Abstract: A biological substance is determined with the use of a marker comprising a lanthanide or other metal ion coupled to the biological substance by means of chelate-forming compound. The chelate complex is dissociated by reduction of the ambient pH to a sufficiently low level to liberate the metal ion and the metal ion is then chelated with a separate chelating chromophore with an increase in the pH to a value closer to the optimum for determination of the metal-chelated chromophore by fluorescence spectroscopy, luminometry, colourometry or the like.

Abstract: Fluorescent lanthanide chelates are formed by reacting a .beta.-diketone, an aldehyde, and an amine to produce a dihydropyridine condensation product which is then chelated with a lanthanide metal ion. These fluorescent chelates are made into wavelength-shifting devices by physically supporting the chelates on a polymer. Such wavelength-shifting devices can be optically coupled to a photoelectric cell to increase the portion of the solar spectrum available to the cell for conversion into electricity. Furthermore, the reaction producing the fluorescent lanthanide chelates is used to detect amines or aldehydes in a sample.

Abstract: Photovoltaic cell and wavelength-shifting device, comprising a dihydropyridine condensation product chelated to a lanthanide metal ion, to expand the solar spectrum available to the cell for conversion into electricity. Method to detect an amine or an aldehyde for forming a dihydropyridine condensation product chelated to a lanthanide metal ion and measuring the long life fluorescence of the chelated metal ion to determine the amount of amine or aldehyde present.

Abstract: Labellable reagents for fluormetric assays comprise a cyclic condensation product of a .beta.-diketone, an aldehyde and an NH.sub.2 -bearing macromolecule, for example an antigen or antibody or a substance having an active group to which an antibody or antigen is linked. The reagents can chelate lanthanide metal ions such as Eu(II) and Tb(III) to form fluorescing complexes which can be used as labelled reagents for fluorometric assay of organic substances, for example antigens, antibodies and other substances occurring in body fluids.

Abstract: Method for fluorescence spectroscopic determination of a biological substance provided with a marker consisting of a lanthanide chelate complex formed by a lanthanide coupled to the substance via a chelate forming compound, such as an EDTA-analogue, the lanthanide ion before the detection is dissociated from the active substance for instance by adding a buffer with a pH value below 3.5 and a splitting detergent, whereafter the excitation in the determination takes place in the solution in the presence of a .beta.-diketone by using a short radiation pulse and the fluorescence from the marker is detected when the fluorescence from the noise sources has substantially ceased.