紫外脉冲激光作用下土壤中多环芳烃的分解与荧光发射特性（英文）

多环芳烃是具有致突变、致癌和致畸作用的一类持久性有机污染物,广泛分布在大气、水、土壤等不同环境介质中。多环芳烃一旦进入土壤便会长期存留于其中,土壤成为环境中多环芳烃的重要储藏库和最终归宿。土壤中的多环芳烃可以通过多种途径进入人体,对人类健康造成威胁。因此,对土壤中多环芳烃的监测十分必要。当前,传统的土壤多环芳烃检测方法过程繁琐、费时,不利于污染场地多环芳烃的大范围快速检测,而基于激光诱导荧光光谱技术的土壤多环芳烃检测法能够快速识别、检测土壤中的有机污染物。多环芳烃类物质具有易挥发,可被紫外光降解等特性,实验中紫外激光能量的选择至关重要,本文利用实验室搭建的266 nm激光诱导荧光系统,以蒽、芘、菲为研究对象,探究不同激光能量下多环芳烃分解和荧光光谱的变化特性。结果表明,当激光的能量密度变化时,荧光中心峰位置未发生偏移,但蒽、芘、菲三种多环芳烃荧光峰处最大强度的相对标准偏差随激光能量密度的下降呈现出先下降后上升的趋势:当能量密度为8.54 mJ·cm~(-2)时,三种物质在10次光谱测量结果的相对标准偏差均为最大,蒽、芘、菲三种物质的荧光峰强度相对标准偏差分别在1.72, 1.00和1.47 mJ·cm~(-2)的能量密度下达到最小值;蒽、芘、菲在100 s时,分解率分别达到59.3%, 69.8%和63.6%,在较高的能量下,蒽、芘、菲三种物质发生了较快的分解,芘相比于其他两种多环芳烃类物质更易发生光降解和热分解等作用,荧光峰强度相对标准偏差也高于蒽与菲;蒽在激光能量密度为1.72 mJ·cm~(-2)时, 10 s时的分解率已经接近于0, 100 s时分解率仅为12.8%,荧光峰强度相对标准偏差达到最低,当激光能量密度降至0.88 mJ·cm~(-2)时,蒽在100 s内的分解几乎可以忽略不计;对于芘而言,当激光能量密度降至1.00 mJ·cm~(-2)以下时,分解作用基本趋于一致, 100 s时分解率在47.3%～47.4%;而对于菲而言,当激光的能量密度低于1.47 mJ·cm~(-2)后,分解率不再随激光能量密度的降低而明显下降,在100 s时的分解率在36.8%～38.6%;在低能量密度土壤中芘与菲下仍发生分解作用。     

基于二维相关荧光谱土壤中PAHs检测方法研究

传统荧光光谱技术已被用于土壤中多环芳烃(PAHs)的检测,但由于土壤体系的复杂性、PAHs污染物的多样化和微量化,传统的荧光光谱技术无法有效提取土壤中PAHs的特征信息。为了解决上述问题,提出并建立一种基于二维相关荧光谱土壤中多环芳烃的检测方法。以土壤中典型的多环芳烃蒽和菲为研究对象,配置38个蒽菲混合标准土壤样品(蒽和菲的浓度范围均为0.000 5～0.01 g·g-1),在激发波长265～340 nm,发射波长350～500 nm范围内采集了所有样品的三维荧光谱。以激发波长为外扰,对外扰变化的动态一维荧光谱进行相关计算,得到每一样品的同步二维相关荧光谱。研究了浓度均为0.005 g·g-1蒽菲混合土壤样品的三维荧光谱和同步二维相关荧光谱特性,在同步谱主对角线398,419,444和484 nm处存在自相关峰,其中,398和484 nm荧光峰来自土壤中的菲,419和444 nm荧光峰来自土壤中的蒽;在主对角线外侧,蒽和菲两组荧光峰之间存在负的交叉峰,进一步验证了其来源不同;同时,在(408,434) nm和(434,467) nm处出现交叉峰,其中408和434 nm荧光峰来自土壤中的菲,467 nm荧光峰来自土壤中的蒽。指出与三维荧光谱表征的信息相比,二维相关荧光谱不仅能提取更多的特征信息(408和467 nm的特征峰在三维荧光谱中未被表征),而且还能提供荧光峰之间的相互关系,对其来源进行有效解析。在上述研究二维相关荧光谱特性的基础上,基于同步相关谱矩阵(38×151×151)建立了定量分析土壤中蒽和菲污染物浓度的多维偏最小二乘(N-PLS)模型,对蒽的校正和预测相关系数分别为0.986和0.985,校正均方根误差(RMSEC)和预测均方根误差(RMSEP)分别为4.33×10-4和5.55×10-4 g·g-1;对菲的校正和预测相关系数分别为0.981和0.984,RMSEC和RMSEP分别为5.20×10-4和4.80×10-4 g·g-1。为了比较,基于三维荧光光谱矩阵(38×16×151)建立了定量了分析土壤中蒽和菲的N-PLS模型,对蒽的校正和预测相关系数分别为0.981和0.972,RMSEC和RMSEP分别为5.09×10-4和6.74×10-4 g·g-1;对菲的校正和预测相关系数分别为0.957和0.956,RMSEC和RMSEP分别为7.36×10-4和7.77×10-4 g·g-1。指出,对于土壤中的蒽和菲检测,基于二维相关荧光谱的N-PLS模型的相关系数r,RMSEC和RMSEP都要优于基于三维荧光谱的N-PLS模型。研究结果表明：所提出和建立的方法-二维相关荧光谱直接检测土壤中PAHs污染物不仅可行,而且能提供更好的分析结果。该研究为激光诱导荧光结合相关谱技术现场直接检测土壤中多环芳烃污染物提供了理论和实验基础,具有较好的应用前景。     

