Top 10 interview questions about GC apparatus .
- What is Gas Chromatography and how does it work?
Gas Chromatography (GC) is an analytical technique used to separate and analyze compounds that can be vaporized without decomposition. In GC, a sample is injected into a heated injection port, where it is vaporized. The vaporized sample is carried by an inert gas (the carrier gas) through a column where components in the sample separate based on their interaction with the stationary phase. The separated components are then detected by a detector.
- What are the main components of a GC system?
The main components of a GC system are:
- Injection Port: Where the sample is introduced into the system
- Carrier Gas Supply: Provides an inert gas (e.g., helium or nitrogen) to carry the sample through the column.
- Column: A long, narrow tube that contains the stationary phase and separates the sample.
- Detector: Measures the separated components as they exit the column.
- Data System: Records and analyses the data from the detector.
- What types of detectors are used in GC and what are their principles?
Common GC detectors include:
- Flame Ionization Detector (FID): Detects ions formed when organic compounds are burned in a hydrogen flame.
- Thermal Conductivity Detector (TCD): Measures changes in the thermal conductivity of the carrier gas as different compounds pass through it.
- Electron Capture Detector (ECD): Sensitive to electronegative compounds like halogens, detecting the reduction in current when electrons are captured.
- Mass Spectrometer (MS): Identifies compounds based on their mass-to-charge ratio and provides structural information.
- How do you choose a carrier gas and why is it important?
- Carrier gases like helium, hydrogen, and nitrogen are chosen based on factors like:
- Viscosity and diffusion properties: Affects separation efficiency.
- Compatibility with the detector: Some detectors are sensitive to certain gases (e.g., FID is compatible with hydrogen).
- Cost and availability: Helium is expensive, so hydrogen may be used when possible. Choosing the right carrier gas is crucial for optimal separation and sensitivity.
- Explain the role of the GC column and the difference between packed and capillary columns.?
The GC column is responsible for separating the components of the sample. It consists of a thin layer of stationary phase inside a long tube
Packed Columns: Filled with small particles coated with stationary phase. They are durable but offer lower separation efficiency compared to capillary columns.
Capillary Columns: Have a thin, wall-coated stationary phase and provide higher resolution, making them suitable for complex samples.
- What are the common causes of poor peak resolution in GC?
Common causes include:
- Overloaded sample: Too much sample can cause broad, overlapping peaks.
- Column contamination: Residual material can cause poor separation.
- Improper temperature programming: Incorrect heating profiles can lead to poor separation.
- Inadequate carrier gas flow: Poor flow rates can affect the separation.
- What steps do you take for GC instrument maintenance and troubleshooting?
- Maintenance and troubleshooting steps include:
- Regularly cleaning and replacing the injector and detector.
- Checking and replacing the column as needed.
- Ensuring proper carrier gas flow and pressure.
- Inspecting and replacing seals, ferrules, and fittings.
- Calibration of the detector and ensuring proper baseline stability.
- How does temperature programming affect a GC run?
Temperature programming involves changing the oven temperature during the run. It helps to separate compounds with different boiling points. A lower initial temperature allows heavier compounds to condense, while increasing the temperature helps lighter compounds elute more quickly. Proper temperature programming enhances resolution and reduces run time.
- How do you prepare a sample for GC analysis?
Sample preparation typically involves:
- Dissolving the sample in a suitable solvent.
- Filtering the sample to remove particulates.
- Concentrating the sample if necessary.
- Ensuring that the sample is volatile and does not decompose at the injection temperature.
- What safety precautions are necessary when operating a GC?
Safety precautions include
- Using appropriate personal protective equipment (PPE) such as gloves and goggles
- Working in a well-ventilated area, as carrier gases and solvents may be toxic.
- Ensuring proper handling and storage of volatile solvents and gases.
- Regularly inspecting the system for leaks and malfunctions.
- Being cautious when handling the GC’s heated components to avoid burns.
- Each of these areas is essential for optimal performance and safe operation of a GC system.
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