Interview questions for Chromatography

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1.What Are The Main Differences Between High Performance Liquid Chromatography And Gas Chromatography?

o In HPLC the mobile phase is a liquid whereas in Gas Chromatography the mobile phase or carrier is a gas.
o HPLC is useful for analysis of samples which are liable to decompose at higher temperatures. GC involves high temperatures so compounds are stable at such temperatures.
o Gas Chromatography is applied for analysis of volatile compounds whereas non volatile compounds can be easily analyzed on HPLC
o Gas Chromatography cannot be used for analysis of high molecular weight molecules whereas HPLC has applications for separation and identification of very high molecular weight compounds
o HPLC requires higher operating pressures than GC because liquids require higher pressures than gases for transport through the system
o HPLC columns are short and wide in comparison to GC columns.

2. What is rs test why we are performing rs test ?

RS stands for related substance, means by-products upon completion of reaction or the unrelated portion present in the product. RS testing help us to identify the adequate quantity of these by-products or unrelated part. More over RS help us during the stability study to know any significant change in the nature of product during long storage in various climatic conditions.

3. Which Type Of Gc Detector Is Most Commonly Used? Explain Its Working Principle And What Are Its Limitations?

The most commonly used detector is the flame ionize detector. The sample is com busted with the help of fuel gas and oxidant in the detector body. Combustible sample components burn and produce ions and electrons which can conduct electricity through the flame. A large potential difference is applied at the burner tip and the collector electrode located above the flame and the current between the electrodes is measured. The detector is mass sensitive and response is not affected by carrier gas flow rate changes. However, the detector is not responsive to inorganic gases such as CO, O2, NH3, N2, CS2, CO2, etc.

4. What is quality control?

Quality control means to maintain the quality of product by calculating their content ,different physical parameters,as per their specificationIP/BP/USP/EP/JP.

5. When Is Isothermal Operation Useful?

Isothermal operation is useful when high resolution is required for separating compounds having narrow boiling range. Temperature is set to around mid range of boiling points of constituents. This results in good resolution of low boiling components but band broadening of higher boiling components can result due to their longer retention in the column.

6. What Measures You Would Adopt To Extend Useful Life Of A Column?

o Condition a column before first use or after long time storage
o Take care not to exceed upper temperature limit specified by the manufacturer
o Avoid injection of solutions which are strongly acidic or basic in nature
o Rinse columns by injection with blank solvents such as methanol, methylene chloride or hexane to remove contamination of column after excessive usage.

7. What is use of acetonitrile compare to methanol in RP-HPLC Method development?

ACN is highly polar as compare to Methanol So provide Better resolution for many compound and it has property to form hydrogen bond so provide better selectivity.

8. What Is The Basic Principle Of Paper Chromatography?

Paper chromatography is a form of liquid chromatography where the components of a mixture of organic compounds get separated as unique spots by unidirectional flow of the developing liquid mobile phase solvent mixture over the filter paper to which a spot of the sample is applied. The distance travelled by each component is specific under the given set of operational conditions.

9. What Information You Get From The Retardation Factor Value?

Retardation factor Rf is a measure of the separation of a particular component. It is expressed as
Rf = distance moved by the component spot/ distance moved by solvent front
Rf is a unit less quantity and lies between 0and 1.A value of 0 indicates no separation has taken place and 1 represents that the component has moved entire length alongwith the solvent front. In case two spots have same value of Rf it indicates that they are not resolved. At least a difference of 0.05 is necessary to discern the separation between two spots.

10. What is the difference between HPLC and GC?

HPLC is useful for analysis of samples which are liable to decompose at higher temperatures. GC involves high temperatures so compounds are stable at such temperatures. Gas Chromatography is applied for analysis of volatile compounds whereas non volatile compounds can be easily analyzed on HPLC.

11. Which of the following is not used for detection in GC?

A. Infrared spectroscopy
B. NMR
C. Flame ionisation
D. Electrical conductivity
Answer: B

12. What is the typical internal diameter of fused silica capillary columns?

A. 0.2-0.3 mm
B. 0.3-0.5mm
C. 0.5-1.0 mm
D. 1.0-2.0 mm
Answer: A

13. In gas chromatography, the basis for separation of the components of the volatile material is the difference in

1. partition coefficients
2. conductivity
3. molecular weight
4. molarity
Answer : 1

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