Isothiocyanates and nitriles are degradation products of glucosinolate hydrolysis, secondary metabolites found in plants form cabbage family. Isothiocyanates exhibit biological activity, which is why analytical methods are being developed for their determination. In this thesis, a rapid method for the determination of 3-phenylpropanonitrile, 2-phenylethyl isothiocyanate, isopropyl isothiocyanate, allyl isothiocyanate, benzyl isothiocyanate, phenyl isothiocyanate, 3-(methylthio)propyl isothiocyanate, 2- methoxyphenyl isothiocyanate, 3-methoxyphenyl isothiocyanate, and 4-methoxyphenyl isothiocyanate was developed. A hyphenated technique gas chromatography-tandem mass spectrometry (GC-MS/MS) was employed to separate the selected isothiocyanates and nitriles from the mixture and determine them qualitatively and quantitatively. Stock solutions were prepared from commercially available standards of these compounds using hexane as solvent. A triple quadrupole mass spectrometer, operated in multiple reaction monitoring (MRM) mode, was used to monitor specific transition reactions (quantitative and two qualitative transitions for each analyte). Mass spectrometry was optimized by determining nitrogen collision energies for each specific transition reaction. Gas chromatography was optimized by changing the temperature programme. Calibration curve range from 0.0005 mg/mL to 0.5 mg/mL was selected. Evaluated validation parameters including accuracy, repeatability, linearity, limit of detection, and limit of quantification were found to be satisfactory, ensuring the suitability of the rapid determination of selected isothiocyanates and nitriles in the mixture.