Investigations of reactions involved in electrothermal atomic absorption procedures : Part 10. Factors Influencing the Determination of Arsenic

Factors of importance for the determination of arsenic by the graphite furnace technique are discussed with special reference to surface reactions. Detailed information with regard to atom formation was obtained by use of an on-line data acquisition system fast enough to monitor signals without distortion. The significance of the surface structure which comes into contact with the sample was assessed by application of the L'vov platform technique. Radioactive measurements showed that losses of arsenic occur even at temperatures as low as 120°C. The different behaviour of γ- and β-radiation was used to study the penetration of arsenic into the graphite. It is shown that arsenic can be stabilized up 1800°C in Standard graphite tubes if an auxiliary oxidizing agent is added. Conditions for stabilization with nickel and lanthanum are also discussed. Reported interference effects caused by chlorine and sulphur were examined experimentally and by use of high-temperature equilibrium calculations. Minimization of interference effects including optimal conditions for atomization are obtained by use of a stabilizing agent in combination with the platform technique.     

Investigations of reactions involved in electrothermal atomic absorption procedures: Part 11. A theoretical and experimental investigation of factors influencing the determination of tin

Factors of importance for the determination of tin by graphite-furnace atomic absorption spectrometry have been investigated. Losses of tin during the drying and ashing stages were monitored by use of radioactivity measurements. It was found that tin could be lost at 100°C when ordinary graphite or glassy carbon surfaces were used. However, if the sample was dispensed into a droplet of ammonia, no losses occurred until 800°C, independent of the graphite surface, because tin is stabilized as SnO₂ (s,l) and chloride is removed as ammonium chloride. High-temperature equilibrium calculations indicate that tin forms volatile oxides, halides and sulphides which are stable up to relatively high temperatures. As is shown experimentally with commercial non-isothermal atomizers, these molecules might be removed from the system before their decomposition temperature is reached. A recently developed constant-temperature furnace was used to vaporize the sample into an environment of high and constant temperature, in which interference effects from chlorine and sulphur were minimized, as predicted by theory.     

Investigations of reactions involved in flameless atomic absorption procedures: Part VI. A Study of some factors influencing the determination of lead in sulphate matrices

The degree of interference from various sulphates in the determination of lead by flameless a.a.s. is high (e.g. the decrease in the signal from lead is 10% for 2 nanomol of sodium sulphate) and decreases in the order sodium ? potassium ? calcium ? magnesium. The interference from magnesium sulphate can be eliminated by ashing the sample at 870 ± 10°C. Results obtained from high-temperature equilibrium calculations show that gaseous lead sulphide is responsible for the interferences in the presence of sodium sulphate. Theoretical conditions for the formation of gaseous lead sulphide are outlined. The influence of carbon on the reactions involved was investigated by use of standard graphite as well as glassy carbon tubes; the results are compared with those found theoretically. In the presence of a tenfold excess of lanthanum(III), the recovery of lead is higher than 90% for all the sulphates investigated, at least up to an amount of 0.2 μ mol. The addition of oxygen as well as hydrogen to the inert gas decreases the interference from sodium sulphate, in accordance with the theoretical predictions.     

Investigations of reactions involved in flameless atomic absorption procedures : Part IV. A theoretical study of factors influencing the determination of aluminium

High-temperature equilibrium calculations are used to study potential interferences in the determination of aluminium by flameless a.a.s. The conditions for the formation of interfering aluminium compounds like AlO(g), Al₂O(g), Al₂O₃(s), AlOH(g), AlH(g), AlHO₂(g), AlS(g), AlN(g), AlN(s) and AlCl(g) have been calculated. The influence of kinetic parameters on the equilibrium calculations for the reactions involving carbon—oxygen and carbon—sulphur has been established by varying the input amount of carbon. The results indicate that even in the nanomole range the presence of elements like H, O, N, Cl and S may cause severe interferences during the atomization step (2300–2900 K)     

Investigations of reactions involved in flameless atomic absorption procedures : Part V. An Experimental Study of Factors Influencing the Determination of Aluminium

An experimental study of various factors influencing the flameless a.a.s. determination of aluminium in graphite furnaces is reported. Even in very low amounts, oxygen, hydrogen, chlorine, sulphur and nitrogen cause interferences during atomization. In addition, hydrogen and chlorine interfere during the ashing step. The interferences are discussed on the basis of high-temperature equilibrium calculations. The interferences can be minimized by using an ashing temperature as high as possible. Hydrogen, in particular, significantly lowers the ideal ashing temperature; its interference increases with the age of the graphite tube and in the presence of iron. The exclusion of atmospheric gases such as oxygen and nitrogen from the tube is an essential requirement for obtaining reliable results.     

