Research Of Dispersive Detection Technology Based On DMD For Atomic Fluorescence Spectrometry

China is the major country for the technology application and instrument production of atomic fluorescence spectrometry（AFS）.Especially,the technique coupling hydride generation-atomic fluorescence spectrometry and atomic fluorescence spectrometry（HG-AFS）has been widely applied and developed in the field of heavy metal analysis for food and agriculture products in China.However,AFS is largely limited by related international industrial standards in United States and the European Union.For instance,the detection for only Hg was recognized by U.S.Environmental Protection Agency（EPA Method 1631,Revision E）,and the main reason is that impure light source or aerosol,water vapor and so on in the fluorescence excitation process may cause spectral and scattering interference,amd the accuracy of the detection results would be affected.Meanwhile,the existing AFS instruments all use a non-dispersive detection method,which can not analyze and eliminate the spectral interference.Traditional dispersive detection methods,such as the filter and rotary grating method and CCD spectrometer,are unable to meet the requirement of AFS for fast detection and high sensitivity.The spectral analysis method based on digital micromirror device（DMD）presents a new possibility for the dispersive detection of AFS.Due to the fact that the micromirrors of the DMD can reverse through electric control in a microsecond level,the weak signal of the atomic fluorescence is realized in a short time by regulating the rotation of several or lines of micromirrors,choosing the wavelength and spectral information of atomic fluorescence,and ultimately converging to the PMT through the reflector.In this essay,an atomic fluorescence dispersion detection technology based on DMD is proposed,the high ultraviolet transmittance DMD is used as a spatial light modulator of an UV digital micromirror spectromter to realize the detection and analysis of atomic fluorescence dispersion and the research of spectral interference.The main contents are as follows:（1）Research on DMD Control Technology for AFSThe control of micromirrors rotating state and timing is the key technology of UV digital micromirror spectromter,which is directly related to the atomic fluorescence wavelength position,fluorescence intensity and signal acquisition time.According to the main characteristics of atomic fluorescence and the specific requirements of dispersion detection technology,a special control method of DMD is proposed for the dispersive detection of AFS.The full-spectrum,single-peak,multi-peak and other scanning modes of atomic fluorescence are realized by setting parameters,such as the start rotating line,the number of rotating lines,the simultaneous number of rotating lines,and the integration time of the DMD in a complete detection process.In addition,Due to the high cost of existing commercial DMD control platforms,poor scalability and compatibility.A special DMD controller was designed and developed.Which used the AppsFPGA,DDC4100 and DAD2000as the controlling core,and the Global Reset mode refresh mode was used as the refreshing method,which is able to regulate the rotating state of DMD scanning mode and sequence control is developed in this paper.The rotating rate can reach 10000frames/second.In addition,the controller of DMD also adds a high-speed acquisition interface based on high-speed Low voltage differential signaling（LVDS）,TCP/IP and CAN bus interfaces.It effectively improves the efficiency and stability of atomic fluorescence signal transmission,which provided convenience for high-speed data transmission of dispersion detection signals and laid a technical foundation for the development of UV digital micromirror spectromter.（2）Design and implementation of UV digital micromirror spectromterTo further improve the detection sensitivity of DMD for short-wave fluorescence signals,a high UV transmittance DMD is adopted as the spatial light modulator.According to the design parameters of optical system and components,the adjustment mechanism of slit,flat field concave grating,DMD,mirror and solar blind photomultiplier tube（PMT）was developed.In order to further improve the dispersive acquisition and anti-interference ability of the atomic fluorescence signal,a dispersion signal collector suitable for AFS is developed,and the atomic fluorescence dispersion signal acquisition function of the UV digital micromirror spectromter realized finally.According to the test results,the spectrometer can meet the high transmittance requirements of fluorescence signals ranging from 180 nm to 280 nm,and can realize multiple scanning modes based on DMD,the spectral resolution is higher than 2 nm,and the wavelength error is less than±0.5 nm,which could meet system design specifications.As the core component of DMD-based atomic fluorescence dispersion detection technology,the UV digital micromirror spectromter lays a foundation for the detection and analysis of the characteristic spectrum of the element to be tested.（3）The Development and Detection Analysis of DMD-AFS Experimental SystemIn this paper,the controlling system’s development and software were designed and integrated with the UV digital micromirror spectromter,sampling system,gas path system,atomizer and other controlling systems.The characteristic curves of the four conventional detection elements of arsenic（As）,antimony（Sb）,bismuth（Bi）and mercury（Hg）were classified and the scattering interference was analyzed.Meanwhile,the detection capability of the atomic fluorescence dispersion detection capability of the UV digital micromirror spectromter was verified:the detection limit（LOD）of As obtained at 234.9 nm ranging from 2 to 50μg/L was 0.23μg/L,and the relative coefficient R=0.9988;the LOD of Sb at 231.2 nm was 0.34μg/L,and the relative coefficient R=0.9989;the LOD of Bi obtained at 223.1 nm was 0.21μg/L,and the relative coefficient R=0.9987;the LOD of Hg obtained at 253.7 nm was 0.12μg/L,and the relative coefficient R=0.9982.The RSD were 1.95%（20μg/L,As,n=9）and 2.86%（20μg/L,Sb,n=9）,2.77%（20μg/L,Bi,n=9）and 2.15%（20μg/L,Hg,n=9）,respectively.All the detection results met the requirements of atomic fluorescence analysis.（4）Research on Spectral Interference of Light Source for Simultaneous Detection of Se and PbDuring the analysis and test of emission lines of the elements of HCL（such as As,Sb and Bi）by UV digital micromirror spectromter,it was found that an obvious spectral interference of lead（Pb）in selenium（Se）element HCL.The main reason is the impure of HCL cathode,while the influence of light source interference on the detection results cannot be directly solved by non-dispersive detection.More importantly,if there is no dispersive detection device,it would introduce influence in the results of Se detection channel.The application of simultaneous determination of Se and Pb was limited.In this paper,the chemical generation system with K₃Fe（CN）₆-KBH₄-HCl for simultaneous determination of Se and Pb was optimized,and results indicated that the LOD of Se at 203.9 nm was 0.89μg/L in the range of 2to 200μg/L,and the standard curve R=0.9975;the LOD of Pb at 283.3 nm was 0.42μg/L,and the standard curve R=0.9987.The RSD of the method was（20μg/L,Se,n=9）and 1.66%（20μg/L,Pb,n=9）,respectively.Meanwhile,the results of simultaneous determination of Se and Pb with national standard water samples（GSBZ50031-94 and GSB07-1183-2000）and multi-element standard samples（GBW（E）080669）using UV digital micromirror spectromter and non-dispersive AFS instrument were compared.The detection results show that the spectral interference problem of Pb exists in the detection result of Se by non-dispersion method.The standard curve and detection process of sample analysis are affected;while the atomic fluorescence dispersion detection technology based on DMD can solve the influence of Se HCL spectral interference problem on the detection results effectively.