Atomemissionsspektrometrie mit induktiv gekoppeltem Plasma (ICP-AES)
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Inductively coupled plasma-atomic emission spectrometry (ICP-AES) is a spectrometric technique, which utilises the fact that excited electrons emit energy at a given wavelength when they return to their unexcited state. Each element emits energy of specific wavelengths, but typically only one wavelength per element is chosen for the anlytical procedure.
ICP-AES is an established analytical method in geochemistry. It is used for a wide range of routine analytical applications, very cost-efficient and therefore ideal for geochemical projects requiring a large number of samples. The advantage of this method is the very high plasma-temperature and that many spectral lines for the elements can be produced, with atom and ion lines available for even the most refractory elements. Traditionally problematic molecular interferences are limited because chemical bonds do not survive the high temperatures of the plasma.
For geological rock-samples all major elements and most of the trace elements can be measured by this technique, except O, N, C, the halogen and inert gas elements. After separation of major and some trace elements it is also possible to measure the rare earth elements (REE). Rb and Cs are difficult to measure at trace levels, they are too easily ionised in the high temperature of the plasma. The elements U, Th, W and Ta are normally below the detection limit.
The instrument is calibrated with multi-element standard-solutions, which are verified by international certified rock-standards. Matrix effects are a minor problem in ICP-AES, but elements in complex matrices are generally calibrated with natural samples. Good detection limits are guaranteed due to low background signals. The ICP-AES as a spectroscopic source gives linear calibration lines over several orders of magnitude. Linearity of calibration lines is an essential tool four routine analysis that permits simultaneous measurements of major- and trace elements.
The ICP-AES in the Department of Geoscience of Potsdam University was bought in September 2001. It is a VARIAN Vista MPX, equipped with an auto sampler for large sample series (bought in 2005). We are mainly analysing REE-concentrations in hard rock samples, to complement major and trace element XRF-data. RE-elements are pre-concentrated and most of the major and some trace elements are separated by ion-exchange columns. Another target are sediments, used for dating of surface exposure with cosmogenic nuclides. In this case we measure some major and trace element concentrations for correction calculations of cosmogenic nuclide determinations.