Determination of manganese by graphite furnace atomic absorption spectrometry: matrix effect control by multiple linear regression model

The multivariate interference effects due to nitrates of sodium, potassium, magnesium and calcium on electrothermal atomization of manganese were modelled by using the multiple linear regression method in conjunction with a suitable experimental design. Since the model proved to be able to efficiently predict the simultaneous effects of the considered salts in a wide range of concentrations, it was applied to provide a computational correction of the matrix effects occurring in the ETAAS analysis of manganese in seawater, after preconcentration of the analyte on Chelex-100 resin and elution with nitric acid. Preliminary results showed that the matrix effects are significantly reduced, leading to an improvement in accuracy of the ETAAS analysis.     

Investigation of interference mechanism of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry

The interferences of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry (ETAAS) were examined using a dual cavity platform (DCP), which allows the gas-phase and condensed phase interferences to be distinguished. Effects of pyrolysis temperature, pyrolysis time, atomization temperature, heating rate in the atomization step, gas-flow rate in the pyrolysis and atomization steps, interferent mass and atomization from wall on sensitivity as well as atomization signals were studied to explain the interference mechanisms. The mechanism proposed for each experiment was verified with other subsequent sets of experiments. Finally, modifiers pipetted on the thermally treated sample+interferent mixture and pyrolyzed at different temperatures provided very useful information for the existence of volatilization losses of analyte before the atomization step. All experiments confirmed that when low pyrolysis temperatures are applied, the main interference mechanisms are the gas-phase reaction between bismuth and decomposition products of cobalt chloride in the atomization step. On the other hand, at elevated temperatures, the removal of a volatile compound formed between analyte and matrix constituents is responsible for some temperature-dependent interferences, although gas-phase interferences still continue. The experiments performed with colloidal palladium and nickel nitrate showed that the modifier behaves as both a matrix modifier and analyte modifier, possibly delaying the vaporization of either analyte or modifier or both of them.     

The interference effect of a mixture of magnesium, aluminium, sulfate and chloride on the atomization and vaporization of manganese in graphite furnace atomic absorption spectrometry.

In this study, the interference effects of Al3+, Mg2+, Cl- and SO4(2-) ions on the determination of manganese by graphite furnace atomic absorption spectrometry (GFAAS) were investigated. At first, the interferences caused by Al2(SO4)3, AlCl3, MgCl2 and MgSO4, which are the most possible major compounds for the combinations of the ions mixed, were individually considered. Then, the effects caused by mixtures containing various amounts of MgSO4 and AlCl3 were studied. If the pyrolysis temperature is below 800 degrees C, AlCl3 changes the vaporization mechanism of manganese. These interferences disappear at higher pyrolysis temperatures. At the same time, aluminum salts may cause the formation of refractory compounds between aluminum and manganese (like spinel MnAl2O4) that shift the absorption signals of manganese to higher temperatures. Magnesium sulfate, by itself, does not cause any depression of manganese signals. In fact, it acts as a modifier, preventing volatilization losses of manganese during the pyrolysis step. A conclusion was reached that detailed investigation of the interferences in a complex media is a very difficult experimental and theoretical task. To solve practical problems, one may better follow the general notions developed in GFAAS toward complex matrices.     

Investigation of interference mechanisms of nickel chloride on copper determination and of colloidal palladium as modifier in electrothermal atomic absorption spectrometry using a dual cavity platform

The interference of nickel chloride on the determination of copper by electrothermal atomic absorption spectrometry was investigated using a specially designed dual cavity platform (DCP), which allows the analyte and interferent to vaporize from separate cavities, so that gas and condensed phase interferences can be distinguished to some extent. It was found that, when low pyrolysis temperatures were used, the interference of nickel chloride on copper originated from the formation of copper chloride in the condensed phase, which is not efficiently dissociated in the atomization stage. Alternately, when analyte and interferent were in separate cavities of the DCP, a gas-phase reaction between copper and chlorine in the atomization stage resulted in a similar signal depression. When higher pyrolysis temperatures were used, interference could be attributed to losses of volatile copper chloride in the pyrolysis stage. These losses were more pronounced when analyte and interferent were in separate cavities of the DCP, indicating again a gas-phase reaction between copper and chlorine, as well as a protective action of nickel oxide, when analyte and interferent were mixed. Colloidal palladium used as modifier removed the chloride interference independent of the pyrolysis temperature applied, when copper and nickel chloride were mixed. Colloidal palladium also increased the integrated absorbance for copper by 40–50%, even when analyte and modifier were in separate cavities of the DCP, indicating a strong gas-phase interaction between copper atoms and the modifier through adsorption/desorption processes.     

