Adsorption Chromatography: Definition, Principle, Procedure, Types, Applications

Adsorption chromatography is a form of chromatography in which the constituents of a mixture are separated via adsorption. The process by which molecules or particles of material adhere to the surface of a liquid or solid substance known as an adsorbent is known as adsorption. One of the oldest chromatography methods still in use today is adsorption chromatography. It uses a mobile phase, which can be gaseous or liquid, during the process. During the adsorptive process, the mobile phase is adsorbed onto the surface of a stationary solid phase.

In adsorption chromatography, molecules of interest are attracted to and retained by a solid phase with a high surface area that serves as the stationary phase. The mobile phase can be either gas or liquid, and the stationary phase, or solid phase, is the adsorbent that absorbs the sample components (solute) through steric and van der Waal forces. It is employed to ascertain the concentration of a substance and eliminate pollution from the water.

What is Adsorption Chromatography?

• Adsorption chromatography is a type of chromatography that separates molecules based on how well they bind to a solid adsorbent. After dissolving the molecules in a solvent, the solvent is run through the adsorbent. While the other molecules pass through the column, the highly adsorbed molecules remain on the adsorbent.
• Adsorption Chromatography is the analytical process of separating a mixture of chemicals by observing how the adsorbate and adsorbent interact. Adsorption Another name for chromatography is adsorption separation. The mixture of gas or liquid splits into its parts after passing over the adsorbent bed, which adsorbs various chemicals at varying speeds.
• Adsorption chromatography functions on the basis that distinct molecules or ions will adsorb—or attach—to a surface in various ways. This means that by passing various molecules or ions down a column that contains a substance that will adsorb them, they can be separated from one another. Depending on how strongly they are adsorbed, the various molecules or ions will then be eluted (released) from the column in a distinct order.
• Adsorption chromatography involves the following phases:
  • Stationary phase: In this stage of adsorption chromatography, the sample remains stationary.
  • Mobile phase: This is the sample-moving phase of adsorption chromatography. The mobile phase is either a gas or a liquid solvent. It is designed to flow through the column, separating the solutes from the solvent according to the rate at which their compounds interact.
  • Adsorbent: An adsorbent is a material that can adsorb chemicals to its surface by intermolecular interactions. It is typically porous and has a large surface area. Some of the adsorbents that are most frequently employed are modified silica gel, alumina, hydrated gel silica, silica gel H, silica gel G, silica gel N, and silica gel.
• Overall, absorption chromatography is the process of separating a mixture of chemicals by observing how the adsorbate and adsorbent interact. This technique involves separating the combination of gas and liquid on an adsorbent bed, which adsorbs various chemicals at varying rates.

Principle of Adsorption Chromatography

• The fundamental principle behind adsorption chromatography is the selective interaction of solid adsorbents with target molecules inside a sample.
• The adsorbent, which is usually carbon, alumina, or silica, can bind and hold molecules to its surface by weak non-ionic interactions such as hydrogen bonding and van der Waals forces.
• The strength of these interactions varies, enabling the adsorbent to separate between various organic molecules (adsorbates) according to their affinities.
• Differences in the rates at which chemicals interact with the stationary phase cause them to separate while a solvent (eluent) constantly runs over the stationary phase (adsorbent) within the chromatographic column.
• Longer retention durations are exhibited by components with stronger interactions, which causes the sequential elution of individual analytes from the column.”

Factors Affecting Adsorption Chromatography

• Choice of the adsorbent
• Selection of the solvent for the mixture
• Rate of flow of the solvent
• Temperature of the system
• Column height for the procedure

Procedure of Adsorption Chromatography

Before starting the adsorption chromatography experiment, some preliminary assumptions on the two phases and the various forces involved in the mixture separation process should be made.

• In adsorption chromatography, the adsorbent serves as the stationary phase. The forces involved aid in the process of removing solutes from the adsorbent so they can travel with the mobile phase.
• Mobile phase: Depending on the use, a liquid or gas can be the mobile phase in adsorption chromatography. For the solutes to be transported with the mobile phase, the forces operating help remove them from the adsorbent. Liquid-solid coexistence (LSC) is the term used to describe the employment of a liquid as a mobile phase in liquid-solid chromatography. GSC (Gas-Solid Chromatography) is the term for the method when a gas is utilized as a mobile phase.
• The apparatus used during adsorption chromatography includes:
  • Chromatography jar with a lid: This jar is made up of glass and designed to hold chromatography samples. It helps to keep a healthy atmosphere during the separation process.
  • Thin-layer chromatography plate: For this process, a borosilicate glass plate measuring 20 by 20 cm, 20 by 5 cm, or 20 by 10 cm is utilized.
  • Capillary tube: The sample mixture is introduced into the TLC apparatus using this tube.
  • Mobile phase: either a gaseous or a liquid
  • Adsorbents in the stationary phase

Types of Adsorption Chromatography

• Column Chromatography: In column chromatography, the stationary phase consists of solid material packed into a column, through which a liquid mobile phase flows. The separation of components in a mixture is carried out by the adsorbent’s strong affinity for the adsorbate. As a result, the component with the highest adsorption tends to remain near the top of the column, leading to slower downward movement. Conversely, substances that are less adsorbed move more rapidly, accumulating towards the column’s outlet, and eventually collecting at the bottom of the collection vessel.
• Thin-layer Chromatography: Thin-layer Chromatography is a technique that uses the adsorbing ability of some substances to analyze the constituents that are present in mixes or solutions. The TLC experiment is carried out in three steps. The first step requires identifying the variations in a mixture; the second entails examining the development that took place over various stages; and the third and final step is visualizing the separation of adsorption levels.
• Gas Solid Chromatography: Gas-solid Chromatography is a technique for separating materials by letting the gas mixture contact with a solid adsorbent substance to separate the constituent parts. This process charges the mobile phase with nitrogen and helium, while the stationary phase provides the solid. In science, gas-solid chromatography is not very common and produces very inconsistent findings.
• Paper Chromatography: Paper chromatography is a technique that makes use of paper sheets or strips as the adsorbent, which is the stationary phase that a solution is made to pass through. The paper’s liquid phase is the mobile phase, and its solid surface is the stationary phase.

