Atomization of Al in a tungsten coil electrothermal atomic absorption spectrophotometer

Electrothermal atomic absorption spectrophotometry of Al in a tungsten coil atomizer was evaluated and applied for its determination in hemodialysis fluid. The system was mounted on a Varian Spectra AA-40 spectrophotometer with continuum background correction and all measurements, in peak height absorbance, were done at 309.3 nm. The purge gas was a mixture of 90% Ar plus 10% H(2). Observation height, gas flow, drying, pyrolysis and atomization steps were optimized. The heating program was carried out by employing a heating cycle in four steps: dry, pyrolysis, atomization and clean. The determination of Al in hemodialysis solutions was performed by using a matrix-matching procedure. Al in hemodialysis solutions was determined by TCA and by electrothermal atomization with a graphite tube atomizer. There is no differences between results obtained by both methods at a confidence level of 95%. The characteristic mass of Al by using the TCA was 39 pg and the detection limit was 2.0 mug l(-1).     

Shadow spectral imaging of absorbing layers in a transversely heated graphite atomizer: Part 1. Analyte atoms

The technique of shadow spectral imaging was used to investigate dynamics of formation and dissipation of Ag, In, Ga, Bi, Mn, Cu and Tl atomic layers in a transversely heated graphite tube atomizer (THGA) with and without integrated platform under gas-stop and gas-flow conditions. It is shown that non-uniform heating of the tube walls and platform surface in the radial cross section is the main reason for analyte transfer from atomizer bottom to less heated sides of the tube and platform before atomization temperature is reached. This transfer in the atomizer transverse cross section can be an additional factor that reduces matrix interferences in the THGA. In all the investigated cases, the atomic absorbing layers are not spatially uniform. Absorbance gradients grow up to 0.2 mm^− 1 even in the case of chemically inert silver atomization. Inverse atomization of In, Bi, Ga and Tl when atoms first appear in the atomizer's upper part was detected in THGA with platform. The effect of the internal gas flow on the spatial structure of analyte atoms is less pronounced in the transversely heated atomizer as compared to the end-heated furnaces.     

Vaporization of atoms and molecules during heating of cadmium,lead and zinc salts in a carbon tube atomizer

Vaporization characteristics of atoms and molecules produced during heating of aqueous solutions of Cd, Pb and Zn salts in the carbon tube atomizer are described. Sulfates, nitrates and fluorides are decomposed completely to free atoms without losses. When concentrated halide solutions are employed, gaseous metal chlorides, bromides and iodides are removed partly from the atomizer in the initial atomization phase, and the atomic absorption response is decreased. This loss can be suppressed effectively by adding nitric or sulfuric acid to the halide solutions.     

An Inexpensive Probe for Sample Introduction in Electrothermal Atomization Atomic Absorption Spectrometry

Abstract

An inexpensive probe system for introduction of samples for analysis by electrothermal atomization atomic absorption spectrometry is described. The system involves mounting a capillary tube on a tripod stand to allow the probe to be inserted into the atomizer for analysis. Comparison between this method of atomization and conventional atomization off the atomizer wall for the measurement of cadmium is described.     

Atomic absorption spectrometry of germanium with a tungsten electrothermal atomizer

The electrothermal atomization of germanium in a metal micro-tube atomizer is described. Tungsten is preferable to other metals for the atomizer. Hydrogen lowers the atomization temperature of germanium, and improves the sensitivity for germanium significantly when the optimum flow rates are applied. There are pronounced interferences from diverse elements and acids on the atomization of germanium. A procedure which involves carbon tetrachloride extraction of germanium tetrachloride and back-extraction of germanium into water avoids many of the interferences and is recommended for rock samples.     

Study of the electrothermal atomization of selenium (IV) in transversely-heated graphite atomizers in the presence of nickel compounds as chemical modifiers

The electrothermal atomization of selenium, in transversely-heated graphite atomizers, was studied with regard to the effect of the addition of nickel nitrate and nickel chloride as chemical modifiers. Particular importance was given to the behavior of the analyte in aqueous standards and in sodium chloride containing solutions, after thermal reduction of the modifiers prior to the injection of the analyte solution into the atomizer. Thermal reduction of either nickel compound brings about an enhancement in the sensitivity of selenium measurements, as compared to those obtained by the injection of both the analyte and the modifier together into the atomizer. Additionally, thermal reduction of the modifiers permits the presence of chloride, as sodium chloride, to be tolerated in amounts as high as 500 μg Cl⁻ with sensitivity losses lower than 10%.     

