The invention provides a mass spectrometric method for analyzing a sample in a solution, including the steps of directing a flow of a solution containing sample compounds to be analyzed towards a supersonic nozzle having an input end and an output end; vaporizing the solution and sample prior to its expansion from the output end of said supersonic nozzle; allowing expansion of the vaporized sample and solution from said supersonic nozzle into a vacuum system, forming a supersonic molecular beam with vibrationally cold sample molecules; ionizing the vaporized sample compounds with electrons while contained as vibrationally cold molecules in said supersonic molecular beam; mass analyzing the ions formed from said sample compounds; detecting said ions formed from said sample compounds after mass analysis, and processing the data obtained from the resulting mass spectral information, for identifying and/or quantifying the chemical content of said sample. The invention also provides apparatus for analyzing a sample in a solution.