Furnace Atomic Non-thermal Excitation Spectrometry Research Articles

A geração química de vapor em espectrometria atômica

The historical development of atomic spectrometry techniques based on chemical vapor generation by both batch and flow injection sampling formats is presented. Detection via atomic absorption spectrometry (AAS), microwave induced plasma optical emission spectrometry (MIP-OES), inductively coupled plasma optical emission spectrometry (ICP-OES) , inductively coupled plasma mass spectrometry (ICP-MS) and furnace atomic nonthermal excitation spectrometry (FANES) are considered. Hydride generation is separately considered in contrast to other methods of generation of volatile derivatives. Hg ¾ CVAAS (cold vapor atomic absorption spectrometry) is not considered here. The current state-of-the-art, including extension, advantages and limitations of this approach is discussed.

Simultaneous determination of hydride forming elements by furnace atomic nonthermal excitation spectrometry (FANES)

Different approaches for the simultaneous determination of arsenic, antimony, bismuth, selenium and tellurium by furnace atomic nonthermal excitation spectrometry (FANES) are described. In the direct analysis of microvolumes of solutions, the results could be improved by working with Pd or Ir as chemical modifiers for the stabilization of the analytes during the thermal pre-treatment. Using Ir as a modifier, absolute detection limits of 0.116 ng (As), 0.062 ng (Bi), 0.044 ng (Sb), 0.316 ng (Se) and 0.016 ng (Te) could be realized. The combination of hydride generation and in situ enrichment of the analytes onto a permanent Ir-treated inner surface of the graphite tube of the FANES source has been used as pre-concentration technique. The conditions for all steps, hydride generation, pre-reduction, in situ enrichment, atomization and excitation have been studied. Using compromise conditions for the simultaneous determination of all the elements using a sample volume of 20 ml, relative detection limits of 0.032 μg l −1 As 3+, 0.015 μg l −1 Bi 3+, 0.012 μg l −1 Sb 3+, 0.047 μg l −1 Se 4+ and 0.009 μg l −1 Te 4+ are obtained. The influence of hydride forming elements on the determination of each of the elements by the technique of vapour generation and in situ enrichment is studied. The results are validated using standard reference materials.

Determination of mercury by furnace atomic nonthermal excitation spectrometry

The determination of Hg using different variants of the Furnace Atomic Nonthermal Excitation Spectrometry (FANES) is described. In the direct analysis of micro volumes of solutions, the results could be improved by working with chemical modifiers for the stabilization of Hg during the thermal pretreatment. The best results were obtained using Ir and Pd as modifiers, with absolute detection limits of 4 and 12 pg, respectively. The determination of mercury in sample volumes up to 10 ml could be achieved by coupling a cold vapour generation system and an amalgam attachment to the FANES source. A detection limit of 22 ng l was obtained with this technique. The best results were obtained by using the cold vapour generation technique and in situ enrichment of Hg onto the modified inner surface of the graphite tube of the FANES source. Using Ir for permanent impregnation of the tube a detection limit of 0.0009 μ;g l was found. The influence of hydride forming elements on the determination of mercury by the technique of vapour generation and in situ enrichment was studied. A reduction of the concentration of NaBH 4 to 0.002% m/v made it possible to determine traces of mercury in presence of a high excess of hydride forming elements without any depression of the Hg emission intensity. The results were validated using standard reference materials.

Study of the atomization of boron in electrothermal atomic absorption spectrometry and hollow cathode furnace atomic non-thermal excitation spectrometry