355 nm纳秒激光作用下荧蒽的时间分辨荧光光谱特征

多环芳烃由于具有三致(致癌、致畸、致突变)特性,其在环境中的检测受到人们广泛关注。利用时间分辨光谱技术,研究了荧蒽乙醇溶液的荧光光谱随延时时间和门宽改变的特性。研究了不同浓度荧蒽的时间分辨荧光光谱特性,以原始浓度的荧蒽为初始溶液,通过逐级稀释的方式,最终将原始溶液稀释16倍,拟合了不同稀释倍数下的荧蒽荧光强度衰减随延时时间变化的动力学曲线,得到了不同浓度荧蒽的拟合荧光寿命。研究结果表明,荧蒽的荧光光谱特性与光谱仪探测器延时时间和门宽宽度密切相关。固定延时时间,随着光谱仪门宽宽度的变化,荧蒽的荧光强度随着门宽的增大而逐渐增强。固定门宽,改变延时时间的过程中,荧蒽的荧光强度随延时时间呈现先增大,后减小的趋势。荧蒽的荧光强度随延时时间的衰减过程符合指数衰减过程,将荧蒽乙醇溶液进行逐级稀释,荧蒽荧光强度与延时时间的衰减进行指数拟合后,得到不同稀释倍数的荧蒽乙醇溶液的衰减动力学参数,随着稀释倍数的增大,拟合得到的荧蒽荧光寿命增大。多环芳烃时间分辨光谱特征的研究,可以为环境中多环芳烃的检测提供技术基础,由于不同荧光物质具有特征的荧光寿命,因此,可以利用多环芳烃与环境中其他荧光物质的不同荧光寿命特性,准确识别环境中的多环芳烃污染物。     

菲及腐殖酸混合液荧光法定量分析研究

多环芳烃作为普遍关注的优先监测污染物,在水环境中其含量很低,易受共存物腐殖酸的干扰。由于多环芳烃与腐殖酸的光谱重叠严重,很难用常规方法快速的定量检测。菲(PHE)作为多环芳烃中的模式化合物,对菲和腐殖酸(HA)的荧光光谱特性进行了研究,分析了腐殖酸共存下对菲定量检测的影响。采用平行因子算法分析混合液的三维荧光光谱,在激发波长为240～360 nm(5 nm为间隔)、发射波长为 260～575 nm(5 nm为间隔)下对该体系进行了分辨研究,并对菲和腐殖酸进行荧光光谱测量。实验结果表明,此方法可用于有干扰共存下多环芳烃化合物的直接快速定量检测。     

多环芳烃时间分辨荧光光谱特性研究

利用时间分辨荧光光谱技术,研究了菲、荧蒽、芴、蒽、芘等五种多环芳烃的荧光时间分辨发射光谱特性。以289 nm受激拉曼光作为激发光源,研究了289 nm激发光作用下五种多环芳烃的延时特性和门宽特性。并以多环芳烃随延时时间的荧光峰强度衰减关系曲线,得到菲、荧蒽、芴、芘的荧光寿命分别为37.0, 32.7, 10.9, 147.0 ns。不同荧光物质具有特定的荧光光谱特性,多环芳烃时间分辨荧光光谱特性的研究可以为复杂水体中不同种类多环芳烃的诊断提供依据。     

