Simultaneous multi-element determination with coherent forward scattering spectrometry employing chromatically corrected polarizers and a fast scanning spectrometer

A new coherent forward scattering spectrometer for simultaneous multi-element determination on up to 20 atomic lines has been constructed and evaluated. The apparatus consists of a continuum primary source, calcite Glan-Taylor polarizers equipped with a laboratory-designed chromatic correction for the wavelength range 214–766 nm, an electrothermal atomizer with magnet and autosampler and a laboratory-constructed wavelength modulated polychromator with medium resolving power. Light intensities of up to 20 resonance lines in the wavelength range of 214–500 nm are transferred from the focal plane to an array of 20 miniature photomultipliers by optical fiber-bundles. The instrumentation is controlled by a computer. Owing to modular construction the graphite furnace can be exchanged by a flame. Simultaneous multi-element determinations of Ag, Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mn, Na, Ni, Pb, Sr, Tl and Zn are carried out. The received analytical curves cover 1.5–2.5 orders of magnitude per atomic line, which is in the same order as with multi-element measurements with electrothermal atomic absorption spectrometry (ETAAS). Further working range expansions are demonstrated with determining on resonance lines with different strengths. The detection limits for the strongest resonance line of most elements are in the μg l⁻¹-range and are one order of magnitude higher than those measured with commercially available ETAAS instrumentation when determining four elements simultaneously. The crossed-to-open extinction ratio of the chromatically corrected Glan-Taylor polarizers is determined to approximately 2.5×10⁻⁵ under installed conditions with the graphite furnace and its two windows in between. The spectral transmissions of these polarizers and the optical fiber-bundles are measured with a photometer. It shows a steep decay for wavelengths below 220 nm.     

Laser atomic absorption spectrometry of excited Hg in a discharge applying sum frequency mixing of two diode lasers (preliminary results)

Wavelength modulation diode laser atomic absorption spectrometry is applied to the detection of atomic mercury. Transitions from metastable energy levels highly populated in a radio-frequency discharge are induced with laser diodes by use of nonlinear techniques. The wavelength of one strong transition at 365.119 nm with a high oscillator strength is obtained by sum frequency generation of two diode lasers. The cold vapor technique is used to transfer ionic into atomic mercury. The mercury in the vapor phase is transported by an argon stream into the discharge tube. From the time-dependent absorption signals detection limits of 100 ng/L are achieved at this state of research.     

Laser atomic absorption spectrometry of excited Hg in a discharge applying sum frequency mixing of two diode lasers (preliminary results)

Wavelength modulation diode laser atomic absorption spectrometry is applied to the detection of atomic mercury. Transitions from metastable energy levels highly populated in a radio-frequency discharge are induced with laser diodes by use of nonlinear techniques. The wavelength of one strong transition at 365.119 nm with a high oscillator strength is obtained by sum frequency generation of two diode lasers. The cold vapor technique is used to transfer ionic into atomic mercury. The mercury in the vapor phase is transported by an argon stream into the discharge tube. From the time-dependent absorption signals detection limits of 100 ng/L are achieved at this state of research.     

Wavelength modulation diode laser atomic absorption spectrometry in analytical flames

The potential of wavelength modulation laser atomic absorption spectrometry in analytical flames is demonstrated by the measurement of titanium, cesium and chromium applying fundamental and frequency doubled radiation of commercially available semiconductor diode lasers. In dependence on the radiation power, absorbances of the order of 10⁻⁴–10⁻⁶ are measured, which reveal very low detection limits even when weak absorption lines are used.     

Status and future prospects for use of the graphite furnace for elemental trace analysis of liquids and solids

Summary An overview of the versatility and use of the graphite furnace for elemental trace analysis of liquids and solids using spectrochemical detection is presented. The analytical performance of conventional graphite furnace atomic absorption spectrometry is compared to other popular state of the art spectrochemical techniques with respect to detection power, precision, sample compatibility and throughput. Some applications of the graphite furnace to practical problem solving in trace analysis are highlighted, including its use with atomic absorption, coherent forward scattering, laser excited atomic fluorescence, laser enhanced ionization and coupled methodologies. Prospects for future use and evaluation are given.     

Element selective detection of chlorine in capillary gas chromatography by wavelength modulation diode laser atomic absorption spectrometry in a microwave induced plasma

A new element selective detector for gas chromatography is presented. The detector, based on wavelength modulation diode laser atomic absorption spectrometry in a microwave induced helium plasma, is used for measurements of chlorinated hydrocarbons by absorption of excited, metastable chlorine atoms. Indications of complete dissociation of the halocarbons in the plasma have been found. Preliminary detection limits of the order of 1 μg ml⁻¹ or 80 pg s⁻¹ have been found for different halocarbons.     

