Quantitative Analysis Of LIBS Technique Based On Calibration-Free Method

Laser-induced breakdown spectroscopy (LIBS) is a new spectroanalysis technique, and is promoted to solve the practical problems in many fields, such as industrial product quality control, environmental situation, water resources, and other fields. LIBS technique demonstrates the advantages of the capability of fast multi-element synchronous analysis, requiring no sampling or significant sample preparation programs, it is widely applied in the quantitative analysis of the soil. The calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is a promising and research value quantitative analysis method. The accuracy is still a challenge for classical CF-LIBS quantitative analysis since absolute theoretical calculation and mathematical model cannot compensate for the self-absorption effect and plasma temperature variability. From the aspects of descreaing self-absorption effect, determining accurately plasma temperature and improving accuracy of CF-LIBS, this paper carry out a series of the study of methods,-and the improved methods are applied to quantitative analysis of Ca and Al elements content and their ratio in soil.First, an Internal reference with external standard calibration free (IRESCF) method is proposed to correct self-absorption effect and plasma temperature in CF-LIBS based on internal reference line and one standard sample. The internal reference line is suffering from negligible self-absorption effect for self-absorption correction. Furthermore, one standard sample matrix-matched with the unknown samples along with the genetic algorithm (GA) is utilized to simulate the accurate plasma temperature of the unknown samples, which contributes to precise elemental composition of unknown samples for CF-LIBS. The proposed method demonstrates significant improvement in accuracy compared with the classical CF-LIBS.Second, the modified CF-LIBS method is applied to determination of calcium-to-aluminum concentration ratios of different kinds of soil based on Saha equation. Using Ca and Al lines of Stark broadening mechanism to calculate electron density, Boltzmann plot method combined with genetic algorithm (GA) is used to calculate the electron temperature. The modified method which combines Saha equation and CF-LIBS method was used to calculate calcium-to-aluminum concentration ratios in different soil samples. The result is consistent with reference value, which shows CF-LIBS can serve as a practical method to quantitative analysis of elements concentration ratios in soil.Finally, a novel method based on an optimized calibration method is presented to determination of calcium-to-aluminum concentration ratios in soil samples, named optimized calibration (OC-LIBS). The OC-LIBS equation is obtained through a series of mathematical theory deduction on the basis of traditional CF-LIBS method and then combining the experimental parameters calculate elements content. On the one hand, OC-LIBS method can reduce the influence of matrix-effects for the quantitative analysis compared with calibration curves and chemometrical approaches. On the other hand, the exponential relation between the calculated elemental composition and the intensity of a very limited number of spectral lines seen in the CF-LIBS approach has been removed, thereby reducing the sensitivity to lines becoming self-absorbed that the CF-LIBS approach suffers from. In addition to, the method only needs four lines to analyse. The accuracy of the method obviously improves in quantitative analysis.