Laser-enhanced Ionization Spectrometry Research Articles

Investigation of the Multielement Capability of Laser-Enhanced Ionization Spectrometry in Flames for Analysis of Trace Elements in Water Solutions

One-step Laser-Enhanced Ionization (LEI) spectrometry of 23 different elements in aqueous solutions has been performed in an acetylene/air flame. All elements were detected by light in the ultraviolet region, produced by frequency doubling of the output from the dye Coumarin 153. This was done in order to investigate the multielement capability of LEI in flames that has been made possible by the recent development of commercially available, widely tunable dyes. Among the elements detected, 9 (As, Au, In, Mn, Pb, Sb, Tl, W, Yb) show detection limits which are superior to those reported in the literature for one-step LEI. The lowest detection limit obtained in this investigation was 1 pg/mL for In. Four of the elements (As, Sb, Yb, W) are reported as being detected by LEI for the first time. The multielement capabilities of LEI as a method for trace element analysis are discussed.

Trace element analysis by two-colour laser enhanced ionization spectroscopy in a graphite furnace

We demonstrate improved performance of laser enhanced ionization (LEI) with two-colour excitation in graphite furnace. With a modified electrode arrangement we have been able to measure LEI signals at atomization temperature of 2600°C without interference from the electric heating current. The sensitivity and selectivity are greatly improved when step-wise excitation is used instead of single photon LEI. Detection limits in the pg range are reported for five different elements. Futhermore we demonstrate and discuss how a simple and efficient correction for spectral interference can be performed in two-colour LEI.

Trends in optical spectrochemical trace analysis with plasma sources

The state-of-art and trends in the development of optical spectrochemical trace analysis with inductively-coupled plasmas (i.c.p.), direct current plasmas (d.c.p.) and microwave-induced plasmas (m.i.p.) are discussed. Innovation in plasma optical emission spectrometry (o.e.s.) is shown ot lie in new sources such as the low-gas-consumption i.c.p., the air and helium i.c.p. as well as the toroidal m.i.p., which is operated at medium power and possibly with moleculary gases. Sample introduction has been improved by using new pneumatic nebulizers, flow injection, electrotheraml vaporization, hydride generation, direct sample insertion and direct solid sampling. Progress in the acquisition of spectral information is attained by high-resolution spectrometry, Fourier-transform spectrometry and by the use of multichannel detectors. D.c.p./o.e.s. is a mature technique for routin work and m.i.p./o.e.s. is a powerful tool for element-specific detection is chromatography. Plasma sources are also suitable atom reservoirs for atomic fluorescence spectrometry and for laser-enhanced ionization spectrometry. Trends in the figures of merit of optical plasma spectrochemical analysis are discussed.

Detection and spectroscopic study of zinc by laser-enhanced ionization spectrometry

En fonction de la longueur d'onde utilisee, les limites de detection varient de 10 μg/ml a 1 μg/ml

Stark Structure Observation in Rydberg States of Li in Flames by Laser-Enhanced Ionization: A New Method for Probing Local Electrical Fields in Flames

In Laser-Enhanced Ionization spectrometry (LEI) in flames the measured signal consists of the electrons and ionized atoms which follow a laser excitation due to the enhanced thermal ionization rate of an excited state compared with the ground state. The charged particles are collected by applying a voltage across the flame and measuring the corresponding current increase. The authors report the observation of the linear Stark effect in highly excited states of Li in flames when laser-enhanced ionization is utilized. The experiments show good agreement with the theory for the linear Stark effect. The atoms were excited by ultraviolet light from the ground state (2s) to np states ( n = 8–22). Collisional broadening is the dominant broadening mechanism for the lower states while the Stark effect dominates at higher values of n for laboratory electrical field strengths. In the analytical use of LEI for trace element analysis the presence of the Stark effect leads to a reduction of the sensitivity of the method, because it decreases the peak-height of the signal. A new method, which utilizes the Stark effect, is presented for nonintrusive determination of the electrical field distribution in flames.

Three-Dimensional Atomic Spectra in Flames Using Stepwise Excitation Laser-Enhanced Ionization Spectroscopy

Stepwise excitation laser-enhanced ionization spectroscopy utilizes two independently tunable dye lasers to populate high-lying excited states of atoms in flames. Two atomic resonances are required, with the upper level of the first-step transition coinciding with the lower level of the second-step transition. Efficient population of a high-lying atomic level is achieved, from which a high rate of collisional ionization can take place. The double-resonance aspect of such excitation adds an extra dimension of spectroscopic selectivity to the measurement. A computer-controlled dual-wavelength LEI spectrometer, including a Fizeau wave-meter for wavelength verification, is used to record three-dimensional spectra–ionization signal as a function of both first- and second-step wavelengths. Examples illustrate the accuracy advantage accorded by the three-dimensional survey.

Laser-Enhanced Ionization Detection of Trace Elements in a Graphite Furnace

A graphite furnace is successfully used as an atomizer in laser-enhanced ionization spectroscopy (LEI). The physical origin of the signals is discussed and a comparison is made with LEI measurements in a flame. Extremely small amounts of analyte atoms can be detected using this method. The reproducibility is good, there are almost no memory effects, and the signal output is linear with the amount of analyte over at least 5 orders of magnitude. The experimental results indicate that the method could become an attractive alternative for trace-element analysis.

