Laser-excited Atomic Fluorescence Spectrometry Research Articles

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.

Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L −1 (20 μL, 3 σ) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3 σ) of 3 ng L −1 (i.e. 54 pM) for total Fe concentration with the use a 20 μL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 μg L −1) seawater sample were in good agreement with the certified values.

Lasers as Light Sources for Analytical Atomic Spectrometry

Lasers have advantages compared to conventional light sources, which include high power, a monochromatic emission profile, stability, and rapid tuning across an atomic line. These advantages have resulted in superior analytical figures of merit and methods of background correction compared to conventional light sources. The most widely used lasers for atomic spectrometry include dye laser systems, optical parametric oscillator systems, and diode lasers. Three principal techniques employ lasers as light sources. Laser‐excited atomic fluorescence spectrometry (LEAFS) involves the use of laser light to excite atoms that emit fluorescence and serves as the analytical signal. Laser‐enhanced ionization (LEI) involves laser excitation of atoms to an excited state energy level at which collisional ionization occurs at a higher rate than from the ground state. Diode laser atomic absorption spectrometry (DLAAS) employs a DL as a source to excite atoms in an atom cell from the ground state to an excited state. The analytical signal is involves the ratio of the incident and transmitted beams. Recent applications of these techniques are discussed, including practical applications, hyphenated techniques employing laser‐induced plasmas, and work to characterize fundamental spectroscopic parameters.

Advances in Laser‐Excited Atomic Fluorescence and Ionization

Laser‐excited atomic fluorescence spectrometry (LEAFS) and laser‐enhanced ionization (LEI) are very sensitive methods for elemental analysis. LEAFS involves excitation of atoms by laser radiation followed by detection of the resulting fluorescence, while LEI involves laser excitation, which serves to enhance ionization, producing electrons and ions that can be collected in an electric field. In this article, the spectroscopic transitions involved in LEAFS and LEI are discussed, followed by a review of the instrumentation employed. Several recent developmens in LEAFS and LEI are reviewed, including the use of tungsten coil atomizers for LEAFS; the determination of mercury, aluminum, lead, thulium, and chromium using various graphite electrothermal atomizers; the use of LEAFS and LEI as detectors for gas chromatography for the determination of volatile tin compounds; and the determination of a variety of elements by LEI with a flame atom cell. LEAFS and LEI will continue in the future to be high‐sensitivity alternatives to conventional methods of elemental analysis.

SPECIATION OF METHYLCYCLOPENTADIENYL MANGANESE TRICARBONYL AND ITS DERIVATIVES: A REVIEW

ABSTRACT Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organomanganese compound that is used as an octane enhancer for gasoline and other fuels. The widespread use of this compound has been suggested to be harmful to human health. In order to accurately assess its impact, high sensitivity instrumentation for the determination of MMT and its derivatives is required. In this paper, three instrumental approaches are reviewed for this analysis. Walton and coworkers [1] employed high-performance liquid chromatography (HPLC) coupled to a flame laser-excited atomic fluorescence spectrometry (LEAFS) detector to evaluate the organomanganese compound responsible for organ damage in rats following subcutaneous injection of this compound. Gas chromatography (GC) was coupled to an alternating current plasma (ACP) detector by Ombaba and Barry [2] for the determination of MMT in gasoline and fuel samples. Butcher et al. [3] employed HPLC with diode laser atomic absorption spectrometry (DLAAS) for the determination of MMT in water, gasoline, and urine. The conclusion of this paper is a comparison of the analytical capabilities of these instruments.

ADVANCES IN ELECTROTHERMAL ATOMIZATION FOR ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE

ABSTRACT Electrothermal atomizers (ETAs) are commonly used atom cells for elemental analysis. In this article, the fundamental principles of ETAs are described, including instrumentation and operating principles. Several recent applications of ETAs are discussed involving atomic absorption spectrometry (AAS) and laser excited atomic fluorescence spectrometry (LEAFS). These include a clean room atomizer cabinet for ETA-AAS, multielement continuum source ETA-AAS, standardless ETA-AAS for medium volatility elements, slurry atomization of food colorants by ETA-AAS, the determination of lead in blood by tungsten coil–AAS, the determination of arsenic and selenium by hydride generation ETA-LEAFS, and the determination of cadmium and zinc by double resonance ETA-LEAFS.

Tungsten coil devices in atomic spectrometry: absorption, fluorescence, and emission.

