Helmut H. Telle

Application of laser-induced breakdown spectroscopy to in situ analysis of liquid samples

A realization of laser-induced breakdown spectroscopy for real-time, in situ and remote analysis of trace amounts in liquid samples is described, which is potentially applicable to the analysis of pollutants in water in harsh or difficult-to-reach environments. Most of the measurements were conducted using a fiber assembly that is capable of both delivering the laser light and collecting the light emitted from the micro plasma, up to about 30 m from the target area. Alternatively, a telescopic arrangement for line-of-sight measurements was employed, with a range of 3 to 5 m. For internal standardization and the generation of concentration calibration curves, reference lines of selected elements were used. In the majority of cases calibration against the matrix element hydrogen was employed using the H?, H?, and H? lines, but also spiking with selected reference species was utilized. In order to provide high reliability and repeatability in the analyses, we also measured plasma parameters such as electron density, plasma temperature, and line- shape functions, and determined their influence on the measurement results. Numerous elements, including a range of toxic heavy metals, have been measured over a wide range of concentrations (Al, Cr, Cu, Pb, Tc, U, and others). Limits of detection usually were in the range of a few parts per million; for several elements even lower concentrations could be measured.

Quantitative laser-induced breakdown spectroscopy analysis of calcified tissue samples

Ž. We report on the application of laser-induced breakdown spectroscopy LIBS to the analysis of important minerals and the accumulation of potentially toxic elements in calcified tissue, to trace e.g. the influence of environmental exposure, and other medical or biological factors. This theme was exemplified for quantitative Ž detection and mapping of Al, Pb and Sr in representative samples, including teeth first teeth of infants, second teeth .Ž

Quantitative analysis using remote laser-induced breakdown spectroscopy (LIBS)

A measurement system for quantitative, remote materials analysis has been realised. It is based on the method of laser-induced breakdown spectroscopy (LIBS), utilising an optical fibre system, both to deliver the laser radiation to the sample specimen and to collect the light emission from the luminous plasma plume. Distances of up to 100 m between the remote location and the apparatus have been demonstrated. All experiments were performed in situ, under standard conditions of air at atmospheric pressure. In particular, quantitative analysis of ferrous specimens has been achieved, detecting traces of the elements Cr, Cu, Mn, Mo, Ni, Si and V, down to relative concentrations of about 200 ppm. This remote analytical technique has been implemented successfully for measurements in the hostile environment of nuclear reactor buildings.

Quantitative analysis of trace metal ions in ice using laser-induced breakdown spectroscopy

Abstract This work reports on a simple, quick-freeze method for the quantitative analysis of trace metal ions in liquids applying the laser-induced breakdown spectroscopy (LIBS) technique. Using this procedure with calibrated samples, well-characterized linear working curves were determined for Na and Al water solutions over the 0.01–1% concentration range. This allowed detection limits of the order of ppm. In addition, optimum experimental conditions were found that allow the analysis to be carried out in a fast and very easy manner, without the limitations and difficulties found with liquid samples. The advantages of this simple and direct method, developed and patented by the Instituto Pluridisciplinar–UCM, are discussed, and potential applications for industrial analysis are also suggested.

Sensitive and selective spectrochemical analysis of metallic samples: the combination of laser-induced breakdown spectroscopy and laser-induced fluorescence spectroscopy ☆

Abstract In order to improve on analytical selectivity and sensitivity, the technique of laser-induced fluorescence spectroscopy (LIFS) was combined with laser-induced breakdown spectroscopy (LIBS). The main thrust of this investigation was to address analytical scenarios in which the measurement site may be difficult to access. Hence, a remote LIBS+LIFS arrangement was set up, and the experiments were carried out on samples surrounded by air at atmospheric pressure, rather than in a controlled buffer gas environment at reduced pressure. Representative for proof of principle, the detection of aluminium, chromium, iron and silicon at trace level concentrations was pursued. These elements are of importance in numerous chemical, medical and industrial applications, and they exhibit suitable resonance transitions, accessible by radiation from a pulsed Ti:sapphire laser system (its 2nd and 3rd harmonic outputs). All investigated elements have an energy level structure in which the laser-excited level is a member of a group of closely-spaced energy levels; thus, this allowed for easy off-resonant fluorescence detection (collisional energy transfer processes). Since numerous of the relevant transition wavelengths are within a narrow spectral interval, this opens the possibility for multi-element analysis; this was demonstrated here for Cr and Fe which were accessed by rapidly changing the tuneable laser wavelength.