土壤湿度对多环芳烃荧光特性的影响

荧光光谱技术已被用于检测土壤中多环芳烃。但土壤湿度对多环芳烃的荧光强度产生很强的干扰,这对于荧光光谱技术的土壤多环芳烃快速实时检测技术的发展无疑是一种挑战。为了研究土壤湿度对多环芳烃荧光特性的影响,分别配置了八个不同湿度(含水量5%～40%,间隔5%)的菲土壤样品。采用美国PE公司的LS-55荧光分光光度计对不同湿度含量的菲土壤样品进行了检测,得到不同湿度含量下的一维动态荧光谱,以土壤湿度为外扰,研究了其二维相关荧光光谱特性,发现菲土在386,408和432 nm处荧光强度随着土壤中湿度的增大而增强,而333 nm处瑞利散射光强度却在减小,提出通过建立菲荧光强度、瑞利散射光强度与土壤湿度之间的关系,有可能实现土壤湿度对菲荧光强度影响的校正。同时,也研究了土壤湿度对定量分析菲浓度标准曲线的影响,指出土壤湿度极大影响着精准定量分析菲浓度标准曲线的建立。     

蒽芘混合溶液二维相关荧光谱定量分析研究

为了实现对水中多环芳烃的快速、准确检测,基于同步二维相关荧光谱中自相关峰强度与水中多环芳烃浓度之间的关系实现其定量分析。配置蒽芘混合水溶液19个(芘浓度范围为1×10-6~1×10-4 g·L-1)。采集了所有样品在320nm波长激发下的荧光谱。在研究单组分蒽、芘水溶液一维荧光特性和蒽芘混合水溶液二维相关荧光谱特性的基础上,建立了同步二维相关荧光谱主对角线394nm处自相关峰强度与水溶液中芘浓度之间的数学关系:F=3 003.56-2843.86c+1 436.92 C2,其复相关系数为0.999。该研究为快速检测水中多环芳烃污染物提供了一种技术手段,同时该方法也可推广到环境中其他污染物的检测中。     

持久性有机污染物荧光光谱检测技术研究进展

持久性有机污染物(POPs)种类繁多,分布范围广,对生态环境和人体健康的危害性已引起广泛关注。环境中POPs的监测分析对于污染评价、污染物修复和生产管理等有着重要的意义。基于色谱分离技术的传统检测方法具有检测限低、灵敏度高、稳定性好等优点,但也普遍存在周期长、消耗高、过程繁琐等弊端。荧光光谱分析法具有样品使用少、预处理简单、快速、无损等优势而发展迅速,国内外学者开展了大量研究工作,形成了比较完善的方法体系。介绍了我国现行环境标准中POPs的控制浓度和检测方法,综述了近年来直接/间接荧光、同步荧光扫描联用技术、化学多维校正-三维荧光光谱法和激光诱导荧光技术对POPs检测方面的应用和研究进展,重点包括土壤及水体中多环芳烃、多氯联苯、有机氯农药等,着重介绍了最新研究成果,总结了技术各自适用的情况,分析了不足与待完善之处,并针对POPs的直接荧光光谱检测技术今后的研究与应用方向提出了展望,为进一步发展POPs的荧光光谱快速检测技术提供参考。     

土壤有机污染物激光诱导荧光光谱检测方法研究进展

土壤有机物污染源广、危害程度高、监测手段有限,是继水污染、大气污染又一个引起全球关注的环境问题。土壤有机污染快速在线检测分析对农业生产、土壤调查、土质修复有着重要的意义。激光诱导荧光(LIF)光谱技术是一种基于光致发光的物质成分和含量分析技术,具有样品使用量少、预处理过程简单、检测速度快等特点,在环境科学、生物分析、生命科学等众多领域有广泛应用。国内外研究人员展开大量研究工作,已形成较完善的方法体系及技术设备。文章介绍了LIF测量系统的组成结构和工作原理,综述了现阶段LIF技术在土壤有机污染物检测研究进展,重点包括土壤中油类污染物、多环芳烃污染物、有机农药污染物的识别及定量分析方法等,以及仪器开发过程中涉及的相关问题,给出了LIF技术在土壤有机污染物检测方面的发展趋势,为进一步发展基于LIF技术的土壤有机污染物现场快速检测仪器提供参考。     

