Gas Chromatography Mass Spectrometry (GC-MS) combine two powerful techniques in order to provide the identification of compounds that have low detection limits and potential required for quantitative analysis. Gas Chromatography Mass Spectrometry analyses works on liquids, solid and gaseous samples but are primarily restricted to semi volatile and volatile compounds.
Under Gas Chromatography, a sample is carried and volatilized and carried by the inter gases through a coated glass Capillary Column. The stationary phase is joined to the interior of the column and the amount of time it takes a specific compound of an element to pass through this column on to a detector is called its “Retention Time”. These measurements are used for identification purpose when compared to references.
Under usual Mass Spectrometry or MS step under the Gas Chromatography Mass Spectrometry, the compounds leaving the GC columns are fragmented by the electron impact. These charged fragments are detected gradually and the subsequent spectrum obtained is used to identify the molecules. Fragmentation patterns are reproducible and thus, can be used to create quantitative measurements.
Gas Chromatography Mass Spectrometry analysis is performed on gases, solids and liquids. For gases and liquids, the samples are usually injected directly into the Gas Chromatogram. For the solid elements, the analysis is carried our through outgrassing or desorption, solvent extraction or pyrolysis. Desorption experiment is performed under the flow of helium gas at controlled temperature ranging between 40 to 300 degree Celsius. The analytes are then collected on a Cryogenic trap during desorption process. The sample chamber is a 1.25″x4″ cylinder.
Pyrolysis is yet another sampling technique used for the analysis of materials that are impossible to be directly injected into Gas Chromatography Mass Spectrometry. Under this process, heat is directly applied to the sample that results in breaking down of the molecules in a reproducible way. These smaller molecules are then introduced in the Gas Chromatogram and analyzed by the GC-MS. By this method, probe temperatures of up to 1400ºC can be used.
Several other sampling methods and sample preparation are available such as static headspace analysis, derivatization, purge and trap, Solid Phase Microextraction etc. having applications based on species of interests and sample types.
Strengths
- Identification of organic components through separating complex mixtures
- Quantitative analysis
- Trace determination of organic contamination (low to mid-ppb level for liquid matrices and low nanogram level for solid matrices?
Ideal Uses
- Identifying and quantifying volatile organic compounds in mixtures
- Outgassing studies
- Testing for residual solvents
- Evaluating contaminants on semiconductor wafers or other technology products (thermal desorption)
- Identifying trace impurities in liquids or gases
Limitations of Gas Chromatography Mass Spectrometry
- Non-volatile matrices (wafers, metal parts oil, etc.) require additional prep (extraction, outgassing, etc.)
- Evaluating extracts from plastics
- Target compounds must either be volatile or capable of derivatization
- Atmospheric gases are challenging (CO2, N2, O2, Ar, CO, H2O)
Advantages
GC MS has long been considered to be the Gold Standard for all sorts of analytical laboratories. It is a strong analytical tool that uses time for the chemical elements to travel through the GC column, the retention time as compared to known standards to identify the chemical. It is a good technique for simple mixtures and for situations where the chemicals of concern are known and calibrated before running samples. Though there are advantages and disadvantages of all the process but together these factors are helpful in evolution and advancement of laboratory processes and identification of elements.