Various aspects of sulfur determination in concrete samples using Laser Induced Breakdown Spectroscopy
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| Year of publication | 2017 |
| Type | Conference abstract |
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| Description | Analysis of concrete is one of the auspiciously developing industrial applications of Laser Induced Breakdown Spectroscopy (LIBS). Knowing the content of chlorine, fluorine and sulfur can be decisive on the current state and security of a particular concrete construction. The sulfur amount in the used cement as a binder of gravel stones in a concrete can influence its solidness. Determination of sulfur in several samples of concrete samples from traffic constructions is the subject of this work. Such task, however, requires more than basic LIBS equipment. Similar to other non-metals, sulfur excitation energies are high and most sensitive emission lines fall to the vacuum ultraviolet range and several much less sensitive lines can be found in visible and lines with higher intensity in near-infrared (NIR) region. To ever visualize the sulfur NIR lines it is often necessary to remove oxygen from the sample neighborhood and to enhance them, helium atmosphere is necessary as well as its pressure should be lowered and further optimized. Owing to the stronger plasma expansion and faster decay of hard lines also the gate delay should be optimized and shifted down to several hundreds of ns. These measurement conditions and parameters and moreover some interference on the emission line S I 921.28 nm were investigated and optimized. The best conditions for maximum lines intensities may not be sometimes applicable due to a parallel increase of an adjacent interfering line. The used LIBS equipment is a SciTrace (AtomTrace) instrument consisting of a 532 nm Q-switched Nd:YAG laser vertically ablating a sample and producing craters of about 0.23 mm in diameter at the pulse energy of 100 mJ. The improvement in detected intensity was investigated in helium atmosphere under various underpressures in a sealed LIBS interaction chamber (AtomTrace). The average content of sulphur was about 0.1-0.3 wt. % by a reference standard procedure employing gravimetry and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). As the LIBS analysis is a spatially resolved method, several spots on the stones without measurable sulfur content were found while the others, in the cement binder, indicate sulfur presence. The obtained sulfur amount from the particular ablation spots is not directly comparable with ICP-MS but a representative average must be taken into account. Simple method using a synthetic limestone enriched by defined amounts of Na2SO4·10H2O was used for achieving the calibration dependence for studied element. This powder material was pressed into pellets and different matrix responses were corrected using selected spectral lines as internal standards. |
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