Gas Chromatography

Q1: A retention gap is placed between the injector and the front of the column to

A retain contaminants and prevent them from reaching the column

B retain the sample and release it gradually to the column

C prevent backflush of the injected solution

D all of the above

ANS:A - retain contaminants and prevent them from reaching the column

No answer description is available.

Q2: In column switching chromatography

A compounds trapped on one column are eluted to another column

B one column is removed and replaced by another

C the flow to the column is switched on and off repeatedly

D any of the above

ANS:A - compounds trapped on one column are eluted to another column

No answer description is available.

Q3: Which of the following are not used as stationary phases in a GC column?

A Polysiloxanes

B Silica

C Cyclodextrins

D None are used as stationary phases

ANS:B - Silica

No answer description is available.

Q4: Which of the following gases is unsuitable for use as a GC carrier gas?

A Nitrogen

B Helium

C Oxygen

D All of the above

ANS:C - Oxygen

Oxygen may react with the analyte to form oxides.

Q5: The GC trace obtained after an experiment is called a

A chromatograph

B chromatogram

C chromatophore

D graph

ANS:B - chromatogram

No answer description is available.

Q6: Resolution is proportional to the

A number of theoretical plates in a column

B square root of the number of theoretical plates in a column

C square of the number of theoretical plates in a column

D cube root of the number of theoretical plates in a column

ANS:B - square root of the number of theoretical plates in a column

No answer description is available.

Q7: Helium is generally preferred as carrier gas over nitrogen and hydrogen because

A it is inert

B it has a lower viscosity

C it doubles up as a party gas for balloons and funny voices

D all of above

ANS:D - all of above

No answer description is available.

Q8: Column bleeding occurs when

A elution of the analyte is extended over time

B the column is cracked and stationary phase leaks out

C traces of the stationary phase are eluted

D the column breaks during installation and causes personal injury

ANS:C - traces of the stationary phase are eluted

No answer description is available.

Q9: Theoretical plates are used to

A estimate the efficiency of a column

B determine the thickness of the stationary phase

C measure the distribution of the analyte between mobile and stationary phases

D None of the above

ANS:A - estimate the efficiency of a column

No answer description is available.

Q10: Which of the following detectors give mass flow-dependent signals?

A Electron capture detector

B Field ionisation detector

C Thermal conductivity detector

D All of the above

ANS:B - Field ionisation detector

No answer description is available.

Q11: Doubling the column's length increases resolution by a factor of

A (2)0.5

B 2

C 3

D 4

ANS:A - (2)0.5

No answer description is available.

Q12: What are the benefits of decreasing the column internal diameter?

A Increased sample capacity

B Increased resolution

C Reduced risk of column overloading

D All of the above

ANS:B - Increased resolution

No answer description is available.

Q13: What does the selectivity factor describe?

A The proportional difference in widths of two chromatographic peaks

B The maximum number of different species which a column can separate simultaneously

C The relative separation achieved between two species

D None of the above

ANS:C - The relative separation achieved between two species

No answer description is available.

Q14: Split injection is carried out by

A splitting the sample into smaller portions to inject sequentially

B splitting the sample into smaller portions to inject at the same time through parallel ports

C splitting off some of the sample so that it does not enter the column

D none of the above

ANS:C - splitting off some of the sample so that it does not enter the column

No answer description is available.

Q15: Which of these effects result from slow injection of a large sample volume?

A Increased resolution

B Decreased resolution

C Non-linear detector response

D Constant resolution

ANS:B - Decreased resolution

No answer description is available.

Q16: 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

ANS:A - 0.2-0.3 mm

No answer description is available.

Q17: Derivatisation of a sample is carried out to

A reduce polarity of the analytes

B increase the detector response

C increase volatility of the analytes

D all of the above

ANS:D - all of the above

No answer description is available.

Q18: Which of the statements is correct?

A Gas chromatography is used to analyse gases

B Gas chromatography is used to analyse solids

C Gas chromatography is used to analyse gases, solutions and solids

D All of the above

ANS:D - All of the above

No answer description is available.

Q19: Sample injection is considered successful if

A all of the sample in the injector has been added to the column

B the sample is concentrated at the start of the column

C the sample is spread evenly along the column

D the sample is homogenously spread along the column

ANS:B - the sample is concentrated at the start of the column

No answer description is available.

Q20: What useful information can be found from a Van Deemter plot?

A The selectivity factor

B Optimum mobile phase flow rate

C Optimum column temperature

D Optimum column length

ANS:B - Optimum mobile phase flow rate

What is the relation between Van Deemter plot and mobile phase flow rate?

Q21: Which of the following detectors give concentration-dependent signals?

A Electron-capture detector

B Thermal conductivity

C Infra-red detector

D All of these

ANS:D - All of these

No answer description is available.

Q22: Headspace analysis is carried out in order to

A analyse volatile compounds from solid or liquid samples

B determine the psychological state of the tutor

C analyse the column contents ahead of the sample

D determine non-volatiles

ANS:A - analyse volatile compounds from solid or liquid samples

No answer description is available.

Q23: What does the retention factor, k', describe?

A The distribution of an analyte between the stationary and the mobile phase

B The migration rate of an analyte through a column

C The velocity of the mobile phase

D All of these

ANS:B - The migration rate of an analyte through a column

No answer description is available.

Q24: The column is heated to

A prevent analyte condensation within the column

B control elution of the different analytes

C reduce band broadening to get sharper peaks

D all of these

ANS:D - all of these

No answer description is available.

Q25: Sample retention in the column is measured by

A retention time

B retention factor

C retention index

D all of these

ANS:D - all of these

No answer description is available.

Q26: Which of the following is not used for detection in GC?

A Infrared spectroscopy

B NMR

C Flame ionisation

D Electrical conductivity

ANS:B - NMR

No answer description is available.



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