Determination of nanogram amounts of nickel by flameless atomic-absorption spectroscopy

A simple flameless atomizer, made from a heated graphite resistor, was investigated for the determination of nickel in various salts. The parameters characterizing its behaviour were optimized, to yield an absolute detection limit of 0.1 ng of nickel.     

Non-atomic absorption from matrix salts volatilized from graphite atomizers in atomic absorption spectrometry

The non-atomic absorption signals obtained from alkali halides atomized from three types of graphite atomizer are examined. The wavelength dependence of the signals identifies the absorption as that of charge-transfer transitions of the alkali halide molecules. The contribution of light scattering to the total non-atomic absorption signal is shown to be of small significance; the observed light-scattering is not Rayleigh scattering. The temperature dependence of the loss of sodium chloride from a rod atomizer is studied experimentally and compared with calculated vaporization rates based on the kinetic theory of gases.     

Signal depression in electrothermal atomic absorption spectrometry by nitrate and sulfate ions

The effects of nitrates and sulfates, which decompose to generate oxidants on heating, on the gaseous atom concentration for Ag,Cu and Ga have been investigated with a graphite filament atomizer and an optical arrangement which allows spatial information above the atomizer surface to be gathered. For the potassium and sodium salts, the largest signal depression, caused by gaseous atom oxidation, was found with the largest relative decomposition at the particular temperature, which therefore gives the largest partial pressure of the oxidants formed above the oxidizer. For the calcium salts, Ca metal was vaporized from the atomizer and competed successfully with the analyte, for any oxidants generated, thereby preventing oxidation of the analyte, so that, in some cases, the analyte atom concentration was increased.     

Electrothermal atomization from metallic surfaces: Part 1. Design and Performance of a tungsten-tube atomizert

A tungsten-tube atomizer has been developed and tested for a number of elements. The atomizer can be accommodated in the support of a commercial Varian carbon rod atomizer (CRA-63 or CRA-90) and operated as an alternative to the graphite tubes and cups. Characteristic concentrations, detection limits, optimum atomization temperatures, reproducibility and profiles of calibration curves obtained for Ag, Al, Ba, Cd, Co, Cu, Mg, Mn, Ni, Pb and V are similar to those obtained with the graphite-tube atomizer. The main advantage of this atomizer is its simple construction, low cost, long lifetime and excellent analytical performance, particularly for elements forming refractory carbides.     

Some aspects of electrothermal atomization of elements from large amounts of involatile matrices

Non-volatile matrices which cannot diffuse into the graphite walls of an electro-thermal atomizer (as obtained by direct sampling of solids, injection of solutions into tubes with pyrolytic coatings or with a hydrophobic film) make a “miniplatform” in the centre of the atomizing tube. A delay in the temperature increase of this platform at the beginning of the atomization step compared to that of the atomizer walls causes enhancement of the peak height sensitivity. This was proven by atomization of nanogram quantities of copper and iron from solutions of aluminium salts.     

Comparative Study of the Effect of Sample Matrix on the Atomic Absorption of High-Volatile Elements in Two-Step and Conventional Atomizers

The space–time dynamics of absorbing atomic layers of cadmium and lead and molecular layers of zinc chloride in a commercially produced transverse-heated graphite atomizer and a newly developed two-step atomizer was studied. It was shown that the limiting temperature of cadmium pyrolysis in the two-step atomizer without the use of modifiers may be as high as 1000°C, whereas in the commercial analyzer is it not higher than 300°C. Levels of nonselective absorption due to sodium chloride were compared. It was found that, for a two-step atomizer, the maximum allowable mass of sodium chloride for which the background at lead and cadmium lines can be adequately compensated is 17–30 times higher than that for the commercial atomizer. The atomization of cadmium in the presence of sodium chloride was studied using time, space, and spectral resolution. It was shown that the effect of the chloride matrix in the two-step atomizer is suppressed because of sample fractionation and distillation in the course of its evaporation and condensation.     

Electrothermal atomic absorption spectrometry of elements after electrochemical deposition on graphite electrodes

The application of electrochemical deposition on graphite rods for separation and preconcentration prior to electrothermal atomic absorption spectrometry (a.a.s.) is examined. The metals to be determined are electrolyzed onto a graphite rod which is tehn transferred to a cup atomizer for a.a.s. Although only some of the element present in the solution is deposited on the surface of the graphite rod, favorable preconcentration rates are obtained. The method was tested on the determination of cadmium in aqueous solution. The precision is satisfactory for concentrations down to 5 × 10^?8 g l^?1 cadmium, and the detection limit is 4 × 10^?9 g l^?1.     

