GC-MS services
GC-MS is the acronym for gas chromatography mass spectrometry, and it is used to describe a process that involves separation of volatile compound in the gas phase using a column, followed by ionization and mass analysis of the compounds with a mass spectrometer. It is the oldest combination of separation technique (GC) with mass spectrometry. The separation is driven by temperature: the components are vaporized in the injector and reach the separation column kept at an initial lower temperature that lets them pass to the liquid phase and interact with the stationary phase (often a film coating the inside of the column). Temperature is then ramped up and the components desorb from the column once they boiling point is reached and the stationary column cannot hold them back anymore. Ionization is commonly achieved via electron ionization (EI) or via atmospheric pressure chemical ionization (APCI), although there are other minor ionization mechanisms that can be employed. EI is particularly useful because it can ionize non-polar compounds such as components of petrol. EI spectra are often characterized by heavy fragmentation, which happens during the ionization process. Therefore, the platform often records the EI fragmentation pattern of an analyte rather than its intact mass. These pattens can be compared to existing databases for identification purposes. The mass spectrometer is usually operated in scanning mode over a preselected m/z range, or in single ion mode (SIM), where the instrument is monitoring a single m/z window.
Description: this type of analysis is aimed at determining the identity of unknown volatile components by comparing their mass fingerprint with database spectra. Semi-volatile and certain non-volatile components can be analyzed after chemical derivatization steps.
Amount needed: for single components mixture, 20 µL at a concentration of 10 ppm. The concentration refers to the mass of the whole sample, not just the component one wishes to detect. Complex mixtures require differing amounts depending on the type of sample and the goal of the analysis.
Type of samples: Any volatile compound and / or compounds made volatile through chemical derivatization.
MSF protocol available: yes
Degree of difficulty: low to medium
Notes: our standard column is intended for non-polar to slightly polar compounds. As such it does not allow injection of samples containing water. If you would like to analyze more polar compound, you will need to provide your own column after contacting the facility.
Description: this is a type of targeted analysis where the mass spectrometer I operated as a mass filter and detect only a single mass window per scan event. It is intended to monitor known compounds and provide a simpler dataset for quantitative measurements.
Amount needed: 20 µL of the final injection solution. This could be an extract or a derivatized sample. The concentration depends on the lower limit of quantification achievable for the compound of interest.
Type of samples: Any volatile compound and / or compounds made volatile through chemical derivatization.
How many replicates: We recommend a minimum of 3, but the number is dictated by the variability of the target(s) under analysis.
MSF protocol available: Yes
Degree of difficulty: low to medium.
Notes: with SIM MS analysis, many factor such as gradient and temperature can be adjusted to suit the compound of interest, and the output is not a spectrum but rather the continuous extraction ion chromatogram centered on the middle of the acquisition window
GC-MS full scan analyses are performed with Agilent Mass Hunter, which offers tools for data analysis and database search. The main database used by the facility is the NIST 2014 database.
Sim analyses are performed with Agilent Mass Hunter, which offers tools for data analysis and quantification of the recorded signal. Further calculations are performed with Microsoft Excel.