Chromatography Methods Quiz Questions

This statement is true because polar supports have a stronger affinity for polar solvents. In chromatography, the mobile phase is the solvent that carries the sample through the stationary phase. The stationary phase can be polar or non-polar, and the mobile phase is chosen based on its compatibility with the stationary phase. In the case of polar supports, a weak mobile phase consisting of a non-polar solvent like hexane or benzene is used, while a strong mobile phase consisting of a polar solvent like water or methanol is used for non-polar supports. This ensures that the mobile phase interacts appropriately with the stationary phase, allowing for effective separation of compounds.

This statement is true because in chromatography, the mobile phase refers to the solvent that carries the sample through the stationary phase. In order to separate non-polar compounds, a polar mobile phase is used, while a non-polar mobile phase is used to separate polar compounds. This is because like dissolves like, meaning polar solvents will interact more strongly with polar compounds and non-polar solvents will interact more strongly with non-polar compounds. Therefore, a weak mobile phase that is polar and a strong mobile phase that is non-polar would be suitable for separating non-polar compounds.

Gradient elution refers to a technique in liquid chromatography where the composition of the mobile phase is changed over time. This is also known as solvent programming. In gradient elution, a solvent gradient is created by increasing or decreasing the concentration of one or more components in the mobile phase. This allows for the separation of compounds with different polarities or affinities for the stationary phase. By gradually changing the composition of the mobile phase, gradient elution improves the resolution and efficiency of the chromatographic separation.

The three general methods for improving resolution in partition chromatography are adjusting the kA and kB by employing a multicomponent mobile phase and varying the ratio of the solvents to find an optimal mixture, varying the chemical composition of the solvent system to make α larger, and employing a different packing in which α is greater. These methods aim to enhance the separation of components in the chromatographic system, either by manipulating the mobile phase or the stationary phase to achieve better resolution.

In a normal-phase packing, the stationary phase is polar and the mobile phase is relatively nonpolar. This means that the stationary phase has a higher affinity for polar compounds, causing them to interact and be retained longer, while nonpolar compounds will move more easily through the column with the mobile phase. This separation technique is commonly used for compounds that are more polar in nature, allowing for effective separation based on their polarities.

In ion-pair chromatography, the addition of a large organic counter-ion to the mobile phase serves as an ion-pairing reagent. This reagent helps in the separation process by either partitioning the neutral ion-pair or by facilitating electrostatic interactions between the ions in solution and the charges on the stationary phase. This interaction occurs due to the adsorption of the organic counter-ion.

Ion chromatography is a technique used to separate and analyze ions in a sample. In this technique, the stationary phase refers to the material that retains the ions and allows for their separation. In ion chromatography, the stationary phase is an ion-exchange resin, which selectively binds and releases ions based on their charge. The detection of ions is typically done using a conductivity detector, which measures the electrical conductivity of the eluent as ions pass through it. This allows for the identification and quantification of different ions present in the sample.

A bulk property detector is a type of detector that is able to detect analytes based on changes in a specific property of the mobile phase, such as thermal or electrical conductivity. When analytes are present, they can alter the conductivity or thermal properties of the mobile phase, which can be measured by the detector. This allows the detector to identify the presence of analytes in a sample.

The correct answer explains that a solute property detector responds to a property of analytes, such as absorption or fluorescence. This means that the detector is able to detect and measure the presence or concentration of analytes by measuring their absorption or fluorescence properties. This explanation highlights the main function and purpose of a solute property detector in analyzing and identifying analytes in a solution.

Both normal-phase partition chromatography and adsorption chromatography have polar stationary phases and relatively nonpolar mobile phases. This similarity in the polarity of the stationary and mobile phases allows for the separation of compounds based on their polarity. In both techniques, polar compounds have stronger interactions with the polar stationary phase, causing them to be retained longer and elute later, while nonpolar compounds have weaker interactions and elute earlier. This similarity in the phase polarity is essential for the effective separation of compounds in both normal-phase partition chromatography and adsorption chromatography.

Gas-liquid chromatography is most applicable to species that are somewhat volatile and thermally stable. This is because in gas-liquid chromatography, the sample is vaporized and carried by an inert gas through a liquid stationary phase. The separation of the components in the sample is based on their affinity for the stationary phase and their volatility. Therefore, species that are somewhat volatile and thermally stable are ideal for gas-liquid chromatography as they can be easily vaporized and do not decompose at the temperatures used in the process.

The liquid-adsorption chromatographic method is most applicable to nonpolar low to moderate molecular mass organics, especially isomeric organic species. This is because the method involves the separation of compounds based on their affinity for the stationary phase, which in this case is a liquid. Nonpolar compounds with similar molecular masses and structures tend to have similar affinities for the stationary phase, making it easier to separate them using this method. Isomeric organic species, which have the same molecular formula but different arrangements of atoms, can also be effectively separated using liquid-adsorption chromatography.

Gas-solid chromatography is most applicable to separate low molecular mass nonpolar gases. This is because in gas-solid chromatography, the stationary phase is a solid material, which interacts with the nonpolar molecules of the sample. The nonpolar gases will have stronger interactions with the stationary phase, leading to better separation and retention times. On the other hand, polar or high molecular mass gases may not interact as strongly with the stationary phase, resulting in poor separation and retention times.

Ion exchange chromatography is most applicable to substances that are ionic or that can be derivatized to form ions. This is because ion exchange chromatography relies on the exchange of ions between the sample and the stationary phase. The stationary phase contains charged groups that attract and retain ions of opposite charge, allowing for the separation of different ionic species. Therefore, substances that are ionic or can be converted into ions are best suited for this chromatographic method.

Isocratic elution refers to the technique of using a constant mobile phase composition to elute solutes in chromatography. In this method, the mobile phase composition remains unchanged throughout the separation process, allowing all solutes to be eluted at the same rate. This is in contrast to gradient elution, where the mobile phase composition is varied over time to achieve better separation of solutes. Isocratic elution is often used when the solutes have similar retention times and do not require a gradient to be effectively separated.

High Performance Liquid Chromatography (HPLC) is a technique used to separate and analyze nonvolatile compounds that cannot be vaporized without decomposition. It is also effective in separating thermally unstable compounds that may decompose at high temperatures required for Gas Chromatography (GC). In contrast, GC is suitable for separating volatile compounds that can be vaporized without decomposition. Therefore, nonvolatile and thermally unstable compounds can be separated by HPLC but not GC.

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A reversed-phase packing refers to a type of packing material used in partition chromatography. It is characterized by being nonpolar, meaning it does not have a charge or affinity for polar molecules. This type of packing is used in conjunction with a relatively polar mobile phase, which is the liquid or gas that carries the sample through the column. The nonpolar packing material and polar mobile phase create a reversed-phase system, allowing for the separation and analysis of polar compounds.