Gas Chromatography, GC) is an efficient separation and analysis instrument widely used in chemistry, pharmacy, food, environment and other fields. The performance of its core components and spare parts directly affects the accuracy, stability and instrument life of the analysis results. This paper briefly introduces the main components and functions of GC, and explains the common spare parts and their functions.
1. The core component of gas chromatograph (GC)
(1) Gas path system
The gas path system is the basis of GC, which provides carrier gas (such as helium, nitrogen and hydrogen) and controls its flow and pressure to ensure the stable flow of samples in the chromatographic column.
Gas generator/steel cylinder: provide high-purity carrier gas (such as helium, nitrogen and hydrogen).
Gas purifier: removes moisture, oxygen and hydrocarbon impurities from carrier gas to protect chromatographic column and detector.
Flow controller (MFC)/ pressure regulating valve: accurately control the flow or pressure of carrier gas.
Injection port: where the sample vaporizes and enters the chromatographic column.
(2) Sampling system
The injection system is responsible for introducing the sample into GC and vaporizing it instantly.
Sample inlet (Split/Splitless):
Split: Some samples enter the chromatographic column and the rest are discharged, which is suitable for high concentration samples.
Splitless: All samples enter the chromatographic column, which is suitable for trace analysis.
Autosampler: It can improve the accuracy and efficiency of sampling, and is suitable for batch sample analysis.
Syringe/injection needle: used for manual injection, which needs to be replaced regularly to avoid pollution.
(3) chromatographic column
Chromatographic column is the core separation component of GC, and different stationary phases are suitable for different types of compound analysis.
Packed Column: It has been seldom used and is suitable for some special analysis.
Capillary Column: most commonly used, the stationary phase (such as DB-5, DB-WAX, etc.) is coated by Shi Ying capillary.
Oven: Control the temperature of chromatographic column and realize programmed temperature rise to improve the separation effect.
(4) Detection system
The detector is used to detect the separated components and convert them into electrical signals for analysis.
FID (Flame Ionization Detector): most commonly used, suitable for most organic compounds.
TCD (Thermal Conductivity Detector): Universal detector, suitable for inorganic gases and some organic substances.
ECD (Electron Capture Detector): Suitable for compounds containing electronegative groups (such as halogen and nitro).
FPD (Flame Photometric Detector): Suitable for trace analysis of sulfur and phosphorus compounds.
MS (Mass Spectrometer): provides molecular weight and structure information, and is suitable for qualitative analysis of complex samples.
(5) Data processing system
Chromatographic workstation (Software): records and analyzes data such as peak area and retention time, and supports quantitative and qualitative analysis.
Integrator (optional): Some old GC equipment, and modern instruments are usually integrated into software.
2. Common spare parts and their functions
(1) Spare parts for injection system
Septum: To prevent carrier gas from leaking, it needs to be replaced regularly (usually every 100-200 injections).
Linertube/Injector Liner: It is necessary to clean or replace it regularly to protect the inlet and reduce the discrimination effect of the sample.
O-Ring: seal the inlet to prevent air leakage, and replace it after aging.
Needle: used for manual injection, and should be replaced when it is bent or blocked.
(2) spare parts related to chromatographic column
Column Nut & Ferrule: connects the column with the inlet/detector, and needs to be replaced after aging.
Guard Column: protects the main column and prolongs its service life.
Column switching Valve: used for multi-column system or back blowing operation to reduce pollution.
(3) Detector spare parts
FID Nozzle: It is easy to be polluted and needs to be cleaned or replaced regularly.
FID Collector Assembly: aging or pollution will affect the sensitivity and need maintenance.
TCD Filament: Replace it when damaged.
ECD Radioactive Source: It needs to be calibrated regularly, and its use is restricted in some countries.
(4) Spare parts for gas circuit system
Gas Filter: remove impurities in carrier gas and prolong the service life of the instrument.
Regulator: it regulates the pressure of carrier gas, and needs to be repaired or replaced in case of failure.
Flow Controller: Ensure the steady flow rate of carrier gas, and need to be calibrated or replaced after aging.
(5) Other wearing parts
Septum Nut & O-Ring
Oven Fan: Failure will affect the temperature stability.
Power Supply: Some instruments may need to be replaced.
3. Spare parts replacement and maintenance suggestions
Replace the injection spacer and liner regularly (for example, every 100-200 injections).
Check O-rings and gas filters regularly to prevent air leakage or pollution.
Detector maintenance (such as FID nozzle cleaning and TCD hot wire calibration).
Column maintenance (such as aging, cutting or replacing gaskets).
Use the original factory or compatible high-quality spare parts to ensure the stable performance of the instrument.