Investigation of thallium hydride generation using in situ trapping in graphite tube by atomic absorption spectrometry

Thallium hydride was generated from aqueous solutions by merging sample and sodium tetrahydroborate reductant in a batch system. In situ preconcentration of volatile thallium hydride in a preheated graphite furnace coated with palladium, which was used as both the collection medium and atomizer, greatly improved the sensitivity for the determination of thallium by hydride generation atomic absorption spectrometry. The presence of tellurium can increase the generation efficiency of thallium hydride. The operating conditions were optimized. The calibration graph is linear up to 100 ng and the characteristic mass for thallium was 0.92 ng which is seventeen times lower than that obtained with the heated quartz tube atomizer.     

On the mechanisms of organic acid modifiers used to eliminate magnesium chloride interferences in graphite furnace atomic absorption spectrometry

Graphite furnace vaporization and inductively coupled plasma excitation, atomic emission spectrometry (GFV-ICP-AES) was applied for monitoring the volatilization of analytes (Cd, Pb, Zn), matrix element (Mg) and the release of carbon containing species. The gas streaming conditions were similar within the horizontal, end-heated graphite tube to that applied conventionally in graphite furance atomic absorption spectrometry (GFAAS). Gas evolution experiments were performed with the use of a quartz furnace, the evolved HCl gas was collected in an absorption vessel for titrimetric determination.The effect of both ascorbic and oxalic acids lies in essence on the promotion of the formation and thermal evolution of hydrochloric acid from the chloride salts at relatively low temperatures. Thus, in the GFAAS analysis, the hydrochloric acid can be evaporated in an extended drying step and/or at the beginning of a properly selected pyrolysis step without loss of analytes. The oxalic acid was found to be more effective than the ascorbic acid in the case of calcium chloride and sodium chloride matrices.     

Determination of mercury(II) ion by electrochemical cold vapor generation atomic absorption spectrometry.

A technique for determination of mercury is described; it is based on electrolytic reduction of Hg(II) ion on a graphite cathode, the trapping of mercury vapor and its volatilization into a quartz tube aligned in the optical path of an atomic absorption spectrometer. The electrochemical cell consisted of a graphite cathode and an anode operating with constant direct current for the production of mercury atoms. A pre-activated graphite rod was used as the cathode material. The optimum conditions for electrochemical generation of mercury cold vapor (the electrolysis time and current, the flow rate, the type of electrode and electrolyte) were investigated. The characteristic electrochemical data with chemical cold vapor using NaBH4-acid were compared. The presence of cadmium(II), arsenic(III), antimony(III), selenium(IV), bismuth(III), silver(I), lead(II), lithium(I), sodium(I) and potassium(I) showed interference effects which were eliminated by suitable separation techniques. The calibration curve is linear over the range of 5-90 ng ml(-1) mercury(II). The detection limit is 2 ng ml(-1) of Hg(II) and the RSD is 2.5% (n = 10) for 40 ng ml(-1). The accuracy and recovery of the method were investigated by analyzing spiked tap water and river water.     

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%.     

Investigations for the determination of lead by in situ hydride trapping within a graphite electrothermal atomizer for routine analysis

A new commercial system consisting of a flow injection analysis system for hydride generation coupled with a transversely heated graphite atomizer-atomic absorption spectrometer for the determination of lead is investigated in detail. The hydride generation is optimized by using an ammonium peroxodisulphate-hydrochloric acid system as oxidant and sodium borohydride as reducing reagent. The addition of sodium cumol sulphonate as surface active substance shows advantages considering efficient plumbane production. The hydride trapping and atomization in a graphite electrothermal atomizer is also optimized. The characteristic concentration was 0.74 mug/l, the detection limit was 0.70 mug/l for 500 mul sample volumes. The relative operation standard deviation of this method was smaller than 2%. Further examinations demonstrate the influence of several heavy metals on the determination of lead. Finally, the measurement of standard reference materials shows the efficiency of the method in combination with decomposition with aqua regia solutions.     

Pyrolysis of acrylonitrile-methacrylic acid copolymers and derivatives

Pyrolyses of acrylonitrile-methacrylic acid copolymers and their sodium salts were studied under inert atmosphere at various heating rates using thermogravimetric analysis coupled with gas liquid chromatography, thermal volatilization analysis, differential scanning calorimetry and flash pyrolysis coupled with GLC and eventually mass spectrometric analysis. The mechanisms of the nitrile oligomerization and subsequent chain scission, giving rise to volatilization, are discussed in connection with the sequence distribution of monomeric units in the copolymers.     

