Modern analytical techniques
Modern techniques of analysis have revolutionised the determination of the structures of organic molecules. Until relatively recently the history of the Nobel Prize for chemistry is littered with prizes won for determining the structure of natural products (natural product synthesis). The only way to identify the structure of a molecule was to make an educated guess based on degredative analysis, then make the structure from scratch and see if it matched the natural molecule in its chemical and physical properties. If it didn't, you had another guess and started again. Not surprisingly the determination of a structure could take decades.
With the advent of modern techniques of analysis the determination of the structure of an unknown that previously might have taken 20 years now takes 20 minutes! This is the power of modern analytical techniques.
There are four techniques which are used in synchrony. Chromatography is used purify compounds but can also be used to identify compounds, mass spectrometry gives the Mr of a compound directly, and high resolution mass spectrometry can also identify a compound directly from its accurate mass. Infra red spectroscopy allows rapid identification of functional groups, and the combination of 13C and 1H NMR allows the molecular framework to be deduced.
Mass spectrometry and infra red spectrosopy are normally studied in year one, whilst chromatography and NMR spectroscopy are studied in year two.
The following list of resources is organised to reflect this split, with those on mass spectormetry and infra red spectroscopy at the beginning of the list.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or other recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.’
Links and Resources
This comprehensive resource, from the Royal Society of Chemistry, provides much detailed material on the topics covered in this module. The resource would be useful for teachers for detailed background reading, and an invaluable resource for planning.
This resource provides worksheets covering mass spectrometry and infra red spectroscopy. The material could be useful to reinforce learning either in class or as homework exercises. Please note that the instrument section covers magnetic sector instruments and not time of flight spectrometers.
This is a short video outlining the use of time of flight mass spectrometry to help to answer an archeological question. The video will add interest to a discussion of mass spectrometry, and the bundled resources include a basic simulation of the operation of a time of flight mass spectrometer.
Several other resources give additional information and background to the project and included are two additional videos of interviews with the researchers involved in the project. A fascinating resource highlighting the power of this technique.
This is an interseting demonstration of a simulation of gas chromatography using a few basic items. The demonstration requires some preparation so planning in advance is essential. Resources such as videos of gas chromatography tend to mask the basic principles involved by focusing on technical aspects such as injection and vapourisation, and this demonstration allows students to focus on principles of the technique rather than details.
This is activity enabling students to apply a number of the concepts learned in this module to a pathological investigation. Students need to be familiar with analytical techniques, particularly gas chromatography, and so this activity is best included towards the end of the module where it would provide valuable consolidation. The activity requires students to construct a calibration curve for the gas chromatography from given data.
Useful summary notes for the teacher are included. The guide time for the activity is two hours.
Here is another problem solving activity, this time using joint application of infra red spectroscopy, mass spectrometry, and nmr in order to identify several compounds. Again this activity is best attempted towards the end of the module when the various techniques have been covered. This is best as a group acyivity in order to stimulate discussion and exchange of ideas. The guide time for the activity is two hours.
Useful summary notes and a suggetsed approach to solving the problem are included.
This article from Catalyst looks at the technique of combined gas chromatography and mass spectrometry (GC-MS) and its application to archeological and paleontological questions. The article will add interset and context to a discussion of analytical methods.