Abstract: The invention provides a method detecting free light chains (FLCs) comprising: (i) providing a sample from a subject; (ii) mixing the sample with an anti-FLC specific antibody, or fragments thereof capable of specifically binding the FLC, to form a mixture; (iii) passing the mixture through a capillary tube by capillary zone electrophoresis (CZE); and (iv) detecting the presence of the antibody or fragment thereof after passage through at least a portion of the capillary tube. Capillary tubes for use in CZE and kits comprising capilliary tubes and at least one anti-FLC antibody are also provided.