Description of LIBS method
LIBS (Laser-Induced Breakdown Spectroscopy) – is a modern analytical method of elemental analysis providing a high-precision multi-element real-time analysis of chemical composition of a sample under investigation.
The method is based on excitation of elements atoms of a sample with a laser radiation pulse, focused to sample surface, on spectral decomposition of radiation of element atoms, measurement of analytical signals proportional to the spectral lines intensity, and on subsequent detection of mass fractions of elements by means of calibration graphs.
Spectrum
Atomic-emission spectrum is a registered as a graph or visually observed dependence of the intensity of radiation emitted by free atoms or ions on the radiation wavelength. Radiation intensity depends on the material temperature and number of emitting atoms or ions. The wavelength of a separate spectral line is defined with the difference of atom quantum transition energies from the excited state to a lower-energy state. The quantum levels structure is unique for each chemical element, and this fact allows one to identify the presence of an element in the substance according to the spectral line.
Calibration graphs
Functional dependence of analytical signal on the content of the chemical element, represented as a graph.
Calibration graphs
Functional dependence of analytical signal on the content of the chemical element, represented as a graph.
LIBS method schematic diagram and block diagram of analyzer parts
Schematic diagram of sample analysis by LIBS method
Block diagram of main analyzer parts
Spectral composition of laser plasma radiation of any chemical element is unique and this fact permits the identification of an element in a sample according to the spectrum and the its concentration detection according to the spectral line intensity. Therefore, a multi-component material spectrum includes spectral lines of all chemical elements it comprises.
The Analyzer consists of the following basic parts: a pulsed laser; a system of collection, transfer and spatial decomposition of optical radiation into monochromatic components – spectrograph; a system of spectra detection (detector) – digital camera, a control unit, analysis data archiving.
There are several important stages of quantitative sample analysis:
Initial condition for a quantitative analysis is a response of the analytical instrument for the identified component in sample. Such response is called analytical signal, and a graph illustrating analytical signal dependence on concentration is called calibration curve (graph). The form of calibration curves strongly depends on a number of factors, which finally define the reproducibility and measurement accuracy.
At element concentration detection in a sample the calculated is executed according to the calibration curve which corresponds to the value of the analytical signal detected with the instrument.
Analytical signal
Signal contains quantitative information on value, functionally connected with the content of the element and registered during the material analysis.
Calibration curve
Element content functional dependence on the analytical signal expressed in the form of a graph.