Evaluation of open-air type electrolyte-as-cathode glow discharge-atomic emission spectrometry for determination of trace heavy metals in liquid samples

Electrolyte-as-cathode glow discharge-atomic emission spectrometry (ELCAD-AES) has been used for on-line determination of trace heavy metals in tap and drinking waters and fresh milk. The fundamental characteristics are: pH of electrolytes; discharge current; discharge gap shown influenced the plasma stability; and the intensity of emission lines emitted from different elements of solution. A stable discharge plasma which significantly improved the sensitivity was achieved when approximately 1.6 kV, several tens of milli-amperes current and a few millimeters discharge gap between the Pt rod anode and acidified electrolyte cathode in atmospheric air pressure were applied. Although the OH band dominates the solution spectra between wavelengths of 300 and 700 nm, nine elements including Pb and Cu have been determined from freshly collected unspiked tap and drinking waters and fresh milk. The limits of detection (LOD) of Hg, Pb, Cd, Cu, Na and K were obtained as 0.001–0.08 mg/l. The open-air ELCAD has used for the first time for Hg, Cd, Na and K detection and an improved LOD of Pb was found compared to reported values. The LOD values of Hg, Pb, Cd and Cu improved by more than one order of magnitude compared to closed-type ECLAD.     

Detection of atmospheric nitrogen dioxide using a miniaturised fibre-optic spectroscopy system and the ambient sunlight

A miniaturised fibre-optic spectrometer based system is presented for direct detection of one of the major atmospheric pollutants, nitrogen dioxide, by absorption spectroscopy using the ambient sunlight as light source. The detection system consists of a 10 cm collimator assembly, a fibre-optic cable and a portable diode-array spectrometer. The absorbance spectrum of the open-path is calculated using a reference spectrum recorded when the nitrogen dioxide (NO2) concentration in the atmosphere is low. The relative concentration of the pollutant is calculated normalising the detected spectra and subtracting the background broadband spectrum from the specific NO2 absorbance features, since the broadband spectrum changes according to atmospheric conditions and solar intensity. Wavelengths between 400 and 500 nm are used in order to maximise sensitivity and to avoid interference from other species. Calibration is carried out using Tedlar sample bags of known concentration of the pollutant. A commercial differential optical absorption spectroscopy (DOAS) system is used as a reference standard detection system to compare the results with the new system. Results show that detection of NO2 at typical urban atmospheric levels has been achieved using an inexpensive field based fibre-optic spectrometer and a readily available, easy to align, light source. In addition the new system can be used to get a semi-quantitative estimation of the nitrogen dioxide concentration within errors of 20%. While keeping the typical benefits of open-path techniques, the new system has important advantages over them such as cost, simplicity and portability.     

Laser-induced breakdown spectroscopy at a water/gas interface: A study of bath gas-dependent molecular species

Single-pulse laser-induced breakdown spectroscopy has been performed on the surface of a bulk water sample in an air, argon, and nitrogen gas environment to investigate emissions from hydrogen-containing molecules. A microplasma was formed at the gas/liquid interface by focusing a Nd:YAG laser beam operating at 1064 nm onto the surface of an ultra-pure water sample. A broadband Echelle spectrometer with a time-gated intensified charge-coupled device was used to analyze the plasma at various delay times (1.0–40.0 μs) and for incident laser pulse energies ranging from 20–200 mJ. In this configuration, the dominant atomic spectral features at short delay times are the hydrogen H-alpha and H-beta emission lines at 656 and 486 nm, respectively, as well as emissions from atomic oxygen liberated from the water and air and nitrogen emission lines from the air bath gas. For delay times exceeding approximately 8 μs the emission from molecular species (particularly OH and NH) created after the ablation process dominates the spectrum. Molecular emissions are found to be much less sensitive to variations in pulse energy and exhibit a temporal decay an order of magnitude slower than the atomic emission. The dependence of both atomic hydrogen and OH emission on the bath gas above the surface of the water was studied by performing the experiment at standard pressure in an atmospheric purge box. Electron densities calculated from the Stark broadening of the H-beta and H-gamma lines and plasma excitation temperatures calculated from the ratio of H-beta to H-gamma emission were measured for ablation in the three bath gases.     

Multi-element selective radio frequency plasma detector for capillary gas chromatography

A radio frequency plasma detector for element specific detection in gas chromatography is described. The detector is comprised of a radio frequency (300 kHz) discharge between electrodes in helium, and utilizes a low-resolution emission spectrometer to monitor selected spectral emission lines produced when the helium discharge decomposes and excites the atomic constituents in the chromatographic column effluent. The spectrometer is tuned to an atomic emission line in the near-infrared portion of the spectrum, and the emission intensity from the discharge region of a selected line is used to monitor the concentration of the element producing that line. Acceptable detector sensitivity was achieved by the use of a high-throughput optical system. Selectivity was achieved by a combination of correct line selection, plasma and carrier gas purification, and plasma gas doping.     

