Table of Contents
Part A: 3
Introduction: 3
Gas Chromatography (GC) 3
Gas- solid chromatography 3
Gas-liquid chromatography 3
Advantages: 3
Disadvantages: 3
High performance liquid Chromatography (HPLC) 4
Advantages: 4
Disadvantages: 4
Part B: 5
Introduction 5
References 6
Part A:
Introduction:
Forensic Chemistry involves a variety of different techniques in which have the ability to analyse samples found on crime scene, one set of techniques is that of chromatography.
Chromatography is a process commonly used to separate substances in accordance to their differential distribution between what is referred to as a stationary phase and a moving or ‘mobile phase’. There are a variety of different types of chromatography some include; paper chromatography, gas chromatography and high performance liquid chromatography.
Chromatography works by analyzing a substance in terms of its retention time when passing through what is referred to as a stationary phase. Retention time refers to the amount of time a substance takes to pass through the stationary phase, upon analysis the retention time determines what substances are present within a sample. For example, if a particular substance within takes longer than another to reach the ‘detector’ results can then be categorized into which substances are present within the sample. The results found are presented in what is called a chromatograph.
A chromatogram…
The stationary phase will absorb or slow down different components of the tested solution to different degrees creating layers as the components of the solution are separated. Chromatography was invented by the Russian botanist, Mikhail Tsvet. Chemists use this process to identify unknown substances by separating them into the different molecules that make them up.
Which one of the statements concerning valence bond (VB) and molecular orbital (MO) bond theories is correct?
The intermolecular forces are pulling the molecules between the stationary phase, the chromatography paper and the mobile phase, the solvent. The molecules of the chromatography paper are trying to pull the molecules to where they are while the molecules of the molecules with them to the top of the paper. 4. Draw a picture of how the chromatography worked. Explain your picture using the following terms: stationary phase, mobile phase and intermolecular forces.
Chromatography is a fairly simple process. First, you put a dot of ink(or in our case, the M&M food dye) near the bottom of some chromotography paper (also known as filter paper), and then hang the paper vertically with its lower edge (the one closest to the spot of dye) dipped in a solvent (In our case, the sodium chloride solution). Capillary action forces the solvent to travel up the paper, where it meets and dissolves the ink. The dissolved ink (which is the mobile phase) slowly travels up the paper (the stationary phase) and separates out into its different elements. Another way of describing it is to think of the liquid as an adhesive-like liquids, some of which stick more to the solid and can travel more slowly than others. This is
The objective of the lab was to purify compounds that can be turned into gas at a reasonable temperature without using decomposition. Gas chromatography was also used to identify the proportions of the volatile compound in the different samples. The mixture of hexane and octane was assigned to me and my partner. The apparatus for simple distillation was assemble using a thermocouple, air condenser, distillation head, metal keck clamps, and a conical reaction vial. The joints of the glassware were greased before assembly. Four boiling chips were placed in the conical ration vial before it was assembled. After being assigned a mixture, 3.5 mL of the mixture was put into a reaction vial. The apparatus
Introduction Thin-layer chromatography, also known as TLC, is a principle that describes how various compounds travel multiple distances when placed as a thin layer on a plate. TLC is a technique that can be used to determine how many components are in a mixture. TLC can also be used to determine a specific compound in a mixture. After performing TLC, the retention factor (Rf) can be used to determine a specific compound in a mixture. The retention factor (Rf) is During TLC, there is a step called elution.
Procedure: First, we began the lab with the chromatography strip positioned 152 mm tall and 19 mm wide. Using a ruler and pencil, we drew 15 mm from the bottom of the paper across the width. We measured 9.5 mm from the edge and placed a dot with the pencil on the line to mark the starting point. The, we measured 20 mm from the top of the strip and folded across the width of the strip. These few steps were repeated with a second strip.
