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The spectroscopy emission characteristics and the detection limit of trace heavy metal nickel in water was studied based on laser induced breakdown spectroscopy technique, with a 1,064 nm wavelength Nd : YAG laser as excitation source, and the echelle spectrometer and ICCD detector were used for spectral separation and high sensitive detection with high resolution and wide spectral range. A round flat solid state graphite as matrix was used for element enrichment for reducing water splashing, extending the plasma lifetime and improving the detection sensitivity, and the experimental sample was prepared by titrating a fixed volume of nickel nitrate solution of different concentrations on a fixed area of the graphite matrix. The results show that the better detection delay time is about 700 ns, the spectrum intensity raises with the concentration increase, a good linear relationship is presented at low concentration with a correlation coefficient 0.996 1, and the lower limit of detection of nickel in water with 0.28 mg x L(-1) was retrieved. A measurement method for further study of trace heavy metals in water is provided with laser induced breakdown spectroscopy technique.

According to the spectral line broadening mechanism of laser induced breakdown spectroscopy, the emission lines from the standard spectral database of NIST were simulated, and they were compared with the spectral data of experiment. In the process of comparison similarity measure was used to measure the similarity between the simulative spectra and the experimental spectra. The automatic recognition method of elemental spectra was studied, and the spectral data of soil between 340 and 345 nm was recognized by computing the proportional coefficients of the spectral lines. Using principle of nonlinear least squares, the recognition process was completed. The feasibility and the advantage of the method were proved by the results of experiment.

According to that the spectral line broadening of laser induced breakdown spectroscopy (LIBS) was lorentz nonlinear function model, using Levenberg-Marquardt (L-M) agorithm to optimally estimate the undetermined parameter in the function, the continuum background radiation and peak position and peak intensity were corrected, and the method of data points automatic extraction for fitting was analysed. Automatic fitting and feature parameter extraction for spectral data of LIBS based on L-M algorithm that was hybrid programming with matrixVB and VB were accomplished,and the result was compared with the origin 7.5 data analysis software which was manual and commonly used and verified its stability and reliability.

The soil samples at six different humidities were prepared for studying the influence of soil humidity on laser-induced plasmas. By analyzing the characteristic spectral lines of Pb with the wavelength of 405.78 nm, it was demonstrated that the intensities of spectral line, SNR and RSD are linearly inversely proportional to the soil humidity. Under the approximation of local thermal equilibrium, by analyzing the characteristic spectral lines of Fe within the wavelength range of 400 to 440 nm, the temperature of plasmas was obtained by means of the two-dimensional Boltzmann plane. The experimental results show that the plasma temperature monotonously changes from 11 800 to 7 800 K and the electron density monotonously changes from 3.3 x 10(6) cm(-3) to 2.8 x 10(6) cm(-3), when the humidity increases from 0 to 20%.

The present paper analyzed the characteristics of laser-induced breakdown spectroscopy (LIBS) of metal element Cu in soil using the Nd:YAG (wavelength: 1064 nm) laser as the excitation source, where the spectral signals were detected by the highly resolved and wide spectral echelle spectrograph and intensified charge coupled device (ICCD). The time evolution of the characteristic spectral line of Cu was obtained by changing the delay time of ICCD at the same concentration and the gate of ICCD with wavelength of 329. 396 nm of Cu as the characteristic spectral line, from which the best delay time 1.1 micros was found. By measuring the intensities of the characteristic spectral line with different Cu concentrations, it was demonstrated that the intensities of the spectral line increased with the concentration of Cu under the condition of low concentration From the results the LIBS calibration curve of Cu was obtained, and by fitting calculation the detection limit of Cu in soil at 13. 36 microg x g(-1) was obtained.