Quantitative Analysis Research Of Crude Oil Based On Laser Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a analytical technique in laser application fields. LIBS uses pulsed laser to generate a plasma, which vaporizes a small amount of the sample. Spectral features emitted by the excited species are used to obtain quantitative and qualitative analytical information. The trace elements of crude oil and dirt in pipeline corrode reactor and pipeline, cause serious consequences. In this paper, based on the technical principle and practical application of LIBS, We had carried out research for the elements of crude oil after ashing and dirt in pipeline as follows.It explained the source and research significance of the topic according to the characteristics of LIBS and the harmful of trace elements of crude oil and dirt in pipeline. The development history, characteristics (the advantages and disadvantages) and experimental principle of LIBS were described. It introduced research status of LIBS technology at home and abroad from three parts:application fields, detection capabilities and equipment development. It briefly described of LIBS. After that, It simply introduced experiment instrument——RT100-HP LIBS and its functions.After introducing the identification and the selection gist of elements analysis lines, it described the method in detail that how to use "scatter diagram" to identify and process abnormal data, and analyzed the effect of the processing. It brought in correlation coefficient R to judge whether the result of regression analysis made sense or not. It had analyzed and discussed the influence of instrument parameters on the spectral intensity, such as laser pulse energy, light spot size, delay time and so on. The analysis shown that within the limits of laser pulse energy, spectral intensity was proportional to the laser pulse energy; spectral intensity was decreasing gradually with the increasing of laser spot diameter; when delay time was greater than 1 u s, spectral intensity gradually reduced with the increase of the delay time.And on the base of these above, two samples were analyzed by LIBS. In the example of LIBS analyzed crude oil after ashing, Na I 588.995nm was the main analysis object. Then it simple summarized the origin of the spectral background and processing method. Na was quantitative analyzed by calibration curve for integrated intensity and peak intensity of spectrum after subtracting noise respectively by using the technology of laser-induced breakdown spectroscopy.6 elements were quantitative analyzed on the basis of Na Ⅰ 588.995 nm, Mg Ⅰ 285.213 nm, Al Ⅱ 308.215 nm, K Ⅰ 404.4 nm, Ca Ⅰ 396.847 nm, Fe Ⅱ 273.955 nm in the experiment. The content of above 6 elements were 5.92%,0.32%,2.12%,0.19%,0.68%,16.86% in corresponding acording to calibration curves for element content and integrated intensity, and it also calculated the linear correlation coefficient and detection limit of calibration curves. It turned out that effect of integrated intensity for calibration curve is better; Na was also quantitative analyzed by using the technology of X-ray fluorescence spectroscopy, compared the measurement results of laser-induced breakdown spectroscopy and X-ray fluorescence spectroscopy, the relative error was 6.28%. The technology of laser-induced breakdown spectroscopy could be applied to measure the content of metal elements in crude oil after ashing.In the example of LIBS analyzed dirt in pipeline. Mg was the main analysis element. Mg in soil of outside the pipe and dirt of inside the pipe were quantitatively analyzed and compared by using LIBS. Firstly, Mg was quantitatively analyzed on the basis of Mg Ⅰ 285.213 nm by calibration curve for integrated intensity and peak intensity of spectrum before and after subtracting noise, respectively. Then it explained how to use Gauss linear fitting peak and Lorentz linear fitting peak to split overlapping spectrum. Finally calibration curves on the basis of Mg Ⅱ 279.553 nm and Mg Ⅱ 280.270 nm were analyzed. The results indicated that the Lorenz line was more suitable for splitting overlapping spectrum; it is better to use integrated intensity after subtracting noise of spectrum line with high relative intensity to make calibration curve.At last, conclusions of the whole paper were summarized, and the directions for the further studies were arranged.