The process of separating unknown mixtures with similar polarity to its counterparts pose a problem for most. One method to separate a mixture based on interactions, in the gaseous phase, is through a process known as gas chromatography. Gas chromatography consists of a mixture going through a mobile phase, being immersed in a gas, and a stationary phase, being physically separated through a non-volatile liquid. A gas chromatograph with a flame ionization detector consists of several components. The components of a gas chromatograph are a heated injection port (to inject an
This process relies on heating a solution to separate out the different components. This is done through the fact that each compound has a specific inherent boiling point, a temperature at which a liquid turns into a vapor. These vapors are then passed through a fractioning column. These columns are often filled with glass or plastic beads to aid in the separation process by increasing surface area for condensation. As the the vapor moves through the column, the compounds with higher boiling points condense on the column and return to the solution, where as components with lower boiling points move through the column and collect near the
Gel-Filtration Chromatography is a commonly used method used in order purify a protein from a mixture, by means of separations. Different biomolecules differ in size, or their molecular weight. In the gel matrix inside the chromatography column, there are gel beads which are porous to allow certain sized molecules to enter. The molecules that are able to enter the pores of the gel, are held in stationary phase and will elute from the column later on, these are usually smaller, to medium sized molecules. Larger molecules that are not able to fit in the pores will elute out of the column first, they are involved in mobile phase where they just go straight through the column without interacting with the gel beads. Smaller molecules will have a higher elution volume, while the larger molecules will have a lower elution volume. The volume to elute the protein is inversely proportional to the molecules size.
Chromatography Investigation Chromatography is a highly regarded technique used to separate the components of a mixture. It is based on the principle that each component possesses a unique affinity for a stationary phase and a mobile phase. The components that are more inclined to enter the mobile phase will migrate further on the chromatogram and distinguish themselves from the other components. The type of solvent used in chromatography is known to directly affect the separation of the mixture. In this experiment, thin-layer and column chromatography will be utilized to separate the numerous chlorophyll and carotenoid pigments of a spinach extract.
Paper chromatography is used to separate mixtures of substances into their components. There are different types of chromatography but they are all based on the same principal. Paper chromatography is an analytical method that is used to separate colored chemicals or substances, especially pigments. They all have a stationary phase and a mobile phase. The moving substance is called the mobile phase while the stationary phase stays put. The mobile phase flows through the stationary phase and carries the components of the mixture with it. The stationary phase is motionless and is the actual medium that performs the separation. Ninhydren reacts with amino acids to give colored compounds and detect the location of the amino acids. This is used because amino acids are colorless. Different components travel at different rates. Each one undergoes adsorption in a slightly different way and spends more or less time in either the solid or the liquid phase. Components of the samples will separate readily according to how strongly they absorb on the stationary phase vs. how readily they dissolve in the mobile phase.
Most chemists and many other scientists must routinely separate mixtures and identify their components. The ability to qualitatively identify the substances found in a sample can be critical. For example, an environmental chemist investigating samples of polluted ground water will want to know which toxic ions might be present in a sample. Chromatography is one of the first tools used in such situations. In this technique, many types of mixtures can be separated into the component pure substances; by comparison to a standard sample, each component substance can also be tentatively identified. Many varieties of chromatography exist, each one designed to separate specific types of mixtures. The common feature of each type of
Forensic science borrows from a number of sciences which include: physics, Biology and chemistry. It therefore involves examination of a wide spectrum as compared to any other method of investigation. Due to the wide spectrum of investigation and evidence analysis the method offers; it ensures that the results are accurate and can be used in the court of law to make a decision. The method establishes the existence of a crime, the connection between the crimes and the
Chromatography is a separation technique in which the mixture to be separated is dissolved in a solvent and the resulting solution, often called the mobile phase, is then passed through or over another material, the stationary phase. The separation of the original mixture depends on how strongly each component is attracted to the stationary phase. Substances that are attracted strongly to the stationary phase will be retarded and not move alone with the mobile phase. Weakly attracted substances will move more rapidly with the mobile phase.