What is Gas Chromatography | Operation and Calibration of GC

Gas Chromatography

• Gas chromatography (GC) is one of the analytical chromatographic separation techniques.
• A mixture of samples injected into a column separates each compound given specified parameters to detect each analyte to given energy levels convert to electrical signals to amplified.
• The total process done instrument is called a gas chromatograph instrument.

Gas chromatography principle

• When the sample is injected the carrier gas goes into the hot oven and distributes between two immiscible phases (stationary phase and mobile phase) to separate their partition coefficient with specified parameters. These are two types of Gas chromatography.
• Gas-Solid Chromatography(GSC): GSC is used in low applications.
• Gas-Liquid Chromatography(GLC): GLC is used in more applications.
• These two types are used based on their separation and measurement.

GC Instrumentation

Carrier gas:

• The carrier gas is a very important role in Gas chromatography.
• The carrier gas is used for carrying vaporised analytes in the GC column.
• Generally, inert gases are used as carrier gas because these are chemically inactive mobile phases for separation.
• GC grade carrier gases are used 99.995% pure which are free from Oxygen and Hydrocarbon traces.
• The most used carrier gases in industries are Nitrogen(N2), Helium(He), Hydrogen(H2) and Argon(Ar).

Injector:

• The sample is injected by manual or autosampler into the injector vaporised flow through into column
• These are three types of injection modes split, splitless and direct.
• The minimum injector temperature is 400c for lower boiling samples.

Column Oven:

• The temperature in the column is oven-controlled by an isothermal programming system.
• Analytes to separate in columns their boiling points and partition between stationary and mobile phases.

GC Columns:

• GC Columns are selected by the polarity and non-polarity nature of the analytes. These are two types.

Packed columns:

• These are made of gas or stainless steel packed used nowadays packed column not used because of broad peak shapes and low separation.

Capillary column:

• These are thin fused silica lined with liquid phase adsorbents.
• Most industries used these columns because of their sharp peaks and clear separation.

Examples:

• HP-5, AB-5, DB-5, ZB-5 USP Phase G27 (5% Diphenyl, 95% dimethyl polysiloxanes)
• DB-624, ZB-624 ,USP Phase G43 (6% cyanopropyl phenyl & 94% polydimethylsiloxanes)
• DB-WAX USP Phase G16 (100% Polyethelene glycol)

Detectors:

• Whenever a mixture of samples is separated in the column each analyte goes to the detector electrical signal is converted and recorded. The most commonly used four types of detectors
• Flame Ionization Detector (FID) Organics and Hydrocarbons
• Thermal Conductivity Detector (TCD) Universal
• Electron-Capture Detector (ECD) Halogenated hydrocarbons
• Mass Spectrometer Detector (MS) Identification of compound.

Operation:

• Ensure that all power connections and in-between connections of all modules of ‘GC’ Headspace and ‘Computer’ switch on. Double Click on the ‘Lab Solutions’ icon then you will get a login screen, enter your user ID and password.

Calibration:

• Column Oven Temperature
• Vial Position check
• Repeatability check for Flame ionization Detector
• Repeatability check for Thermal Conductivity Detector
• Repeatability check for Electron Capture Detector
• Injection Linearity
• Flow rate check
• Repeatability check for Headspace

Calibration frequency:

• Once in six months.

Applications of Gas Chromatography:

• Pharmaceuticals, Chemicals, Cosmetics, Food, Petroleum, Environmental, Pesticides, Forensics, Research labs etc…