Match the following term used in chromatography with their abbreviation :List IList II(a) N(i) Dead time(b) B/A(ii) Capacity factor(c) K(iii) Retention time(d) RT(iv) Asymmetry factor(v) Efficiency

The correct match is a-v, b-iv, c-ii, d-iii.N, the number of theoretical plates, measures column efficiency.B/A, the ratio of the back and front half-widths of a peak at 10% of its height, is the asymmetry factor.K (k') is the capacity factor or retention factor, how long a compound is retained relative to the dead time.RT is the retention time.Dead time (tM or t0) is the time an unretained compound takes and is the extra item in List II. Every other option gives N or K the dead time or swaps B/A and N, which is why they fail.

Match the undermentioned light source in List I with that of corresponding technique in List II :List IList II(a) Low pressure mercury vapour lamp(i) Near infrared(b) High pressure xenon arc lamp(ii) Spectrofluorimeter(c) Nd : YAG laser(iii) Filter fluorimeter(d) Ordinary tungsten filament lamp(iv) Photoluminescence(v) Atomic absorption

The correct match is a-iii, b-ii, c-iv, d-i.A low pressure mercury vapour lamp gives a few intense lines and is the usual source of the simple filter fluorimeter.A high pressure xenon arc lamp gives an intense continuum from the ultraviolet to the visible and is the standard source of the scanning spectrofluorimeter.An Nd:YAG laser is used to excite photoluminescence, for example in laser detection of latent prints.An ordinary tungsten filament lamp radiates strongly in the near infrared and is the source for that region.Atomic absorption uses hollow cathode lamps, not any of these sources, so options using (v) are wrong.

Forensic Instrumentation and Spectroscopy Questions and Answers

Q: Capillary electrophoresis is an example of HVE where the applied voltage is not more than :

The applied voltage is usually not more than 30 kV.Capillary electrophoresis is a form of high-voltage electrophoresis. Commercial instruments apply up to about 30 kV across a capillary typically 25-100 μm in internal diameter. The narrow capillary dissipates the heat well enough to allow such high fields, which give fast, high-resolution separations, as in forensic DNA fragment analysis.10 kV and 15 kV are within the working range but are not the upper limit, and 60 kV is beyond what the instruments use.

Q: Molarity is defined as :

Molarity is the moles of solute present in 1 liter of solution.\[ M = \frac{\text{moles of solute}}{\text{litres of solution}} \]For example, 58.5 g of sodium chloride (one mole) made up to 1 litre of solution is a 1 M solution.Moles of solute per kilogram is molality, and it is defined per kilogram of solvent, not solution. Equivalents of solute per litre is normality. Grams of solute per litre is a mass concentration (g/L), which ignores the molar mass and so is not molarity.

Q: Separation of two compounds A and B is done by reverse phase chromatography. If A is more polar than B, which statement is correct ?

In reverse phase chromatography A will elute followed by B.Reverse phase uses a non-polar stationary phase (typically C18 bonded silica) and a polar mobile phase such as water with methanol or acetonitrile. A polar compound is attracted to the polar mobile phase and spends little time on the non-polar packing, so it comes out first. The less polar compound B is held longer by the stationary phase and elutes after A.B first would be the order in normal phase chromatography, where the stationary phase is polar. Two compounds of different polarity do not co-elute, and one compound does not prevent the elution of another.

Q: The process of separation based on the differential rate of migration of charged species in a buffer solution across which an electric field is applied is known as :

The technique is electrophoresis.In electrophoresis an electric field is applied across a buffer, and charged species move towards the electrode of opposite charge at rates that depend on their charge, size and shape. Differences in that rate of migration separate them, which is how DNA fragments, serum proteins and isoenzymes are separated in forensic work.The chromatographic options separate by partition or exchange between a stationary and a mobile phase. Ion chromatography uses an ion-exchange resin, paper chromatography a liquid held on paper, and micellar liquid chromatography a surfactant mobile phase; none of them is driven by an applied field.

Q: Which of the following is not the advantage of reciprocating pump used in UHPLC ?

Small solvent capacities is not an advantage of the reciprocating pump.Reciprocating pumps are the standard pumps of HPLC and UHPLC. The advantages usually listed for them are a small internal volume, high output pressure, ready adaptability to gradient elution and a constant flow rate. Their main drawback is a pulsed flow, which needs a pulse damper.A small solvent capacity describes the displacement or syringe pump, whose limited reservoir has to be refilled. The other three options are the textbook advantages of the reciprocating design, so they are not the answer.

Q: Assertion (A) : In most of commercial spectrophotometer lamp as source is preferred over laser as source.Reason (R) : Laser as source is used only while using very small sample amount or volume as in case of coupling with separation technique.

