| Laser induced breakdown spectroscopy is a kind of spectral analysis technology which uses laser pulse to breakdown the target sample to induce plasma and utilizes the emission spectra of plasma to realize the analysis of the element composition in the sample.Because the LIBS technology itself has the unique advantages of fast,high sensitivity,multi-element analysis and so on,it has received wildly attention to in past decades.LIBS technology has great potential advantages in the detection of metallic elements in liquid samples.But in the application of LIBS technology in water detection,the energy absorption of laser by bulk water,the shock wave generated by the plasma and the bubble environment cause adverse effects on the sensitivity and stability of LIBS.The signal enhancement LIBS methods developed to solve the above problems often fail to keep all the advantages of LIBS,especially the abilities of continuous and fast.Obviously,it is difficult for these methods to be developed into continuous,on-line and highly sensitive water sample detection techniques needed in marine detection and other fields.Aiming at the requirements of on-line,real-time,accurate,stable and highly sensitive properties for the on-site detection of marine metal elements,and according to the characteristics of ultrasonic nebulizer assisted LIBS technology,an online ultrasonic nebulizer assisted LIBS method was proposed in this paper.This method can be used to analyze the metallic elements in water samples continuously and rapidly,with high stability and sensitivity.According to the proposed method,a set of OUN-LIBS seawater metal element detection system was designed and implemented.The hardware of the system is composed of three modules: adaptor,ultrasonic nebulizer auxiliary device and optical load.The automatic control of the system can be realized through a USB port.On the basis of parameter optimization and laboratory experiment,the quantitative inversion algorithm is established,and the quantitative analysis method of on-site standard sample correction is put forward,and the high precision online quantitative analysis is realized.According to the application requirements of marine scientific investigation,a special automatic control operation software was developed in this paper,which has the functions of complete control of hardware system,real-time spectral data processing,on-site self-correction,alarm and protection for abnormal events,etc.The results of laboratory experiments and field sea tests show that the OUN-LIBS system designed in this paper has obvious advantages in the detection stability and detection limit of metal elements in the target seawater.Besides the traditional calibration curve method,an online and on-site standard sample calibration method is adopted in the concentration quantitative analysis.The results of research show that the accuracy of online quantification analysis is very impressive even in the marine field testing.In the future,the system is expected to be applied in the fields of Marine scientific investigation,water environment monitoring and industrial water detection. |
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