Nickel chloride interferences on zinc and cobalt in graphite furnace atomic absorption spectrometry using a dual cavity platform

The interference mechanisms of nickel chloride in the determination of cobalt and zinc by graphite furnace atomic absorption spectrometry were investigated using a dual cavity platform. This platform, which has two separate cavities instead of one, allows interferences in the gas phase and in the condensed phase to be differentiated by pipetting the analyte and the interferent onto the separate locations as necessary. The interference mechanism of nickel chloride is found to depend upon the pyrolysis temperature. In the presence of excess nickel chloride, analyte chlorides are formed both in the condensed phase and by reaction between analyte species and HCl(g) generated by the hydrolysis of nickel chloride. The analyte chlorides are then lost during pyrolysis or at the very beginning of the atomization step. At low pyrolysis temperatures, where nickel chloride is not significantly hydrolysed, the drop in sensitivity can be attributed to the expulsion of the analyte species together with rapidly expanding decomposition products of nickel chloride, and/or to gas-phase reaction between analyte atoms and chlorine in the atomization step.     

Determination of arsenic, cadmium, lead and selenium in highly mineralized waters by graphite-furnace atomic-absorption spectrometry

A graphite-furnace AAS method using the stabilized-temperature platform furnace (STPF) concept, mixed palladium and magnesium nitrates as chemical modifier and Zeeman background correction has been applied to the direct determination of As, Cd, Pb and Se in highly mineralized waters used for medicinal purposes. These contain 20-40 g/l. concentrations of salts, mainly sodium and magnesium chlorides, bicarbonates and sulphates. The use of a pre-atomization cool-down step to 20 degrees in the graphite-furnace programme reduced the background absorption. Increasing the mass of magnesium nitrate modifier to 5 times that originally proposed improved the analyte peak shape. Under these conditions, no interference was found in analysis of the chloride/bicarbonate type of water, but the sodium and magnesium sulphate type of water had to be diluted, and even then an interference remained. Calibration with matrix-free standard solutions was used, but use of spike recovery is strongly recommended for testing the accuracy. The limits of determination (4.65sigma) of the proposed method for undiluted samples are 2.0 mug/l. for As, 0.05 mug/l. for Cd, 1.0 mug/l. for Pb and 1.5 mug/l. for Se.     

Mechanism of modification by palladium in graphite furnace atomic absorption spectrometry

The effects of palladium and mixtures containing palladium on the absorbance characteristics of lead, thallium, cadmium, selenium, manganese and cobalt are described. These data, together with results of scanning electron microscopy showing the distribution of palladium on the graphite surface, indicate that palladium has a physical mechanism of analyte modification. During furnace heating, the analyte dissolves in molten palladium and may combine with it chemically. However, the rate limiting step leading to atomization appears to be diffusion of the analyte from palladium. The addition of magnesium, molybdenum or powdered carbon increases the speed of diffusion by causing palladium to form smaller droplets, and hence produces sharper absorbance peaks. Palladium becomes less effective as the atomization temperature increases, because the rate of diffusion is higher. This accounts for palladium having only a small stabilizing effect on less volatile elements such as manganese and cobalt. The addition of ascorbic acid to palladium has no significant effect on its modifying properties in a dilute nitric acid matrix. Results of kinetic studies on the atomization of gold are consistent with analyte diffusion out of palladium as the rate-limiting step leading to atomization.     