The key reads both (A) and (R) are correct but (R) is not the correct explanation of (A).The Assertion is true: commercial spectrophotometers use lamps such as tungsten-halogen and deuterium, which are cheap, stable and give a continuous range of wavelengths that a monochromator can scan. A laser gives only one or a few fixed lines.The Reason is also accepted: lasers are used where a very intense, narrow beam has to be focused into a tiny volume, as in detectors coupled to capillary electrophoresis or micro-column separations. But that does not explain why lamps are preferred; the preference comes from cost and the need for a continuous spectrum. So the options calling either statement wrong do not fit.

Q: Which of the following statements is not correct regarding radionuclide analytical methods ?

The statement that is not correct is Synthesis of labelled compound is easy.Preparing a compound labelled with a radionuclide is one of the recognised drawbacks of radiochemical methods: the synthesis is often difficult and costly, and it must be done quickly with short-lived isotopes and with radiation safeguards.The other statements are true. Radioactive decay is a nuclear process, so the signal does not depend on temperature, pressure or the chemical form of the atom. Because counts follow known statistics, the counting precision can be fixed in advance by choosing the counting time. And a sample made radioactive or mixed with a tracer cannot simply be returned to normal use afterwards.

11.

Capillary electrophoresis is an example of HVE where the applied voltage is not more than :

A.10 kV
B.15 kV
C.30 kV
D.60 kV

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: C

The applied voltage is usually not more than 30 kV.

Capillary electrophoresis is a form of high-voltage electrophoresis. Commercial instruments apply up to about 30 kV across a capillary typically 25-100 μm in internal diameter. The narrow capillary dissipates the heat well enough to allow such high fields, which give fast, high-resolution separations, as in forensic DNA fragment analysis.

10 kV and 15 kV are within the working range but are not the upper limit, and 60 kV is beyond what the instruments use.

Discuss in Forum

12.

Molarity is defined as :

A.Moles of solute present in 1 liter of solution
B.Moles of solute present in 1 kg of solution
C.Number of equivalent of solute present in 1 liter of solution
D.Is expressed as amount of solute in (g) in 1 liter of solution

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: A

Molarity is the moles of solute present in 1 liter of solution.

\[ M = \frac{\text{moles of solute}}{\text{litres of solution}} \]

For example, 58.5 g of sodium chloride (one mole) made up to 1 litre of solution is a 1 M solution.

Moles of solute per kilogram is molality, and it is defined per kilogram of solvent, not solution. Equivalents of solute per litre is normality. Grams of solute per litre is a mass concentration (g/L), which ignores the molar mass and so is not molarity.

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13.

Separation of two compounds A and B is done by reverse phase chromatography. If A is more polar than B, which statement is correct ?

A.A will elute followed by B
B.B will elute followed by A
C.A and B both elute together
D.B will prevent elution by A

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: A

In reverse phase chromatography A will elute followed by B.

Reverse phase uses a non-polar stationary phase (typically C18 bonded silica) and a polar mobile phase such as water with methanol or acetonitrile. A polar compound is attracted to the polar mobile phase and spends little time on the non-polar packing, so it comes out first. The less polar compound B is held longer by the stationary phase and elutes after A.

B first would be the order in normal phase chromatography, where the stationary phase is polar. Two compounds of different polarity do not co-elute, and one compound does not prevent the elution of another.

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14.

The process of separation based on the differential rate of migration of charged species in a buffer solution across which an electric field is applied is known as :

A.Ion chromatography
B.Paper chromatography
C.Micellar liquid chromatography
D.Electrophoresis

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The technique is electrophoresis.

In electrophoresis an electric field is applied across a buffer, and charged species move towards the electrode of opposite charge at rates that depend on their charge, size and shape. Differences in that rate of migration separate them, which is how DNA fragments, serum proteins and isoenzymes are separated in forensic work.

The chromatographic options separate by partition or exchange between a stationary and a mobile phase. Ion chromatography uses an ion-exchange resin, paper chromatography a liquid held on paper, and micellar liquid chromatography a surfactant mobile phase; none of them is driven by an applied field.

Discuss in Forum

15.

Which of the following is not the advantage of reciprocating pump used in UHPLC ?

A.High output pressure
B.Small solvent capacities
C.Adaptability to gradient elution
D.Small internal volume

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

Small solvent capacities is not an advantage of the reciprocating pump.

Reciprocating pumps are the standard pumps of HPLC and UHPLC. The advantages usually listed for them are a small internal volume, high output pressure, ready adaptability to gradient elution and a constant flow rate. Their main drawback is a pulsed flow, which needs a pulse damper.

A small solvent capacity describes the displacement or syringe pump, whose limited reservoir has to be refilled. The other three options are the textbook advantages of the reciprocating design, so they are not the answer.

Discuss in Forum

16.

Which of the following is caused by collisions of the absorbing atoms with other molecules or atoms present in flames ?

