Laser-enhanced Ionization Detection Research Articles

Use of Sol−Gels as Solid Matrixes for Trace Analysis by UV Laser Ablation and Laser-Enhanced Ionization Detection

Zirconium and silicon sol-gels were investigated as solid materials for trace elemental analysis of pelletized solid samples by laser ablation and laser-enhanced ionization. The highly homogeneous dispersion of an internal standard spiked in the solid material obtained with the sol-gel formation process leads to a significant improvement in signal repeatability and to an increase in the precision of measurements through better correction of variations in the laser ablation rate. Signal repeatability values of 5-8% RSD were obtained for Pb in NIST 1632c Bituminous Coal sample pellets prepared using both sol-gels, as compared to 9-21% for graphite-based sample pellets. Furthermore, the zirconium sol-gel was shown to offer better resilience to signal bias due to preferential ablation and a more accurate correction of ablation rate using the internal standardization method.

Trace level determination of lead in solid samples by UV laser ablation and laser-enhanced ionization detection.

Laser-enhanced ionization was investigated as a detection technique for trace elemental analysis of solid samples by laser ablation. Laser ablation of aluminum samples was performed in an ablation cell, and the ablated material was carried by a flow of gas to a miniature LEI flame where Pb was detected. This decoupling of ablation cell and detector allowed the independent optimization of vaporization and detection processes. We have investigated the different excitation schemes for Pb and uncovered five new LEI-active transitions in the visible range. We have demonstrated that the use of an argon-oxygen/acetylene flame sheathed with argon resulted in the elimination of background interference from the two-photon ionization of nitric oxide. We have shown that the use of helium as a carrier gas results in a higher ablation yield and lower pulse-to-pulse variations in LEI signal and in better analytical figures of merit. We have characterized the performance of the technique in terms of detection limits and dynamic range, and we have obtained a detection limit of 60 ng/g for the determination of Pb in high purity aluminum.

Development of ultratrace laser spectrometry techniques for measurements of arsenic

Several techniques based on laser induced fluorescence (LIF) spectrometry and laser enhanced ionization (LEI) spectrometry have been investigated for ultratrace measurements of arsenic. Studies by our group in this area that have been published previously are reviewed here, and are presented along with the results of recent studies that have not yet been published. The techniques presented include LIF detection in the inductively coupled plasma atomizer, the electrothermal atomizer, the tungsten coil atomizer, the flame atomizer and LEI detection in the flame atomizer, and include approaches that utilize hydride generation or laser ablation sample introduction. Recent efforts have been directed towards developing speciation approaches for arsenic that utilize LIF spectrometric detection. The capabilities of each technique are summarized including the sensitivity and limits of detection, which range from sub-pg ml −1 to ng ml −1 levels. Selected applications of the techniques are presented to demonstrate their utility for environmental and biological samples, and areas for future investigation and further development are discussed.

Far-Ultraviolet Excited Laser-Enhanced Ionization Spectrometry of As, Se, Cu, and Sb in Air/Acetylene and Ar/O2/Acetylene Flames

Laser-enhanced ionization (LEI) measurements of As, Se, Sb, and Cu in air/acetylene and Ar/O2/acetylene flames are reported. The use of far-UV excitation wavelengths to perform one- and two-step LEI excitation from the ground states of As, Se, and Sb is reported for the first time. Significant ionization background signals are observed for far-UV excitations in the air/acetylene flame, but are reduced by substituting an (80:20) Ar/O2 mixture for air as the flame oxidant. The sensitivities of the individual LEI techniques are also increased by the Ar/O2 gas substitution. The limits of detection for As, Se, Sb, and Cu are 30, 0.5, 9 and 2 ng/mL, respectively, and compare favorably with previous LEI reports. Due to the poor atomization characteristics of As and Se, the utility of hydride generation (HG) sample introduction with LEI detection has been explored. Although high sensitivity has been observed for the HG-LEI approach, limits of detection were not evaluated due to nonlinear responses of the signals with respect to analyte concentration.

Laser-enhanced ionization detection of Pb in seawater by flow injection analysis with on-line preconcentration and separation.

