Continuum source tungsten coil atomic fluorescence spectrometry

A simple continuum source tungsten coil atomic fluorescence spectrometer is constructed and evaluated. The heart of the system is the atomizer: a low-cost tungsten filament extracted from a 150 W light bulb. The filament is resistively heated with a small, solid-state, constant-current power supply. The atomizer is housed in a glass chamber and purged with a 1 L/min flow of a conventional welding gas mixture: 10% H(2)/Ar. A 25 μL sample aliquot is pipetted onto the tungsten coil, the liquid is dried at low current, and then the atomic vapor is produced by applying a current in the range 3.5-5.5 A. The atomization current does not produce temperatures high enough to excite atomic emission. Radiation from a 300 W xenon lamp is focused through the atomic vapor, exciting atomic fluorescence. Fluorescence signals are collected using a hand-held charge-coupled device (CCD) spectrometer. Simultaneous determination of ten elements (Ag, Bi, Cr, Cu, Ga, In, Mg, Mn, and Tl) results in detection limits in the range 0.3 to 10 ng. The application of higher atomization currents (10 A) leads to straightforward detection of atomic emission signals with no modifications to the instrument.     

测定汞的原子荧光法和冷原子吸收法比对研究

从监测方法和质量控制的角度出发,比对研究了测定水中汞的原子荧光法和冷原子吸收法,并提出了质量控制指标.研究结果表明:(1)两种方法具有可比性;(2)质量控制指标与样品浓度之间没有明显相关性;(3)对于标准样品,两种方法的室内相对标准偏差(RSD)、室间相对标准偏差(RSD′)和相对误差(RE)结论一致,即RSD≤5％,RSD′≤10.0％,RE≤±15.0％;(4)两种方法的标准样品和实际样品的加标回收率基本一致,为85％～115％,原子荧光法的空白加标回收率略低于冷原子吸收法.     

Determination of methylmercury in environmental matrixes by on-line flow injection and atomic fluorescence spectrometry

The precision and bias of monomethylmercury (MMHg) determinations in environmental samples can be improved by directly coupling and automating the numerous steps involved with analysis of this toxic Hg species. We developed a simple and robust mercury speciation analyzer (MSA) for measurement of MMHg in environmental matrixes. This on-line hyphenated system couples the main analytical steps, including sample introduction, aqueous-phase ethylation, Tenax preconcentration, and gas chromatographic separation, to cold vapor atomic fluorescence detection and data acquisition. Here we describe the MMHg-MSA, present results of laboratory optimization and performance tests, and compare the reproducibility between dual analytical channels. With alternating sample concentration and analysis, a dual-channel system permits six high-accuracy MMHg determinations per hour. Additional advantages compared to the traditional manual method include ease of operation and high precision (<5% relative standard deviation). The MSA is applicable to the determination of MMHg in various environmental matrixes, and it can be fully automated. This method was validated by analysis of MMHg in certified reference materials of sediment and biological tissue. Estimated detection limits for MMHg with the MSA are approximately 0.01 ng g(-1) for a 0.1-g sample of dry sediment or fish and approximately 0.01 ng L(-1) for 0.15 L of water.     

氢化物发生-原子荧光光谱法同时测定食盐中的砷和汞

建立一种氢化物发生-原子荧光光谱法同时测定食盐中砷和汞的方法.研究样品前处理对测定结果的影响,探索同时测定砷、汞的最佳实验条件.优化条件下,砷、汞质量浓度分别在0～10.0 μμg/L和0～2.0μg/L范围内,线性关系良好.方法检出限:As为0.0043 μg/L,Hg为0.003 2 μg/L;相对标准偏差:As为0.37％,Hg为0.61％;样品加标回收率:As为97.80％ ～ 102.40％,Hg为96.78％～ 100.80％.试验表明:该方法具有操作简便、快速、准确度高等优点,可用于食盐中砷汞的同时测定.     