Coating a total pyrolytic graphite tube with tungsten carbide or lanthanum carbide increased the optimum pyrolysis temperature of B from 850 to > 2200 °C. Addition of a calcium–magnesium modifier to the boron solutions increased the pyrolysis temperature to 1200 °C, whereas a titanium-ascorbic acid modifier had no significant effect. The lowest characteristic mass of B, 0.8 ng, was obtained with the calcium–magnesium modifier. The low temperature loss of boron, without a modifier, was investigated using dynamic secondary-ion mass spectrometry, which confirmed that vaporization of boron species occurs above 900 °C. Boron atomic emission signals were obtained at <800 °C by hollow cathode furnace atomic non-thermal extraction spectrometry (HC-FANES) with a 30 Torr helium plasma. Molecular dissociation and boron atom excitation apparently occurred through a one-step collisional process. The detection limit of B by He HC-FANES, under non-optimum conditions, was 71 pg (no modifier). The study suggests that atomization of B in electrothermal atomic absorption spectrometry (ETAAS) is likely to occur through molecular dissociation rather than solely by sublimation of B. The modifiers probably prevent low temperature dissociative desorption of B2O3 occurring at active carbon sites and so increased the optimum pyrolysis temperature to >850 °C. The poor detection limit of B in ETAAS is due to the inefficient thermal dissociation of the B-containing species (probably oxides and carbides) produced by dissociative desorption of B2O3. Also, once formed, B atoms apparently undergo a series of condensation–vaporization steps, which cause a persistant plateau in the tail of the AAS signal, and result in severe memory effects.

Evaluation of cold vapour furnace atomic non-thermal excitation spectrometry for the determination of mercury in environmental samples

Furnace atomic non-thermal excitation spectrometry (FANES) was used to determine Hg following reduction with tin(II) chloride and in situ preconcentration in the graphite tube lined with Pt gauze. Response surface methodology was used to optimize the discharge pressure and current for maximum signal-to-noise ratios. The absolute detection limit under optimum conditions was 20 pg, and the linear calibration range extended to 20 ng, limited by incomplete removal of Hg from the FANES source during one atomization sequence. Three environmental standard reference materials (SRM 1572 “Citrus leaves”, SRM 1575 “Pine needles” and SRM 1645 “River sediment”) were prepared for analysis by microwave-assisted digestion, and accurate results were obtained for the determination of Hg at the sub μg g −1 level using calibration against simple aqueous standards.

Studies on the application of platform atomization to furnace atomic non-thermal excitation spectrometry for the simultaneous multi-element analysis of environmental materials

Response surface methodology was used to optimize the discharge current and pressure with respect to detection limits for the simultaneous multi-element determination of Al, Cd, Cr, Cu, Fe, Ni and Pb by furnace atomic non-thermal excitation spectrometry (FANES). Comparison of wall and platform atomization showed improved detection limits for most elements with the latter. Despite the use of automatic background correction by wavelength modulation, residual background signals were observed at all lines, those on the Cd, Cu, Fe and Pb channels being rectified by including an ‘autozero’ procedure in the data processing software. For the remaining elements, spectral interferences disrupted the baseline during the atomization step, although blank subtraction provided satisfactory correction. Nevertheless, the presence of structured background emission poses a potentially serious source of error in FANES measurements. In the multi-element analysis of microwave-assisted digests of three environmental reference materials [National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1572 Citrus Leaves, SRM 1575 Pine Needles and SRM 1645 River Sediment] by platform-equipped FANES, non-spectral interferences arose for all analytes except Cd and Pb. The use of the standard additions method was thus necessary for calibration purposes.

Graphite furnace analysis—getting easier and achieving more?

The impact of microwave digestion, hot injection of solutions and chemical modification on the analysis of biological samples by electrothermal atomic absorption spectrometry (AAS) has been assessed. The stabilizing effects of palladium and ruthenium modifiers were compared. Although ruthenium has a higher atom appearance temperature, palladium was the more useful modifier when samples other than water were analysed. When 2 μg of palladium (as PdCl 2) was preconditioned in hydrogen at 500°C, volatile elements were retained at char temperatures up to 1000–1100°C. This allowed similar atomizer programmes to be used for Cd, Cu, Fe, Mn and Pb and accurate determination of these analytes in solutions of reference materials was achieved aqueous standards. Rapid drying of the solutions by hot injection at 120°C reduced the programme time to just over 1 min. A combination of microwave digestion, hot injection of 40% (w/v) HNO 3 solutions and Pd modification produced a rapid and sensitive method for determination of Cd and Pb at sub-μg g −1 levels in vegetable and protein foodstuffs. Palladium modification also proved useful in simultaneous multi-element determination by continuum source AAS. The picogram detection limits obtained for Cr, Mn and Pb were similar to line source AAS values recorded with the same compromise programme. Accurate determination of Cd, Cr, Cu, Mn, Mo and Pb in NIST SRM 1566 Oyster Tissue indicated the potential of continuum source AAS for multi-element determinations. The advantages of palladium modifications were also illustrated for furnace atomic non-thermal excitation spectrometry ( FANES) with a hollow-cathode discharge. The maximum char temperatures of Ag, Ga, Hg, Pb, Sb and Se were increased by 300–600°C in the presence of 1 μg of Pd, although the detection limits were a factor of two poorer.

