MCQs On Chromatography With Answers

Back flush is a technique used to clean an LC column from materials deposited on the head of the column. This technique involves reversing the flow of the mobile phase through the column, which helps to dislodge and remove any particles or contaminants that may have accumulated at the top of the column. By doing so, the column can be effectively cleaned and its performance can be restored, ensuring accurate and reliable chromatographic analysis.

The retention of a solute in gas chromatography (GC) is influenced by its vapor pressure and polarity. Vapor pressure determines the ease with which a solute can be vaporized and carried through the column. Solute polarity affects its interaction with the stationary phase, with polar solutes having stronger interactions and longer retention times. Therefore, the vapor pressure and polarity of the solute are important factors in determining its retention in GC. The other options, such as the size and charge of the solute, the method of sample introduction, the type of detector used, and the type of column used, may also have some influence on retention but are not as directly related as vapor pressure and polarity.

A Van Deemter plot provides useful information about the optimum mobile phase flow rate in chromatography. This plot shows the relationship between the plate height (H) and the linear velocity (u) of the mobile phase. By analyzing the plot, the flow rate at which the plate height is minimized can be determined, which corresponds to the optimum mobile phase flow rate. This information is crucial for achieving efficient separations and obtaining accurate and precise results in chromatographic analyses.

The term "split ratio" has a greater impact in GC (Gas Chromatography). In GC, the split ratio refers to the ratio of the carrier gas flow that is split between the column and the detector. This ratio affects the separation efficiency and sensitivity of the analysis. By adjusting the split ratio, one can control the amount of sample that reaches the detector, allowing for better detection and quantification of analytes.

In chromatography, "normal phase" and "reversed phase" refer to different types of stationary phases and their interactions with the compounds being separated.

Normal Phase Chromatography: The stationary phase is polar (e.g., silica gel), and the mobile phase is non-polar. In this setup, polar compounds are retained longer and elute later because they interact more strongly with the polar stationary phase.

Reversed Phase Chromatography: The stationary phase is non-polar (e.g., C18 silica), and the mobile phase is polar. Here, non-polar compounds are retained longer and elute later because they interact more strongly with the non-polar stationary phase.

Therefore, a compound that elutes last and is retained more in both normal and reversed phases would be:

Retained more in the normal phase (polar stationary phase) because it is polar.

Retained more in the reversed phase (non-polar stationary phase) because it is non-polar.

Since it is not feasible for a single compound to be both highly polar and highly non-polar, we consider the compound's behavior in each phase.

So, the correct answer reflects the typical interactions in each phase:

Non-polar and Polar

The correct statement is that resolution is proportional to the square root of the number of theoretical plates in a column. This means that as the number of theoretical plates increases, the resolution also increases, but at a decreasing rate. The square root relationship indicates that the improvement in resolution becomes less significant as the number of plates increases.

In chromatography, absorption refers to the process of partitioning, where the components of a mixture separate based on their affinity for the stationary phase and the mobile phase. The stationary phase can be a solid or liquid, and the mobile phase is usually a liquid or gas. During absorption, the components of the mixture are absorbed onto the stationary phase to varying degrees, depending on their solubility and interaction with the stationary phase. This separation occurs due to the differences in partitioning behavior between the components, allowing for their identification and analysis.

The activity coefficient of an ideal solution is equal to 1.0. This means that the behavior of the solution is ideal, with no deviations from Raoult's law. In an ideal solution, the interactions between the solute and solvent molecules are the same as those between the solvent molecules themselves. This results in a solution where the solute molecules do not affect the vapor pressure or other properties of the solvent. Therefore, the activity coefficient is equal to 1.0, indicating ideal behavior.

UV spectroscopy is least useful for the structural determination of small organics because it primarily provides information about the presence and extent of conjugated pi-electron systems in molecules. While this can be helpful in determining the presence of certain functional groups, it does not provide detailed information about the overall structure and connectivity of atoms in the molecule. NMR, GC-MS, FT-IR, and mass spectrometry are all better suited for structural determination as they provide more comprehensive data about the composition, connectivity, and functional groups present in the molecule.

The correct answer is a and b. This means that channeling results in a decrease in column efficiency and an increase in tailing. Channeling refers to the uneven flow of the mobile phase through the column, which can lead to poor separation and distorted peaks in chromatography. This uneven flow decreases the efficiency of the column, making it less effective at separating compounds. Additionally, channeling can cause tailing, which is the elongation of peaks in chromatography.