不同土壤物理性质下石油类污染物LIF发射特征研究

利用激光诱导荧光技术可对土壤中石油类污染物快速检测,不同土壤物理性质下,污染物荧光发射特征具有一定差异。为实现外场检测时快速制备合适的土壤样品,实验研究了土壤疏松度、颗粒度、湿度与土壤中石油类污染物荧光强度及光谱稳定性之间的关系。压片机压强大于2 MPa时土壤样品荧光光谱的稳定性较好,九种不同疏松度的土壤样品荧光强度的相对标准偏差为3.51%。不同粒径的机油土壤样品荧光强度差异较小,其中100目土壤样品的荧光光谱RSD值为2.25%。结果表明,土壤样品表面呈平整洁净时,所得样品荧光光谱的稳定性较好,土壤疏松度和颗粒度对荧光光谱的影响较小。湿度对土壤样品荧光发射的影响较大,当土壤湿度低于10%,荧光强度变化较小;湿度范围大于10%时,荧光强度变化较大。为利用LIF技术对外场土壤中石油类污染物检测时,快速有效制备土壤样品及准确测量提供参考。     

Quantitative measurement of hydroxyl radical(OH) concentration in premixed flat flame by combining laser-induced fluorescence and direct absorption spectroscopy

An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence(LIF)methods is developed to quantitatively measure the concentrations of hydroxyl in CH_4/air flat laminar flame. In our approach, particular attention is paid to the linear laser-induced fluorescence and absorption processes, and experimental details as well. Through measuring the temperature, LIF signal distribution and integrated absorption, spatially absolute OH concentrations profiles are successfully resolved. These experimental results are then compared with the numerical simulation. It is proved that the good quality of the results implies that this method is suitable for calibrating the OH-PLIF measurement in a practical combustor.     

Visualization of soot formation from evaporating fuel films by laser-induced fluorescence and incandescence

Late-evaporating liquid fuel wall-films are considered a major source of soot in spark-ignition direct-injection (SIDI) engines. In this study, a direct-injection model experiment was developed to visualize soot formation in the vicinity of evaporating fuel films. Isooctane is injected by a multi-hole injector into the optically accessible part of a constant-flow facility at atmospheric pressure. Some of the liquid fuel impinges on the quartz-glass windows and forms fuel films. After spark ignition, a turbulent flame front propagates through the chamber, and subsequently sooting combustion is detected near the fuel films. Overlapping laser light sheets at 532 and 1064 nm excite laser-induced fluorescence (LIF) of polycyclic aromatic hydrocarbons (PAH) -potential soot precursors- and laser-induced incandescence (LII) of soot, respectively. The 532 nm light sheet has low fluence to avoid the excitation of LII. The LII and LIF signals are detected simultaneously and spectrally separated on two cameras. In complementary line-of-sight imaging, the fuel spray, chemiluminescence, and soot incandescence are captured with a high-speed color camera. In separate experiments, toluene is added to the isooctane as a fluorescent tracer and excited by pulsed 266 nm flood illumination. From images of the LIF signal, the fuel-films’ thickness and mass evolutions are evaluated. The films survive the entire combustion event. PAH LIF is found in close vicinity of the evaporating fuel films. Soot is found spatially separated from, but adjacent to the PAH, both with high spatial intermittency. Average images additionally indicate that soot is formed with a much higher spatial intermittency than PAH. Images from the color camera show soot incandescence earlier and in a similar region compared to soot LII. Chemiluminescence downstream of the soot-forming region is thought to indicate the subsequent oxidation of fuel, soot, and PAH.     

Xe1v离子激光感生荧光用于医用X射线ZnCdS:Ag荧光屏的性能研究

本文叙述了利用同轴结构Xe1v离子激光器的UVλ=365nm激光作为激发光源的激光感生荧光(LIF)实验系统,对医用X射线ZnCdS:Ag荧光屏的发光性能进行了研究.LIF方法能方便而高灵敏地同时测得荧光光谱与寿命,和传统的紫外灯激发及X射线激发的结果一致,可以完全避免X射线对人体的有害辐射.     

Measurement of chlorophyll in water based on laser-induced fluorescence spectroscopy: Using spiral-wound unclad optical fiber system and partial least squares regression

The feasibility of laser-induced fluorescence (LIF) method for chlorophyll concentration determination in water was investigated in this study. The chlorophyll fluorescence spectra were received by a spiral-wound unclad optical fiber system. Baseline and smoothing correction methods were studied. Statistical equations were established between reference data and fluorescence spectra by linear regression and partial least squares (PLSs) regression. The PLS regression outperformed linear regression by higher correlation coefficient of 0.9996063 and root mean square error value of 0.0221807. Based on the results, it was concluded that laser-induced fluorescence method with a spiral-wound unclad optical fiber system was suitable for chlorophyll concentration determination in water, and PLS regression was a reliable method for fluorescence spectra analysis.     

