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Adsorption/Partition Chromatography

Adsorption/Partition Chromatography. Normal Phase Reversed Phase. Adsorption/Partition Chromatography. Choosing mobile and stationary phases Stationary phase must have a similar polarity to the analyte Mobile phase is of substantially different polarity Polarity Series

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Adsorption/Partition Chromatography

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  1. Adsorption/Partition Chromatography • Normal Phase • Reversed Phase

  2. Adsorption/Partition Chromatography Choosing mobile and stationary phases • Stationary phase must have a similar polarity to the analyte • Mobile phase is of substantially different polarity Polarity Series In general, polarity of organic compound in increasing order is: Alkyl < alkenyl < aromatic < halides < sulfides < ethers < nitro < esters ~ aldehydes ~ ketones < alcohols ~ amines < sulphones < sulphoxides < amides < carboxylicacids < phosphates < water Bold means that these groups can also be substantially affected by pH changes NB Avoid conditions that could decompose the analyte

  3. Normal Phase Stationary phase: • normally a solid • Analyte adsorbs to the stationary phase • Packing is usually Silica or Alumina and is therefore polar Mobile phase: • normally organic (i.e. not aqueous) • wide choice of mobile phase Retention: • TR increases with polarity of analyte • Increasing the polarity of the mobile phase reduces elution time • Optimisation normally consists of varying the mobile phase R=OH, CN, NH2 & more

  4. Reversed Phase Stationary phase: • normally a liquid • Analyte dissolves in the stationary phase • Packing is usually modified Silica or Alumina Mobile phase: • normally aqueous, plus MeOH orMeCN • wide choice of mobile phase buffers Retention: • TR decreases with polarity of analyte • Increasing the polarity of the mobile phase increases elution time • Optimisation normally consists of varying the mobile phase R= C18, C8, Ph& more

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