1. What is Gas chromatography?
Ans. Gas Chromatography (GC) is a widely used analytical technique for separating and. analyzing volatile substances in a mixture
2. What is Principle Of GC?
Gas chromatography separates and analyzes volatile compounds by passing a sample through a column with a stationary phase.
The compounds separate based on their interaction with the phase, and are detected, providing information about their identity and concentration.
3. What are components Of GC System?
1. Injector
Vaporizes the sample for entry into the column.
2. Column
Separates components, typically coated with a stationary phase.
3. Carrier Gas
Moves the sample through the column.
4. Detector
Identifies separated components and generates a signal.
5. Data System
Analyzes the detector signals and creates a chromatogram.
4. What is Gas Chromatography Process?
Gas Chromatography Process
1. Sample Injection
Sample is injected into the GC system using a syringe.
2. Vaporization
Liquid sample is vaporized into a gas.
3. Separation in the Column
The sample is carried by carrier gas through the column, separating components.
4. Detection
Components are detected as they exit the column, creating a chromatogram.
5. Analysis
Retention time and peak area are used for identification and quantification.
5. What are Types of Detectors?
1. Flame lonization Detector (FID):
Detects ions formed during combustion of organic compounds. Commonly used for detecting hydrocarbons.
2. Thermal Conductivity Detector (TCD)
Measures changes in thermal conductivity as the sample passes through a heated filament.
3. Mass Spectrometer (MS)
Provides detailed information about the molecular structure of the components.
4. Electron Capture Detector (ECD)
Highly sensitive to halogenated compounds.
6. What are Types of Columns?
Capillary Columns (Open Tubular Columns)
Narrow columns with a stationary phase coating the inside. They offer high resolution and efficiency.
Packed Columns
Larger diameter columns filled with a solid stationary phase or particles coated with the stationary phase.
Q. What is the ratio of gases used in Gas Chromatography (GC)?
Standard GC gas ratio ≈ H₂ : Carrier : Air = 1 : 1 : 10 (optimized for best detector performance).
In Gas Chromatography, gas ratios depend on the detector type and column requirement, but the goal is to ensure stable flame and optimum separation.
Typical Gas Ratios (for FID – Flame Ionization Detector):
Carrier Gas (Nitrogen / Helium): ~30–40 mL/min
Hydrogen Gas: ~30–35 mL/min
Air (for flame support): ~300–400 mL/min
Ratio (approximate): 1 : 1 : 10 (H₂ : Carrier : Air)
Purpose of Each Gas:
Carrier Gas: Transports the sample through the column.
Hydrogen: Acts as the fuel for the flame.
Air: Provides oxygen for combustion in the FID.
Optimization:
Ratios may vary slightly based on instrument model, column length, and sample type.
Correct gas flow ensures sharp peaks, stable baseline, and high sensitivity.
Q. Which detectors are used in Gas Chromatography (GC)?
Most common detectors:
- FID – for hydrocarbons & organics
- TCD – for general gases
- ECD – for halogenated compounds
- NPD – for nitrogen/phosphorus compounds
- MS – for advanced identification.
Gas Chromatography uses different detectors based on sample type and analysis purpose.
The most commonly used detectors are:
1. Flame Ionization Detector (FID)
Most widely used in GC.
Detects organic compounds that can be ionized in a hydrogen flame.
High sensitivity, wide linear range, and stable baseline.
Commonly used in pharma, petrochemical, and environmental analysis.
2. Thermal Conductivity Detector (TCD)
Works on the difference in thermal conductivity between carrier gas and sample components.
Universal detector — detects both organic and inorganic compounds.
Non-destructive and suitable for gas analysis.
3. Electron Capture Detector (ECD)
Detects compounds that capture electrons (mainly halogenated or electronegative compounds).
Highly sensitive for pesticides, halocarbons, and environmental pollutants.
4. Nitrogen–Phosphorus Detector (NPD) / Thermionic Detector
Selective for compounds containing nitrogen and phosphorus.
Commonly used in pharmaceutical and pesticide analysis.
5. Mass Spectrometry Detector (GC–MS)
Detects based on mass-to-charge ratio (m/z) of ions.
Provides structural identification and qualitative + quantitative data.
Used in forensic, environmental, and research applications.