A method for controlling a plant for synthesis of urea, including a quantitative analysis of at least one process stream of said plant with the application of Raman spectroscopy, wherein: urea is synthesized from ammonia and carbon dioxide with a urea synthesis process at a pressure in the range of 100 to 300 bar and temperature in the range of 50 to 250 °C, said quantitative analysis is an in-line quantitative analysis of at least one process stream of said urea synthesis process, the use of Raman spectroscopy for said in-line quantitative analysis includes: the concentration of urea in said process stream is determined by Raman spectroscopy through the detection of a spectroscopy band corresponding to excitation of the carbonyl di-amide bond; the concentration in said process stream of carbon dioxide is determined by determining the concentration of carbon-containing molecules other than urea and having a carboxyl group by Raman spectroscopy through the detection of a spectroscopy band corresponding to excitation of the atomic bonds in the carboxyl form, and using this concentration of carbon-containing molecules other than urea as an equivalent concentration of carbon dioxide, wherein: excitation of the carbonyl di-amide bond of molecules of urea is detected by means of Raman shift of an incident laser beam having a suitable wavelength, in a frequency range of 900 to 1050 cm -1, said carbon-containing molecules other than urea are detected by means of Raman shift of said incident laser beam, in a frequency range of 1000 to 1150 cm -1, the concentration of ammonia is determined by means of Raman shift of said incident laser beam, in a frequency range of 1350 to 1750 cm-1. urea is synthesized from ammonia and carbon dioxide with a urea synthesis process at a pressure in the range of 100 to 300 bar and temperature in the range of 50 to 250 °C, said quantitative analysis is an in-line quantitative analysis of at least one process stream of said urea synthesis process, the use of Raman spectroscopy for said in-line quantitative analysis includes: the concentration of urea in said process stream is determined by Raman spectroscopy through the detection of a spectroscopy band corresponding to excitation of the carbonyl di-amide bond; the concentration in said process stream of carbon dioxide is determined by determining the concentration of carbon-containing molecules other than urea and having a carboxyl group by Raman spectroscopy through the detection of a spectroscopy band corresponding to excitation of the atomic bonds in the carboxyl form, and using this concentration of carbon-containing molecules other than urea as an equivalent concentration of carbon dioxide, wherein: excitation of the carbonyl di-amide bond of molecules of urea is detected by means of Raman shift of an incident laser beam having a suitable wavelength, in a frequency range of 900 to 1050 cm -1, said carbon-containing molecules other than urea are detected by means of Raman shift of said incident laser beam, in a frequency range of 1000 to 1150 cm -1, the concentration of ammonia is determined by means of Raman shift of said incident laser beam, in a frequency range of 1350 to 1750 cm-1. the concentration of urea in said process stream is determined by Raman spectroscopy through the detection of a spectroscopy band corresponding to excitation of the carbonyl di-amide bond; the concentration in said process stream of carbon dioxide is determined by determining the concentration of carbon-containing molecules other than urea and having a carboxyl group by Raman spectroscopy through the detection of a spectroscopy band corresponding to excitation of the atomic bonds in the carboxyl form, and using this concentration of carbon-containing molecules other than urea as an equivalent concentration of carbon dioxide, wherein: excitation of the carbonyl di-amide bond of molecules of urea is detected by means of Raman shift of an incident laser beam having a suitable wavelength, in a frequency range of 900 to 1050 cm -1, said carbon-containing molecules other than urea are detected by means of Raman shift of said incident laser beam, in a frequency range of 1000 to 1150 cm -1, the concentration of ammonia is determined by means of Raman shift of said incident laser beam, in a frequency range of 1350 to 1750 cm-1. excitation of the carbonyl di-amide bond of molecules of urea is detected by means of Raman shift of an incident laser beam having a suitable wavelength, in a frequency range of 900 to 1050 cm -1, said carbon-containing molecules other than urea are detected by means of Raman shift of said incident laser beam, in a frequency range of 1000 to 1150 cm -1, the concentration of ammonia is determined by means of Raman shift of said incident laser beam, in a frequency range of 1350 to 1750 cm-1.