Extraction and atomic absorption spectrometric determination of bismuth with electrothermal atomization

Summary A sensitive method for the extraction and atomic absorption spectrometric measurement with electrothermal atomization has been developed for the determination of bismuth in tea and orchard leaves. Bismuth is extracted into m-xylene as diethyldithiocarbamate complex. 2.5–3.0 l/min of argon flow rate, 650–800° C of ashing temperature and 2,200–2,600° C of atomization temperature were the best experimental conditions. A detection limit of 0.02 ng was obtained with a precision of 2–7% and minimal interference effects.Paper read at the meeting of the Japan Society for Analytical Chemistry, October 1978     

Investigations of reactions involved in electro-thermal atomic absorption procedures : Part 8. A theoretical and experimental study of factors influencing the determination of phosphorus

Ideal conditions for the determination of phosphorus by graphite-furnace atomic absorption spectrometry are investigated by the use of high-temperature equilibrium calculations. All reasonable reaction products resulting from the reaction between P, C, O, H, N, Ca and Ar are considered. The calculations show that phosphorus forms the volatile monoxide and dioxide molecules below 1800 K (P_o2? 10^-13 atm.). At higher temperatures the relative amount of atomic phosphorus is mainly controlled by the equilibrium between monatomic and diatomic phosphorus. The significance of the theoretical ' study was investigated experimentally. The relative amounts of P₂ and PO were monitored by molecular absorption using vaporization under isothermal conditions; the interfering effects of Ca, N₂, H₂, and O₂ on the atomic absorption signal for phosphorus were also studied. The sensitivity was greatly dependent on graphite tube conditions as well as the heating rate of the furnace. For CaHPO₄ the sensitivity for phosphorus was 4.5 × lO^-8 g. If samples were introduced into a preheated tube, this value was improved to 2 × 10^-9 g.     

Direct determination of molybdenum in mineral waters by atomic absorption spectrometry with electrothermal atomization

A new method for the direct determination of molybdenum by ETA-AAS in mineral waters without prior separation or concentration is proposed. With careful control of the graphite furnace conditions selective volatilization of the salt matrix is successfully attained. The possible spectroscopic interference due to common metals as well as the reproducibility, precision and repeatability of the method has been studied and the molybdenum content of 21 mineral waters measured.     

Direct determination of nickel in gas oil by atomic absorption spectrometry with electrothermal atomization

A rapid graphite-furnace atomic absorption procedure with simple dilution of samples was tested for the direct determination of sub-ppm levels of nickel in gas oils. The selection of appropriate graphite-furnace parameters, the type of solvent and organometallic standard, the effect of gas oil concentration in diluted samples, precision, accuracy and detection limit were investigated. Sample dilution was necessary because of high viscosity. Results obtained by standard addition for heavy gas oils were confirmed by a wet-ashing flame atomic absorption procedure. The relative standard deviation (r.s.d.) for consecutive determinations of nickel in gas oil solution containing 19 μg Ni l^?1 was 3.1%, and day-to-day r.s.d. for a reference gas oil sample was 5.3%. Accuracy was determined with an NBS standard reference oil GM-5 (4.6 ± 4.7% relative error in four determinations). Recovery experiments gas 104 ± 12% of the added nickel.     

Kinetics of selenium atomization in electrothermal atomization atomic absorption spectrometry (ETA-AAS). Part 2: selenium with palladium modifiers

The kinetics of the atomization process of selenium with prereduced and unreduced palladium nitrate modifiers were investigated. It was found that stabilization, in both forms, occurred by principally physical processes, as opposed to compound formation. For the unreduced modifier, it was shown that higher pyrolysis temperatures resulted in a higher activation energy of atomization and that the selenium vapour-surface interaction was increased. The importance of the second high temperature step in the stabilization mechanism was stressed, and an additional conditioning step in the furnace program was proposed for the unreduced palladium modifier. The reaction order for the unreduced modifier was near first order (1.29) with an activation energy of 330 kJ mol⁻¹ and a frequency factor in the order of 1 × 10⁹. For the reduced palladium modifier, a reduction temperature of 500°C–700°C was shown to be most effective. The reduced palladium modifier showed second order kinetics and the activation energy of 500 kJ mol⁻¹, was nearly 50% higher than that of the unreduced form. This and the large frequency factor (ca. 1 × 10¹⁵) indicated strong surface interactions, thus providing an explanation to the better stabilization properties observed for the reduced form of the modifier.     