New methodology for checking of absence of the systematic errors in the determination of sulphate ion in MgCl2·6H2O

A new methodology is proposed for obtaining analytical results free from bias errors, it is based on a modification of the standard addition method. Bias or systematic errors are taken as the differences between the amounts of analyte in the test portion and the image of the analytical signal on a calibration relationship where the amounts of added analyte act as the predictors. The constant component of the error, the matrix interactive effect and the direct matrix interference are jointly discussed as the main sources of bias. The latter two are considered to be different forms of interference. As an example, the new methodology was applied to the determination of sulphate ion in a magnesium chloride sample (Merck AR) using a spectrophotometric and an atomic absorption spectrophotometric procedure. No direct matrix interference or interactive matrix effect on the analytical results was found.     

Determination of sodium sulphate, calcium chloride and sodium chloride in gypsum plaster

Summary It has been shown that chloranilic acid and its salts can be used to determine sodium sulphate in the presence of calcium sulphate, calcium chloride in the presence of calcium sulphate, and sodium chloride in the presence of calcium chloride. The analysis is direct, the separation from non-desired components being carried out at the same time as the determination itself.One aspect of the use of chloranilic acid should be stressed, namely, that it sometimes is possible to differentiate between two salts that have the same anion but different cations, and examples have been given in this paper.     

Complexometric estimation of ferric iron

Summary Ferric iron has been determined alone or in presence of barium chloride, calcium chloride, magnesium sulphate, mercuric chloride, manganese sulphate, strontium nitrate, chromic sulphate or zinc sulphate by titrating it with EDTA, using potassium thiocyanate-p-anisidine indicator. In these complexometric titrations, the quantitative results obtained by using potassium thiocyanate-p-anisidinie indicator are comparable with those obtained with Bindschedler's green indicator; and the metallic salts mentioned above do not interfere in the estimation of ferric iron by this method.     

Low-temperature migration of lead,thallium, and selenium onto a palladium modifier during the analysis of solutions and slurries by electrothermal atomic absorption spectrometry

A palladium/magnesium modifier, when premixed with solutions or slurries, stabilizes many analytes to higher pyrolysis and atomization temperatures. Similar behavior was seen when analyte and modifier were physically separated by pipetting them onto opposite sides of a L'vov platform. During the pyrolysis stage of the furnace heating cycle, lead, thallium, and selenium migrated from the platform surface and interacted with the modifier on the opposite side. This behavior explains the consistent stabilization by palladium of analytes in slurry samples. Under conventional operating conditions the modifier is premixed with the slurry, and on drying in the furnace, the analyte and modifier may not make close contact. However, this is unimportant since the analyte will migrate to the palladium on heating. Then the rate-limiting step leading to atomization is the release of analyte from palladium, and it is the same for solutions and slurries. Therefore, aqueous standards can be used for slurry analysis.     

La matrice eau de mer et le signal du cuivre en spectrometrie d'adsorption atomique sans flamme : Partie 1: Etude de l'influence des principaux composants

(Copper signals from seawater matrices in electrothermal atomic absorption spectrometry. Part 1: study of the effects of principal inorganic ions.)The effects of the main inorganic ions of seawater (Na⁺, Mg²⁺, Ca²⁺, Cl^?, SO^2?₄), and of nitrate as modifier, on the electrothermal atomic absorption spectrometric signal of copper are studied. Sodium chloride, sulfate or nitrate, magnesium chloride or nitrate, and calcium chloride can cause serious interferences. Thermal treatment at about 700°C prevents the interference of MgCl₂ by its hydrolysis. Ashing can be done without loss of copper at higher temperatures in the presence of sulfate salts (1300°C) and nitrate salts (1200°C) than in the presence of chloride salts (1100°C). This is ascribed to the stabilising effect of oxides and sulfides. A study of the influence of two-component matrices, MCl-MNO₃ or MCl-MSO₄, on the atomization signal of copper confirms this stabilizing effect which adds to the decrease in interference connected with removal of chloride in acidic medium.     

Improvement of direct determination of Cu and Mn in seawater by GFAAS and total elimination of the saline matrix with the use of hydrofluoric acid

Hydrofluoric acid, added to seawater, can assist in the removal of chloride in the drying step by precipitating fluoride salts, thus suppressing the chloride interference effects induced on the atomization signals of Cu and Mn. By adding HF to seawater before the analysis, MgF₂ and CaF₂ are precipitated at the bottom of the sampling flask, without precipitating Cu and Mn, and are consequently not introduced into the graphite furnace. Because sodium salts are eliminated at the pretreatment step, the whole seawater matrix is eliminated before the atomization of Cu or Mn. Therefore, the analyzed volume of seawater can be increased by using the multi-injection procedure without degradation of the limit of detection and risks of spectral interferences. The limit of detection obtained for Cu and Mn are 0.05 and 0.01 μg L⁻¹, respectively, for a 50 μL analyzed seawater volume.     