Deuterium is commonly used in variable wavelength detectors for UV in HPLC. Deuterium lamps emit light in the UV range, making them suitable for detecting UV-absorbing compounds in HPLC analysis. These lamps provide a stable and continuous source of UV light, allowing for accurate and reliable measurements. Tungsten, carbon arc, and xenon lamps are not typically used in variable wavelength detectors for UV in HPLC.

Sieving is the mechanism of separation in SEC (Size Exclusion Chromatography). In SEC, a stationary phase with porous beads is used, which allows smaller molecules to enter the pores and get trapped, while larger molecules pass through the column more quickly. This separation is based on the size of the molecules, with smaller molecules being retained longer in the column. Therefore, SEC is commonly used for the separation and analysis of macromolecules, such as proteins and polymers, based on their size.

Bleed refers to the process of the release of volatile or soluble components from a GC or HPLC stationary phase. This can occur when the stationary phase is not stable and starts to release these components, which can affect the accuracy and reproducibility of the analysis.

Back diffusion refers to the phenomenon where analyte molecules that have been eluted from the stationary phase of a chromatographic column move back into the mobile phase. This can occur due to a concentration gradient between the stationary and mobile phases. In gas chromatography, the analyte molecules are vaporized and carried by a gas mobile phase through the column. Therefore, back diffusion is more likely to occur in gas chromatography compared to other techniques such as SEC (size exclusion chromatography), HPLC (high-performance liquid chromatography), HPTLC (high-performance thin-layer chromatography), and TIC (total ion chromatography) where the mobile phase is a liquid.

TLC is a quick, powerful tool to check a reaction mixture or solution of a compound. By determining the number and Rf values that appear on a developed TLC plate, you will know how many components are in the mixture, know if a reaction has proceeded to produce the product, or know if a compound is pure.

TLC separates on the basis of the strength of the adsorption of compounds to the TLC plate (the adsorbent). The strength of this adsorption is greater the more polar a compound, and therefore, a polar compound will not move as far up a plate as a non-polar compound would. (Note that compounds are spotted near the bottom of a TLC plate and travel up the plate with the solvent.)

A compound that is not naturally present in the sample matrix but is intentionally added to the sample before the preparation step in HPLC is called a surrogate. This compound is used as a reference to monitor the efficiency of the preparation step and to account for any losses or changes that may occur during the sample preparation process. By analyzing the surrogate compound, the accuracy and reliability of the HPLC method can be ensured.

A check valve is a device that allows fluid to flow in only one direction. In the context of pump reciprocation, a check valve is used to prevent backflow, which is the undesired reversal of fluid flow. By allowing fluid to flow in only one direction, the check valve ensures that the fluid moves in the intended direction during the pumping process and prevents any backflow from occurring. Therefore, a check valve is the appropriate choice for preventing backflow during pump reciprocation.

Xerogel is the correct answer because it is a stationary phase that is known for its low polarity. Non-polar compounds tend to elute first on a stationary phase with low polarity, as they have less affinity for the polar stationary phase and are not strongly retained. Therefore, Xerogel would be the preferred stationary phase for the elution of non-polar compounds.

Xerogel is the correct answer because it is the form of the end product of silica gel after polymerization used in HPLC packing material. Xerogel refers to a dry, solid material that is formed by removing the liquid component from a gel through evaporation. In the context of HPLC packing material, xerogel is preferred because it has a high surface area and porosity, making it ideal for efficient separation of compounds in the chromatographic process.

If the two analytes present in the sample are of similar chemical type, partition chromatography would be the correct chromatographic technique for separation. Partition chromatography separates compounds based on their distribution between a stationary phase and a mobile phase. It is effective for separating analytes of similar chemical type because it relies on differences in their partitioning behavior rather than specific interactions with the stationary phase. This allows for efficient separation and elution of the analytes.

In reversed-phase chromatography, a mobile phase that contains no water is used because the analyte being analyzed is extremely hydrophobic or incompatible with water. This type of separation is effective for compounds that have a non-polar nature and are not soluble in water. The non-aqueous reversed-phase chromatography technique allows for the separation of these hydrophobic analytes by using a non-polar stationary phase and a non-aqueous mobile phase, typically an organic solvent. This method is commonly used in pharmaceutical and environmental analysis.

Chemisorption is a type of adsorption process that involves a strong chemical interaction between the analyte and the sorbent surface. In chemisorption, the adsorbed molecules form chemical bonds with the surface, resulting in an irreversible chemical reaction. This is different from physisorption, where the adsorbed molecules are only weakly attracted to the surface through van der Waals forces and can be easily desorbed. Therefore, the correct answer is "an adsorption process results in an irreversible chemical reaction of the analyte with sorbent surface."