Different platform and tube geometries and atomization temperatures in graphite furnace atomic absorption spectrometry: Cadmium determination in whole blood as a case study

In the present work the performance of different platform and tube geometries and atomization temperatures in graphite furnace atomic absorption spectrometry was investigated, using the determination of Cd in whole blood as an example. Grooved, integrated and fork platforms as well as atomization temperatures between 1200 °C and 2200 °C were investigated in a longitudinally heated graphite atomizer and compared with the performance of a transversely heated furnace. In the longitudinally heated furnace the increase of the atomization temperature in the studied range resulted in an increase of matrix effects for all platform geometries. The integrated platform exhibited slightly lower sensitivity and increased multiplicative interferences in comparison to the other two platform designs. Interference-free Cd determination was possible with all types of platforms and 1200 °C as the atomization temperature as well as with grooved and fork platforms at 1700 °C. On the other hand, lower atomization temperatures resulted in poorer limits of detection, due to the longer integration time needed. No matrix effect was observed at any atomization temperature using the transversely heated atomizer; in addition, limits of detection were better than those observed with the longitudinally heated atomizer. Best values were around 0.02 μg L^− 1 with the latter atomizer compared to values around 0.02 μg L^− 1 with the former one.     

Isotope selective element analysis by diode laser atomic absorption spectrometry

The analytical figures of merit of isotope selective diode laser atomic absorption spectrometry (DLAAS) in low-pressure graphite furnaces are given for lithium and rubidium. While⁶Li and⁷Li were measured by Doppler-limited as well as by Doppler-free absorption spectroscopy of the 670.79 nm resonance line, Doppler-free saturation spectroscopy was applied for analysis of the⁸⁵Rb and⁸⁷Rb D2 resonance line at 780.03 nm. Three different modulation techniques were applied and compared: (i) intensity modulation, (ii) wavelength modulation, and (iii) a combination of intensity and wavelength modulation.     

Measurement of Cr(III)/Cr(VI) species by wavelength modulation diode laser flame atomic absorption spectrometry

High-performance flow atomic spectrometry of Cr(III) and Cr(VI) species by high-performance liquid chromatography (HPLC) separation, hydraulic high-pressure nebulization (HHPN) for sample introduction and wavelength modulation-laser atomic absorption spectrometry (WM-LAAS) with diode lasers in an analytical flame is reported. 3σ detection limits of 0.5 and 1 ng ml⁻¹ have been obtained for Cr(VI) in deionized and drinking water, respectively. Due to relatively high blank levels, the corresponding detection limits of Cr(III) are higher than for Cr(VI), i.e. 1.6 ng ml⁻¹ in deionized water and 5 ng ml⁻¹ in drinking water.     

A direct solid sampling electrothermal atomic absorption spectrometry method for the determination of silicon in biological materials

A solid sampling electrothermal atomic absorption spectrometry method for direct determination of trace silicon in biological materials was developed and applied to analysis of pork liver, bovine liver SRM 1577b and pure cellulose. The organic matrix was destroyed and expelled from the furnace in the pyrolysis stage involving a step-wise increasing the temperature from 160 °C to 1200 °C. The mixed Pd/Mg(NO₃)₂ modifier has proved to be the optimum one with respect to the achievement of maximum sensitivity, elimination of the effect of the remaining inorganic substances and the possibility of using calibration curves measured with aqueous standard solutions for quantification. For the maximum applicable sample amount of 6 mg, the limit of detection was found to be 30 ng g^− 1. The results were compared with those obtained by different spectrometric methods involving sample digestion, by electrothermal atomic absorption spectrometry using slurry sampling, by wavelength dispersive X-ray fluorescence spectrometry and by radiochemical neutron activation analysis. The method seems to be a promising one for analysis of biological materials containing no significant fraction of silicon in form of not naturally occurring volatile organosilicon compounds. The still incessant serious limitations and uncertainties in the determination of trace silicon in solid biological materials are discussed.     