Investigations on the determination of chloride and bromide by furnace atomic non-thermal excitation spectrometry and furnace ionic non-thermal excitation spectrometry

The determination of chloride and bromide by non-thermal excitation spectrometry in a graphite furnace using both atomic and ionic spectral lines was investigated. The most sensitive determinations could be made at the ionic lines Cl II 479.545 nm and Br II 470.486 nm. The addition of an ionization buffer provided constant plasma conditions resulting in improved linearity of the calibration function. Under optimum conditions and in the presence of appropriate buffers detection limits of 0.6 ng for chloride and 2 ng for bromide were obtained.

Tandem sources using electrothermal atomizers: analytical capabilities and limitations

Tandem emission sources with electrothermal volatilization and atomization of the sample, such as furnace atomic non-thermal excitation spectrometry (FANES) or furnace atomization plasma emission spectrometry, are compared with other excitation sources, e.g., an inductively coupled plasma. The interdependence between the excitation and atomization processes, which causes restrictions for analytical procedures, is considered. Of particular interest for the analytical applications of tandem sources is the influence of matrix constituents on the excitation conditions. Furnace atomizers are able to form relatively high matrix concentrations in the excitation plasma, which can lead to a breakdown of the initial electron energy distribution. Correspondingly, depression of the analytical signals by the matrix has been found for FANES, which leads to some general conclusions on tandem sources.

Application of furnace atomic non-thermal excitation spectrometry for the determination of non-metals

Various atomic spectrometry techniques are used for the determination of elemental concentrations in a wide range of samples. Although procedures for the determination of metallic impurities are well established, the development of successful methods for the measurement of non-metal elements at trace levels has proved more difficult. In particular, better methods are required for the determination of B, Cl, P, S, Si, etc., in industrial and clinical samples.

Analytical applications of furnace atomic non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part. 5. Study of the MONES of PO and HPO for the determination of trace amounts of phosphorus

A method for the determination of phosphorus by the molecular non-thermal excitation spectrometry (MONES) of PO and HPO has been developed. The phosphorus was introduced into the furnace atomic non-thermal excitation spectrometry (FANES) source as a solution of sodium dihydrogen phosphate. The measurements were carried out at the bands that gave the maximum signals, for PO at 246.4 nm and for HPO at 507 nm. The electrical, thermal and chemical conditions were optimised and are discussed. In addition, the influence of La3+ as a chemical modifier on the MONES of PO and HPO was investigated. The best values for the detection limit were 700 pg of P (MONES of PO) and 3400 pg of P (MONES of HPO). By comparison with the best values obtained with commercial electrothermal atomisation atomic absorption spectrometry instruments, these values are better by factors of 8 and 1.6, respectively. However, the determination of P by FANES at 213.5/213.6 nm is the best method for investigations of phosphorus using the FANES source, in the presence of La3+ as a chemical modifier.

Furnace atomic non-thermal excitation spectrometry with the furnace as a hollow anode

Furnace atomic non-thermal excitation spectrometry with the furnace as the hollow anode (HA-FANES) was characterised for the determination of Cd and Cu. Operating in the abnormal glow discharge region, the current was limited by the current density at the cathode. Higher currents were attained with a larger diameter cathode and at higher pressures. The emission signals were dependent on the current density. More intense signals were observed when viewing the top and left of the discharge. This positional dependence of the signal strength was much more pronounced for Cu than for Cd. Peak areas and signal to noise ratios increased linearly with the discharge pressure to a maximum of 25.3 kPa. Emission intensities were constant as a function of the discharge current above a threshold of 20 mA for Cd and 50 mA for Cu. Both Cd and Cu gave the largest peak areas at the lowest atomisation temperature (1390 °C). The peak areas decreased roughly in proportion to the increased diffusion coefficients at higher temperatures. The detection limits for HA-FANES (0.8 and 1.5 pg for Cd and Cu, respectively) are comparable to those for conventional FANES with the furnace as a hollow cathode and graphite furnace atomic absorption spectrometry.

