[The measurement of methane dissolved in water using raman spectroscopy assisted with CCl4 extraction].

While under laboratory conditions, the concentration of methane dissolved in water is too low to be detected because of the low solubility of methane using Raman spectroscopy. In the present paper, a novel approach based on CCl4 extraction was introduced, and used in the measurement of methane dissolved in water using Raman spectroscopy under laboratory conditions. Saturated aqueous solution of CH4, CCl4 solution after extraction of CH4 from the saturated aqueous solution and the saturated CCl4 solution of CH4 were prepared, and the Raman spectra of three samples were obtained. The obtained results show that the CH4 dissolved in saturated aqueous solution(the concentration of CH4 is about 1.14 mmol x L(-1)) can't been detected using Raman spectroscopy under laboratory conditions, but the CH4 Raman peak can be clearly seen in the spectra obtained for CCl4 solution after extraction. All the results demonstrate that the proposed approach can improve the Raman spectroscopy sensitivity of methane detection dissolved in water, and this approach has significant potential to be developed as an effective method for detection of methane dissolved in water.

[Study of cuttings identification using laser-induced breakdown spectroscopy].

Cutting identification is one of the most important links in the course of cutting logging which is very significant in the process of oil drilling. In the present paper, LIBS was used for identification of four kinds of cutting samples coming from logging field, and then multivariate analysis was used in data processing. The whole spectra model and the feature model were built for cuttings identification using PLS-DA method. The accuracy of the whole spectra model was 88.3%, a little more than the feature model with an accuracy of 86.7%. While in the aspect of data size, the variables were decreased from 24,041 to 27 by feature extraction, which increased the efficiency of data processing observably. The obtained results demonstrate that LIBS combined with chemometrics method could be developed as a rapid and valid approach to cutting identification and has great potential to be used in logging field.

[Time-resolved evaluation of self-absorption in laser induced plasma from nickel sample].

Laser induced breakdown spectroscopy (LIBS) has been shown to be a promising technique for element analysis. However, self-absorption effect deeply influences the LIBS measurements. In the present paper, a Q-switched Nd:YAG laser operated at 1 064 nm was used to generate nickel plasmas in air. Four atomic lines Ni I 341.476/351.034/351.505/352.454 nm which belong to the same electronic configuration (3d9 (2D)4p-3d9 (2D)4s) of Ni were chosen for self-absorption investigation. Self-absorption of Ni I 351. 034 nm corresponding to the highest energy level 3D1 of 3d(9) (2D)4s was not observed in the plasma emission investigated. While for the other three lines, a strong self-absorption appeared at the prophase of the plasma and tended to weaken. The self-absorption at Ni I 352.454 nm was the most serious and still visible at the delay of 1100 ns, compared with the lines of Ni I 341.476/351.505 nm whose self-absorption duration is 900 and 500 ns respectively. It was also found that the self-absorption effect had power dependence and decreased with the increase in laser pulse energy. The obtained results suggest that the self-absorption effect could be alleviated by suitable atomic line selection, operating at a higher pulse energy and detecting with a longer delay. The possible reasons for the self-absorption duration difference for different lines were also discussed.

[Experimental investigation of Pb in soil slurries by laser induced breakdown spectroscopy].

Laser induced breakdown spectroscopy (LIBS) has been shown to be a promising technique for element analysis with many advantages including on-line, real time, standing off and multi-element detection capability. In the present paper, the LIBS experiments for Pb in slurry samples were carried out with the motivation of developing an in-situ sensor for monitoring heavy metal. A Q-switched Nd : YAG laser operating at 532 nm with repetition frequency of 10 Hz was utilized to generate plasma on the prepared slurry samples, which were doped with same weight manganese as reference and varied concentration of lead. The induced plasma emission was recorded by CCD. The LIBS signals at PbI 405.78 nm and MnI 403.07 nm from the slurry samples were investigated. It was found that the intensity ratio of I(Pb)/ I(Mn) increased as a linear function of the concentration of Pb with correlation coefficient R2 of 0.994 9. The obtained results show that LIBS with conjunction of referent element could be developed as a potential technique for contamination analysis of soil slurries. The main influence factors in LIBS signal detection were also discussed.