Atomic absorption determination of elements in solid samples using an electrothermal atomizer ‘crucible with separated zones’

A model of an electrothermal atomizer given the name ‘crucible with separated zones’ has been proposed. It provides the filtration of sample vapors through porous walls of a graphite tube placed in the atomization zone and heated independently of the evaporation zone. The inner volume of the tube is an isothermal analytical zone. The atomizer has been applied to the analysis of solid sea and river suspensions, DETATA concentrates of waters, and bottom sediments weighing 30–50 mg and more. As a result, the performance characteristics of the direct atomic absorption determination of Cd, Ag, and Pb in geochemical samples of complicated composition have been improved.     

Spatially resolved absorption measurements of antimony atom formation and dissipation in quartz tube atomizers following hydride generation

The cross-sectional distribution of free antimony atoms generated from admission of stibine into quartz tube atomizers was measured by atomic absorption spectrometry. A CCD camera was used for the spatially resolved detection. In the unheated flame-in-tube atomizer, the highest free atom concentration was found near the tube axis, decreasing towards the walls. The free atom distribution was not influenced by atomization conditions such as purge gas flow rate and oxygen delivery. Significant changes in the free atom distribution were obtained by changing the position of the oxygen delivery capillary tip. Analyte reactions within the tube were revealed from an analysis of the curvature of the calibration curve. In the externally heated atomizer (900°C), the free atom distribution was much more homogeneous compared to the unheated atomizer under analytical conditions. However, pronounced inhomogeneity (higher concentration of free atoms near the tube axis and in the regions close to the walls) was obtained at high Sb concentrations in a roll-over part of the calibration curve (over 300 ng ml⁻¹). This is explained on the basis of free atom decay on the surface of polyatomic particles formed at high analyte concentrations. From a practical point of view, no effects caused by the inhomogeneous free atom distribution are to be expected in the heated `flameless' tubes, the most widely used in routine analysis, since cross-sectional inhomogeneity observed under typical working conditions was negligible.     

Gas-phase atomization in analytical atomic spectrometry

Summary The most important problems of analytical atomic spectrometry are introduction of the sample into the atomizer and atomization of the sample. To solve these problems gas-phase atomization is suggested. This consists of preliminary isolation of the elements to be determined in the form of gaseous (volatile) compounds with subsequent gas-chromatographic separation. Separated compounds are fed into the atomizer individually in a stream of inert gas. This technique is the basis of development of dispersionless modes of atomic emission, atomic fluorescence and atomic absorption multielement analysis using non-selective detection.

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Gasphasen-Atomisierung in der analytischen Atomspektrometrie

     

Application of Microflame Atomizer to Gas Chromatography-Atomic Absorption Spectrometry

One of the successful methods for the determination of organometallic compounds is the combination of Gas Chromatography-Atomic Absorption Spectrometry (GC-AAS). The atomizer of AAS was connected with the column of GC by a transfer tube. Three types of the atomizer were reported as flame burner,electrothermal quartz tube and graphite furnace. A large amount of gas or electric energy was required to produce a high temperature for the atomization of analytes, A microflame atomizer of GC-AAS was developed in this paper to circumvent above problems. The volume of the atomizer is one-fifth of the normal flame burner, and a hydrogen gas was used as the carrier gas (35ml/min) and the fuel gas for the atomization of analytes.     

Study on the Atomization Mechanism of Hydrides in Graphite Furnace Atomizers

The influence of the surface state of the graphite furnace atomizer on the atomization of hydrides has been studied by means of surface film coating and quantum chemistry CN-DO/2 calculations. The results of the study prove that the atomization of AsH3, SbH3 and BiH3 in the graphite furnace atomizer is not a simple gas phase pyrolytic process, but a surface catalysis pyrolytic process.     

Electrothermal atomization from metallic surfaces: Part 2. Atom formation Processes in the tungsten-tube atomizer

A modified carbon rod atomizer (Varian M-63) is used to study the mechanism of atom formation of Al, Ba, Co, Pb, Ni and V in a tungsten-tube atomizer by a combined thermodynamic—kinetic approach. The atomizer is made from two profiled tungsten strips held in two copper supporting electrodes and forming a cylindrical cavity (5 mm long, 4 mm i.d.). Appearance temperatures and atomization energies are compared with those obtained for a graphite-tube atomizer. The major pathways leading to gaseous atoms are thermal dissociation of the metal oxide (or hydroxide) and reduction of the metal oxide followed by the atomization of free metal, depending on the protecting atmosphere (argon or argon—hydrogen mixture) and analyte.     