Diode-laser atomic-absorption spectrometry by the double-beam—double-modulation technique

The limitations of absorption measurements in atomic-absorption spectrometry with tunable diode lasers are investigated. It is shown that the double modulation technique (diode-laser wavelength modulation and sample modulation) with detection at the sum or difference frequency suppresses spurious etalon effects, background absorption, residual diode-laser-amplitude modulation and the noise which accompanies these effects, and enables measurement of detection limits determined by the laser excess noise. Detection limits in absorption, defined as absorption equal to the root-mean square value of noise, as low as 1 × 10⁻⁶ AU (absorption units) were achieved for metastable Cl atoms in a modulated low-pressure microwave-induced plasma with a time constant of 1 s. In order to eliminate laser excess noise and signal variations due to changes of optical transmittance, a double-beam arrangement with logarithmic subtraction of sample and reference detector currents was developed. It enables suppression of variations of the laser radiation power outside the detection pass-band and the achievement of a detection limit of about 2 × 10⁻⁷ AU determined by shot noise only.     

Atomic absorption with ultracold atoms

Recent advances in laser-atom cooling techniques and diode-laser technology now allow one to conduct an idealised atomic absorption experiment comprising a sample of ultracold, quasi-stationary absorbing atoms and a source of near-monochromatic resonant light. Under such conditions, the atomic absorption coefficient at line centre is independent of the oscillator strength of the atomic resonance line. This offers the prospect of ‘oscillator-strength-free’ atomic absorption spectroscopy in which the absorption signal is equally large for both strong and weak (closed) transitions of the same wavelength and in which absolute atomic absorption could be performed without knowledge of the oscillator strength. Moreover, the resolution and sensitivity for a given atom density are greatly enhanced, typically by approximately three orders of magnitude (and even more for weak transitions), compared with conventional flame or graphite-furnace atomic absorption. We describe an atomic absorption experiment based on samples of ultracold, laser-cooled caesium atoms and a narrow-bandwidth diode laser source that approximates the idealised conditions for oscillator-strength-free atomic absorption. The absorption measurements are used to determine the number density and temperature (approx. 6 μK) of the sample of ultracold atoms. Some of the technical obstacles that would have to be overcome before samples of ultracold atoms and diode laser sources could be used in analytical atomic absorption spectroscopy are discussed.     

Diode laser atomic absorption spectrometry

The paper reviews the past 11 years of literature on the application of diode lasers in atomic absorption spectrometry with graphite furnaces (GF), plasmas and flames as atomizers. Experimental arrangements and techniques for powerful absorption measurements as well as the theoretical background are covered. The analytical possibilities of high-resolution spectroscopy, including Doppler-free techniques for isotope selective measurements and isotope dilution analysis are discussed and various applications of element-selective detection by diode laser atomic absorption in combination with separation techniques, such as liquid (LC) and gas chromatography (GC), and with laser ablation of solid samples, are presented.     

The contributions of magnetically induced dichroism and the resonant Voigt effect to the detection of silver by atomic spectroscopy

A simple theoretical analysis, based on the classical theory of the transmission of polarized light through a polarizing medium, has been developed to examine the factors determining the intensity of resonance radiation transmitted by a magnetized atomic vapour interposed between a pair of crossed polarizers. In common with other studies, this analysis predicts a quadratic dependence of the transmitted intensity on atom concentration but in addition, indicates that even at low atom concentrations differential absorption (dichroism) may make a significant addition to the transmitted intensity arising from differential refraction (birefringence). Further, by introducing a small angular off-set between the crossed polarizers, the concentration dependence of the transmitted intensity at low concentration may be increased and linearized. Experiments using a flame-generated atomic vapour of silver with a silver hollow cathode lamp or deuterium lamp as light source confirmed these predictions. When a strong magnetic field (9.75 kG) was used, a detection limit of 0.3 ppm (= μg/ml) for silver, with a near linear response up to 20 ppm was obtained.     

原子吸收光谱和原子发射光谱法测定工业废水中的总铬

为了探讨原子吸收光谱法和原子发射光谱法测定工业废水中的总铬分析方法的异同,分别采用两种方法对工业废水中的总铬进行了对比分析,对样品前处理方法,方法的标准曲线、检出限、准确度、精密度、干扰及消除等进行了比较,并对两种方法的测定结果进行t检验。结果表明,两种方法具有良好的一致性。相对来说,原子发射光谱法各方面指标要优于原子吸收光谱法。     

Comparison of atomic absorption,mass and X-ray spectrometry techniques using dissolution-based and solid sampling methods for the determination of silver in polymeric samples

In this work, the capabilities and limitations of solid sampling techniques – laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), wavelength dispersive X-ray fluorescence spectrometry (WD-XRFS) and solid sampling electrothermal atomic absorption spectrometry (SS-ETAAS) – for the determination of silver in polymers have been evaluated and compared to those of acid digestion and subsequent Ag determination using pneumatic nebulization ICPMS (PN-ICPMS) or flame AAS (FAAS).     

