School of Earth and Environment

Spectroscopy

We have various different spectrocopic techniques including:

FTIR

Background to the technique

Fourier Transform Infra-red Spectroscopy (FTIR) can be used to:

  • identify unknown materials,
  • determine the quality or consistency of a sample, check for contamination,
  • determine the amount of components in a mixture (standards needed)

An FTIR spectrometer measures the intensity of absorption or transmission of infra-red light through a sample as a function of wavelength/-number.

All frequencies are measured at the same time, giving a frequency spectrum (a plot of the intensity at each individual frequency). This is then converted for you into an absorbance/transmittance vs. wavelength/-number spectrum by the instrument using Fourier transformation.

The infrared spectrum obtained represents a fingerprint of a sample with absorption peaks which correspond to the frequencies of vibrations between the bonds of the atoms making up the material. Because each different material is a unique combination of atoms, no two compounds produce the exact same infrared spectrum.

Instrument capabilities

We have a portable A2 Technology Microlab Portable mid-IR spectrometer with a Diamond internal re?ection cell (DATR). This instrument is usually used to analyse powder samples. However, solid samples can be analysed, for example flexible plastics or layered materials like clays or soft minerals (e.g. gypsum).

Liquid samples can also be analysed. However, for aqueous solutions, high concentrations (around 1 M) are required. For wet solid samples or liquid samples the spectrum will show water peaks.

We also have several licenses for the Nicolet FTIR OMNIC software, E.S.P. 5.1 used for processing of FTIR spectra.

Practical Considerations

FTIR analyses:

  • Require very little preparation: samples can be analysed in solid (generally powdered) or liquid form (high concentrations for aqueous solutions),
  • Require little sample material: only about 1 mm3 is needed for an analysis,
  • Are fast: a single sample can be analysed in 15 minutes (including collection of background),
  • Non-destructive: the sample is not affected by the measurement and can be used for further analyses after FTIR.

 For a range of FTIR data of minerals, check http://rruff.info/.

Written by Daniela Meier (26/06/2014)

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Raman

The Raman microscope, with 785- and 514nm lasers, is equipped with a bespoke temperature- and humidity-controlled stage.Temperatures can be controlled from -80 to +50oC and humidities from dry to water saturation (i.e. 100% RH). We use this instrument to study:

  • diffusion coefficients in ultraviscous liquids and glassy aqueous solutions
  • phase changes in metastable solution droplets under conditions relevant to the atmosphere
  • crystallisation in acid solutions relevant for stratospheric clouds the properties of single-celled organisms

A new, prize-winning method of measuring diffusion coefficients has been developed using this microscope.

UV-Vis

Background to the technique

UV-Vis spectroscopy uses light in the visible and adjacent (near-UV and near-infrared) ranges. Electromagnetic radiation in this region can excite molecules to undergo electronic transitions. This allows molecules or species to be detected with a solution (or solid). Analysis is usually carried out with a finger printing technique (i.e. comparison with spectra of already characterised compounds). The concentration of these molecules can also be measured using the Beer-Lambert law

The technique can also be used to detect changes in colour or turbidity of a solution and so monitor the progress of chemical reactions. With the appropriate flow call this can be done in real time.

Instrument capabilities

We have various UV-vis spectrophotometers. Our most versatile is a UVIKON XL (SCHOTT Instruments). This is a highly adaptable double-beam spectrophotometer with a Peltier cryobath system. We have various accessories including a flow cell.

Practical Considerations

The majority of the samples we handle are liquids and are tested in transparent plastic cuvettes of various volumes depending on sample availability. Volumes required can be as little as 1.5ml. Quartz and other cuvettes are also available.

If concentration of a solution is required a calibration curve must be created using solutions of known concentration.

 

Written by Andy Connelly (25/07/2014)

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