Abstract: In a method for infrared-optical determination of the concentration of at least one chemical analyte in a liquid sample, where the liquid sample is passed through a measuring cell and irradiated with infrared radiation of a single narrow waverange and infrared absorption is measured, the analyte being determined is subject to a chemical reaction before measurement, which should leave the other components of the liquid sample unaffected, and the change in infrared absorption caused by the chemical reaction with the analyte is measured as a unique function of the analyte concentration to be determined.

Abstract: A luminescence-optical indicator for determining the activity of alkali metals based on decay time includes at least three components that are chemically bound to one another, i.e., a fluorophor, a functional group with which the luminescence decay time of the fluorophor can be influenced, and a ionophor binding the alkali metal ions to be measured in a selective and reversible manner, the effect of the functional group on the decay time of the fluorophor being altered in dependence on the activity of the alkali metal ions.

Abstract: An indicator for use in a luminescence-optical configuration for continuous and reversible measurement of the pH of a sample within a relevant measuring range (M), whose luminescence decay time .tau. is dependent on the pH of the sample, is characterized by the following properties. The pK.sub.a value of the acidic or basic indicator is in the relevant measuring range when the indicator is in its electronic ground state (S.sub.0). The protonation rate k.sub.p of the base, or deprotonation rate k.sub.dp of the acid in the excited state (S.sub.1, X) of the indicator is lower than the decay rate k.sub.A of the excited state, and the luminescence decay times .tau..sub.S and .tau..sub.B of the acidic forms (AH*, BH.sup.+*) and the basic forms (A.sup.-*, B*) of the indicator are different from each other. If the pK.sub.a .tau. value of the indicator in its electronically excited state (S.sub.1, X) is within the relevant measuring range, the protonation rate k.sub.p of the base, or deprotonation rate k.sub.