Super Sensitive Detection Of Trace Toxic Heavy Metal In Water By LIBS-LIF Technique

There are common problems of lead contamination in drinking water sources and rivers in our lives.Lead is a kind of natural toxic heavy metal element commonly found in water,atmosphere and soil.Lead pollution has become a common and important health problem now.The application of laser-induced breakdown spectroscopy(LIBS)in the detection of trace lead in water environment has some advantages of simple and rapid,multi-element real-time synchronous analysis.However,when laser induced breakdown spectroscopy(LIBS)technology is used to analyze and detect water samples directly;the spattering of water samples will affect the light transmittance of the optical elements that collecting the atomic spectrum signals.In addition,water will rapidly quench the atomic radiation in the ablated plasma,shorten the life of atomic radiation and reduce the intensity of atomic radiation signals.These problems lead to the low sensitivity of LIBS technology in the detection of lead in water environment directly,and it is difficult to meet the requirement of high sensitivity detection of trace lead in water.In order to improve the sensitivity of the detection of trace lead in water environment,this paper uses the laser-induced breakdown spectroscopy(LIBS)and laser-induced fluorescence(LIF)technology together to achieve high sensitivity detection of trace lead in water environment based on the wood chip adsorption method.Poplar-wood chips convert the liquid sample analysis into solid sample analysis to eliminate the effects of water on the atomic radiation and the optical harvesting system when analyzing the water sample directly by using LIBS technology.The LIF resonant laser pulse excites the atomic fluorescence spectroscopic signal from specific particles such as lead atoms in the plasma of the sample ablated by the LIBS laser pulse.This combined experimental technique has some advantages of strong fluorescence signal,less background interference and higher signal to background ratio.In the experiment,we designed and built a set of tunable dye laser system with a 532 nm double-frequency laser as the pumping laser that produced by an electro-optic Q-switched Nd:YAG solid-state laser.The wavelength of the output dye laser is tuned by adjusting the angle of the grating,and the output can make the dye element of the dye wavelength of 283.31 nm excited by the lead element to be detected resonantly.In the experimental process,the experimental variables,such as the moving speed of the two-dimensional platform,the wavelength and energy of LIBS laser pulse,the energy and relative delay of the LIF laser pulse,will affect the signal background ratio of the lead element in water environment.We set up several comparative experiments to conduct in-depth comparisons and discussions.Under the optimal experimental conditions,we obtained the calibration curve of lead atoms in water environment and the minimum detection limit of 0.32 ppb.The limit has been raised by two orders of magnitude which is more direct than the analysis of lead in water using LIBS technology.In addition,lead was detected in two water samples under optimal experimental conditions to realize ultra-sensitive detection of trace lead in water environment.