Gas Chromatography-Mass Spectrometry (GC-MS) Information

Once the components leave the GC column, they are ionized and fragmented by the mass spectrometer using electron or chemical ionization sources. Ionized molecules and fragments are then accelerated through the instrument’s mass analyzer, which quite often is a quadrupole or ion trap. It is here that ions are separated based on their different mass-to-charge (m/z) ratios. GC-MS data acquisition can be performed in either full scan mode, to cover either a wide range of m/z ratios, or selected ion monitoring (SIM) mode, to gather data for specific masses of interest.

The final steps of the process involve ion detection and analysis, with fragmented ions appearing as a function of their m/z ratios. Peak areas, meanwhile, are proportional to the quantity of the corresponding compound. When a complex sample is separated by GC-MS, it will produce many different peaks in the gas chromatogram and each peak generates a unique mass spectrum used for compound identification. Using extensive commercially available libraries of mass spectra, unknown compounds and target analytes can be identified and quantified.

Single quadrupole GC-MS

When gas chromatography is combined with a mass spectrometer that includes just one quadrupole, it is often referred to simply as GC-MS. GC-MS is well suited to the everyday analysis of samples where either targeted or untargeted analysis is required as these systems can be operated using either targeted selected ion monitoring (SIM) or untargeted full scan acquisition. Typical applications include pesticide analysis in food and environmental samples, analysis of biological samples for drugs of abuse and analysis of volatile organic compounds in water samples.

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Triple quadrupole GC-MS/MS

Gas chromatography combined with a triple quadrupole mass spectrometry system is referred to as GC-MS/MS. The triple quadrupole MS provides a higher level of selectivity and is best suited to analyses where the highest sensitivity is required. This is often the case when quantitating pesticides in food or environmental contaminants. GC-MS/MS systems are typically operated in selective reaction monitoring (SRM) mode. The high selectivity of the SRM helps reduce interferences from background ions and produce a high signal-to-noise for excellent detection capability.

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HRAM GC-MS/MS

For comprehensive characterization of samples in a single analysis with high-confidence compound discovery, identification and quantitation, a GC system can be combined with a high resolution accurate mass (HRAM) mass spectrometer. These GC-MS/MS systems offer the quantitative power of a triple quadrupole GC-MS/MS combined with high-precision, full-scan HRAM capabilities available only from the most sensitive and accurate mass spectrometers. These systems are ideally suited for applications that require both accurate targeted analysis and confident unknown compound identification.

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Samples for GC-MS analyses often need to be separated from complex and dirty matrices before being introduced into the gas chromatograph. Different manual and automated sample extraction processes are often used prior to gas chromatography. These processes differ depending on the sample matrix, the degree of selectivity required and the initial cleanliness of the samples. Automated on-line sample preparation with sample injection into a GC-MS is possible through robotic autosamplers, which can replace many basic and more complex manual sample handling operations.

For more information about sample preparation prior to GC-MS analysis, visit our GC-MS Sample Preparation Learning Center.

You can also check out the sample preparation products offered by Thermo Fisher Scientific when you download our Chromatography Consumables Catalog – Sample preparation products.

GC columns represent the stationary phase and separation tool of a gas chromatography analysis. The stationary phase ensures that different compounds are adequately separated and eluted from the column at different times. Different types of columns with different stationary phases can be used for different applications, such as determining volatile organic compounds (VOCs) or dioxins. They can be designed to separate polar or non-polar compounds or process samples at different speeds. It is important that columns do not release stationary phase compounds, thus providing minimal background signal in the resulting chromatogram, sometimes referred to as being “low bleed”. Inertness of GC column material is also a critical factor to considering in order to prevent unwanted chemical interactions with the sample.

To learn more about the different types of GC columns Thermo Fisher Scientific offers, visit our Gas Chromatography Columns page or download our Chromatography Consumables Catalog – GC Columns and accessories.