Spectroscopic,calibration and RET issues for linear laser-induced fluorescence measurements of nitric oxide in high-pressure diffusion flames

Two different strategies are compared for linear laser-induced fluorescence (LIF) measurements of nitric oxide concentration ([NO]) in counter-flow diffusion flames at high pressures via the A-X(0,0) system. Excitation of NO via a rovibronic transition at 226.03 nm is found to be slightly better compared to a previously utilized excitation wavelength of 225.58 nm. An indirect approach based on the computed spectral overlap fraction is verified and applied to calibrate [NO] measurements in counter-flow diffusion flames at high pressures. A five-level model for NO molecular dynamics is presented and utilized to investigate the effects of rotational energy transfer (RET) on linear LIF measurements of [NO] at pressures up to 15 atm. The results indicate that rotational relaxation effects are essentially negligible under high-pressure conditions at low laser fluences, and thus they need not be accounted for when measuring [NO] using linear LIF. The calibration technique is validated by direct comparisons to [NO] measurements made at pressures up to 5 atm via another calibration method, based on doping NO in counter-flow premixed flames at the same pressure. Using this calibration technique, LIF measurements of [NO] are obtained in a series of counter-flow diffusion flames at pressures up to 15 atm. These measurements are found to be in excellent agreement with previously reported measurements of [NO] in similar flames. PACS 07.35.+k; 33.20.Sn; 42.62.Fi     

Measurement of Electron Densities and Temperatures in the Plasma Boundary Combining Neutral Beam Probes and Laser-Induced Fluorescence

A new diagnostic method using both techniques of neutral beam probing and laser-induced fluorescence (LIF) is proposed to measure electron density (1011-1013 cm-3) and electron temperature (1-100 eV) of a boundary layer plasma in devices like tokamaks. The local electron density can be obtained by measuring the photon flux of the resonance line produced by electron impact excitation of an injected neutral Li-beam which is produced by laser-induced evaporation (LIE). The density of the neutral Li-beam which is necessary for the determination of the electron density is measured by LIF. The local electron temperature can be obtained by determining the attenuation of two neutral beams (Li, and Al or Ti) produced by LIE, of which the measurements are carried out by means of LIF. The applicability of this method to the TEXTOR tokamak is discussed in detail.     

Numerical analysis of quantitative measurement of hydroxyl radical concentration using laser-induced fluorescence in flame

The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF(laserinduced fluorescence) in flame.The detailed physical models of spectral absorption lineshape broadening,collisional transition and quenching at elevated pressure are built.The fine energy level structure of the OH molecule is illustrated to understand the process with laser-induced fluorescence emission and others in the case without radiation,which include collisional quenching,rotational energy transfer(RET),and vibrational energy transfer(VET).Based on these,some numerical results are achieved by simulations in order to evaluate the fluorescence yield at elevated pressure.These results are useful for understanding the real physical processes in OH-LIF technique and finding a way to calibrate the signal for quantitative measurement of OH concentration in a practical combustor.     

激光诱导水体频率上转换的荧光发射

用Nd：YAG的二倍频532 nm激光对几种不同水体的激光诱导荧光(LIF)光谱进行了测量,利用特征光谱荧光标记(SFS)技术指认出水体中溶解有机物(DOM)、叶绿素a(Chl a)及类胡萝卜素等物质的特征光谱带。指出在455 nm波长处具有较大强度的荧光峰是附属色素中抗氧化作用的类胡萝卜素(PPC)的贡献。提出了激光诱导PPC荧光频率上转换发射的动力学模型。     

Optical pumping with laser-induced-fluorescence

We describe a new procedure for optical pumping that is based on laser-induced fluorescence (LIF). The procedure is demonstrated by optically exciting a sample of Rb⁸⁵ atoms, which then creates a population imbalance between the ground state hyperfine levels of Rb⁸⁷ by “LIF depopulation pumping”. Though optical pumping with this technique increases the intensity dependent light-shift coefficient (i.e., ac Stark shift) of the Rb⁸⁷ 0-0 hyperfine transition, it reduces the frequency dependent light-shift coefficient by at least an order of magnitude. Since the stabilization of the diode laser wavelength is a significant challenge in the development of laser-pumped gas-cell atomic clocks, it is anticipated that optical pumping with LIF will be of benefit to atomic clock technology.