In this work, tungsten coil (W-Coil) devices are used as atomizers for electrothermal atomization atomic absorption spectrometry (ETAAS), electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS), and electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES). For most cases in ETAAS and ETA-LEAFS, limits of detection (LODs) using the W-Coil are within a factor of ten of those observed with commercial graphite furnace systems. LOD for Cd by W-Coil AAS is 10 pg, while LODs for As, Se, Cr, Sb and Pb by W-Coil LEAFS are 950, 320, 1400, 330, and 160 fg, respectively. The compact W-Coil device makes it an ideal atomizer for portable atomic spectrometry instrumentation, especially when coupled with a miniature charge coupled device spectrometer. Alternatively, the atomizer can be used as an inexpensive, modular add-on to an existing commercial ICP-AES system; and the thermal separation of Pb with interference elements Al, Mn, and Fe is demonstrated.

Studying element vaporization and atomization processes in electrothermal atomizers by laser-excited atomic fluorescence spectrometry: indium, matrix effects

Indium vaporization and atomization processes were studied in a variable-pressure atomizer by laser-excited fluorescence spectrometry for various analyte masses over a wide range of buffer-gas pressures. It was found that the atomization processes are of intricate nature and depend on the element mass, pressure, and heating rate. Based on the data obtained over a wide range of pressures, individual atomization processes were singled out and their parameters were determined. The effects of KC1 and CuCl2 matrices on the kinetics and other characteristics of the processes were investigated. Possible mechanisms of indium vaporization and atomization under various experimental conditions and mechanisms of matrix effects on the analytical signals of indium and gallium are discussed.

Ultratrace determination of thulium by laser-excited atomic fluorescence spectrometry with atomization in a rhenium lined tube furnace

In the present work, a method for the determination of ultratrace levels of thulium by laser induced atomic fluorescence (LEAFS) was developed. High sensitivity was achieved by using a dye laser pumped by a high repetition copper vapor laser and electrothermal atomization (ETA) in a tube furnace. Four different atomizer surfaces (pyrolytic graphite, tungsten, tantalum and rhenium) as well as coating treatments of the graphite with noble metal solutions were evaluated with the objective of improving the atomization efficiency of thulium. The best results in terms of intensity, reproducibility and lifetime were obtained with rhenium-lined graphite tubes. Since the rhenium surface was more resistant to oxidation under the operational conditions, the sample was atomized under a stop flow regime rather than in an argon miniflow regime, which was required when tantalum and tungsten foils were employed. Atomization under the stop flow regime avoided dilution of the analyte in the analytical zone, thereby improving sensitivity. In addition, the lifetime of the rhenium foil lined atomizer was longer than those observed with tantalum or tungsten linings. Furnace parameters were optimized to maximize the fluorescence signal–background ratio. The limit of detection for the rhenium lined atomizer was 200 fg with a precision of 6.0% at the 10 ng ml −1 level. Thulium was determined with excellent results in urine and coal fly ash samples using the new method.

Development of an electrothermal atomization laser-excited atomic fluorescence spectrometry procedure for direct measurements of arsenic in diluted serum.

A procedure for the direct determination of arsenic in diluted serum by electrothermal atomization laser-excited atomic fluorescence spectrometry (ETA-LEAFS) is reported. Laser radiation needed to excite As at 193.696 and 197.197 nm is generated as the second anti-Stokes stimulated Raman scattering output of a frequency-doubled dye laser operating near 230.5 and 235.5 nm, respectively. Two different LEAFS schemes have been utilized and provide limits of detection of 200-300 fg for As in aqueous standards. When measurements of serum samples diluted 1:10 with deionized water are performed, a stable background signal is observed that can be accounted for by taking measurements with the laser tuned off-wavelength. No As is detected in any of the bovine or human serum samples analyzed. Measurements of 100 pg/mL standard additions of As to a diluted bovine serum sample utilizing either inorganic or organic As species demonstrate a linear relationship of the fluorescence signal to As spike concentration, but exhibit a sensitivity of approximately half that observed in pure aqueous standards. The limit of detection for As in 1:10 diluted serum samples is 65 pg/mL or 650 fg absolute mass, which corresponds to 0.65 ng/mL As in undiluted serum. To our knowledge, the ETA-LEAFS procedure is currently the only one capable of directly measuring As in diluted serum at these levels.

Determination of Lead in Whole Blood by Filter Furnace Laser-Excited Atomic Fluorescence Spectrometry

Filter furnace laser-excited atomic fluorescence spectroscopy was used for the determination of lead in whole blood. The use of a Katskov filter has enabled the direct comparison between lead fluorescence signals obtained with blood standards and water standards. Only a simple dilution of the blood wasrequired. This direct correlation has allowed the interpolation of the lead signal of blood samples using a lead water standard calibration curve. NIST certified blood samples were analyzed using the method with excellentresults.