Single-pulse laser-induced breakdown spectroscopy of samples submerged in water using a single-fibre light delivery system

Abstract Using a novel laser-induced breakdown spectroscopy set-up, accurate quantitative analysis of samples submerged in liquids has been demonstrated. The measurements were conducted using a single-fibre plus plastic tube assembly of 20 m length. This delivered the ablation laser light pulse and a buffer gas flow to the sample surface, and collected the light emitted by the micro-plasma for analysis. No distil optics were used at the sample end of the fibre. Argon, nitrogen and compressed air were used as buffer gases; while the rare gas resulted in slightly better signal-to-noise ratios, most analytical measurements were carried out with nitrogen for convenience and to provide comparability with in-air measurements. Detection limits and reproducibility were comparable to those achieved for the same samples placed in standard ambient air, with all other experimental conditions unchanged. In standard steel samples, detection limits of 310±45, 325±48 and 455±55 ppm for Cr, Mn and Si, respectively, could be achieved. Pattern recognition algorithms were used to identify, for classification, spectra of specimen submerged in turbid and non-transparent liquids.

Monitoring of tritium purity during long-term circulation in the KATRIN test experiment LOOPINO using Laser Raman Spectroscopy

Abstract The gas circulation loop LOOPINO has been set up and commissioned at Tritium Laboratory Karlsruhe (TLK) to perform Raman measurements of circulating tritium mixtures under conditions similar to the inner loop system of the neutrino-mass experiment KATRIN, which is currently under construction. A custom-made interface is used to connect the tritium containing measurement cell, located inside a glove box, with the Raman setup standing on the outside. A tritium sample (purity > 95 %, 20 kPa total pressure) was circulated in LOOPINO for more than three weeks with a total throughput of 770 g of tritium. Compositional changes in the sample and the formation of tritiated and deuterated methanes CT4-nXn (X=H,D; n=0,1) were observed. Both effects are caused by hydrogen isotope exchange reactions and gas-wall interactions, due to tritium β decay. A precision of 0.1 % was achieved for the monitoring of the T2 Q1-branch, which fulfils the requirements for the KATRIN experiment and demonstrates the feasibility of high-precision Raman measurements with tritium inside a glove box.

Design and operation of a two-stage positron accumulator

A compact positron accumulator based upon a simple two-stage buffer gas cooling scheme is described. Its operation to produce 10–20ns wide bursts containing around 105 positrons with cycling times in the 100msto1s range is discussed. Departures of the behavior of the accumulator from that expected of such an instrument are presented. The utility of these effects in diagnosing accumulator performance is described.

Automated Quantitative Spectroscopic Analysis Combining Background Subtraction, Cosmic Ray Removal, and Peak Fitting

An integrated concept for post-acquisition spectrum analysis was developed for in-line (real-time) and off-line applications that preserves absolute spectral quantification; after the initializing parameter setup, only minimal user intervention is required. This spectral evaluation suite is composed of a sequence of tasks specifically addressing cosmic ray removal, background subtraction, and peak analysis and fitting, together with the treatment of two-dimensional charge-coupled device array data. One may use any of the individual steps on their own, or may exclude steps from the chain if so desired. For the background treatment, the canonical rolling-circle filter (RCF) algorithm was adopted, but it was coupled with a Savitzky–Golay filtering step on the locus-array generated from a single RCF pass. This novel only-two-parameter procedure vastly improves on the RCFs deficiency to overestimate the baseline level in spectra with broad peak features. The peak analysis routine developed here is an only-two-parameter (amplitude and position) fitting algorithm that relies on numerical line shape profiles rather than on analytical functions. The overall analysis chain was programmed in National Instruments LabVIEW; this software allows for easy incorporation of this spectrum analysis suite into any LabVIEW-managed instrument control, data-acquisition environment, or both. The strength of the individual tasks and the integrated program sequence are demonstrated for the analysis of a wide range of (although not necessarily limited to) Raman spectra of varying complexity and exhibiting nonanalytical line profiles. In comparison to other analysis algorithms and functions, our new approach for background subtraction, peak analysis, and fitting returned vastly improved quantitative results, even for “hidden” details in the spectra, in particular, for nonanalytical line profiles. All software is available for download.

Laser ablation for mineral analysis in the human body: integration of LIFS with LIBS

Trace mineral analysis of the body is invaluable in biology, medicine and dentistry when considering the role of mineral nutrition and metabolism in the context of maintaining human health. The presence of key elements in the body, such as boron, calcium, chromium, copper, iron, silicon and zinc are known to be of vital importance, but are often found to be present in inadequate quantity. In sharp contrast, the accumulation of other elements, such as aluminum, cadmium, lead and mercury is less favorable, since frequently these metals are already toxic at extremely low concentration levels, interfering with essential chemical processing of vitamins and minerals. Here we report on the application of laser-induced breakdown spectroscopy and laser-induced fluorescence spectroscopy to the analysis of important minerals and toxic elements within the body. Samples from different parts of the body have been studied, including specimens of skin tissue, finger nails and teeth. It is particularly noteworthy that specific sample preparation was not needed for any of these laser spectroscopic measurements, but that specimens could be used as taken from the source.