UMD CHEM 425 - Labreport (15 pages)

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Labreport



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Labreport

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Pages:
15
School:
University of Maryland, College Park
Course:
Chem 425 - Instrumental Methods of Analysis

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1 Introduction For this experiment we used High Performance Liquid Chromatography HPLC in order to separate and identify an unknown mixture of different aromatic compounds We were given four solutions for this experiment 1 methylnapthalene 1 ethylnapthalene 1 napthol and an unknown consisting of one or more of the 3 aromatics dissolved in acetonitrile ACN Like other types of chromatography HPLC is able to determine the identity of a mixture by separating its components based on the analyte mixture s relative affinities for the mobile and stationary phase of the column There are two types of partitioning chromatography normal phase and reverse phase Normal phase corresponds to a non polar stationary phase and a polar mobile phase while reverse phase follows the opposite motif Since we were interested in separating aromatics this experiment employed a reverse phase separation which is more commonly used This is due to recent technological improvements such as gradient elution that allow reverse phase to cover a very large range of analytes1 There are four commonly used types of HPLC adsorption ion exchange size gel exclusion chromatography and partition Adsorption chromatography is used for solid analytes and is able to separate compounds based on competitive surface interactions between the sample and the mobile phase molecules1 Adsorption chromatography usually employs normal phase parameters and uses a polar stationary phase and a non polar mobile phase For the stationary phase adsorption chromatography uses acidic silica in order to retain basic analyte components such as amines When trying to retain acids or phenols a basic alumina or a very basic magnesia stationary phase is used depending on the analytes relative acidity1 One disadvantage associated with adsorption chromatography is it s inability to separate homologous series of analytes well such as hydrocarbons and carboxylic acids Size exclusion chromatography is used in order to 2 separate large MW compounds such as proteins and polymers via a sieving mechanism rather than a partitioning one1 Size exclusion contains a stationary phase consisting of porous silica or polymer particles with pore sizes ranging from 40 2 500 When running the analyte through a size exclusion column molecules that are larger in size are able to pass through more quickly than smaller molecules that get caught via the sieving mechanism This allows researchers to determine the relative weight of the analyte by comparing retention time to known standards For our experiment we used partition chromatography which allows for the separation of compounds in a liquid solution such as our unknown mixture via a liquid mobile phase Partition chromatography is the most commonly used type of HPLC and is used to separate analytes with a molecular weight of less than 3 0001 Since we are attempting to separate naphthalene derivatives we used a reverse phase partition HPLC Our non polar stationary phase consisted of silica



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