Analytical applications of furnace atomic non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part 4. Determination of trace amounts of phosphorus by FANES

A method of determining phosphorus by furnace atomic non-thermal excitation spectrometry (FANES) has been developed. The phosphorus is introduced into the FANES source as a solution of sodium dihydrogen phosphate. The measurements are carried out at 213.5/213.6 and 253.3/253.5 nm, the transition at 213.5/213.6 nm being the more sensitive one. The thermal and chemical conditions were optimised, the best chemical modifier being La3+ ions as they stabilise phosphate ions as LaPO4. Using the optimum amount of lanthanum (2 µg) the pre-treatment temperatures could be increased considerably (300 to 800 °C at normal pressure and 350 to 400 °C at low pressure). The best detection limit obtained is 90 pg of phosphorus, which is an improvement by a factor of 60 in comparison with the best values obtained with commercially available electrothermal atomisation atomic absorption spectrometric (ETAAS) instruments. Examples for real analyses with associated matrix interferences are given.

Contributions to biological analysis by atomic spectrometry — A summary of the achievements of Professor John Michael Ottaway

John Ottaway was the head of the Analytical Chemistry Research Group at the University of Strathclyde for almost 20 years and during that period much of the research performed by the Group was devoted to the development of improved analytical procedures for the determination of trace metals in clinical and biological samples. Although this was only one aspect of the Group's activities in analytical chemistry, a number of significant contributions were made in the clinical field and a summary of Professor Ottaway's achievements is given in this brief review. The techniques covered include electrothermal atomisation atomic absorption spectrometry (ETA-AAS), electrothermal atomisation atomic emission spectrometry (ETA-AES), furnace atomic non-thermal excitation spectrometry (FANES), continuum source atomic absorption spectrometry (CSAAS) and atomic fluorescence spectrometry (AFS).

Multivariate optimisation of simultaneous multi-element analysis by furnace atomic non-thermal excitation spectrometry (FANES)

For the simultaneous determination of Ni, Co, Cu and Cr by furnace atomic non-thermal excitation spectrometry (FANES), the optimum atomisation temperature Tat, gas discharge pressure pAr and discharge current iHK of the FANES emission source with respect to the signal to noise ratio (SNR) are determined. As the maximum values of each of the SNRs are not achieved simultaneously, a statistical optimisation method including both grid search and differential extreme value evaluation is applied to the compromise conditions.

Comments on the characteristics of an atomiser for furnace atomic non-thermal excitation spectrometry (FANES)

A brief study of the analytical characteristics of a commercial FANES atomiser is reported. Experiments were performed to assess the influence of the FANES discharge on Cd analyte atom formation and matrix interference effects. An attempt was made to measure changes in the electron concentration under different operating conditions from Hβ line profile measurements but only general trends could be identified. The temperature of the atomiser tube was shown to have an influence on the nature of the FANES background spectrum.

Studies on the determination of cadmium in blood by furnace atomic non-thermal excitation spectrometry.

Cadmium atomic emission can be detected in a FANES low-pressure Ar discharge at atomiser temperatures as low as 140 deg;C when the analyte is present as CdCl2. Cadmium chloride molecules vaporised at this temperature are dissociated by electron impact in the discharge, giving a substantial Cd atom concentration before thermal dissociation of the molecules becomes feasible. This results in a 100-fold greater tolerance towards chloride matrix chemical interferences than encountered for Cd in ETA-AAS with tube-wall atomisation. However, the determination of cadmium in deproteinised whole blood by FANES is not totally interference free and a standard additions procedure is required to give an accurate determination. The FANES instrument detection limit for Cd was calculated to be 0.04 µg l–1. For the deproteinisation procedure applied, the detection limit for cadmium in whole blood was 0.2 µg l–1.

FANES (furnace atomic nonthermal excitation spectrometry)—a new emission technique with high detection power

A new emission source with independent atomization and excitation processes is described. The sample vapour formed by an electrothermal furnace is excited with the help of a glow discharge. The limits of detection found with FANES are comparable with the best values of furnace absorption and better than those of the ICP emission technique. Finally a practical example is given showing the high dynamic range and multi-element capability of the new method.