A.Lorentz broadening
B.Resonance lines
C.Walsh phenomena
D.Doppler phenomena

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: A

Collisions of absorbing atoms with other atoms and molecules cause Lorentz broadening.

In a flame the absorbing atoms collide continually with gas molecules. Each collision shortens the lifetime of the excited state and slightly shifts its energy, so the absorption line widens. This collisional or pressure broadening is named after Lorentz.

Doppler broadening has a different cause: the random thermal motion of atoms towards and away from the detector. Resonance lines are the lines themselves, between the ground state and an excited state, not a broadening effect, and 'Walsh phenomena' is not a line-broadening mechanism; Walsh is known for introducing atomic absorption spectroscopy.

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17.

Assertion (A) : In most of commercial spectrophotometer lamp as source is preferred over laser as source.
Reason (R) : Laser as source is used only while using very small sample amount or volume as in case of coupling with separation technique.

A.(A) is correct but (R) is wrong
B.(A) is wrong but (R) is correct
C.Both (A) and (R) are correct but (R) is not the correct explanation to (A)
D.Both (A) and (R) are wrong

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: C

The key reads both (A) and (R) are correct but (R) is not the correct explanation of (A).

The Assertion is true: commercial spectrophotometers use lamps such as tungsten-halogen and deuterium, which are cheap, stable and give a continuous range of wavelengths that a monochromator can scan. A laser gives only one or a few fixed lines.

The Reason is also accepted: lasers are used where a very intense, narrow beam has to be focused into a tiny volume, as in detectors coupled to capillary electrophoresis or micro-column separations. But that does not explain why lamps are preferred; the preference comes from cost and the need for a continuous spectrum. So the options calling either statement wrong do not fit.

Discuss in Forum

18.

Which of the following statements is not correct regarding radionuclide analytical methods ?

A.Quality and quantity of signal producing decay are independent of influences like temperature, pressure, chemical environment of the nucleus
B.Synthesis of labelled compound is easy
C.Pre-determination of counting precision
D.The sample material cannot returned to normal use after analysis

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

The statement that is not correct is Synthesis of labelled compound is easy.

Preparing a compound labelled with a radionuclide is one of the recognised drawbacks of radiochemical methods: the synthesis is often difficult and costly, and it must be done quickly with short-lived isotopes and with radiation safeguards.

The other statements are true. Radioactive decay is a nuclear process, so the signal does not depend on temperature, pressure or the chemical form of the atom. Because counts follow known statistics, the counting precision can be fixed in advance by choosing the counting time. And a sample made radioactive or mixed with a tracer cannot simply be returned to normal use afterwards.

Discuss in Forum

19.

Match the following term used in chromatography with their abbreviation :

List I	List II
(a) N	(i) Dead time
(b) B/A	(ii) Capacity factor
(c) K	(iii) Retention time
(d) RT	(iv) Asymmetry factor
	(v) Efficiency

A.a-ii, b-iv, c-i, d-iii
B.a-v, b-iv, c-ii, d-iii
C.a-ii, b-v, c-i, d-iv
D.a-v, b-ii, c-iii, d-i

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

The correct match is a-v, b-iv, c-ii, d-iii.

N, the number of theoretical plates, measures column efficiency.
B/A, the ratio of the back and front half-widths of a peak at 10% of its height, is the asymmetry factor.
K (k') is the capacity factor or retention factor, how long a compound is retained relative to the dead time.
RT is the retention time.

Dead time (t_M or t₀) is the time an unretained compound takes and is the extra item in List II. Every other option gives N or K the dead time or swaps B/A and N, which is why they fail.

Discuss in Forum

20.

Match the undermentioned light source in List I with that of corresponding technique in List II :

List I	List II
(a) Low pressure mercury vapour lamp	(i) Near infrared
(b) High pressure xenon arc lamp	(ii) Spectrofluorimeter
(c) Nd : YAG laser	(iii) Filter fluorimeter
(d) Ordinary tungsten filament lamp	(iv) Photoluminescence
	(v) Atomic absorption

A.a-i, b-v, c-iv, d-iii
B.a-iii, b-ii, c-iv, d-i
C.a-iii, b-iv, c-ii, d-i
D.a-ii, b-iii, c-i, d-v

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

The correct match is a-iii, b-ii, c-iv, d-i.

A low pressure mercury vapour lamp gives a few intense lines and is the usual source of the simple filter fluorimeter.
A high pressure xenon arc lamp gives an intense continuum from the ultraviolet to the visible and is the standard source of the scanning spectrofluorimeter.
An Nd:YAG laser is used to excite photoluminescence, for example in laser detection of latent prints.
An ordinary tungsten filament lamp radiates strongly in the near infrared and is the source for that region.

Atomic absorption uses hollow cathode lamps, not any of these sources, so options using (v) are wrong.

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