We use an Agilent 7890A GC coupled to HP-6890 MS Detector for identification of volatile organic compounds (VOCs). We identify and quantify the components of a complex mixture of volatiles e.g. essential oils, synthetic volatiles or head space of a natural source using recorded mass spectrum and calculated relative retention indices (RRI). The instrument has a selected ion monitoring to find traces of a specific substance with a certain molecular weight or a mass of fragment ion.