3.2.3 Chromatographic methods

High Performance Liquid Chromatography (HPLC-PDA) and combined techniques with mass spectroscopy.

HPLC is used with a variety of detection methods, photodiode array (PDA), ultra-violet (UV), refractive index (RI) and mass spectroscopy (MS). It is a chromatographic technique, and since its early development in the late 1960s it has become one of the most commonly used techniques for both qualitative and quantitative analysis. It makes use of the interactions of molecule(s) with the mobile liquid phase and solid column phase. This allows separation of complex mixtures based on their retention time in the column. Identification of the molecules and derivatives can then be achieved, based on retention time, molecular weight etc. Frequently software packages contain extensive libraries which greatly assist in identification. Increasingly improved detectors allow for successful identification of samples in the nano, pico and even femto-scale range. In archaeological and other heritage science it has been used for the analysis of a number of materials, for example to identify wine residues in ceramics, identification of dyes in textiles and pigments in paintings.

Used at: NMS

Gas Chromatography Mass Spectrometry (GC/MS)

GC is an extensively used chromatographic technique which was developed in the 1950’s. It is used for the qualitative and quantitative analysis of organic materials. A liquid sample is injected into a port, which is held at a high temperature (150-250°C,) the sample is then vaporized and moved by the inert carrier gas across a solid column phase. Like HPLC, components within a mixture are interact and then are eluted from the column with differing retention times, these then flow into the mass spectrometer detector. Compounds and derivatives can be identified by using a spectral library as each compound has an unique fragmentation pattern. Successful GC/MS depends on samples having suitable vapour pressures and thermally stabilities. It is an extremely sensitive technique and is therefore able to identify the constituents of very small amounts of sample material. The major archaeological applications of this technique are in organic residue analysis, but it is also used for the identification of organic materials such as bog butter, waxes, resins and adhesives either used in the construction of an object or later conservation treatments, particularly in paintings.

Used at: Glasgow University Chemistry and Earth Sciences Departments, Bristol (Chemistry), Bradford (Archaeological Sciences) and York (Archaeology)

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