The retention factor, k, describes the migration rate of an analyte through a column. It is a measure of how strongly an analyte is retained by the stationary phase compared to its movement in the mobile phase. A higher retention factor indicates a slower migration rate, as the analyte is more strongly bound to the stationary phase. Therefore, the correct answer is the migration rate of an analyte through a column.

Channeling refers to the presence of empty spaces within a packed column. These voids can cause various issues in chromatography, including band broadening, peak splitting, a decrease in column efficiency, and increased tailing. Therefore, all of the options mentioned (band broadening, peak splitting, decrease in column efficiency, and increased tailing) can be attributed to the presence of channeling in a packed column.

The correct answer is b, c only. This means that for tailed peaks, Ax is less than 1.0 and for fronted peaks, Ax is greater than 1.0. This implies that Ax is not true for perfect peaks, as stated in option a.

Retention factor, k, is most commonly used in describing Gas Chromatography (GC). In GC, the retention factor represents the ratio of the time a compound spends in the stationary phase to the time it spends in the mobile phase. It is a measure of the compound's affinity for the stationary phase and helps in characterizing its separation and elution behavior. By determining the retention factor, GC can provide valuable information about the identity and quantity of compounds present in a sample.

Radioactivity detectors are commonly used in High Performance Liquid Chromatography (HPLC) to detect and quantify radioactive compounds. HPLC is a technique used to separate, identify, and quantify components in a mixture. Radioactive compounds can be analyzed using HPLC by incorporating a radioactivity detector, which measures the amount of radioactivity emitted by the analyte as it passes through the detector. This allows for accurate quantification of radioactive compounds in a sample. Therefore, the use of radioactivity detectors is commonly associated with HPLC.

The BET method uses the adsorption isotherm of N2.

Nuclear magnetic resonance spectroscopy does not use the mass spectrometer as a detector. NMR spectroscopy is a technique that analyzes the magnetic properties of atomic nuclei, specifically the spin and magnetic moments of the nuclei. It does not involve the measurement of mass-to-charge ratio, which is the principle used in mass spectrometry. Atomic absorption spectroscopy uses a light sensor to measure particle concentrations.

The equation given is used to calculate the peak capacity in a chromatographic analysis. Peak capacity refers to the ability of a chromatographic system to separate and resolve individual peaks in a chromatogram. It is a measure of the efficiency of the separation process and indicates the number of distinct peaks that can be resolved within a given time frame. Therefore, the correct answer is peak capacity.

The BET test is a method used to determine the surface area, pore volume, and pore size distribution of porous materials. This test involves adsorption of gas molecules onto the surface of the material and measuring the amount of gas adsorbed at different pressures. By analyzing the data, the surface area, pore volume, and pore size distribution can be calculated. Therefore, the correct answer is a, b, c.

TEA (Triethylamine) is the most commonly used basic mobile phase modifier in RP-HPLC (Reversed-Phase High Performance Liquid Chromatography). It is often added to the mobile phase to adjust the pH and improve the separation of analytes. TEA acts as a weak base and helps in ionization and retention of acidic compounds. TFA (Trifluoroacetic acid), OPA (O-phosphoric acid), and THF (Tetrahydrofuran) are not commonly used as basic mobile phase modifiers in RP-HPLC.

The main advantage of the mass spectrometer over the flame ionization detector as a GC detector is sensitivity. Mass spectrometry is a highly sensitive technique that can detect and measure very small amounts of compounds in a sample. It is capable of providing detailed information about the structure and composition of molecules, making it a powerful tool for compound identification. In comparison, the flame ionization detector is less sensitive and may not be able to detect low levels of compounds in a sample. Therefore, sensitivity is a significant advantage of the mass spectrometer as a GC detector.

The Brockmann Activity Scale is used in the characterization of the stationary phase in chromatography. This scale helps to determine the activity of the stationary phase, which is important in understanding its interaction with the analytes being separated. The activity of the stationary phase can affect the selectivity and efficiency of the separation process. Therefore, the Brockmann Activity Scale is a useful tool for evaluating and comparing different stationary phases for chromatographic applications.

The application of zeta potential for Electro Osmotic Mobility is useful in CE (Capillary Electrophoresis). Capillary Electrophoresis is a technique used to separate and analyze charged particles based on their electrophoretic mobility. Zeta potential, which is the potential difference between the surface of a particle and the surrounding liquid, is a crucial parameter in CE as it affects the electroosmotic flow, which helps in the separation and movement of the analytes. Therefore, understanding and utilizing zeta potential in CE can enhance the efficiency and accuracy of the analysis.

