Laser-induced Breakdown Spectroscopic Sensitive Measurement And Quantitative Analysis

Laser induced breakdown spectroscopy(LIBS)is an atomic emission spectroscopy technique.It is an elemental analysis technique with promising application prospects.It has attractive advantages,including simple apparatus,rapid response for in-situ and real-time detection,non-contact measurement,no complicated sample preparation.It is suitable for simultaneous detection of multiple elements in solids,liquids,and gases,and the experimental system is developing fast.The advantages of LIBS technology determine that it has great application prospects in many physical,chemical and even environmental detection fields.However,due to the complexity of physical processes between laser and matter,there are considerable problems in LIBS quantitative analysis.The poor detection sensitivity and the complex matrix effect problem seriously restrict the application and development of the technology in quantitative analysis.This paper mainly focuses on the analyses of metal elements in aqueous solutions,tea,and soil samples,improving the sensitivity of detection and overcoming the matrix effect,in order to promote the development of LIBS technology and facilitate the quantitative detection of LIBS.In this paper,the analysis of aqueous solution and soil was carried out by means of metallic substrate assisted LIBS.Based on the previous work,metal matrix assisted LIBS for solution detection overcame the matrix effect and improved detection sensitivity by 1 ~ 3 orders of magnitude.The quantitative analysis of the real water sample-Suzhou River water was successfully realized.Then the characteristics of plasma temperature and electron density were analyzed and compared when different materials were used as deposition targets.Also surface-enhanced LIBS technique was extended to soil detection,and the LIBS detection of soil is carried out through coating soil slurry on the surface of laser-pretreated metal substrate surface,which can effectively weaken the matrix effect.In this paper,a method for the detection of liquid by LIBS using nano metal oxides to adsorb heavy metal cations in solution is proposed for the first time.The LOD reached the order of ?g/kg(ppb),the sensitivity of LIBS detection was improved significantly,and the matrix of samples was unified into the same kind of nanooxidation so that the problem of matrix effect could be solved.It provides an effective method for the quantitative analysis of heavy metal elements in real water samples and sewage.Furthermore,the effects of different laser wavelengths and laser irradiance on the detection results of LIBS were studied.The absorption efficiency of shortwavelength laser energy is higher,and for long-wavelength laser,when the irradiance is too high,the spectrum will be saturated because of self-absorption effect.In this paper,a method for solid detection using nano-oxide doping combined with continuous laser sintering assisted LIBS is proposed for the first time.Dry tea powder was mixed with nano-alumina or nano-silica at the percentage of 80 uniformly and then pressed into pellets for LIBS detection.After laser sintering,the spectral signal intensity of the target element is enhanced 3 to 7 times compared with that of un-sintered mixture pellets,and doping with a large amount of nano oxide unified the sample matrix and the overcoming of the matrix effect makes quantitative analysis possible.For soil sample detection,with the aid of this method,more than twice the enhancement could come true,indicating that the method can be generally applied to improve the sensitivity of metal element detection in solid materials and realize quantitative analysis of complex samples.In order to improve the plasma shielding effect,the extremely high background signal in the early stage of evolution,the large amount of ablation material,and the incomplete excitation of atomic ions in the nanosecond laser induced breakdown spectroscopy,this paper first proposed a method of using femtosecond plasma grating as the excitation source to induce breakdown spectroscopy.A plasma grating induced breakdown spectroscopy experimental system was build.The plasma grating is used as an excitation source for sample detection,the spectrum has no obvious background signal from the initial stage of evolution,compared with that from ns-LIBS.The plasma grating breaks through the clamping of power density inside the single filament,and has higher laser power density and electron density,so that when the pulse energy of fs laser is the same,the signal intensity of spectrum excited by plasma grating is enhanced more than 3 times,and the corresponding plasma lifetime is also extended twice,compared with those obtained from single filament.This paper also studied the influence of experimental gas environment.When the gas had higher ionization potential,the characteristic spectral signal intensity of the target element was higher and the plasma life would also be longer.When the filament or plasma grating was used as the excitation source to detect soil samples,since the femtosecond pulse width is short,no further plasma shielding effect or light absorption process would affect the formation of the subsequent plasma.Moreover,the plasma channel of the plasma grating has a very high laser power density and electron density,which generates particularly intense excitation on the surface of the sample,so that the sample particles can be thoroughly ablated and excited,which can effectively overcome the complex matrix effect problem.This method provides a new approach to quantitatively analyze complex materials.