A Desolvation Unit for Introducing Microliter Volumes of a Dry Aerosol to an Atomic Spectrometric System

Recent communications from this laboratory describe an impaction-electrothermal atomization atomic absorption spectrometric (I-ETAAS) system for direct and near-real-time determination of metallic compounds in the atmosphere. Calibration was achieved by introducing aqueous standards by a pipet or by using a pneumatic nebulization aerosol deposition technique. This assumes that the transport and final atomization processes are identical for a sample introduced as an ion in solution or as a dry particle from the atmosphere. A more accurate and comparable calibration would be achieved if the standard could be introduced to the I-ETAAS system as a dry aerosol. The introduction of a dry aerosol to an atomic spectrometric system has been achieved with the use of a graphite furnace, although the major advantage of this method of sample introduction was the use of micro-volumes, minimizing sample preconcentration, and reducing interferences. The cost and availability may prevent the widespread use of the graphite furnace for sample introduction of dry aerosol. A dry aerosol has been achieved for laser-enhanced ionization spectrometry using a microcondenser with a heated injection port for introduction of sample, but only a few details of the system have been given. Browner and Boorn have recently reviewed sample introduction techniques for atomic spectrometry, pointing out that pneumatic nebulization for flames and plasmas is the preferred, most widely used, and most readily available approach in the majority of situations. Sample introduction to an electrothermal atomizer using a pneumatic nebulization aerosol deposition technique has been described. The use of pneumatic nebulization is unlikely to change in the near future despite concern over poor transport efficiency.

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.

Lifetime Measurements of Metastable Levels of Thallium and Lead in the Air-Acetylene Flame by Laser-Enhanced Ionization Spectrometry

Laser-enhanced ionization spectrometry with two-step excitation has been used to evaluate the collisional lifetime of the metastable P levels of thallium and lead in an air-acetylene flame burning at atmospheric pressure and supported by a three-slot burner head fitted on a conventional nebulizing chamber. A water-cooled molybdenum electrode immersed in the flame was maintained at high negative potential with respect to the burner body. The ionization current resulting after the two-step excitation was amplified and measured with a digital storage oscilloscope and a boxcar averager. The two excimer lasers were triggered externally with two trigger pulses, one being delayed in time with respect to the other one. In this way the second laser photon, tuned at a transition starting from the metatable level under study, could be correspondingly delayed from the first photon tuned at a transition starting from the ground state. The lifetimes measured were found to be 81 ns and 360 ns for T1 and Pb, respectively.

Trace element determination in flames by laser enhanced ionization spectrometry

Trace element determination in flames by laser enhanced ionization spectrometry

Trace element determination in flames by laser enhanced ionization spectrometry : Axner, Ove, Ingvar Lindgren, Inemar Magnusson and Halina Rubinsztein-Dunlop, 1985. Analyt. Chem., 57(3):773–776. Dept. of Phys., Chalmers Univ. of Tech./Univ. of Gothenburg, S-412 96 Goteborg, Sweden

Trace element determination in flames by laser enhanced ionization spectrometry : Axner, Ove, Ingvar Lindgren, Inemar Magnusson and Halina Rubinsztein-Dunlop, 1985. Analyt. Chem., 57(3):773–776. Dept. of Phys., Chalmers Univ. of Tech./Univ. of Gothenburg, S-412 96 Goteborg, Sweden

Ion-fraction determination by laser-enhanced ionization spectrometry

Role de la concentration totale en ion et de la mobilite ionique sur le signal d'ionisation renforce par laser. Mesure des fractions ioniques relatives pour les metaux alcalins

THEORY OF LASER-ENHANCED IONIZATION IN FLAMES - COMPARISON WITH EXPERIMENTS

Opto-galvanic or laser-enhanced ionization (LEI) spectroscopy has been performed on trace elements in a flame using one- and two-step laser excitations. The sensitivity, defined as the LEI signal divided by the laser pulse energy and the concentration of the trace element in the water solution aspirated into the flame, has been measured for a number of elements. A theoretical model for the LEI process has been developed and tested. The importance of energy levels, not involved in the laser transitions, is emphasized. The agreement between theory and experiment is satisfactory. Possible reasons for discrepancies which arise are discussed.

Laser-enhanced ionization spectrometry with a total consumption burner

Les diverses configurations d'electrode possibles sont comparees en utilisant l'indium comme analyte

Dual Laser Ionization in Flames: A Search for Electrical Interferences

Experimental studies of electrical interferences in the dual laser ionization technique are reported and compared to those commonly encountered in laser-enhanced ionization spectrometry. For the dual laser ionization of sodium, the addition of easily ionized matrix components such as cesium, lithium, and potassium were found to have little or no effect on signal recovery. Similar results were obtained in experiments with lithium and strontium as the analytes. Some chemical interferences were found and discussed.

Evaluation of electrode configurations for high voltage interferent removal in laser-enhanced ionization spectrometry

The laser-enhanced ionization (LEI) signal results from a change in flame impedance produced by collisional ionization of laser-excited analyte atoms. Perturbations in the electrical composition of the flame due to high ion concentrations suppresses the LEI signal. Since the predominant source of electrical interferences is low ionization potential concomitants, high voltage electrodes might be used to remove interfering species prior to signal collection. High voltage interference removal precludes the use of the burner head as the signal collection anode so other electrode configurations were investigated. The optimum electrode geometry was determined and used for experimental evaluation of various removal electrode configurations. The appearance of anomalous signals was investigated and explained. The combination of the optimum signal collection and interference removal electrode geometry produced improvement in LEI signal recovery. The advantages and deficiencies of this system are discussed and compared with other approaches.

Continuous wave excitation in laser-enhanced ionization spectrometry

Continuous wave excitation in laser-enhanced ionization spectrometry

Reduction of matrix ionization interference in laser-enhanced ionization spectrometry

Reduction of matrix ionization interference in laser-enhanced ionization spectrometry

Acid effects in laser-enhanced ionization spectrometry

Acid effects in laser-enhanced ionization spectrometry