Calcium carbonate is commonly used as an intermediate adsorbent for the separation of xanthophylls and carotenoids. It has a high affinity for these compounds and can effectively adsorb them from a mixture. Calcium carbonate is also readily available and cost-effective, making it a popular choice for this separation process.

The concept of "Triple Point" is useful for Supercritical Fluid Chromatography (SCFC). In SCFC, the separation technique utilizes a supercritical fluid, which is a substance that is above its critical temperature and pressure. At the triple point, all three phases of a substance (solid, liquid, and gas) coexist in equilibrium. This concept is important in SCFC because it allows for the precise control of the fluid's properties, such as density and viscosity, which affects the separation efficiency and selectivity of the technique.

A slow response time in a detector can result in peak distortion. This means that the peak shape of the signal becomes altered, leading to inaccurate measurements or difficulty in identifying and quantifying the components of the sample. The slow response time causes the detector to take longer to reach the desired level of 98% of the final response signal, resulting in distorted peaks.

The reduced plate height is a parameter used to compare the relative column efficiencies for a column with different particle sizes in the packing material. It takes into account the partial diameter and HETP (Height Equivalent to a Theoretical Plate) to determine the efficiency of the column. Therefore, the correct answer is reduced plate height.

Stagnant mobile phase in the column can greatly contribute to peak broadening. When the mobile phase flow rate is slow or the viscosity is high, the mobile phase can become stagnant in the column, causing the analyte to spend more time in the column and resulting in broader peaks. This can also be influenced by the nature of the stationary phase, as different stationary phases can have different affinities for the analyte, leading to variations in peak broadening. Detector sensitiveness, on the other hand, refers to the ability of the detector to accurately measure the analyte concentration and is not directly related to peak broadening. Column fitting is also not directly related to peak broadening.

 IIC Ion Interaction Chromatography is a common technique, which is a type of chromatography technique commonly known as "Soap Chromatography". In this technique, a stationary phase, which is impregnated with a soap solution, is used. The soap acts as a surfactant and helps in separating the components of a mixture based on their different affinities towards the stationary phase. Therefore, IIC is the correct answer to the given question.

The correct statement among the following is that all of the above statements are true. The M value ranges from 2-29, with 2 indicating polarity and 29 indicating non-polarity. If the M number differs by less than 15, the pair of solvents are miscible at room temperature, while if the M number differs by more than 15, the pair of solvents are also miscible at room temperature. Additionally, if M=16, the miscibility is strongly temperature dependent around room temperature.

Reverse phase chromatography (RPC) is a technique that uses non-polar stationary phases and polar mobile phases. In RPC, the mobile phase is pushed through the column by centrifugal forces, which accelerates the solvent flow from the center of the plate. This allows for efficient separation of compounds based on their polarity. HPTLC, adsorption chromatography, bonded phase chromatography, and non-bonded phase chromatography do not specifically use centrifugal forces to accelerate the solvent flow, making RPC the correct answer.

Perfusion chromatography is a technique used for the separation of macromolecules. This technique involves the continuous flow of the mobile phase through the stationary phase, allowing for efficient separation of macromolecules based on their size and shape. Unlike other chromatographic techniques, such as diffusion chromatography, adsorption chromatography, and exclusion chromatography, perfusion chromatography specifically focuses on the separation of macromolecules. Therefore, the correct answer is perfusion chromatography.

In the context of chromatography techniques, migration time refers to the time it takes for a compound to move through the stationary phase of the column. It is commonly used to measure the separation and elution of compounds in various chromatographic methods. While retention time is typically used in gas chromatography (GC) and high-performance liquid chromatography (HPLC), migration time is used specifically in capillary electrophoresis (CE). This technique utilizes an electric field to separate charged compounds based on their migration rates. Therefore, migration time is a more appropriate term to describe the separation process in CE.

 In PTGC, the temperature of the entire column changes with time, so separation is dependent upon the boiling points of analytes.

The statement "None of the above" is the correct answer because all of the statements mentioned in the options are true regarding "Radial thin-layer chromatography". This technique involves spotting a sample in the center of a circular plate, and as the solvent moves away from the wick, the sample is carried out radially from the center spot. The solvent is applied to the spot through a wick. Therefore, none of the statements mentioned in the options are false, making "None of the above" the correct answer.

OPLC is a type of planar chromatography where a sorbent layer is pressed against a cover membrane and the solvent is forced through the sorbent layer. It has an advantage over HPLC in that viscous solvents can be used. However, the development of chromatogram in OPLC is faster than that of TLC, not slower. Therefore, the incorrect statement is "The development of chromatogram is slower than that of TLC."