4.3.1 Chromatography

Types of chromatography

Paper chromatography can be used to illustrate the separation process.
Candidates should be able to:
(a) describe chromatography as an analytical technique that separates components in a mixture between a mobile phase and a stationary phase;
(b) state that: (i) the mobile phase may be a liquid or a gas, (ii) the stationary phase may be a solid (as in thin-layer chromatography, TLC) or either a liquid or solid on a solid support (as in gas chromatography, GC);
(c) state that: (i) a solid stationary phase separates by adsorption, (ii) a liquid stationary phase separates by relative solubility;
(d) explain the term Rf value, and interpret one-way chromatograms in terms of Rf values;
(e) explain the term retention time, and interpret gas chromatograms in terms of retention times and the approximate proportions of the components of a mixture;
(f) explain that analysis by gas chromatography has limitations, eg: (i) similar compounds often have similar
retention times, (ii) unknown compounds have no reference retention times for comparison;
Combining mass spectrometry with chromatography
Mass spectrometry is used with GC as GC-MS and with high pressure liquid chromatography as HPLC-MS; separated components are directed into the mass spectrometer.
Candidates may be expected to interpret provided gas chromatograms and mass spectra

Use of GC-MS by society in modern analysis and the use of such evidence in courts.
(g) explain that mass spectrometry can be combined with chromatography: (i) to provide a far more powerful analytical tool than from chromatography alone, (ii) to generate mass spectra which can be analysed or compared with a spectral database by computer for positive identification of a component;
(h) state the use of GC-MS in analysis, eg in forensics, environmental analysis, airport security and space probes. 4.3.2 Spectroscopy

NMR Spectroscopy

Candidates will be expected to identify aromatic protons from chemical shift values but will not be expected to analyse their splitting patterns.
Candidates should be able to:
(a) state that NMR spectroscopy involves interaction of materials with the low-energy radiowave region of the electromagnetic spectrum;
(b) analyse a carbon-13 NMR spectrum of a simple molecule to make predictions about: (i) the different types of carbon present, from chemical shift values, (ii) possible structures for the molecule;
(c) analyse a high resolution proton NMR spectrum of a simple molecule to make predictions about: (i) the different types of proton present, from chemical shift values, (ii) the relative numbers of each type of proton present from relative peak areas, using integration traces or ratio numbers, when required, (iii) the number of non-equivalent protons adjacent to a given proton from the spin– spin splitting pattern, using the n + 1 rule, (iv) possible structures for the molecule; (d) predict the chemical shifts and splitting patterns of the protons in a given molecule;
(e) describe the use of tetramethylsilane, TMS, as the standard for chemical shift measurements;
(f) state the need for deuterated solvents, eg CDCl3, when running an NMR spectrum;
(g) describe the identification of O–H and N–H protons by proton exchange using D2O;
(h) explain that NMR spectroscopy is the same technology as that used in ‘magnetic resonance imaging’ (MRI) to obtain diagnostic information about internal structures in body scanners; (i) For organic compounds containing any of the following atoms: C, H, N and O: (i) analyse infrared absorptions in an infrared spectrum to identify the presence of functional groups in a molecule
(ii) analyse molecular ion peaks and fragmentation peaks in a mass spectrum to identify parts of structures (iii) combine evidence from a number of spectra: NMR, IR and mass spectra, to deduce structures.

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A-Level Chemistry (F324: Module 3 - Analysis) Notiz am F324: Module 3 Specification, erstellt von gallen96 am 02/04/2014.