GC is one of the most used techniques in different organizations including Pharmaceuticals. So, there is a lot to provide for these instruments. If you want to work with it and preparing for interview then these Gas Chromatography Interview Questions and Answers are prepared based on the previously asked questions in top companies. GC Related questions in the interview can assist you a chance to get success in a Pharmaceutical Field.
List of Gas Chromatography Interview Questions with Answers
Q. What are the differences between QA and QC?
Ans: QC is a subcategory of QA that deals with checking if materials and medicinal products fulfill acceptance requirements. The QA function is often composed of verifying all activities., whereas the QC function is mainly composed of execution operations.
Q. What is Gas Chromatography?
Ans: In analytical chemistry, gas chromatography is primarily utilized for the separation and examination of those compounds that can be vaporized without disintegrating. In the majority cases, GC comprises the determination of purity of a certain substance or conducting the separation of substance’s constituents, some portions of the mixtures.
Q. What is the principle of Gas chromatography?
Ans: The principle of separation in gas chromatography is “partition”. the mixture of the components to be separated is converted to vapor and mixed with the gaseous mobile phase.
the components that are more soluble in the stationary phase travel slower and are eluted later. the components that are less soluble in the stationary phase travel faster and eluted out first.
Q. What are the mobile phases used in Gas Chromatography (GC)?
Ans: In gas chromatography, the mobile phase consists of inert gases. eg. Helium, Nitrogen, Hydrogen.
Q. Why is GC called Gas chromatography?
Ans: The mobile phase that is used in GC is a carrier Gas.
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Q. What is gas chromatography instrumentation?
Ans: GC has the following instrumentation:
- Gas Chamber
- Injection Port
- Detector
- Column compartment
- Recorder
Q. What is the stationary phase in Gas chromatography?
Ans: The stationary phase may be a solid adsorbent called gas-solid chromatography (GSC) or can be a liquid inert support called gas-liquid chromatography
Q. What do you mean by inert Gas?
Ans: Inert gas is a non-reactive gas. In general, An inert gas is a gas that does not form any chemical bonds. commonly, they are chemically inert to all substances and therefore are often referred to as gas that is inert.
Q. Which types of components are used to separate in GC?
Ans: Only volatile components are used to separate in gas chromatography. for eg. IPA, ethanol, acetate, etc.
Q. What are the types of gas chromatography?
Ans:
- Gas chromatography is of two types:
- Gas solid chromatography (GSC)
- Gas-liquid chromatography (GLC)
Q. How to identify the peak in GC?
Ans: This question may be hard but you can explain it in sample ways as; GC works on different factors such as temperature, gas flow, and column length. because of the factor affecting retention time, it is important that, if the gas chromatography has a specified method then it will be easy to identify the peaks in GC and understand the elution pattern of the peak.
In another way, peaks can be identified in GC by using the method name GCMS. Ans: In GCMS, as a mass spectrometer is present, a peak is identified with respect to mass.
Q. How does Gas chromatography work?
Ans: A sample solution is injected through an injection port and the sample enters into a column. Because of the elevated column temperature the sample gas comes out of the sample and is carried out in the present mobile phase.
The temperature is controlled in such a manner that constituent gets a response only at its respective boiling points. As opposed to high boiling point components, those with a lower boiling point will elute first.
Q. Out of ALS and Headspace, which is more preferable?
Ans: ALS is meant for sampling liquids and evaporating them for injecting into the column while headspace is meant for giving liquid and solid forms a gas like state for purposes of column injection.
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Q. What are gas chromatography detectors?
Ans: The following are the GC Detectors:
- Flame ionization detector (FID)
- Thermal conductivity detector (TCD)
- Nitrogen phosphorous detector (NPD)
- Electron capture detector (ECD)
- Flame photometric detector (FPD)
- Photoionization detector (PID)
- Electrolytic conductivity detector (ELCD)
- Mass spectrometer (MS)
Q. What is the difference between FID and TCD?
Ans: FID as instrumentation is making use of flame which instead of the typical combustion makes use of a mixture of hydrogen and air which ionizes organic compounds by combustion. (Source)
TCD uses the differential thermal conductance of the gas to be analyzed and its carrier gas to create and maintain an imbalance.
