one or more predetermined antibodies or fragments from a target antigen, wherein: the elution buffer has a pH of 1 to 5; and the elution buffer comprises a predetermined amount of an acid stable mass spectrometry ionisation control protein. The use of the elution buffer in the detection and quantifying of analytes, for example by mass spectrometry is also described.

Abstract: An anti-immunoglobulin specific antibody (or fragment thereof), characterised that the antibody or fragment thereof comprises one or more non-disulphide cross-links between at least one heavy chain or fragment thereof and at least one light chain or fragment thereof of the antibody or fragment thereof. A method purifying an anti-immunoglobulin specific antibody (or fragment thereof), characterised that the antibody or fragment thereof comprises one or more non-disulphide cross-links between at least one heavy chain or fragment thereof and at least one light chain or fragment thereof of the antibody or fragment thereof.

Abstract: The application describes a method of quantifying a multimeric analyte in a sample comprising: (i) treating the multimeric analyte with a separating agent selected to convert at least a portion of the multimeric analyte into monomeric analyte; (ii) binding the analyte to an analyte-specific binding agent; (iii) comparing the amount of binding of the analyte to the analyte-specific binding agent to a calibration curve, wherein the calibration curve is obtained (i) by binding the analyte-specific binding agent to one or more predetermined amounts of separating agent treated analyte, prior to contacting with analyte-specific binding agent or (ii) by binding the analyte-specific binding agent to a predetermined amount of substantially monomeric analyte; and (iv) determining an amount of the multimeric analyte in the sample.

Abstract: The invention provides an immunoassay kit providing an immunoassay kit comprising one or more analyte specific antibodies or fragments thereof, characterised that the antibody or fragment thereof comprises one or more non-disulphide cross-links between at least one heavy chain or fragment thereof and at least one light chain or fragment thereof of the analyte- specific antibodies or fragments thereof.