Gas leak detection by diode laser absorption spectrometry

Diode laser atomic absorption measurements of argon traces in low-pressure discharges were carried out to detect and measure gas leaks in a test chamber. Helium flows as a carrier gas through the test chamber and the discharge. In the case of a leak, air and thus also its natural content of argon is mixed to the helium gas-flow through the chamber. The argon content of the mixed gas flow through the discharge is determined by wavelength modulation diode laser atomic absorption spectrometry. The resulting absorption signal is a measure for the existing leak-rate. For barometric pressure of ambient air lowest detectable leak rates are typically 10⁻⁶ mbar l s⁻¹. By application of pure Ar with pressures above 1 bar detectable leak rates can in practice be lower than 10⁻⁸ mbar l s⁻¹.     

Determination of trace impurities in aluminum nitride by direct solid sampling graphite furnace atomic absorption spectrometry

The trace impurities Cr, Cu, Fe, K, Mn, Sb and Zn were determined in powdered aluminum nitride by direct solid sampling graphite furnace atomic absorption spectrometry using a ZEEnit 60 atomic absorption spectrometer. This spectrometer features inverse Zeeman-effect background correction and a variable magnetic field enabling measurements in two sensitivity modes over a concentration range of three orders of magnitude. The measurement sensitivity can be adjusted to the analyte concentration in the sample. The use of chemical modifiers was not necessary. Calibration was carried out by means of calibration curves obtained with aqueous standard solutions. Accuracy was checked mainly by comparison of the results with those obtained by instrumental and radiochemical neutron activation analysis whereby, excluding the results for potassium, no significant differences were found by carrying out the t-test at the significance level 0.05. The limits of detection were between 0.05 ng g⁻¹ (Zn) and 80 ng g⁻¹ (Fe) and the relative standard deviations below 11 %. With the proposed method, up to ten measurement cycles can be carried out in one hour.     

Comparison of Pyrolysis and Microwave Acid Digestion Techniques for the Determination of Mercury in Biological and Environmental Materials

 Microwave digestion reduction-aeration and pyrolysis combined with cold vapour atomic absorption and cold vapour atomic fluorescence are compared for the determination of total mercury in several biological and environmental matrices. The biological samples were digested in a mixture of HNO₃/H₂O₂, the environmental samples in a mixture of HNO₃/HClO₄. After reduction with SnCl₂, the mercury was collected by two-stage gold amalgamation. After microwave digestion reduction-aeration, detection limits of 1.4 ng g⁻¹ and 0.6 ng g⁻¹ were obtained for cold vapour atomic absorption spectrometry (CVAAS) and cold vapour atomic fluorescence spectrometry (CVAFS), respectively, for 250 mg of environmental samples. For biological samples (500 mg) the detection limits were 0.7 ng g⁻¹ (CVAAS) and 0.4 ng g⁻¹ (CVAFS). After pyrolysis, detection limits of 3.5 ng g⁻¹ and 1.6 ng g⁻¹ for CVAAS and CVAFS, respectively, were obtained for a 10 mg sample. Pyrolysis can only be applied when the organic content of the sample is not too high. Accurate results were obtained for 8 certified reference materials of both environmental and biological origin. In addition, a real sludge sample was analysed. Author for correspondence. E-mail: richard.dams@rug.ac.be Received September 18, 2002; accepted December 3, 2002 Published online May 5, 2003     

Use of Te2 for frequency referencing and active stabilisation of a violet extended cavity diode laser

This paper reports on the use of ¹³⁰Te₂ absorption lines in active laser-locking, and in frequency referencing, of the emission of a violet extended cavity diode laser with a wavelength of around 410 nm. We note the existence of closely spaced tellurium absorption lines, suitable for referencing purposes in gas sensing applications, at wavelengths below the lower limit (417 nm) of the spectral region covered by the tellurium atlas [J. Cariou, P. Luc, Atlas du spectre d’Absorption de la Molecule de Tellure, CNRS, Paris, 1980]. The absolute positions of the lines in the acquired spectra were estimated by comparison to a simultaneously acquired fluorescence spectrum of atomic indium, and were identified using calculations based on fundamental spectroscopic data. The laser frequency was stabilised within a range of 40 MHz, which is negligible compared to typical transition widths at atmospheric pressure.