Element for immunoassay and process of using the same

A process for the quantitative analysis of a sample antigen contained in an aqueous liquid sample wherein said sample antigen reacts with an immobilized antibody in competition with an antigen labelled with a marker in an antigen-immobilized antibody reaction, and wherein the quantity of said labelled antigen which has not combined with the immobilized antibody and which is a function of the concentration of said sample antigen is determined, comprising the steps of:

• (a) immersing a dipstick analytical element into the aqueous liquid sample, said element comprising:
• a first matrix,
• a carrier in said first matrix containing immobilized antibody capable of immunochemical reaction with sample antigen wherein the immobilized antibody is not released into the aqueous liquid sample upon immersion therein;
• and, a second matrix containing labelled antigen and a hydrophilic polymer binder wherein the labelled antigen and the hydrophilic polymer binder dissolve in the aqueous liquid sample upon immersion therein to release said labelled antigen into said aqueous liquid sample;
• whereby said labelled antigen reacts with said immobilized antibody in competition with said sample antigen in the antigen-immobilized antibody reaction between said sample antigen and said immobilized antibody, so that only that portion of the labelled antigen which has not combined with said immobilized antibody remains in said aqueous liquid sample;
• and
• (b) applying an aliquot of said aqueous liquid sample resulting from step (a) to a separate analytical element to determine the quantity of labelled antigen remaining in said aqueous liquid sample after the competition of the competitive antigen-immobilized antibody reactions and determining the amount of the sample antigen.