Abstract: The present invention relates to enzyme immunoassays employing one or more enzyme label-substrate pairs which give rise to colored products and in which absorption by the product of substrate conversion by at least one enzyme label at a first wavelength, at or close to the optimum wavelength for absorbance, exceeds the linear range of the detector, which immunoassay includes the steps of measuring the said substrate conversion at a second wavelength at which absorbance by the relevant product is significantly lower than at the said first wavelength and calculating the true absorbance at the said first wavelength by utilizing the result of linear regression analysis of absorbance measurements obtained with product standards at the said first and second wavelengths within the linear range of the detector.

Abstract: A container for determining antibodies or antigens in a biological liquid by the formation of specific antibody-antigen complexes, in which one partner element is initially associated with suspended magnetic particles that are subsequently regrouped against a collecting area of a first side wall of the container when the container is positioned within a magnetic field that extends through that area of the side wall. To prevent the particles from sliding down when the magnetic field is eliminated and to allow effective pipetting, the lower part of the side wall is adjacent to a planar surface formed at an obtuse angle to said side wall and tangent to a concave bottom surface that is itself tangent to a second side wall of the container located opposite to the first side wall.