Electrothermal atomization with atomic detection

Laser-excited atomic fluorescence spectrometry is capable of extremely low detection limits, particularly when combined with electrothermal atomization. Detection limits in the femtogram (10 g) to attogram (10 g) range have been shown for many elements. Commercial instrumentation has not been developed for laser-based AFS, probably because of its expense and the nonroutine nature of high-powered lasers. Atomic fluorescence has the disadvantage of being a singleelement method unless tunable lasers with their inherent complexities are used. 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

Electrothermal atomic absorption spectrophotometry with Zeeman background correction was used by Zhang et al. [141] for the determination of cadmium in seawater. Citric acid was used as an organic matrix modifier and was found to be more effective than EDTA or ascorbic acid. The organic matrix modifier reduced the interferences from salts and other trace metals and gave a linear calibration curve for cadmium at concentrations < 1.6 pg/1. The method has a limit of detection of 0.019 pg/1 of cadmium and recoveries of 95-105% at the 0.2 pg of cadmium level. 

Nishioka et al. [525] coprecipitated nickel from seawater with sodium di-ethyldithiocarbamate, filtered, and redissolved the precipitate with nitric acid followed by electrothermal atomic absorption spectrophotography determination of the nickel. The detection limit was 0.5 p,g/l and the relative standard deviation was 13.2% at the 2 ig/l level. 

Chang et al. [952] used a miniature column packed with a chelating resin and an automatic online preconcentration system for electrothermal atomic absorption spectrometry to determine cadmium, cobalt, and nickel in seawater. Detection limits of 0.12,7 and 35 ng/1 were achieved for cadmium, cobalt, and nickel, respectively, with very small sample volume required (400-1800 xl). 

One often unsuspected source of error can arise from interference by the substances originating in the sample which are present in addition to the analyte, and which are collectively termed the matrix. The matrix components could enhance, diminish or have no effect on the measured reading, when present within the normal range of concentrations. Atomic absorption spectrophotometry is particularly susceptible to this type of interference, especially with electrothermal atomization. Flame AAS may also be affected by the flame emission or absorption spectrum, even using ac modulated hollow cathode lamp emission and detection (Faithfull, 1971b, 1975). 

Electrothermal atomizers are also suitable for AFS as, when an inert gas atmosphere is used, quenching will be minimized. In the nuclear, electronic, semiconductor and biomedical industries where detection limits have to be pushed as low as 1 part in lO (or 0.1 pg g- in the original sample), electrothermal atomization with a laser as excitation source (LIF-ETA) may be used. Figure 6.5 shows schematically a common way of observing the fluorescence in LIF-ETA. The fluorescence signal can be efficiently collected by the combination of a plane mirror, with a hole at its centre to allow excitation by the laser, positioned at 45° with respect to the longitudinal axis of the tube and a lens chosen to focus the central part of the tube into the entrance slit of the fluorescence monochromator. 

P Vinas, N Campillo, I Lopez-Garcfa, M Hemandez-Cordoba. Identification of vitamin B,2 analogues by liquid chromatography with electrothermal atomic absorption detection. Chromatographia 42 566-570, 1996. 

Kimbrough and Wakakuwa [276,330] reported on an interlaboratory comparison study involving 160 accredited hazardous materials laboratories. Each laboratory performed a mineral acid digestion on five soils spiked with arsenic, cadmium, molybdenum, selenium and thallium. The instrumental detection methods used were inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry, flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry and hydride generation atomic absorption spectrometry. At most concentrations, the results obtained with inductively coupled plasma atomic emission spectrometry... 

Barium is present at very low concentrations in most environmental samples. Thus, in spite of the availability of a detection limit of only a few ng ml 1 by flame AES, the element is rarely determined by flame methods AAS with electrothermal atomization or ICP-AES is more commonly used. A notable exception is in the determination of the element in barium-rich geological deposits.8 Another exception is in the analysis of formation waters from offshore oil wells.9 However, in this matrix, inter-element interferences are encountered from alkali and alkali-earth elements. These could be effectively eliminated by the addition of 5 g 1 1 magnesium and 3 g 1 1 sodium as a modifier.9... 

Traditional flame atomization methods have been preferred for atomic absorption analysis of ceramics. Very little mention has been made of electrothermal atomization (ETAA) in the literature. Although ETAA offers increased sensitivity with lower detection limits and smaller sample sizes, the problems of matrix interference (22-25) have resulted in the development of sample-specific methods for ETAA. 

