Introduction and chromatography Starter… H/W… Summary notes – and find out about applications of gas chromatography. What different methods of separation can you name and how do they work? Challenge q… Who was the 1st person to use the technique of chromatography? (not a German) Review question maybe using a mind map on a white board

5 week plan double lessons Week 1 – Chromatography Week 2 – Introduction to NMR Week 3 – Structure determination / problem solving Week 4 – TEST Week 5 – Rates CPAC core practical If you miss a session you MUST download the PowerPoint from the shared area and collect associated materials, this is your responsibility. You must complete all homeworks or you will not be allowed onto Y13 chemistry. No excuses The CPAC will be explained in more detail in your first single session with either Miss Watts or Dr Butterworth.

A2 chemistry topics Rates of reaction Entropy Equilibria Further organic chemistry Spectroscopy and chromatography Redox chemistry / electrochemistry Chemistry of transition metals Arenes, Nitrogen compounds Synthesis

Warm up… CPAC 1 – Follow written instructions Take a piece of chalk between 2 Mark a circle around the circumference of the chalk about 1 cm from one end Check with your teacher Place it in the sample tube with a appropriate amount of water (solvent) Replace the lid and leave to run

Chromatography Is a technique used to separate and identify the components of a mixture. Works by allowing the molecules present in the mixture to distribute themselves between a stationary phase and a mobile phase. Molecules that spend most of their time in the mobile phase are carried along faster.

Chromatography To perform a chromatography experiment you need Support material aka stationary phase (usually either a solid or a liquid). Solvent aka mobile phase (usually either a liquid or a gas)

Chromatography Paper  TLC  Column  GC  HPLC All use the same “partition” principle, separating mixtures of substances by their affinity between the two phases. Substances with a greater affinity for the mobile phase will travel furthest/fastest with the solvent.

TLC

TLC TLC The stationary phase (often silica) is coated as a thin layer on plastic or aluminium plates. The mobile phase (often ?) is a liquid. The mixture is spotted on the plate and solvent is allowed to run up the plate by capillary action to separate the compounds. Substances that are less attracted to the solid or are more soluble in the liquid move faster. And so move further up the plate by the time that the process has been stopped by taking the plate out of the liquid. - larger Rf

Can TLC be used for colourless compounds? Compare mixtures in sample with known substances

Retention factor …is a measure of how far it has moved up a plate under certain conditions it is can be use a quick way of identification. Differences in Retention Factors are important when considering solvent systems for Column Chromatography.

Retention factor Rf = distance moved by substance distance moved by solvent front For substances that are very soluble in the liquid Rf will be close to .... For substances that are rather insoluble in the liquid Rf will be close to ....

Column Chromatography The stationary phase in placed in a column and the solvent is allowed to move the mixtures through whilst collecting fractions of the emerging solvent. Separation by column chromatography depends on the balance between solubility in the moving phase and retention in the stationary phase. This can be carried out by allowing the solvent to flow under gravity or under a moderate pressure to increase the solvent flow rate The fractions are usually analysed by TLC in order to identify which contain the components of the mixture. https://www.youtube.com/watch?v=P8Mmpb4OShw

Column Chromatography https://www.youtube.com/watch?v=EytuRMS1154 https://www.youtube.com/watch?v=P8Mmpb4OShw

The Column is contained in a thermostatic oven. Gas Chromatography Injection port Recorder Oven Detector Column The Column is contained in a thermostatic oven. (Why ?) Nitrogen cylinder

Gas Chromatography GC About 1μL of liquid is injected into one end of the column. The Retention Time is characteristic of a particular substance. (for the same column, temperature, gas flow etc.) As each component reaches the other end it is detected and registered on a chart recorder. The area under each peak indicates the relative quantities.

Factors affecting retention time: Gas Chromatography flow rate of carrier gas length of column Factors affecting retention time: temperature of column. packing material type of carrier gas

Gas Chromatography Uses of GC Very sensitive - small quantities of substances detected, explosives, drugs etc. Separation of pure substances for collection. Uses of GC Can be connected to mass spectrometer for direct identification of substances.

Gas Chromatography Suggest identities of some of the unlabelled peaks.

Column chromatography Your turn Gas chromatography Food dye – paper Food dye - TLC HPLC Column chromatography

Paper chromatography Equipment capillary tubes food dye samples (made up in EtOH) solvent bottles A = H2O, B = 50:50 H2O : EtOH C = 100% EtOH Chromatography paper Beaker Watch glass What you need to do Test the food dye samples using three different solvents to determine which solvent is most suitable. You are looking for the solvent that gives the best separation.

TLC Equipment Food dyes made up in EtOH TLC plates 50:50 EtOH : H2O Beaker Watch glass What you need to do Test the food dye sample using a solvent to determine whether the TLC plate gives a better separation than the paper chromartography

Column chromatography Equipment Mini columns Cotton wool Alumina / silica Nichrome wire pokey sticks Clamp stands Solvent mix 50:50 MeOH: EtOH Berol black ink Plastic pipette What you need to do Pack the columns using a cotton plug and either alumina or silica. Place a few drops of the ink in the top of the column and allow the mixture to separate

Gas chromatography Equipment U-tube packed Syringe Hydrocarbon mixture Reference flame Water bath Methane carrier gas What you need to do Inject a sample of the volatile hydrocarbons into the rubber septum and watch the flame. Compare it to the reference flame to determine when the fractions of the mixture have travelled through.

HPLC - Video

How does HPLC work? https://www.youtube.com/watch?v=kz_egMtdnL4

Plenary 1 Paper / Silica gel on plastic film Paper / TLC Inert gas High boiling point liquid on inert solid support Organic or aqueous solvent HPLC Organic or aqueous solvent Silica gel GC

Plenary 2 What is the difference between chromatography and spectroscopy? What key words would you use when describing how chromatography works? What types of chromatography can you now name? What are the key differences and similarities between HPLC and GC?

Useful references Link 1 Link 2