Amino Acids
Separation of Amino Acids by Paper Chromatography
Chromatography is a common technique for separating chemical substances. The prefix “chroma,” which suggests “color,” comes from the fact that some of the earliest applications of chromatography were to separate components of the green pigment, chlorophyll. You may have already used this method to separate the colored components in ink. In this experiment you will use chromatography to separate and identify amino acids, the building blocks of proteins. The proteins of all living things are composed of 20 different amino acids, some of which are described below. Chromatography is partially characterized by the medium on which the separation occurs. This medium is commonly identified as the “stationary phase”. Stationary phases that are typically used include paper (as in this experiment), thin plates coated with silica gel or alumina, or columns packed with the same substances. The “mobile phase” is the medium that accompanies the analyzed substance as it moves through the stationary phase. Both liquids and gases can be used as mobile phases depending on the type of separation desired. To refer to gas or liquid chromatography, chemists often use the abbreviations GC or LC, respectively. These abbreviations explicitly identify the phase of matter of the mobile phase. The term “paper chromatography” used in this experiment’s title identifies the composition of the stationary phase. The compositions of the stationary and mobile phases define a specific chromatographic method. Indeed, many different combinations are possible. However, all of the methods are based on the rate at which the analyzed substances migrate while in simultaneous contact with the stationary and mobile phases. The relative affinity of a substance for each phase depends on properties such as molecular weight, structure and shape of the molecule, and the polarity of the molecule. The relationship between molecular shape and polarity will be
Chromatography is a common technique for separating chemical substances. The prefix “chroma,” which suggests “color,” comes from the fact that some of the earliest applications of chromatography were to separate components of the green pigment, chlorophyll. You may have already used this method to separate the colored components in ink. In this experiment you will use chromatography to separate and identify amino acids, the building blocks of proteins. The proteins of all living things are composed of 20 different amino acids, some of which are described below. Chromatography is partially characterized by the medium on which the separation occurs. This medium is commonly identified as the “stationary phase”. Stationary phases that are typically used include paper (as in this experiment), thin plates coated with silica gel or alumina, or columns packed with the same substances. The “mobile phase” is the medium that accompanies the analyzed substance as it moves through the stationary phase. Both liquids and gases can be used as mobile phases depending on the type of separation desired. To refer to gas or liquid chromatography, chemists often use the abbreviations GC or LC, respectively. These abbreviations explicitly identify the phase of matter of the mobile phase. The term “paper chromatography” used in this experiment’s title identifies the composition of the stationary phase. The compositions of the stationary and mobile phases define a specific chromatographic method. Indeed, many different combinations are possible. However, all of the methods are based on the rate at which the analyzed substances migrate while in simultaneous contact with the stationary and mobile phases. The relative affinity of a substance for each phase depends on properties such as molecular weight, structure and shape of the molecule, and the polarity of the molecule. The relationship between molecular shape and polarity will be