The flame laser-enhanced ionization (LEI) technique is coupled with the flow injection analysis system to measure the trace lead amounts in aqueous solution and in seawater. The flow injection (FI) manifold is incorporated with a microcolumn packed with a C18 bonded silica. The chelating agent DDPA is used to form the Pb-DDPA complex, which may be sorbed in the microcolumn and then eluted with methanol. The preconcentrated Pb is then detected by the LEI technique with either single-step or two-step excitation. At 5- and 15-mL volume-fixed sample loading, the detection limits of 0.011 and 0.0033 ng/mL (11 and 3.3 ppt) and enrichment factors of 16 and 48 are achieved, respectively, using a two-step FI-LEI. The sensitivity of the current system proves to be better by at least 1 order of magnitude than that of conventional LEI method. The FI-LEI also increases the tolerance of matrix interference. The LEI signal is slightly reduced to 80% intensity as 10,000 micrograms/mL (ppm) Na and K matrixes are mixed in the lead solution. The resistance to the alkali matrixes is enhanced approximately 4 times that reported previously using a similar water-immersed probe as a LEI collector. Finally, the FI-LEI is for the first time applied to detect the Pb content in seawater, achieving a result of 0.0112 +/- 0.0006 ng/mL (ppb) consistent with the certified value of 0.013 +/- 0.005 ng/mL (ppb).

Spatially Resolved Temperature Determination of an Air/Acetylene Flame Using the Two-Step Laser-Enhanced Ionization Technique

We have demonstrated a two-step laser-enhanced ionization (LEI) technique to be potentially useful in measuring a spatially resolved temperature in an atmospheric air/acetylene flame. As a complement to the existing optical methods, LEI detection shares the advantages of extremely high sensitivity and the capability of achieving a high spatial resolution, confined to the dual-beam intersection area of 1 mm × 1 mm. A theoretical model was developed to precisely extract the temperature information from the obtained two-step LEI signal. The physical parameters required in the experiment include simply the relative values of the LEI signals, associated with the fine-structure doublets of a selected thermometric species, and their corresponding laser energies. The subsequent treatment is also convenient without the need to know the absolute energy of the incident laser beam and to accurately calibrate the detection system. Al and Ga were selected as the thermometric species. The resultant radial and axial temperature mappings are consistent with each other and are also comparable with those reported by other optical methods.

Laser-Enhanced Ionization of Mercury Atoms in an Inert Atmosphere with Avalanche Amplification of the Signal

A new method for laser-enhanced ionization detection of mercury atoms in an inert gas atmosphere is described. The method, which is based on the avalanche amplification of the signal resulting from the ionization from a selected Rydberg level reached by a three-step laser excitation of mercury vapor in a simple quartz cell, can be applied to the determination of this element in various matrices by the use of conventional cold atomization techniques. The overall (collisional + photo) ionization efficiency is investigated at different temperatures, and the avalanche amplification effect is reported for Ar and P-10 gases at atmospheric pressure. It is shown that the amplified signal is related to the number of charges produced in the laser-irradiated volume. Under amplifier noise-limited conditions, a detection limit of ∼15 Hg atoms/laser pulse in the interaction region is estimated.

Laser-enhanced ionization detection of magnesium atoms by a combination of electrothermal vaporization and flame atomization

A system for the electrothermal vaporization flame atomization laser-enhanced ionization (ETV-FL-LEI) detection of Mg was optimized and completely characterized. The vaporization, transport, atomization, probing, and detection efficiencies were all determined experimentally. The overall efficiency of the system was found to be 0.00251%. The experimental detection limit of 2 ng ml–1(20 pg) for Mg was limited by noise due to the blank signal. A detection limit of 590 fg ml–1(5.9 fg) could be achieved in the absence of the blank and a reduction of radiofrequency noise.

Automatic determination of optimum dilution levels for laser-enhanced ionization detection of matrix-interfered sample by flow injection

A flow injection (FI) system is interfaced to laser-enhanced ionization (LEI) apparatus to handle the sample introduction. With the use of FI–LEI apparatus, the electrical interference induced by the matrix may be effectively diminished. A significant LEI signal of trace In is recovered in a solution containing an Na-matrix concentration greater than the threshold level, 4–10 ppm (µg ml–1) in our conditions, at which no conventional LEI signal is detectable. The dilution gradient, resulting from injection of a water plug into the carrier stream of sample solution, leads to the appearance of a double-peak LEI signal. By taking into account the dispersion behaviour of sample solution and the ion-sheath effect, we are able to derive an explicit formula. According to the formula, we may successfully predict the measured intensity of the FI–LEI signal and characterize the features of the double-peak observed.

