Determination of the ozone dose delivered into liquids by plasma systems is of importance in many emerging plasma applications, such as plasma medicine. Quantification of this dose remains extremely challenging due to the complex physico-chemical processes encountered in the gas plasma, the plasma-liquid interface and the liquid itself. Chemical probes have the potential to address the limitation of more traditional plasma diagnostic techniques but most commercial chemical probes are not specific enough to be used in plasma applications. Here we report on the development of a method for the quantification of the ozone delivered into a liquid using Pittsburgh Green, a novel ozone-selective fluorescence probe. Entailed within this work is a method for the preparation of the probe solutions, the design of a calibration system and a normalized calibration curve correlating fluorescence intensity to actual ozone dose delivered to the liquid. This enables the quantitative comparison of ozone measurements performed with different spectrofluorometers and in different institutions.