Multi-block analysis coupled to laser-induced breakdown spectroscopy for sorting geological materials from caves

Discriminating organic carbon from endokarstic moonmilk-type deposits by LIBS. The case of a natural carbonated Martian analogue

Moonmilk-type deposits exemplify carbonated Martian analogues existing in the subsurface of Earth, an endokarstic speleothem with a possible biochemical origin composed principally by carbonates, mainly huntite and dolomite. In this work, samples of moonmilk located in Nerja Cave (southern Spain) have been studied by LIBS with the aim of identifying carbon of biogenic origin by establishing a relationship between a molecular emission indicator, CN signal, and the organic carbon content. The characterization of this kind of carbonate deposit with a multiple mineralogical composition has been completed using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction techniques for qualitative and semi-quantitative analysis. The information attained from LIBS regarding energy thresholds and time-resolved kinetics of CN emissions provides useful insight into the identification of different molecular emitters, namely organic and inorganic CN, depending on the laser irradiance and time settings conditions. These promising results are of application in the search and identification of biosignatures in upcoming planetary missions with astrobiological purposes.

Investigation of the self-absorption effect using time-resolved laser-induced breakdown spectroscopy

Self-absorption seriously affects the accuracy and stability of quantitative analysis in laser-induced breakdown spectroscopy (LIBS). To reduce the effect of self-absorption, we investigated the temporal evolution of the self-absorption effect by establishing exponential calibration curves. Meanwhile, the temporal evolution mechanism of the self-absorption effect was also investigated. The results indicated that self-absorption was weak at the early stage of plasma expansion. For determination of manganese (Mn) in steel, as an example, the concentration of upper bound of linearity (C_int) was 2.000 wt. % at the early stage of plasma expansion (in a time window of 0.2-0.4 μs)-much higher than 0.363 wt. % at a traditional optimization time window (2-3 μs). The accuracy and stability of quantitative analysis at the time window of 0.2-0.4 μs was also much better than at the time window of 2-3 μs. This work provides a simple method for improving quantitative analysis performance and avoiding the self-absorption effect in LIBS.