Gas chromatography–mass spectrometry (GC-MS) is an analytical method that combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample. After complex mixtures are separated on the GC column, they are detected by mass spectrometry, which generates a characteristic mass spectrum for each compound which may be used as a “fingerprint” for identification purposes. Measured mass spectra may be screened against a NIST mass spectral libraries for identification. The compounds available for testing in our laboratory are alkanes, fatty acids, alcohols, saccharides, polycyclic aromatic hydrocarbons, nitrophenols, hopanes, phthalic acid, phthalates and etc.