Development and application of acousto-optic background correction for inductively coupled plasma atomic emission spectrometry

In two configurations, a solid-state acousto-optic (AO) deflector or modulator is mounted in a 0.5 m monochromator for background correction with inductively coupled plasma atomic emission spectrometry (ICP-AES). A fused silica acousto-optic modulator (AOM) is used in the ultraviolet (UV) spectral region applications while a glass AO deflector (AOD) is used for the visible (VIS) region. The system provides rapid sequential observation of adjacent on- and off-line wavelengths for background correction. Seventeen elements are examined using pneumatic nebulization (PN) and electrothermal vaporization (ETV) sample introduction. Calibration plots were obtained with each sample introduction technique. Potable water and vitamin tablets were analyzed. Flame atomic absorption (FAA) was used to verify the accuracy of the AO background correction system.     

Low-frequency wavelength modulation spectroscopy with D2 transition of atomic cesium by use of an external-cavity diode laser

Low-frequency wavelength modulation spectroscopy is acquired with an external-cavity diode laser. The wavelength modulation is achieved with voltage tuning by means of scanning with the piezoelectric stepper motor, which rotates the end mirror in the laser cavity. With optimum 1-kHz frequency modulation and harmonic detection, direct absorption experiments for the 6S(1/2)(F = 4) --> 6P(3/2) transition of the cesium D(2) line were carried out. We found that 6f-harmonic detection is best here with a signal-to-noise voltage ratio of 460.     

Imaging time-resolved electrothermal atomization laser-excited atomic fluorescence spectrometry for determination of mercury in seawater

In this study, direct determination of mercury at the nanogram per liter level in the complex seawater matrix by imaging time-resolved electrothermal atomization laser-excited atomic fluorescence spectrometry (ITR-ETA-LEAFS) is described. In the case of mercury, the use of a nonresonant line for fluorescence detection with only one laser excitation is not possible. For measurements at the 253.652 nm resonant line, scattering phenomena have been minimized by eliminating the simultaneous vaporization of salts and by using temporal resolution and the imaging mode of the camera. Electrothermal conditions (0.1 M oxalic acid as matrix modifier, low atomization temperature) have been optimized in order to suppress chemical interferences and to obtain a good separation of specific signal and seawater background signal. For ETA-LEAFS, a specific response has been obtained for Hg with the use of time resolution. Moreover, an important improvement of the detection limit has been obtained by selecting, from the furnace image, pixels collecting the lowest number of scattered photons. Using optimal experimental conditions, a detection limit of 10 ng L(-1) for 10 μL of sample, close to the lowest concentration level of total Hg in the open ocean, has been obtained.     

On-line coupling of capillary electrophoresis to hydride generation atomic fluorescence spectrometry for arsenic speciation analysis

A novel hyphenated technique, on-line coupling of capillary electrophoresis (CE) to atomic fluorescence spectrometry (AFS), was developed for speciation analysis of four environmentally significant and toxic forms of arsenic: arsenite, arsenate, monomethylarsenic acid, and dimethylarsenic acid. Baseline separation of the four arsenic species was achieved by capillary electrophoresis in a 50 cm x 100 microm i.d. fused-silica capillary at 20 kV and using a 20 mmol L(-1) phosphate buffer (pH 6.5). A hydride generation (HG) technique was employed to convert the arsenic species from the CE effluent into their respective hydrides. The CE-AFS interface was constructed on the basis of a cross design for introducing a sheath flow around the CE capillary and a Pt electrode, which provided an electrical connection for stable electrophoretic separations and allowed on-line volatile hydride formation. A laboratory-made gas-liquid separator was used to isolate the generated volatile species from the reaction mixture solution, and an argon flow was used to transport the volatile hydrides into the atomizer of AFS for on-line detection. The precision (RSD, n = 7) ranged from 2.1 to 3.1% for migration time, from 2.8 to 4.2% for peak area response, and from 2.0 to 4.1% for peak height response for the arsenic species at the 1 mg L(-1) (as As) level. The detection limits were in the range of 9-18 microg L(-1) (as As). The recoveries of the four arsenic species in locally collected water samples and urine sample ranged from 91 to 115%. The developed technique was successfully applied to the speciation of the water-methanol extractable arsenic in a sediment sample.     