捕汞金管富集-冷原子荧光光谱法测定空调颗粒物中的汞

对国产原子荧光仪进样系统进行改造,采用在线热解样品捕汞金管富集冷原子荧光法测定空调颗粒物中的汞。试样热解温度为700～750℃,捕汞金管释放温度为550℃,试样载气流速为120 mL/min。方法检出限为1 pg,汞含量在0～1.5 ng范围内呈线性关系,测定标准偏差为2.23%。用国家土壤标准GBW07410中的汞验证了方法的准确性,并对某医院空调颗粒物中汞含量进行了分析。     

小型化尖端放电原子发射光谱检测微量碘

采用尖端放电激发源和电荷耦合检测器(CCD)组装了小型化原子发射光谱仪,并将其用于检测微量碘。在酸性条件下以H_2O_2氧化碘离子产生碘蒸气,并由氩气载入尖端放电光源中,激发后产生碘原子发射光谱信号,用CCD光谱仪在206 nm处检测。经优化得到的最佳实验条件为:H_2O_2浓度为2%,尖端放电电压为90 V,载气流速为450 m L·min~(-1);检测信号稳定,相对标准偏差为2.5%,标准曲线的线性范围为0.5~500 mg·L~(-1),线性相关系数大于0.99,碘的检出限低至0.1 mg·L~(-1)。该小型化原子发射光谱仪具有简单、高灵敏度、便携式适用于现场分析等优点。     

用低功率微波热雾化器与十字交叉气动雾化器作为ICP-AES进样装置的比较

在 ICP- AES中 ,最常用来引入液体样品的方法是雾化法 .因此 ,雾化器雾化效率的高低直接影响到 ICP- AES的分析性能 [1,2 ] .目前 ,在 ICP- AES中最常用的雾化器是气动雾化器 (PN) .它的优点是简单、稳定性好 ;缺点是产生的雾滴的直径范围很宽 (一般为 1～ 50 μm) ,进样效率低 ,一般仅为 1 %～3% [3] .热雾化器是近年发展起来的一种雾化效率较高的雾化法 ,已被越来越多地用于 ICP- AES[4～ 7] .热雾化法的雾化原理与同轴气动雾化法类似 ,不同之处在于 :对于热雾化法来说 ,(1 )雾化所需的气体来自于液体样品本身而不是外加的惰性…     

Elemental analysis of steel scrap metals and minerals by laser-induced breakdown spectroscopy

The atomic emission of laser-induced plasma on steel samples has been studied for quantitative elemental analysis. The plasma has been created with 8 ns wide pulses using the second-harmonic from a Q-switched Nd:YAG laser, in air at atmospheric pressure. The plasma emission is detected with temporal resolution, using an Echelle spectrometer of wide spectral range (300–900 nm) combined with an intensified charge coupled device camera. A plasma temperature of 7800 ± 400 K is determined using the Boltzmann plot method, from spectra obtained under optimized experimental conditions.As an example of an industrial application the concentration of copper in scrap metals is studied, which is an important factor to determine the quality of the samples to recycle. Cu concentrations down to 200 ppm can be detected. Another application of the laser-induced plasma spectroscopy method is the measurement of the nickel and copper concentrations in an iron-containing sample of reduced magma from the 1870s expedition to western Greenland by Adolf Erik Nordenskiöld. Different spectral lines of nickel are used for calibration, and their results are compared.     

液相辉光放电原子发射光谱法测定溶液中Cd的方法研究

通过改进放电装置,建立了一种新的液相辉光放电原子发射光谱(LGD-AES)测量溶液中Cd元素的方法。探索了放电电压和Cd浓度对放电稳定性、光谱信号强度、测定灵敏度和检出限的影响,并将测试结果与电解液阴极放电-原子发射光谱(ELCAD-AES)的分析结果进行比较。结果表明,当放电电压从600V升至720 V时,电子温度从2 000 K升至3 300 K,电子密度从2.47×10~(16)cm~(-3)降至1.77×10~(16)cm~(-3),Cd的发射光谱强度增强,灵敏度升高,检出限为1.22~2.95 mg/L。LGD-AES技术检测水中金属离子具有放电设备小型、能量消耗低、放电稳定性高、背景光谱干扰小和灵敏度高等优点。     

Investigation of a novel hollow cathode configuration for Grimm-type glow discharge emission

A hollow cathode configuration was designed for a Grimm-type glow discharge atomic emission spectrometer (GD-AES). The operating conditions including the hollow cathode dimension, applied pulsed voltage and argon pressure, were optimized. The 10-μs pulses at 1.8 kV in a 3-torr discharge worked best. A pulsed hollow cathode Grimm discharge (HCG) offers several advantages: efficient excitation and ionization; high sensitivity; temporal spectral resolution; and rapid sample interchange. The capability of this source for the determination of elemental composition in metals, alloys and in solution residues is investigated. Samples used in this study included copper and steel standards.     