Electrothermal Atomization Laser-Excited Atomic Fluorescence Spectroscopy for the Determination of Indium

A dye laser pumped by a high-repetition-rate copper vapor laser was used as the excitation source to determine indium at parts-pertrillion level by electrothermal atomization laser-excited atomic fluorescence spectrometry (ETA-LEAFS). A comparison was made between wall atomization, in pyrolytic and nonpyrolytic graphite tubes, and platform atomization. The influence of several chemical modifiers either in solution or precoated in the graphite tube was evaluated. The influence of several acids and NaOH in the analyte solution was also studied. Optimization of the analytical conditions was carried out to achieve the best signal-to-background ratio and consequently an absolute limit of detection of 1 fg. Some possible interferents of the method were evaluated. The method was evaluated by determining indium in blood, urine, soil, and urban dust samples. Recoveries between 99.17 and 109.17% are reported. A precision of 4.1% at the 10 ng g-1 level in water standards was achieved.

Ultrasensitive determination of gold in geogas by laser excited atomic fluorescence spectrometry

Ultratrace gold (Au) in geogas samples has been determined by means of laser excited atomic fluorescence spectrometry combined with graphite electrothermal atomization and time-gate technique. Gold atoms were excited from the ground state to the 6p 2P 3/2 state by a pulsed laser beam with a wavelength of 242.8 nm. Fluorescence photons with a wavelength of 312.3 nm were measured by a photon-counting unit. The time-gate technique was used to reduce the background radiation caused by the furnace. This method has proved to be highly sensitive with minimal background interference. Eighty-two geogas samples were analysed and the Au contents obtained were in the range of 0.002–0.182 ng l −1. The study of Au concentration of geogas in soil is of great interest in prospecting gold deposits.

Progress in laser excited atomic fluorescence spectrometry

Laser excited atomic fluorescence spectrometry, LEAFS, is a high sensitivity, high selectivity, atomic spectrometric technique. This paper reviews progress in LEAFS over the last several years, with emphasis on new lasers, new detectors, modifications to atomizers, and multi-element measurement approaches. Applications of LEAFS to real sample analyses are also highlighted.

Laser-induced fluorescence determination of thallium in sediments

A simple dissolution procedure is decribed for sediments to be analyzed for thallium by Laser-Excited Atomic Fluorescence Spectrometry (LEAFS). It simply uses a nitric – hydrofluoric acid mixture at room temperature (a “cold dissolution” procedure as opposed to the hot acid digestion) followed by a dilution with water (as opposed to the tedious steps of separation and preconcentration). Excellent accuracy (91–106% recoveries) and precision (4–10% relative standard deviation) were demonstrated by the use of five sediment reference materials of diverse origins. The detection limit was estimated to be 0.5 ng/g of thallium. Additionally, a hot plate digestion procedure, using an in-house designed semi-enclosed Teflon beaker, was also investigated; its analytical results agreed with certified values and confirmed the adequacy of the cold dissolution technique. The method is being applied to study the sediment – water interactions in lake environments.

Laser-excited atomic fluorescence spectrometry in a graphite furnace with an optical parametric oscillator laser for sequential multi-element determination of cadmium, cobalt, lead, manganese and thallium in Buffalo river sediment

It is demonstrated, for the first time, that solid-state lasers based on optical parametric oscillation (OPO) allow relatively rapid sequential multi-element analysis of samples by laser-excited atomic fluorescence spectrometry (LEAFS) in a graphite furnace. These lasers are tunable by facile computer keyboard control over the wavelength region 220–2000 nm. A method is described for the sequential multi-element determination of cadmium, cobalt, lead, manganese and thallium in a river sediment standard reference material (NIST SRM 2704) by graphite furnace LEAFS. With a slew rate of 0.125 nm s–1, the OPO laser could be tuned to cover the wavelength range needed for these elements, from 228 to 304 nm, in 15 min. This allowed each element to be determined sequentially with the analysis time determined primarily by the slow heating cycle of the furnace rather than the laser wavelength tuning. Detection limits in the multi-element mode were 545, 111, 28, 445 and 24 fg for cadmium, cobalt, lead, manganese and thallium, respectively, limited primarily by the low repetition rate of the laser (10 Hz). The multi-element detection limits were within a factor of 2–4 of those in the single element mode. Higher excitation energies, by a factor of 2–5, were required to optically saturate the transitions of the analytes in the sediment sample solution compared with aqueous standards. By use of several aliquots of one sample solution, and simple aqueous calibration, it was possible to analyze the sample, accurately, for the five elements over a concentration range between 1 ng ml–1 for thallium and 460 ng ml–1for manganese. Different dilutions were not necessary owing to the long calibration range of the technique. The high sensitivity of LEAFS allowed sufficient initial dilution to remove an interference on thallium that is normally irresolvable by atomic absorption measurements of the same sample in the same graphite furnace.