Increasing measurement quality by atomic fluorescence analysis

Methods for measurement of atomic-fluorescence signals that allow for the effect of scattered radiation are considered. The proposed methods are based on broadening of the emission line of the spectrometer lamp. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 31–33, July, 2000.     

A review of attenuation correction techniques for tissue fluorescence.

Fluorescence intensity measurements have the potential to facilitate the diagnoses of many pathological conditions. However, accurate interpretation of the measurements is complicated by the distorting effects of tissue scattering and absorption. Consequently, different techniques have been developed to attempt to compensate for these effects. This paper reviews currently available correction techniques with emphasis on clinical application and consideration given to the intrinsic accuracy and limitations of each technique.     

Simultaneous determination of trace cadmium and arsenic in biological samples by hydride generation-double channel atomic fluorescence spectrometry

Hydride generation atomic fluorescence spectrometry (HG-AFS) has been used for determination of hydride-forming elements because of its high sensitivity, simplicity, and low costs, but most of such work has been concentrated on single element analysis, and reports dealing with multielement determination by HG-nondispersive (ND)AFS are rare. In this work, a sensitive HG-NDAFS method was developed for simultaneous determination of trace cadmium and arsenic in biological materials. The conditions for the generation of volatile cadmium and arsenic species from the reaction with KBH4 in aqueous solution were investigated using a double-channel AFS integrated with an intermittent flow reactor. Like thiourea and Co(II), ascorbic acid was found to significantly enhance the generation efficiency of volatile Cd and As species. The interferences of coexisting ions were evaluated. Under optimal conditions, the detection limits for Cd and As were determined to be 10 and 150 ng L(-1), respectively. The precision for 11 replicate determinations at the 1 microg L(-1) Cd level and the 10 microg L(-1) As level were 3.5 and 2.7% (RSD), respectively. The recoveries of spike analytes in the biological samples studied ranged from 94 to 109%. The proposed method was successfully applied to the simultaneous determination of Cd and As in a variety of biological samples.     

Nanosemiconductor-based photocatalytic vapor generation systems for subsequent selenium determination and speciation with atomic fluorescence spectrometry and inductively coupled plasma mass spectrometry

We reported novel Ag-TiO(2)- and ZrO(2)-based photocatalytic vapor generation (PCVG) systems as effective sample introduction techniques for further improving the sensitivity of the atomic spectrometric determination of selenium for the first time, in which the conduction band electron served as a "reductant" to reduce selenium species including Se(VI) and convert them directly into volatile H(2)Se, which was easily separated from the sample matrix and underwent more effectively subsequent atomization and/or ionization. These two PCVG systems helped us to overcome the problem encountered in the most conventional KBH(4)/OH(-)-H(+) system, in that Se(VI) was hardly converted into volatile selenium species without the aid of prereduction procedures. The limits of detection (LODs) (3σ) of the four most typical Se(IV), Se(VI), selenocystine ((SeCys)(2)), and selenomethionine (SeMet) species were, respectively, down to 1.2, 1.8, 7.4, and 0.9 ng mL(-1) in UV/Ag-TiO(2)-HCOOH, and 0.7, 1.0, 4.2, and 0.5 ng mL(-1) in UV/ZrO(2)-HCOOH with the relative standard deviations (RSDs) lower than 5.1% (n = 9 at 1 μg mL(-1)) when using atomic fluorescence spectrometry (AFS) under flow injection mode. They reached 10, 14, 18, and 8 pg mL(-1) in UV/Ag-TiO(2)-HCOOH, and 6, 7, 10, and 5 pg mL(-1) in UV/ZrO(2)-HCOOH with the RSDs lower than 4.4% (n = 9 at 10 ng mL(-1)) when using inductively coupled plasma mass spectrometry (ICPMS). After the two PCVG systems were validated using certified reference materials GBW(E)080395 and SELM-1, they were applied to determine the total Se in the selenium-enriched yeast sample and used as interfaces between high-performance liquid chromatography (HPLC) and AFS or ICPMS for selenium speciation in the water- and/or enzyme-extractable fractions of the selenium-enriched yeast.