[Detection of metal ions in water solution by laser induced breakdown spectroscopy]

Environmental concerns about the hazardous heavy metals in seawaters have been greatly increased in these years. To evaluate the potential application of laser induced breakdown spectroscopy (LIBS) to on-line toxic metals pollution monitoring in ocean, some experimental investigations with LIBS technique to detect metal ions in CuSO4 and Pb(NO3)2 water solutions have been carried out in our laboratory. A Q-switched Nd:YAG laser operating at 532 nm with pulse width of 10 ns and repetition frequency of 10 Hz was utilized to generate plasma on a flowing liquid surface. The ensuing plasma emission was coupled by a quartz lens to a double grating monochromator and recorded with a PMT in conjunction with a computer controlled boxcar integrator. The temporal characteristic of the laser induced plasma and the power dependence of LIBS signal were investigated. The operation condition was improved with the optimal ablation pulse energy and the delay time for LIBS signal detection. The ablation location was varied to achieve better LIBS signal. The optimized ablation location for lead was found to be different from that for copper due to the breakdown of the ambient air. The detection limit of metal ion in water solution under the optimized operation conditions was found to be 31 ppm for copper and 50 ppm for lead. The experimental results proved that the flexibility of LIBS has the potential to be applied to the detection of toxic metals in seawaters, but the limits of detection for each element should be improved further to make a practical application of LIBS in this field.