Novel Technique To Reduce Electrical Interference Inherent in Laser-Enhanced Ionization Detection by Using Flow Injection Analysis

The influence of electrical interference induced by the easily ionized sodium matrix upon the laser-enhanced ionization (LEI) detection of indium analyte is studied. As the LEI signal is electrically suppressed but still detectable, the original sample concentration may be effectively recovered by using the standard addition method. Nevertheless, this method fails to apply when the added Na matrix reaches a threshold level, at which the LEI signal is completely suppressed

Graphite furnace vaporization with laser-enhanced ionization detection

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGraphite furnace vaporization with laser-enhanced ionization detectionB. W. Smith, G. A. Petrucci, R. G. Badini, and J. D. WinefordnerCite this: Anal. Chem. 1993, 65, 2, 118–122Publication Date (Print):January 15, 1993Publication History Published online1 May 2002Published inissue 15 January 1993https://doi.org/10.1021/ac00050a005RIGHTS & PERMISSIONSArticle Views38Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (568 KB) Get e-Alerts Get e-Alerts

Laser-Enhanced Ionization Detection in a Laser-Produced Plasma at Atmospheric Pressure: Theoretical and Experimental Considerations

The essential data of matter-laser interaction which govern the creation of the plasma are described and are shown to permit the determination of several plasma parameters. The choice of an electrical detection adapted to a continuous plasma under atmospheric pressure allows the study by analogy of the transient laser-produced plasma (LPP). Experimental results confirm that laser-enhanced ionization detection in an LPP at atmospheric pressure is not feasible because ionization is “strong” and collection is “weak.”

Analytical applications of laser-enhanced lonization spectrometry in flames and furnaces

This paper is concerned with a critical analysis of the analytical performance of laser-enhanced ionization (LEI) spectrometry in flames and furnaces as an ultra-sensitive trace-element technique. Updated tables of LEI detection limits, both in flames and furnaces, are given. Special attention is paid to interference phenomena which are unique to the LEI technique. Ways of reducing their influence on the analytical signals are proposed. Finally, advantages and disadvantages of LEI spectrometry as a tool for ultra-sensitive trace element analysis are discussed.

Laser-enhanced ionization detection of trace copper in high salt matrices

Laser-enhanced ionization (LEI) is used to determine trace levels of metals in high salt matrices, an analysis that is difficult by conventional methods. Copper is presented in detail to demonstrate the capability of the method. Three-dimensional spectra of the stepwise excitation of copper are presented which illustrate the one photon, stepwise, and two-photon transitions. Seven copper transitions have been studied for analytical utility, and detection limits have been determined for each. Ionization interferences were accommodated by both matrix matching and separation of the interferences using ion exchange resin. Absolute determinations at the 0.05-ng level are possible with the use of a Teflon microsampling cup for low volume quantitative analysis. In addition to copper, silver, cobalt, iron, and nickel have been detected within the same dye tuning range. Twelve new LEI transitions have been identified for these elements along with detection limits.

Laser-Enhanced Ionization of Refractory Elements in a Nitrous Oxide-Acetylene Flame

Laser-enhanced ionization (LEI) spectrometry using a water-cooled electrode immersed directly in a nitrous oxide-acetylene flame has been examined for the determination of refractory elements. LEI detection limits for refractory elements in aqueous solution are comparable to or better than detection limits obtained by flame atomic absorption, plasma emission, and atomic fluorescence techniques. Only graphite furnace atomic absorption spectrometry exhibits superior detectability for certain refractory elements in aqueous solution over LEI spectrometry using a nitrous oxide-acetylene flame. The successful application of the nitrous oxide-acetylene flame now extends the applicability of LEI spectrometry to include most of the elements in the periodic table which can be determined by other common atomic spectrochemical techniques.