The present invention relates to the use of compounds with at least one pH-sensitive chemical shift for determining pH and/or measuring pH changes in magnetic resonance. More specifically, the present invention is related to compounds with at least one pH-sensitive chemical shift, such compound being selected from pyruvic acid and its metabolites, compounds produced from pyruvic acid after interaction with acid, and compounds comprising at least one enolic group whose pKa value is lowered through effects of at least one neighboring group into a physiological and/or pathological pH-range, and wherein the compound exhibits at least one pH-sensitive chemical shift in an NMR spectrum. The present invention further relates to biosensors comprising at least one of the compounds. The present invention is furthermore related to in vitro and in vivo methods for determining pH and/or measuring pH changes using the compounds or biosensors. The present invention also relates to methods of diagnosing and/or monitoring treatment of a disease causing changes in pH wherein the compounds or biosensors are applied. The present invention also relates to use of the compounds or biosensors in quality control of food or in the examination of plants and organisms.