Liquid analysis dielectric capillary barrier discharge

In this study a simple micro-tube-based system for analysis of metal-containing liquids is introduced and its analytical performance is evaluated. It is based on a miniaturised dielectric barrier discharge driven at atmospheric pressure. The emission lines of various elements are observed. The system is developed for quantitative measurements and the limits of detection are determined. Because of very low flow rates of just μL min⁻¹ the approach requires extremely low sample volumes.     

Sliding spark spectroscopy

Summary A new analytical radiation source combined with fiber optics linked to a diode array detection device with modified software is described. The direct-reading spectrometer simultaneously covers the wavelength range 185–510 nm with a spectral resolution of <1.5 nm. Intense optical emission is observed when positionally stable high-current surface sparks supplied by a pulse-generator with definite discharge parameters (max. 800 Ampere/pulse) are sliding over compact non-conductive materials such as plastics, glasses, quartz filters or powder pellets. Substrate vaporization, ionization and excitation processes in the surface discharge plasma channel generate emission corresponding to neutral and ionic states. The spectra are essentially composed of lines emitted by the electrode material (e.g. copper, silver), from the substrate under investigation, radiation continuum as well as structured background from the surrounding air atmosphere. Due to the occurrence of emission lines of reactive fillers, inorganic pigments and stabilizers, a rapid multi-element screening method is demonstrated. A rapid identification system (mix-up test) of PVC or fire-retardant thermoplastics within one second has been realized from the atomic emission line intensity originating from the sputtered copper electrode material according to its increased volatility in the presence of chlorine (modified Beilstein test).Puls-Plasma-Technik GmbH, Dortmund     

低功率微波热雾化器与同轴气动雾化器作为电感耦合等离子体发射光谱法进样装置的比较

对用低功率微波热雾化器(MWTN)和同轴气动雾化器(PN)作为电感耦合等离子体发射光谱仪(ICP-AES)进样装置时，仪器的操作条件(样品提升速率(Q1)、载气流速(Fc))进行了选择和比较。在选定的条件下，比较了两种雾化器的分析性能。发现HCI的浓度对两种雾化器的影响不同，对于MWTN，Cr、Cd、Co、Mn和Ls，谱线的发射强度随HCl浓度的增加而略有增加；而对于PN，谱线的发射强度随HCl浓度的增加而略有降低；MWTN对于上述5种元素的检出限均优于PN，而精密度则不如后者。     

Spatially-resolved observation of glow discharge plasma for atomic emission spectrometry.

An imaging spectrograph equipped with a CCD detector was employed to measure two-dimensional emission images from a glow discharge plasma in atomic emission spectrometry. The emission images at Zn I 334.50 nm for a zinc sample and at Cu I 324.75 nm for a copper sample could be obtained. Their emission intensities were not uniform in the radial direction of the plasma region but became weaker at larger distance from the central zone. The two-dimensional distribution would result from a spatial variation in the excitation efficiency of the plasma and thus provide useful information for understanding the excitation processes occurring in the plasma.     

Analytical performance of high-voltage neon plasma in glow discharge optical emission spectrometry

In a high-voltage Ne glow discharge plasma (Ne-GDP), calibration factors as well as the limit of determination were compared between atomic resonance lines and singly-ionized lines of copper and aluminium in optical emission spectrometry. These elements have intense ionic lines which are excited by resonance charge-transfer collisions of Ne ions. The ionic lines gave better detection sensitivity in the Ne-GDP, whereas the atomic resonance lines were commonly employed as analytical lines in the other plasma sources such as Ar-GDP and ICP. The limit of determination was 1.3 × 10^–3 mass % for the Cu II 248.58 nm line and 1.0 × 10^–3 mass % Al for the Al II 358.66 nm line at a discharge parameter of 1.60 kV/36 mA.     

