Paper Chromatography
Paper chromatography is a widely utilized scientific technique designed to separate and analyze the components of mixtures and solutions. Developed in the late 1800s, it involves a stationary phase, which is an absorbent paper, and a mobile phase, typically a liquid solvent. As the solvent moves through the paper via capillary action, it carries along the particles of the tested material, allowing them to separate based on their differing absorption rates. The outcome of the process can be visualized on the paper, resulting in a chromatogram that displays the separated components, often as distinct lines or spots.
This method is particularly effective for analyzing mixtures such as inks, dyes, and food colorings, making it valuable in both scientific research and practical applications, such as detecting substances in biological fluids or environmental samples. Additionally, paper chromatography serves as a foundational technique from which various other forms of chromatography have evolved, including thin-layer chromatography and gas chromatography. Overall, paper chromatography is an essential tool in chemistry and biology, helping scientists identify and understand complex mixtures.
Paper Chromatography
Paper chromatography is a scientific process that helps scientists study the components of mixtures and solutions. Paper chromatography separates the parts of mixtures and solutions on a piece of paper. The process was developed in the late 1800s, and it is used widely today.
In general, chromatography is a process that separates parts of solutions or mixtures into their individual components. Chromatography requires two phases. One phase, called the stationary phase, is a solid or a liquid supported by a solid. The other phase, called the mobile phase, is a liquid or a gas. The mobile phase flows through the stationary phase. As the mobile phase flows through the stationary phase, it carries particles from the tested material and separates different parts of the mixture.
Paper chromatography is just one type of chromatography. In paper chromatography, the stationary phase is paper, but not just any paper will do; the paper must be uniform and absorbent. The mobile phase in paper chromatography is a liquid, usually a solvent. The results on the paper will differ slightly depending on the type of solvent used because different solvents will absorb into the paper at different rates. The place where the solvent stops on the paper is called the solvent front.
Paper chromatography helps scientists study different types of mixtures. Matter may be classified as either a pure substance or a mixture. Pure substances are either elements or compounds. Mixtures can be solutions (solid particles in a liquid where particles can settle to the bottom), suspensions (homogeneous mixtures with two or more substances), or colloids (small particles in liquid that are too small to settle at the bottom). Mixtures may be physically separated since they are physically, rather than chemically, combined. Paper chromatography works best with materials such as food colorings, dyes, and inks, which are mixtures rather than pure substances.
Paper Chromatography Process
People can use paper chromatography to separate the parts of many different types of mixtures, but it is commonly used to separate the constituent parts of ink or dye. These steps explain an experiment using paper chromatography to study different types of ink:
The experimenter collects the paper (which is the stationary phase), the materials being tested (e.g., different inks), and the mobile phase (e.g., a solvent).
The experimenter puts dots or spots of the ink at the bottom of the paper in a straight line. This line is sometimes called the pencil line. The experimenter allows the dots to dry.
The experimenter suspends the paper vertically into the mobile phase (e.g., water, isopropyl alcohol, hydrogen peroxide).
The mobile phase then moves up through the paper through capillary action. This movement eventually causes the material being tested to move through the paper and separate into its constituent parts.
When the tested materials have been separated, the experimenter removes the paper from the solvent. The chromatogram (which is what the paper is called when the experiment is over) will have lines and dots from the separated materials.
The experimenter can measure and analyze the results on the chromatogram.
The experimenter can find the retention factor (Rf) value for each tested material. (Rf is equal to the distance moved by a component divided by the distance moved by the solvent.)
When the experiment is finished, the experimenter can review the results and draw conclusions about the different inks that were tested. For example, if two materials are the same color and have the same Rf values, they are most likely the same mixture, or they are very similar.
Origins of Paper Chromatography
A Russian scientist named Mikhail Tsvett (1872–1919) wanted to find a process that would reveal the red and yellow pigments from inside green leaves. Tsvett found that the mixture of pigments inside the leaves separated when he mashed the leaves and added powder to the mixture. He found that different colors of dyes traveled through the powder at different rates. Tsvett shared his findings, and soon other scientists began practicing chromatography.
Since Tsvett’s time, chromatography has developed into a number of different subcategories, including paper chromatography. Although paper chromatography is one of the simplest types of chromatography, it is not the only type. Thin-layer chromatography uses a thin layer of alumina or silica as the stationary phase. The thin layer is supported on a base of glass or plastic. The mobile phase is usually a solvent and moves up the stationary phase. Gas chromatography uses gas as the mobile phase and uses either a solid or a liquid for the stationary phase. Liquid chromatography is similar to gas chromatography, but it uses liquid as its mobile phase. It can use either a solid or a liquid for a stationary phase.
Paper chromatography can be used for a number of different purposes. Scientists can use paper chromatography to separate organic materials from inorganic materials that are combined in a mixture. They use it to determine which materials make up particular mixtures. Paper chromatography can also be used to separate solids in mixtures from liquids in mixtures. In everyday use, chromatography can be used to detect drugs in urine, alcohol in blood, and lead in water.
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