Gas Chromatography (GC) Basics
Applications, Solutions, Components and Principles
Gas Chromatography (GC): Applications, Analysis Solutions, and Instrumentation Principles
Gas chromatography (GC) is an analytical technique applicable to gas, liquid, and solid samples (components that are vaporized by heat). If a mixture of compounds is analyzed using a GC system, or gas chromatograph, each compound can be separated and quantified.
When a mixed solution sample is injected into the GC system, the compounds contained in the sample, including the solvent components, are heated and vaporized within the sample injection unit.
Within the GC system, the mobile phase (referred to as the carrier gas) will flow in sequence from the sample injection unit to the GC column, and then to the detector. The target components that were vaporized in the sample injection unit are transported by the carrier gas to the column.
In the column, a liquid stationary phase (for example, silicone polymers) is chemically bonded or coated, the vaporized sample is repeatedly dissolved and vaporized in the liquid stationary phase and travels downstream with the carrier gas.
Since the process of dissolving and vaporizing the sample in the stationary phase depends on the physicochemical properties such as the boiling point and the nature of the column, the time of dissolving in the liquid phase and the time of vaporizing will be different for each compound. Therefore, even when mixed components are injected, the time for the components to arrive at the column exit is different, and separation can be detected.
Finally, the column exit connects to a detector and when the components other than the carrier gas are eluted from the column, the detector converts them into electrical signals which are amplified and sent to a data processor. By analyzing the electric signal of the detector on the data processor, the GC will be able to identify the sample and determine its quantity.
Want to learn more about gas chromatography and its applications? Check out our Resource Library here.
Applications of Gas Chromatography
The table below shows some examples of industry applications using gas chromatography.
| Industry | Type of Analysis |
|---|---|
| Pharmaceutical | Residual solvent analysis |
| Food and Beverages | Component analysis, food safety analysis, halal analysis of alcohol |
| Environmental | Air, water, soil |
| Petrochemical | Simulated distillation, component analysis |
| Chemicals | Material, polymer, additive, gas purity analysis, gas emission in automotives |
| Energy and Gas | Artificial photosynthesis research |
Typically, the characteristics of compounds can be analyzed using GC analysis and those that are difficult to analyze are summarized here:
- Compounds Suitable For GC Analysis
- Compounds with a boiling point up to 400°C
- Compounds that are not decomposed at their vaporization temperature
- Compounds that decompose at their vaporization temperature, but always by the same amount (this is called pyrolysis GC)
- Compounds Difficult To Analyze With GC
- Highly adsorptive compounds (compounds containing a carboxyl group, hydroxyl group, amino group, or sulfur)
- Compounds for which standard samples are difficult to obtain (qualitative and quantitative analyses are difficult)
- Compounds That Cannot Be Analyzed With GC
- Compounds that do not vaporize (inorganic metals, ions, and salts)
- Highly reactive compounds and chemically unstable compounds (hydrofluoric acid and other strong acids, ozone, NOx and other highly reactive compounds)
Key Considerations of Gas Chromatography
Gas chromatography consists of key components that should be considered to enable effective separation and analysis of sample components in a gas phase.
- Sample injection Methods
Hot Injection
- Split: Most of the sample is eliminated as only a portion is injected into the column.
- Splitless: Not split, but only for 1 to 2 minutes after injection.
- Total volume injection (direct injection): There is no splitting mechanism.
Cold Injection
- Cold on-column injection (OCI)
- Programmed temperature vaporization (PTV)
| Method | Hot Injection | Cold Injection | |||
|---|---|---|---|---|---|
| Split | Splitless | Total Volume | Cold On-Column Injection | Programmed Temperature Vaporization | |
| Liquid Sample | Yes | Yes | Yes | Yes | Yes |
| Gas Sample | Yes | －*1 | Yes | - | - |
| Injection Volume | Liquid sample: 2 µL max Gas sample: 1 mL max |
2 µL max | Liquid sample: 2 µL max Gas sample: 0.5 mL max |
0.5 to 2 µL | 1 to 8 µL |
| Column | No limits on I.D. or length | I.D. 0.25 mm min | Wide bore columns with an I.D. between 0.45 and 0.53 mm | Wide bore columns with an I.D. of 0.53 mm × 30 m | No limits on I.D. or length |
*1: If an additional low-temperature oven controller is attached and the column’s initial temperature can be reduced to 0°C or less, there will be some components that can be analyzed using the splitless method.