Electrothermal atomization laser-excited atomic fluorescence spectrometry for direct analysis of germanium in water and blood samples

Laser-excited atomic fluorescence spectrometry using a copper vapor laser as the excitation source has been used to develop a very sensitive method for direct determination of ultratrace amounts of germanium. For more efficient sample atomization, a graphite furnace was employed. Two excitation-detection schemes were evaluated. The best conditions for the analysis of germanium in water and blood are described. The effect of matrix modifiers and some possible interferences are reported. Absolute limits of detection of 0.7 pg (3σ) with a precision of 3.5% at the 2 ppb level for water samples and 1.0 pg (3σ) with 8.0% precision at the 2 ppb level for blood samples were achieved with no need for preconcentration.

Determination of heavy metals in polar snow and ice by laser excited atomic fluorescence spectrometry with electrothermal atomization in a graphite cup

The strategy of direct analysis at the femtogram level is exemplified by the determination of Bi traces in the sections of two Greenland ice cores by laser excited atomic fluorescence spectrometry (LEAFS). The importance of all stages of the analysis: field sampling, mechanical decontamination, labware precleaning, standards and samples storage and transportation, and final analytical measurements are discussed in terms of getting unbiased accurate data. The potentialities of Pd and Ir matrix modifiers for the determination of femtogram contents of Bi were examined. The Ir modifier provided better limit of detection for real ice samples (0.15 pg ml −1) because of its higher purity and thermal stability. The contents of Bi well above LOD (1.4 and 0.8 pg ml −1) were measured in two sections of ice core, dated to 1783–1784 AD (the period of the activity of Laki volcano in Iceland) and in the sections of deep ice core, dated to Last Glacial Maximum (LGM)-Holocene transition (Bi content ranges within 0.3–0.7 pg ml −1).

Characterization of a tunable optical parametric oscillator laser system for multielement flame laser excited atomic fluorescence spectrometry of cobalt, copper, lead, manganese, and thallium in buffalo river sediment.

A pulsed (10 Hz) optical parametric oscillator (OPO) laser system based on beta-barium borate (BBO) crystals and equipped with a frequency-doubling option (FDO) was characterized for use in laser excited atomic fluorescence spectrometry (LEAFS). This all-solid-state laser has a narrow spectral line width, a wide spectral tuning range (220-2200 nm), and a rapid, computer-controlled slew scan of wavelength (0.250 nm s-1 in the visible and infrared, and 0.125 nm s-1 in the ultraviolet). The output power characteristics (15-90 mJ/pulse in the visible, 1-40 mJ in the infrared, and 1-11 mJ in the ultraviolet), laser pulse-to-pulse variability (3-13% relative standard deviation, RSD, of the laser pulses), conversion efficiency of the FDO (2-17%), and spectral bandwidth in the visible spectrum (0.1-0.3 cm-1) were measured. The laser was used as the excitation source for a flame LEAFS instrument for which rapid, sequential, multielement analysis was demonstrated by slew scan of the laser. The instrument allowed about 640 measurements to be made in about 6 h, with triplicate measurements of all solutions and aqueous calibration curves, which yielded accurate analyses of a river sediment (National Institute of Standards and Technology, Buffalo River Sediment, 2704) for five elements with precisions < 5% RSD. Comparable or improved flame LEAFS detection limits over literature values were obtained for cobalt (2 ng mL-1), copper (2 ng mL-1), lead (0.4 ng mL-1), manganese (0.2 ng mL-1), and thallium (0.9 ng mL-1) by flame LEAFS.

Use of laser-excited atomic fluorescence spectrometry with a novel diffusive graphite tube electrothermal atomizer for the direct determination of silver in sea water and in solid reference materials

Laser-excited atomic fluorescence spectrometry is used with a novel diffusive graphite tube electrothermal atomizer for the determination of silver in sea water and three National Institute of Science and Technology (NIST) soil reference materials (SRM 2709, 2710 and 2711). The samples are contained in a small graphite boat which is attached to one of two graphite electrodes. The boat is inserted into the center of a graphite tube which is then sealed by the electrodes and heated. The vaporized sample diffuses through the heated graphite walls and is excited by a laser beam which passes a few mm above the tube. The seawater matrix causes a two-fold suppression in the silver fluorescence signal compared with a pure aqueous standard of the same concentration. The depression is constant over a concentration range of 6 orders of magnitude. When aqueous standards were used for the determination of Ag in the solid samples, no significant difference between the measured values and the certified values were found. A limit of detection of 40 fg (4 ppt) was obtained for pure aqueous solutions and 90 fg (9 ppt) in a 1:1 diluted seawater matrix. A concentration of silver of 14 ng L −1 was determined in a sample of coastal Atlantic water.