Direct determination of tin in tap waters by electrothermal atomization atomic absorption spectroscopy

Summary A method is described for the direct determination of tin in tap waters by electrothermal atomization atomic absorption spectroscopy (ETA-AAS), using magnesium-nitric acid and palladium-magnesium as chemical modifiers. The charring and atomization temperatures and times, and the amount of modifier were optimized. The calibration and addition graphs, detection limit, quantitation limit, precision, accuracy, interferences and characteristic mass were also investigated. The method was applied to the determination of tin in tap water samples.     

The determination of beryllium and manganese in aerosols by atomic absorption spectrometry with electrothermal atomization

The determination of beryllium and manganese in air particulate matter collected on filter material is discussed. Destruction by digestion with nitric and perchloric acids and by low-temperature ashing with dissolution of the ash in a hydrofluoric-nitric acid mixture were tested. The graphite furnace parameters were investigated for different acid solutions. Interferences of some cations and anions that are abundant in aerosol material are described. Accuracy was checked against standard samples. For manganese, the results are compared with those obtained by energy-dispersive x-ray fluorescence.     

Removal of chloride interference in the determination of chromium by atomic absorption spectrometry with electrothermal atomization

Two mechanisms of chloride interference are described. The first arises from coordination of chloride to chromium(III), which can be prevented by addition of a masking agent such as tetraammonium—EDTA, The other is due to chloride salts remaining at the atomization step; this can be prevented by volatilizing the chlorides or converting them to oxides before atomization.     

Investigation of reactions involved in graphite furnace atomic absorption procedures: Part 12. A study of some factors influencing the determination of selenium

An experimental and theoretical study of various factors influencing the determination of selenium by graphite furnace atomic absorption spectrometry (g.f.a.a.s.) is reported. It is shown that the atomization efficiency can be increased as compared to the L'vov platform technique by means of a constant temperature furnace as a consequence of the possibility of choosing a higher atomization temperature. This is explained by means of high temperature equilibrium calculations, which include the formation of the thermodynamically relatively stable gaseous diselenium, hydrogen selenide and selenium sulphide. The extent of losses of selenium during thermal pretreatment was established by measurements with ⁷⁵Se for different types of selenium compounds, Se(-II)-methionine, selenite and selenate, in aqueous solutions as well as in chloride and sulphate matrices. It is shown that the addition of 20 μg of nickel is effective in stabilizing Se(IV) and Se(VI) in the presence of sodium chloride, sodium sulphate and pure water. However, in the presence of both an organic matrix (glucose) and sodium chloride, nickel is shown to lose its stabilizing effect.     

Slurry atomization of wheat-milled fractions for electrothermal atomic absorption spectrometric determination of nickel and chromium.

A slurry electrothermal atomic absorption spectrometric technique was used to determine Ni and Cr in wheat flour and its by-products. Slurries (3%, w/v) were prepared in a mixture of 15% HNO3-10% H2O2 as suspended medium. Differences in Ni and Cr contents due to origin and texture of the wheat and to the effects of the milling process were studied. Ni and Cr levels were more markedly influenced by the geographical origin of the wheat than by its texture. Both metals were related to the amount of bran present in each milled fraction and varied over the ranges of 212-298 ng/g (Ni) and 34-85 ng/g (Cr) in flours (with minimal bran contents); 297-460 ng/g (Ni) and 67-118 ng/g (Cr) in shorts; and 424-723 ng/g (Ni) and 106-165 ng/g (Cr) in brans. The Ni and Cr contents were not significantly affected by the technological processes typically performed in a flour-producing factory.     

The removal of chloride interference in determination of chromate ion by atomic absorption spectrometry with electrothermal atomization

Two mechanisms of chloride interference in the atomic absorption spectrometry of chromate in a graphite furnace have been established. The first is due to chloride salts remaining at the atomization step; this can be prevented by volatilizing the chlorides or converting them to oxides before atomization. The other arises from formation of chlorochromate ions, which can be removed by addition of an organic acid. The tetraammonium salt of EDTA is very suitable for this purpose.     

The atomic absorption spectrometric determination of arsenic and selenium in mineral waters by electrothermal atomization

A procedure for the determination of arsenic and selenium in mineral waters based on electrothermal atomic absorption spectrometry is described. Because of matrix effects and the inadequate detection limits for direct determinations, both elements are separated from the macrocomponents by co-precipitation in hydrated iron(III) oxide. The precipitate is dissolved in 0.2 M sulphuric acid for injection. The detection limits are 0.2 and 0.5 μg l^?1 for arsenic and selenium, respectively.     

Determination of arsenic in urine by atomic absorption spectrometry with electrothermal atomization

A cheap device which can be used to follow transient signals with a chart recorder is described.