- Separation Columns
There are two main types of separation columns used in GC available on the market: capillary and packed columns. The GC user chooses the column based on certain attributes such as: the target compounds, the number of components and the instrument configuration. A smaller diameter and longer column is suitable if higher resolution is needed, while a larger diameter column can be used if higher resolution is unnecessary.
| Polarity | Example of Column | Typical Liquid Phase |
|---|---|---|
| Non-polar | Squalane | |
| SH-Rtx-1 | 100% Dimethylpolysiloxane | |
| Low-polar | SH-Rtx-5 SH-Rtx-1301, 624 |
5% Diphenyl 95% Dimethylpolysiloxane 6% Cyanopropylphenyl 94% Dimethylpolysiloxane |
| Mid-polar | SH-Rtx-1701 | 4% Cyanopropylphenyl 86% Dimethylpolysiloxane |
| SH-Rtx-17 | 50% Phenyl 50% Methylpolysiloxane |
|
| High-polar | SH-Rtx-200 | Trifuoropropylmethylpolysiloxane |
| SH-Rtx-Wax | Polyethyleneglycol | |
| BPX-90 | 90% Bis-cyanopropyl 10% Cyanopropylphenylpolysiloxane |
- Carrier Gas
The carrier gas should be an inert gas, carrying the sample but not interacting with the target compounds. Such examples are He, N2 , H2 , and Ar, of which, He and N2 are the most commonly used. In capillary columns, He is preferred due to its ability to maintain the separating resolution at high linear velocity (the speed at which the sample travels through the column).
Carrier gas always flows into the detector, therefore it is necessary to use one with a high purity (99.995% or higher). Carrier gases with high purity can suppress baseline noise.
Below are the advantages and disadvantages of carrier gases:
| Carrier Gas | Advantages | Disadvantages |
|---|---|---|
| Helium |
• Safe
• Relatively wide optimum linear velocity range |
• Expensive |
| Nitrogen | • Cheap • Safe |
• Optimum linear velocity range is narrow and slow • Long analysis time |
- Detectors
The detectors that can be used with Shimadzu gas chromatographs are shown below. They are broadly divided into general-purpose detectors and selective, high-sensitivity detectors. General-purpose detectors can analyze a wide range of compounds, of which the flame ionization detector (FID) is the most common because it can analyze almost all organic compounds. In contrast, selective, high-sensitivity detectors are only capable of detecting specific types of compounds selectively and with high sensitivity.
| Detector | Detectable Compound | Detection Limit* |
|---|---|---|
| General-Purpose Detectors | ||
| Flame ionization detector (FID) | Organic compounds (other than formaldehyde and formic acid) | 0.1 ppm (0.1 ng) |
| Thermal conductivity detector (TCD) | All compounds other than the carrier gas | 10 ppm (10 ng) |
| Barrier discharge ionization detector (BID) | All compounds other than He and Ne | 0.05 ppm (0.05 ng) |
| Selective, High-Sensitivity Detectors | ||
| Electron capture detector (ECD) | - Organic halogen compounds - Organic metal compounds |
0.1 ppb (0.1 pg) |
| Flame thermionic detector (FTD) | - Organic nitrogen compounds - Inorganic and organic phosphorus compounds |
1 ppb (1 pg) 0.1 ppb (0.1 pg) |
| Flame photometric detector (FPD) | - Inorganic and organic sulfur compounds - Inorganic and organic phosphorus compounds - Organic tin compounds |
10 ppb (10 pg) |
| Sulfur chemiluminescence detector (SCD) | - Inorganic and organic sulfur compounds | 1ppb (0.1pg) |
*The detection limits are approximations. Actual values will vary depending on the compound structure and analytical conditions.
Analysis Solutions Using GC and GCMS
Explore our Technology Solutions to discover analysis solutions using GC and GCMS. From screening of phthalate esters and brominated flame retardants to analysis of ethylene oxide (EO) and 2-chloroethanol (2-CE) and more, discover how Shimadzu’s GC and GCMS solutions offer exceptional performance and high-throughput capabilities to seamlessly meet diverse user requirements across various markets.
Get to access our Technology Brief to explore the latest technological advances in the instruments’ capabilities in powering the analysis. Learn how you can speed up GCMS analysis with low pressure GCMS, unlock the potential of using next-generation deconvolution software in conjunction with Shimadzu’s GCMS and so much more in our Resource Library.
For more, discover our Digital Classrooms and our instruments here.
Accelerate your analyses with our solutions today.