Adsorption Chromatography Experiment (TLC)

• A cleaned and dried chromatographic jar should be used.
• Before the experiment starts, a piece of paper soaked in the mobile phase is put to the jar’s walls to make sure the environment inside is saturated with solvent vapors.
• After adding the mobile phase to halfway full the jar, cover it.
• Maintain equilibrium in your life.
• To indicate the beginning point, mark the adsorbent.
• Apply the sample to the TLC plate using a capillary tube, and then let it dry.
• After inserting the plates, cover the jar with a lid.
• Await a deviation of the solvent from the baseline value.
• After removing the TLC plate, let it air dry.

Is TLC partition or Adsorption Chromatography?

Thin-layer chromatography (TLC) is a type of adsorption chromatography that utilizes a thin layer of stationary phase material, such as silica gel, alumina, or cellulose, coated onto a solid support substrate like glass, plastic, or aluminum foil. The stationary phase is applied as a uniform layer onto the support, forming a thin, flat surface.

When a sample mixture is spotted onto the stationary phase near the bottom edge of the TLC plate, and the plate is then placed vertically in a developing chamber containing a mobile phase solvent or solvent mixture, capillary action causes the solvent to ascend the plate, carrying the sample components along with it. The components interact with the stationary phase based on their affinities, leading to differential migration rates. As the solvent front progresses up the plate, the components separate into distinct spots or bands based on their relative interactions with the stationary and mobile phases.

TLC is widely used in analytical chemistry for qualitative analysis, compound identification, and monitoring reactions due to its simplicity, rapidity, and effectiveness in separating and visualizing complex mixtures.

Differences between Adsorption Chromatography and Partition Chromatography

Application of Adsorption Chromatography

• Pharmaceutical analysis: The pharmaceutical industry uses adsorption chromatography extensively for the analysis and separation of drug components, including antibiotic purification, drug metabolite separation, and drug purity assessment.
• Environmental monitoring: Pollutants in air, water, and soil samples are analyzed using in environmental science. The separation and measurement of industrial pollutants, pesticides, and organic pollutants is made easier by adsorption chromatography.
• Food and Beverage Industry: In the food and beverage sector, adsorption chromatography is used for quality control and safety evaluation. It helps in the identification and measurement of poisons, pollutants, pesticides, and additives in food items.
• Biochemical Research: It is used in biochemistry for protein purification, amino acid separation, and biomolecule characterization, including nucleic acids and carbohydrates.
• Clinical Diagnostics: Clinical laboratories use adsorption chromatography to analyze biological materials, such as blood, urine, and tissue extracts. It facilitates the detection and measurement of hormones, metabolites, and medications in biological fluids.
• Forensic Analysis: Adsorption chromatography is used in forensic labs to analyze forensic samples, including dangerous substances, drugs of abuse, and traces of evidence like fibers and dyes.
• Petroleum industry: It is essential for the analysis and characterization of petrochemicals and petroleum products, as well as for the control of fuel and lubricant quality, impurity identification, and hydrocarbon separation.
• Phytochemical Analysis: Natural products, antioxidants, and secondary metabolites are among the phytochemicals that can be separated and identified from plant extracts using adsorption chromatography.
• Polymer Chemistry: It is used in polymer research to analyze and characterize polymer materials, such as identifying polymer additives, determining molecular weight, and analyzing copolymer composition.
• Treatment of water: Heavy metals, pesticides, and organic pollutants are among the inorganic and organic contaminants that are removed from drinking water and wastewater streams using adsorption chromatography.

Advantages of Adsorption Chromatography

• It can use a range of mobile phases to separate compounds.
• Adsorption chromatography is an essential technique for the separation of many components that are impossible to separate from traditional techniques.
• Complex sample mixes can be easily separated with this method.
• The equipment needed for isolation comes in a wide variety.

Disadvantages of Adsorption Chromatography

• Some adsorption chromatography methods produce results that are hard to repeat.
• Differences in catalysis may arise from this.
• One significant disadvantage of adsorption chromatography is the lengthy separation times of certain solutes.
• It is more expensive and complex.

Summary of Adsorption Chromatography

Adsorption chromatography involves separating a chemical mixture based on how its components interact with an adsorbent material. For instance, amino acid separation relies on this principle. Similarly, it’s instrumental in extracting antibiotics from various sources. Thin Layer Chromatography (TLC) employs an adsorbent layer on a support, with the mobile phase passing over it. Alternatively, paper chromatography utilizes paper sheets or strips as the stationary phase. In both cases, the sample solution moves through the adsorbent, facilitating separation.

Column chromatography allows solutes to migrate down a column, where they’re adsorbed by the stationary phase. Gas-solid chromatography (GC) separates substances using adsorption as its primary principle. These techniques play vital roles in analytical chemistry, offering efficient means to isolate and identify compounds within complex mixtures.

References

• https://testbook.com/chemistry/adsorption-chromatography
• https://byjus.com/chemistry/adsorption-chromatography/
• https://unacademy.com/content/neet-ug/study-material/chemistry/a-short-note-on-adsorption-chromatography/
• https://infinitylearn.com/surge/chemistry/adsorption-chromatography/
• https://www.vedantu.com/chemistry/adsorption-chromatography
• https://www.aakash.ac.in/important-concepts/chemistry/adsorption-chromatography