1. A mass spectrometric based method for sample identification, comprising the steps of: introducing sample compounds into a vacuum chamber of a mass spectrometer in a seeded supersonic molecular beam; ionizing with electrons the sample compounds, being vibrationally cold molecules, in said supersonic molecular beam during their flight through an electron ionization ion source; mass analyzing the ionized sample compounds with a mass analyzer of a mass spectrometer to obtain a mass spectrum of at least one compound in said sample; identifying the molecular ion group of isotopomers in said mass spectrum; generating various molecular elemental formulas from the identified molecular ion and a pre-allocated list of elements; reducing the number of said molecular elemental formulas by the incorporation of chemical valence considerations and constraints; calculating isotope abundances for said generated elemental formulas; comparing said calculated isotope abundances with the experimentally obtained mass spectral isotope abundance, and listing said generated elemental formulas according to their degree of matching to said experimentally obtained mass spectral isotope abundance.