Schemes For Qualitative Identification And Quantitative Detection Of Alcohol Congener Based On Libs

Laser-induced breakdown spectroscopy (LIBS), as a kind of chemical element analysis technology, can be used to identify elemental compositions of liquids, solids, and gases under almost any environment. With high efficiency, specificity, simplicity and remote real time sensing capability as its main feature, LIBS technology has been widely used in many fields including chemical analysis, industry, environment and bioengineering. HoweVer, the application of LIBS in molecular analysis, especially in quantitatively detecting and identifying organic congener is still in developing stage. This dissertation reports some trial investigations on qualitative identification and quantitative assay of alcohol congener using LIBS. By calibrating the relative spectral intensities and intensity ratios of some characteristic lines of the atomic constituents in the laser induced breakdown plasmas of alcohol congeners, a spectroscopic scheme for qualitative identification and quantitative detection of alcohol congeners based on LIBS is proposed, aiming presenting the possibility to use LIBS for organic compounds analysis.To apply LIBS for qualitative detection, spectral intensity ratios of some atomic characteristic lines are used for identification of alcohol congeners. Firstly, using the LIBS spectral signal-noise ratio (S/N) as optimization criteria, the spectral intensity of the chosen atomic characteristic lines is optimized by using different carrier gas, delay time and optical collection geometry. Under the optimal experimental conditions with best S/N, the emission intensity of atomic characteristic lines of alcohol samples including methanol, ethanol, propanol and butanol is investigated under different excitation laser energy. In view of the different C/H and C/O atom ratios in different alcohols, the relative emission intensity ratios of C/H and C/O are reasonably suitable for qualitative analysis for alcohol congeners due to the well-known local thermal equilibrium of laser induced breakdown plasmas.In order for quantitative detection, the room temperature vapors of methanol and ethanol are used as sterling and two quantitative detection quantities are constructed for calibration curves. By mixing the methanol or ethanol vapors into carrier gas with trace concentrations to prepare standard testing samples, quantitative detection and qualitative identification of alcohol congeners based on LIBS is realized. One quantity is the spectral intensity ratio (H/C) of characteristic line H (656.35nm) and C (247.85nm) for identification, the other is the ratios (C/Ar) of the above C line or (H/Ar) of H line to Ar (866.66nm). With excitation laser energy ranging from200to300mJ and aleohol concentration in the samples below1300ppm, the intensity ratio H/C shows almost independence on the concentration and laser energy. The value of the H/C is about34and23for methanol and cthanol respectively. Since each alcohol congener presents specific H/C. it is competent for alcohol congener identification. Moreover, the intensity ratio C/Ar and H/Ar show good linearity with sample concentration below1300ppm, which indicates the applicability of the quantity for alcohol quantitative detection. With the ratio C/Ar, a methanol detection limit of140ppm is reached by using excitation laser energy of300mJ.