The effect of OH radicals on Cr–I spectral lines emitted by DC glow discharges

The intensity distribution of the Cr–I 428.97 nm resonant and 520.60 nm non-resonant lines was studied as a function of the distance from the anode in a low pressure DC-GD fitted with a Cr metal cathode and operated in various gas atmospheres, including helium (P = 4 mbar), ambient air and water vapor (P = 0.8 mbar). In the helium and ambient air atmospheres, the intensity peaks occurred in the near cathode region (cathode glow) in accordance with the literature. When operated in water vapor, however, the Cr–I 428.97 nm resonant line disappeared, whereas the intensity of the non-resonant 520.60 nm line was enhanced. This result may be attributed to resonant energy transfer collisions taking place between OH radicals excited to the first vibrational level and Cr^*₄₂₈ atoms excited to the z⁷P⁰ upper level of the 428.97 nm transition. The similar gas phase composition encountered with a DC electrolyte cathode atmospheric pressure glow discharge (ELCAD) and the Cr metal cathode GD operating under a low pressure of water vapor suggests that the zero intensity of the Cr resonance lines (428.97 nm, 360.53 nm) produced in the ELCAD may be attributed to similar energy transfer processes. Our results show that the intensity of the Cr–I 520.60 nm line can be used for analytical purposes in the ELCAD.     

Plasmas for lab-on-the-chip applications

Two small-size plasmas used as detectors of halogenated hydrocarbons and suitable for miniaturized instrumentation are discussed. A reduced pressure dielectric barrier discharge was integrated in a diode laser atomic absorption spectrometer and the already reported chlorine detection limits of 5 ppm (v/v) can be improved with one order of magnitude by spatially resolved measurements. A microstructured electrode discharge at atmospheric pressure was coupled with a miniaturized Échelle spectrometer and detection limits were found to be 20 ppb for chlorine as well as for fluorine.     

Analytical Potentials and Features of Atomic Emission Analysis Using Electron-Impact Excitation of Atoms in Helium under Atmospheric Pressure

A device is described for the atomic emission analysis of vaporous samples using electron-impact excitation in helium under atmospheric pressure. The device consists of a cathode atomizer with a test sample applied onto it and the anode located at 1–3 mm from the cathode. The electrons emitted by the cathode upon heating are accelerated by applying a constant voltage to the electrodes. The mechanism for the formation of a non-self-sustained gas discharge between the cathode and anode is considered and the properties of the discharge are compared to those of the known discharges used in atomic emission spectrometry. The influence of atomization temperature and helium pressure on the analytical and background signals was studied. It is shown that, under certain conditions, the analytical signal increases with helium pressure. The relative detection limits attained for a number of elements are from tenths to dozens of nanogram per liter; this is two or three orders of magnitude lower than those in inductively coupled plasma atomic emission spectrometry and of the same order of magnitude as detection limits in inductively coupled plasma mass spectrometry.     

Dielectric barrier discharge non-thermal micro-plasma for the excitation and emission spectrometric detection of ammonia

Dielectric-barrier discharge (DBD) in argon as a cold source is used for the excitation of gaseous inorganic small molecules at atmospheric pressure. By choosing ammonia as a model molecule, the excitation process and the characteristics of the emission spectra are investigated. The emission spectra are recorded by designing either an open-end or an enclosed DBD excitation/emission source. The enclosed excitation mode effectively eliminates the background emissions arising from the ambient air components, especially those from nitrogen. Two emission lines attributed to the excitation of ammonia, i.e., 326.2 and 336.5 nm, are clearly isolated from the background emission spectra of argon, providing the basis for quantitative analysis. A detection limit of 0.37 ppm is achieved within a linear range of 1.2-35 ppm by monitoring at 326.2 nm. In practice, gaseous samples containing ammonia collected in a public toilet are excited in an enclosed excitation source and the emission at 326.2 nm is monitored for quantitative analysis. An ammonia concentration of 2.4 ppm is derived in the original atmospheric sample, and a spiking recovery of 94.7% is achieved at a 10 ppm ammonia level. This study shows that DBD cold excitation in combination with optical emission spectrometry (OES) offers a promising approach for the detection of ammonia pollution.     

Research on Dispersive Detection Technology Based on Digital Micromirror Device by Atomic Fluorescence Spectrometry

A ultraviolet (UV) digital micromirror spectrometer using a digital micromirror device (DMD) as a spatial light modulator, a grating as a spectroscope and a photomultiplier tube (PMT) as a detector, was specially designed for dispersive hydride generation atomic fluorescence spectrometry (HG-AFS). To improve the detection ability of the UV digital micromirror spectrometer for weak fluorescence signals at 180–320 nm, a high UV transmittance DMD was used and the signal acquisition system was improved, and the control parameters of DMD and PMT negative high voltage were optimized. The feasibility of the spectrometer was demonstrated with standard sample analyzing of As, Sb, Bi, and Hg, the emission and atomic fluorescence spectra were obtained, and the scattering interference caused by the light source was discussed. The results showed that the UV digital micromirror spectrometer had a preliminary ability for the excitation fluorescence analysis by HG-AFS. In addition, due to no macroscopic moving parts, the UV digital micromirror spectrometer had simple construction and fast analysis speed (0.848 s per spectrum scan).