Q. How many types of columns are used in gas chromatography?
Ans: Mainly two types of columns used in gas chromatography:
- Packed column (glass or stainless steel)
- Capillary column: (Fused quartz)
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Q. What are the 3 types of autosamplers?
Ans:
- Headspace autosampler
- Liquid autosampler
- Solid phase microextraction (SPME)
Q. which type of component is detected by the FID detector?
Ans. To detect organic types of compounds (other than formaldehyde and formic acid).
Q. What is the length of the packed & capillary column in GC?
Ans: Packed column lengths are 1 to 3 m, internal diameters vary from 2 to 4 mm.
Capillary column: Variable length varies between 10 and 100 meters and internal diameter between 0.1 and 1mm.
Q. What are the stationary phase materials used in the GC column?
Ans: Silicone grease or silicone wax is used as the stationary phase in GC.
Q. What are the components of gas chromatography?
Ans: Carrier gas>flow controller> injector port> column> column oven> detector> recorder.
Q. What is the function of Makeup Gas in GC?
Ans: Makeup gas is a gas flow that is used to move the less active or instead non-active components of the ghosts through a detector in order to cut down on the band-broadening effects. depending on the GC Brand and the design of the detector, enhancement of sensitivity can be achieved with the use of makeup gas.
Q. What does zero air contain which includes gas chromatography?
Ans: Zero air is that air which is treated for hydrocarbon removal by oxidative catalysis processes and the level of total hydrocarbon is maintained below 0.1 PPM, Accordingly, for such applications, either pressurized gas cylinders or gas generators are commonly used for ‘zero’ air.
Q. Which detector is commonly used for gas chromatography?
Ans: The flame ionization detector (FID) is the most widely used flame ionizing detector in gas chromatography because of the ease of use and detection of any vapor organic substances.
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Q. On what account different molecules are separated in gas chromatography?
Ans: In GC the principle of molecular separation is based on differences in boiling point. More thermal energy is required for thermal dissociation to occur to more boiling point molecules first their elution is less billing point molecules.
Q. What can be stated if both boiling points are the same, and what happens to the elution of the molecules in that case?
Ans: In the situation of same boiling points of the molecules, it is the size of the molecules that affect their differentiation, with smaller size molecules eluting first as against large size.
Q. What is the split ratio in GC?
Ans: The split ratio may be defined mathematically as the ratio of the column carrier gas flow to the split flow rate. For example, In a split ratio of 1: 5, there is five times the amount of carrier gas leaving the split vent as opposed to what is coming to the column.
Q. What are the parameters of the GC calibration?
Ans: Calibration parameters of Gas chromatography (GC) are carrier gas flow accuracy, flame ionization detector (FID) calibration by linearity, auto-injector liner calibration by linearity, column oven temperature calibration, etc.
Also, There are Interview Questions Relating to the Applications of Gas Chromatography, the Advantages, and the Limitations.
Q. What is the advantage of Gas chromatography?
- Ans: Compared to other methods, gas chromatography displays high-resolution power.
- High sensitivity.
- High precision and accuracy.
- High speed of work (minutes or even seconds are needed to analyze a sample).
- A very small quantity of sample is needed (in the order of Ul – ug).
Q. What are the disadvantages of Gas chromatography?
- Ans: GC analytes must possess good thermal stability.
- Analyte Must be properly volatized.
- Biological conditions are not applicable for operation of GC.
- Assuming the above conditions are not critical, then GC is perhaps the best method for the analysis of the complex sample.
Q. What types of molecules elute first in GC?
Ans: The molecules which have Low boiling points are eluting first in GC.
Q. What are the applications of GC?
Ans: The following are the applications of GC:
- Chemical industries
- R&D
- QC in the pharmaceutical industries
- Forensic science labs
- Food industries
- Petroleum and Petrochemical
- Air pollution measurement
- Wine industries
- Alcohol analysis in blood
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