Shadow spectral imaging of absorbing layers in a transversely heated graphite atomizer: Part 2. Molecules and condensed-phase species

The dynamics of formation and dissipation of chloride, nitrate and sulfate matrix vapors in a transversely heated graphite tube atomizer (THGA) with and without integrated platform was investigated with the use of multi-channel atomic absorption spectrometry and the shadow spectral imaging technique. It is shown that non-uniform heating of the tube walls and platform in the furnace radial cross-section causes vapor transfer from atomizer bottom to less heated sides of the tube and platform. This transfer in the atomizer cross-section can be an additional reason for lower level of matrix interferences in the THGA and is a prerequisite for explosive atomization of some elements that appear as absorbance spikes. The cross-sectional structures of molecular layers and the cloud of condensed phase particles are highly inhomogeneous, resulting in absorbance gradients up to 0.2–0.5 mm^− 1. These structures differ significantly from those observed earlier in end-heated atomizers. Local vortices of the sheath gas, toroid-shaped and bridge-like structures of vapor layers were observed in the atomizer volume. The role of light scattering on the finally dispersed condensed phase particles in the transverse heated furnace is greater than that in the end heated atomizers because of near axis location of the cloud.     

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.     

Two-Stage Atomizer for Electrothermal Atomic Absorption Spectrometry: Dynamics of the Spatial Temperature Distribution

A two-stage atomizer for atomic absorption spectrometry is proposed. Its distinctive feature is the introduction of an extra stage of the fractional condensation of analyte atoms and the carrying out of the analytical cycle by a vaporization–condensation–atomization scheme. A special computer-driven power supply unit allows the heating of the upper and lower parts of the graphite furnace to be controlled independently. The dynamics of the temperature of the inner surface of the furnace for various temperature programs is studied. Using aqueous solutions of lead as an example, it is shown that one can control the processes of condensation–revaporization of elements to be determined proceeding in the atomizer volume.     

Dynamics of the Spatial Distribution of Atomic and Molecular Absorbing Layers in the Electrothermal Vaporization and Electrostatic Precipitation of an Analyte in an Atomizer

An experimental device was described for atomic absorption analysis with the electrothermal vaporization of the initial sample followed by the condensation of vaporization products and the electrostatic precipitation of the resulting aerosol in the secondary atomizer. Working conditions ensuring the maximum transfer of the sample to the atomizer were determined. The dynamics of the spatial distribution of the absorbing atomic and molecular layers was studied for atomization in a graphite furnace after the direct sample injection and electrostatic precipitation. The contribution of some physicochemical processes to the formation of the structure of cadmium atomic layers was assessed for different methods of sample injection into the atomizer. It was shown that an additional vaporization–condensation step significantly decreases the level of nonselective absorption and smoothes its gradients.     

Some observations on the interferences in flameless atomic-absorption spectrometry of magnesium

Interferences in flameless atomic-absorption spectrometry of magnesium were investigated by the use of a molybdenum micro-tube atomizer with a double indentation. Two atomization processes were compared in order to understand the interference mechanism: atomization from separate indentations, and mixture-atomization. Most elements tested gave no interference in atomization from separate indentations, whereas magnesium absorption was somewhat reduced in mixture-atomization. However, zinc and lead caused broadened absorption profiles in mixture-atomization. Chromium interfered in both atomization processes. The origin of these interferences is discussed.     

Electrothermal atomic-absorption spectrometry of arsenic and its application to environmental samples

Electrothermal atomization of arsenic with a metal micro-tube atomizer has been studied. Thiourea and thionalide were found to give effective atomization of arsenic. A method involving extraction of the thionalide complex for determining traces of arsenic in water and soil is described.     

Multiple microflame quartz tube atomizer — further development towards the ideal hydride atomizer for atomic absorption spectrometry

The development of an improved type of hydride atomizer for atomic absorption spectrometry — multiple microflame quartz tube atomizer (MMQTA) — is presented. The main feature of this atomizer is recurrent analyte atomization proceeding over its whole optical tube length, which is achieved by production of H-radicals at multiple points within the tube by oxygen microflames burning in the hydrogen-containing atmosphere. The MMQTA design optimization leading to a complete filling of the observation volume with H-radicals is described. The influence of individual atomization parameters is discussed. Optimum H-radical producing oxygen intake into the MMQTA was found to correspond to a H₂:O₂ stoichiometric (3:1) ratio. The performance of the individual MMQTA tube designs is evaluated and compared to a typical externally heated quartz tube atomizer (EHQTA) — the linearity of calibration graphs for As, Se and Sb is significantly improved in all MMQTA tubes, without compromising the sensitivity, simplicity, low cost and easy operation. In fact, the free atom reactions within the tube causing calibration curvature are avoided up to an analyte concentration of at least 200 ng ml⁻¹ for Se and Sb and 100 ng ml⁻¹ for As. Tolerance limits of 0.7, 1.4, 0.2 and 0.2 μg ml⁻¹ are achieved for the atomization interferences of As on Se, Se on As, Sb on Se and Se on Sb, respectively, which is an improvement by 1–2 orders of magnitude in comparison to the conventional EHQTA with the same hydride generation system.