Detection And Analysis Of Heavy Metal Elements Copper And Chromium In Water Based On Laser-induced Breakdown Spectroscopy Technology

Laser-induced Breakdown Spectroscopy technology has the advantages of rapid,multiple,and in-situ,and has become an important means of substance detection and analysis.However,due to the particularity of the liquid phase matrix,when LIBS technology is directly applied to the detection of heavy metal elements in water,it is accompanied by bubble generation,liquid level fluctuations,plasma quenching and other problems,resulting in unsatisfactory detection results,and the sensitivity of quantitative analysis are relatively low.In order to solve the above problems,this article uses gelatin hydrogel curing method for the first time(that is,gelatin is mixed with the solution to be tested and made into a gel-like solid through heating,stirring,aging,etc.)and circulating thin laminar flow method(that is,using self-made circulation thin laminar flow device converts a static solution into a thin liquid layer with a stable flow rate)assisting LIBS to detect copper and chromium in water.The main research contents and results are as follows:(1)Study the spectral characteristics of laser-induced breakdown gelatin copper sulfate gel samples.The study found that the copper characteristic spectral line intensity increased with the increase of gelatin mass fraction,first increased and then decreased,and the best gelatin mass fraction was 2.5%.The gelatin hydrogel curing method has higher sensitivity and spectral line intensity than the direct detection of LIBS spectra of static solution.The spectral intensity of Cu I 324.7nm and Cu I 327.4nm are enhanced by2.62,2.11 times.(2)Quantitatively detect the detection limit of copper in gelatin copper sulfate gel samples under different laser energy.The research results show that under different laser energy(100m J,80m J,60m J),lower detection limits can be obtained,and the linear fitting effect is improved and the detection limit is reduced with the increase of laser energy.The laser energy is 100m J.At this time,the coefficient of fit R~2 of Cu I 324.7nm is 0.999,and the detection limit is 0.30mg/L,which can reach the detection level of the enrichment method.(3)The spectral characteristics of laser-induced breakdown gelatin chromium nitrate gel samples were studied.The study found that the signal-to-background ratio of the chromium characteristic spectral line increases first and then decreases with the increase of the laser energy.The best laser energy is 140m J.Under the best laser energy,the gelatin hydrogel curing method has higher spectral line intensity and resolution than directly detecting the LIBS spectrum of static chromium nitrate solution.Compared with the method of directly collecting static chromium nitrate solution,the gelatin hydrogel curing method can excite the unexcited lines Cr I 427.48nm and Cr I 428.97nm,and the spectral intensity of the line Cr I 425.4nm is enhanced by 2.39 times.The FWHM is narrowed to 82.78%of the static chromium nitrate solution directly collected.(4)Quantitative detection limit of chromium in gelatin chromium nitrate gel sample.Under optimized experimental conditions(laser energy 140m J),the linear fitting coefficient of the chromium calibration curve reached 0.9994,and the detection limit reached 1.05 mg/L.(5)The spectral characteristics of the laser-induced breakdown cycle laminar flow are studied.The research results show that the spectral intensity of copper and chromium elements increase first and then decrease with the increase of laser energy.The best breakdown laser energy of copper element is 260m J and that of chromium element is220m J.The best collection delay for copper is 2.9μs,and for chromium is 3.4μs.The net signal intensity of the spectrum decreases with the increase of the water flow speed.Appropriately reducing the water flow speed has an enhancement effect on the laser-induced circulating laminar flow plasma spectrum.