A in-liquid fluorescence detection device for determining a first substance and a second substance in a liquid comprising: a cell arranged to receive a predetermined liquid comprising a first substance and a second substance, wherein the first substance emits light having higher intensities in a first fluorescence wavelength band with respect to a second fluorescence wavelength band, and the second substance emits light having higher intensities in the second fluorescence wavelength band with respect to the first fluorescence wavelength band; a light source configured to emit, towards the cell, an excitation light having a wavelength in which Raman scattered light is generated in the liquid in a wavelength band between first and second fluorescence wavelength bands; a fluorescence detection unit connected to the cell comprising: - a first photodetector arranged to receive light in the first fluorescence wavelength band and a second photodetector arranged to receive light in the second fluorescence wavelength band, - measuring devices (21A, 21B; 23A, 23B), connected to the first photodetector and second photodetector, respectively, arranged to calculate the light intensity of the light received by said first photodetector and second photodetector, respectively, a comparison unit, connected to the fluorescence detection unit, configured to read reading the value of the intensity of the detected light in the first fluorescence wavelength band and the value of the intensity of light in the second fluorescence wavelength band and to compare the intensity of light in the first fluorescence wavelength band with the intensity of light in the second fluorescence wavelength band; a fluorescence reference determination unit, connected to the comparison unit, configured to determine that the liquid contains the first substance when the intensity of light in the first fluorescence wavelength band is higher than the intensity of light in the second fluorescence wavelength band, and to determine that the liquid contains the second substance when the intensity of light in the second fluorescence wavelength band is higher than the intensity of light in the first fluorescence wavelength band. a cell arranged to receive a predetermined liquid comprising a first substance and a second substance, wherein the first substance emits light having higher intensities in a first fluorescence wavelength band with respect to a second fluorescence wavelength band, and the second substance emits light having higher intensities in the second fluorescence wavelength band with respect to the first fluorescence wavelength band; a light source configured to emit, towards the cell, an excitation light having a wavelength in which Raman scattered light is generated in the liquid in a wavelength band between first and second fluorescence wavelength bands; a fluorescence detection unit connected to the cell comprising: - a first photodetector arranged to receive light in the first fluorescence wavelength band and a second photodetector arranged to receive light in the second fluorescence wavelength band, - measuring devices (21A, 21B; 23A, 23B), connected to the first photodetector and second photodetector, respectively, arranged to calculate the light intensity of the light received by said first photodetector and second photodetector, respectively, - a first photodetector arranged to receive light in the first fluorescence wavelength band and a second photodetector arranged to receive light in the second fluorescence wavelength band, - measuring devices (21A, 21B; 23A, 23B), connected to the first photodetector and second photodetector, respectively, arranged to calculate the light intensity of the light received by said first photodetector and second photodetector, respectively, a comparison unit, connected to the fluorescence detection unit, configured to read reading the value of the intensity of the detected light in the first fluorescence wavelength band and the value of the intensity of light in the second fluorescence wavelength band and to compare the intensity of light in the first fluorescence wavelength band with the intensity of light in the second fluorescence wavelength band; a fluorescence reference determination unit, connected to the comparison unit, configured to determine that the liquid contains the first substance when the intensity of light in the first fluorescence wavelength band is higher than the intensity of light in the second fluorescence wavelength band, and to determine that the liquid contains the second substance when the intensity of light in the second fluorescence wavelength band is higher than the intensity of light in the first fluorescence wavelength band.