Detection techniques of high sensitivity, selectivity, and ease of coupling with sample preparation procedures are of special interest for measuring PGM content in biological and environmental samples. ICP MS, electrothermal atomic absorption spectrometry (ET AAS), adsorptive voltammetry (AV), and neutron activation analysis (NAA) have fotmd the widest applications, both for direct determination of the total metal content in the examined samples and for coupling with instrumental separation techniques. Mass spectrometry coupled with techniques such as electrospray ionization (ESI) and capillary electrophoresis (CE) (e.g., ESI MS", LC ESI MS", LC ICP MS, CE MS", and CE ICP MS) offer powerful potential for speciation analysis of metals. MS is widely used for examination of the distribution of the metals in various materials (elemental analysis) and for elucidation of the... 

Persson and Irgum determined sub-p.p.m. concentrations of DMAA in seawater by electrothermal atomic absorption spectrometry. Graphite-furnace atomic absorption spectrometry was used as a sensitive and specific detector for arsenic. The technique allowed DMAA to be determined in a sample (20 ml) containing a 10 -fold excess of inorganic arsenic with a detection limit of 0.02ng As ml ... 

Whatever the analytical method and the determinand may be, the greatest care should be devoted to the proper selection and use of internal standards, careful preparation of blanks and adequate calibration to avoid serious mistakes. Today the Antarctic investigator has access to a multitude of analytical techniques, the scope, detection power and robustness of which were simply unthinkable only two decades ago. For chemical elements they encompass Atomic Absorption Spectrometry (AAS) [with Flame (F) and Electrothermal Atomization (ETA) and Hydride or Cold Vapor (HG or CV) generation]. Atomic Emission Spectrometry (AES) [with Inductively Coupled Plasma (ICP), Spark (S), Flame (F) and Glow Discharge/Hollow Cathode (HC/GD) emission sources], Atomic Fluorescence Spectrometry (AFS) [with HC/GD, Electrodeless Discharge (ED) and Laser Excitation (LE) sources and with the possibility of resorting to the important Isotope... 

Values taken from V. A. Fassel and R. N. Knisely, Anal. Chem., 1974,46, 111 A J. D. Ingle, Jr., and S. R. Crouch, SpectrochemicalAnalysis. Upper Saddle River, NJ Prentice-Hall, 1988 C. W. Fuller, Electrothermal Atomization for Atomic Absorption Spectroscopy. London The Chemical Society, 1977 Uhrapure Water Specifications. Quantitative ICP-MS Detection Limits. Fremont, CA, Balazs Analytical Services, 1993. With permission. 

The relative precision of electrothermal methods is generally in the range of 5% to 10%, compared with the 1% or better that can be expected for flame or plasma atomization. Furthermore, furnace methods are slow and typically require several minutes per element. Still another disadvantage is that chemical interference effects are often more severe with electrothermal atomization than with flame atomization. A final disadvantage is that the analytical range is low, usually less than two orders of magnitude. Consequently, electrothermal atomization is ordinarily applied only when flame or plasma atomization provides inadequate detection limits or when sample sizes are extremely limited. 

Electrothermal atomization, because of its high analyte vapor generation efficiency (in theory 100%), allows it to obtain extremely high absolute as well as concentration power of detection with any type of atomic spectrometry. In the case of two-... 

For the homogeneity studies, the extractants (0.05 mol L EDTA, 0.43 mol L" acetic acid and 0.005 mol L DTPA) were prepared as laid out in the certification reports [15, 17], The trace element contents (Cd, Cr, Cu, Ni, Pb and Zn) in the extracts were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) for the CRMs 483/484, flame atomic absorption spectrometry (FAAS) or electrothermal atomic absorption spectrometry with Zeeman background correction (ZETAAS) for the CRM 600. In the case of the CRM 483, little analytical difficulty was experienced as illustrated by the good agreement obtained between the within-bottle and between-bottle CVs for the CRM 484, lower extractable contents, closer to the detection limits and consequent poorer analytical precision was observed in particular for Cr (EDTA extractable contents), Cd and Pb (acetic acid extractable contents). No particular difficulties were experienced for the CRM 600. On the basis of these results, the materials were considered to be homogeneous at a level of 5 g for EDTA- and acetic acid-extractable contents and 10 g for DTPA-extractable contents (as specified in the extraction protocols). 

In-line retention of electro-active chemical species, separation, accumulation at a specific manifold site and further release can be accomplished by taking advantage of electrolytic deposition, as originally demonstrated in the determination of lead in high-purity sodium chloride and sodium sulphate reagents by electrothermal atomic absorption spectrometry [303]. Selectivity was improved because the analyte was electro-deposited inside a 3 iL flow cell, thus separating it from the bulk matrix. By optimising the operation of a potentiostat linked to the flow cell, a deposition efficiency of 70% and analyte dissolution in 40 pLof eluent were reported. With a 3 min in-line concentration, a detection limit of 1.2 ng L-1 was achieved. 

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