Spatiotemporal Dynamics of Vapors of Chloride Matrices in a Transversely Heated Graphite Furnace for Atomic Absorption Spectrometry

The dynamic of the formation and dissipation of sodium and nickel chloride vapors in the THGA transversely heated graphite furnace atomizer of a SIMAA 6000 multielement spectrometer was investigated by shadow spectral filming. The spatial distribution for the entire vaporization cycle of vapors is strongly inhomogeneous, due mainly to the transverse non-isothermal conditions of the atomizer. It also depends on the addition of a chemical modifier and the rate of the internal flow of the sheath gas. At the normal brightness of the spectral lamps, the spectrometer's Zeeman-based background corrector reliably compensates for the nonselective light absorption by molecular vapors and condensed particles with an amplitude of up to 1. For the minimum allowable brightness of lamps, this value decreases to as low as 0.6 because of an increase in the noise of the measurement path.     

Electrochemical generation of mercury cold vapor and its in-situ trapping in gold-covered graphite tube atomizers

The combination of more efficient flow-through electrochemical mercury cold vapor generation with its in-situ trapping in a graphite tube atomizer is described. This coupled technique has been optimized to attain the maximum sensitivity for Hg determination and to minimize the limits of detection and determination. A laboratory constructed thin-layer flow-through cell with a platinum cathode served as the cold vapor generator. Various cathode arrangements with different active surface areas were tested. Automated sampling equipment for the graphite atomizer with an untreated fused silica capillary was used for the introduction of the mercury vapor. The inner surface of the graphite tube was covered with a gold foil placed against the sampling hole.     

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.     

ET-AAS determination of traces of As, Sb and Sn in pure gold after matrix separation with hydrazine

Summary The possibilities of ET-AAS using the graphite furnace or the tungsten coil atomizer were compared by the trace As, Sb and Sn determination in the chloride-containing solution resulting after gold reduction with hydrazine. It was found that the tungsten coil atomizer tolerates higher concentrations of chloride ions than the conventional graphite furnace.     

Einsatz der flammenlosen Atom-Absorption (Graphitrohrküvette) zur Bestimmung von Kupferspuren in Stahl und anderen Metall-Legierungen nach Extraktion

The determination of small and smallest amounts of copper in steel and other metal alloys by atomic absorption spectroscopy was investigated. It has been found, that the interferences caused by accompanying elements in the determination in aqueous solution with the flame can be completely removed by extracting the copper with Pb-DDTC in chloroform and determining this extract with the heated graphite atomizer. Moreover, it was recognised, that working with the heated graphite atomizer in organic solutions shows great advantages compared with the flame, because any solvent may be used. The methods of continuous variation by Job and the molar ratio by Yoe and Jones for the determination of the complex stoichiometry were transferred to the system Cu-DDTC by working with the heated graphite atomizer.     

Sensitive detection of ionic organolead compounds by coupling hydride generation (HG) with transversely heated graphite atomizer-atomic absorption spectrometry (THGA-AAS)

The detection of ionic alkyllead compounds using the coupling of flow injection analysis system-hydride generation (FIAS-HG) with transversely heated graphite atomizer atomic absorption spectrometry (THGA-AAS) has been worked out. Very low limits of detection can be achieved if the hydride products are enriched in the graphite furnace. Under optimised conditions (concentration of sodium borohydride, hydrogen peroxide and acidity as well as the furnace temperature) calibrations are carried out in the range of 0.1 to 5 μg/L. With a 1.5 mL sample loop, the limit of detection is calculated to be about 7 ng/L, but it can be lowered to below 1 ng/L if larger sample volumes are used for the enrichment.     

Mechanism of cobalt atomization from different atomizer surfaces in graphite-furnace atomic-absorption spectrometry

The mechanism of cobalt atomization from different atomizer surfaces in graphite-furnace atomic-absorption spectrometry has been investigated. The atomizer surfaces were pyrolytically coated graphite, uncoated electrographite, and glassy carbon. The activation energy of the rate-determining step in the atomization of cobalt (taken as the nitrate in aqueous solution) in a commercial graphite furnace has been determined from a plot of log k_s vs. 1/T (for T values greater than the appearance temperature), where k_s is a first-order rate constant for atom release, and T is the absolute temperature. The activation energy E_a, can be correlated either with the dissociation energy of CoO_(g) or with the heat of sublimation of Co_(s), formed by carbon reduction of CoO_(s), the latter being the product of the thermal decomposition of Co(NO₃)₂. The mechanism for Co atomization seems to be the same for the pyrolytically coated graphite and the uncoated electrographite surfaces, but different for the glassy carbon surface. The suggested mechanisms are consistent with the chemical reactivity of the three atomizer surfaces, and the physical and thermodynamic properties of cobalt and its chemical compounds in the temperature range involved in the charring and atomization cycle of the graphite furnace.