A method for determining a property of at least a fluid component of a fluid present in a compartment of an electrical apparatus by means of a measurement device arranged outside the compartment and comprising a chamber for receiving a quantity of the fluid from the compartment, comprising the steps of: a) attaching the measurement device to a port of the compartment, b) optionally evacuating the chamber of the measurement device, c) illuminating an optical path in the chamber with light emitted by a light source, d) measuring a first intensity of light received by a light detector, e) releasing fluid from the compartment into the chamber, f) measuring a second intensity (Ix) of light received by the light detector, g) calculating a partial particle density (px) of the fluid component from the first and the second intensity (10, Ix), and either h1) determining the property of the fluid component by using the partial particle density (px); or h20) measuring at least one additional parameter of the fluid in the chamber and/or of a fluid portion in the optical path, and h21) determining the property of the fluid component by using the partial particle density (px) and the at least one additional parameter, wherein the fluid present in the compartment of the electrical apparatus is a dielectric gas which comprises a background gas and an organofluorine compound selected from the group consisting of: fluoroethers, fluoroketones, fluoroolefins, fluoronitriles, and mixtures and/or decomposition products thereof, and the measurement is done non-continuously such that no material incompatibility of the dielectric gas with the measurement device arises, wherein after determining the property of the fluid component a step k1) of closing a connection between the compartment and the chamber and subsequently evacuating the fluid from the chamber is carried out. arranged outside the compartment and comprising a chamber for receiving a quantity of the fluid from the compartment, comprising the steps of: a) attaching the measurement device to a port of the compartment, b) optionally evacuating the chamber of the measurement device, c) illuminating an optical path in the chamber with light emitted by a light source, d) measuring a first intensity of light received by a light detector, e) releasing fluid from the compartment into the chamber, f) measuring a second intensity (Ix) of light received by the light detector, g) calculating a partial particle density (px) of the fluid component from the first and the second intensity (10, Ix), and either h1) determining the property of the fluid component by using the partial particle density (px); or h20) measuring at least one additional parameter of the fluid in the chamber and/or of a fluid portion in the optical path, and h21) determining the property of the fluid component by using the partial particle density (px) and the at least one additional parameter, wherein the fluid present in the compartment of the electrical apparatus is a dielectric gas which comprises a background gas and an organofluorine compound selected from the group consisting of: fluoroethers, fluoroketones, fluoroolefins, fluoronitriles, and mixtures and/or decomposition products thereof, and the measurement is done non-continuously such that no material incompatibility of the dielectric gas with the measurement device arises, wherein after determining the property of the fluid component a step k1) of closing a connection between the compartment and the chamber and subsequently evacuating the fluid from the chamber is carried out. a) attaching the measurement device to a port of the compartment, b) optionally evacuating the chamber of the measurement device, c) illuminating an optical path in the chamber with light emitted by a light source, d) measuring a first intensity of light received by a light detector, e) releasing fluid from the compartment into the chamber, f) measuring a second intensity (Ix) of light received by the light detector, g) calculating a partial particle density (px) of the fluid component from the first and the second intensity (10, Ix), and either h1) determining the property of the fluid component by using the partial particle density (px); or h20) measuring at least one additional parameter of the fluid in the chamber and/or of a fluid portion in the optical path, and h21) determining the property of the fluid component by using the partial particle density (px) and the at least one additional parameter, wherein the fluid present in the compartment of the electrical apparatus is a dielectric gas which comprises a background gas and an organofluorine compound selected from the group consisting of: fluoroethers, fluoroketones, fluoroolefins, fluoronitriles, and mixtures and/or decomposition products thereof, and the measurement is done non-continuously such that no material incompatibility of the dielectric gas with the measurement device arises, wherein after determining the property of the fluid component a step k1) of closing a connection between the compartment and the chamber and subsequently evacuating the fluid from the chamber is carried out.