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 metals in phospholipids by atomic-absorption spectrophotometry

A procedure is described for the determination of sodium, potassium, calcium, magnesium and manganese in phospholipids by atomic-absorption spectrophotometry. The method uses a solution of phospholipid in isopentyl acetate; phosphate interference is controlled by the addition of aqueous lanthanum chloride solution homogenized with ethanol. Standards are prepared in a similar solvent mixture. A comparison between the described method and that of standard additions show it to be free of phospholipid matrix effects.     

Investigations of reactions involved in electrothermal atomic absorption procedures: Part 9. An atomization system with controlled atmosphere and temperature for the determination of volatile elements in complex matrices

A controlled temperature controlled atmosphere atomization system is described. The sample is placed on a tungsten wire provided with temperature-controlled heating. After thermal pretreatment of the sample the wire is inserted into a hot quartz tube and rapid vaporization is accomplished by separate electrothermal heating. The pyrolysis products formed are mixed with a gas buffer and are passed through two equilibrium zones. The residence time of the analyte in the system is of the order of seconds so that the probability of attaining a state close to equilibrium is high for high temperatures. A third zone is placed perpendicularly to the others and constitutes the atomic absorption measuring cell. The usefulness of the system is illustrated for the determination of lead, bismuth, cadmium and zinc. The system provides unique possibilities in controlling interference effects in complex matrices. Examples are given for lead in concentrated chloride and sulphate solutions. Good agreement between the experimental results and high-temperature equilibrium calculations was obtained for a large variation in the composition of the gas phase.     

Single-ion activities and Mn(Hg)/Mn(II) reactions in aqueous solutions of alkaline-earth chlorides

Combined thermodynamic and kinetic studies have yielded convenient single-ion activity coefficients for manganese(II), alkaline-earth, and chloride ions and standard exchange currents for the two steps of the Mn(Hg)/Mn(II) electrode in 0.005 M MnCl₂+0.495 M MeCl₂ (for Me=Mg, Ca, Sr, Ba, and Mn) at 25°C. The results indicate that the fall in mean ionic activity coefficient for the alkaline-earth chlorides along the sequence from magnesium to barium is carried to a larger extent by the cation than by the anion, that also the activity coefficient for the minority cation Mn(II) falls along this sequence, and that other than activity-coefficient effects on the Mn(Hg)/Mn(II) reactions appear only with barium ions, which retard the reactions additionally. The results are discussed with emphasis on ionic interactions and double-layer effects.     

吸收光谱电化学测定铜的研究

West等人^[1-2]首先研究了镉、钴、铬、铜、铁、锰、镍、铅等金属离子和某些有机化合物在铂电极上的吸收光谱电化学特性,并导出定量分析公式,但迄今为止,此法还未用于实际样品分析。本文在以前工作基础上,用原子吸收分光光度计,着重试验了钠、钙、镁、铝等对铜的影响,直接测定了腐蚀剂和氯化钠中的铜,获得了良好的结果。     

Electrothermal atomic absorption spectroscopy - preseht understanding and future needs

A comparison is made between Massmann-type furnaces (with and without the L'vov platform) and constant temperature atomizers. It is shown that there is no major difference between these types of furnaces with regard to peak height sensitivities. On the other hand, the Massmann-type furnaces shoved to a greater extent susceptibilities towards matrix interference effects. The effect of the sample residence time on gas phase interference effects has been investigated at various constant temperatures for lead in large excesses of iron chloride and sodium sulphate, respectively. These experimental results are discussed and they are correlated to data obtained by high temperature equilibrium calculations. As a conclusion we found that there is a need for a better control of the gas phase inside graphite tubes. Advantages of separating the volatilization and atomization processes are discussed. The potentialities of constant temperature atomizers for atomic emission spectroscopy are lined out.Since its inception, conventional GFAAS has been developed considerably with regard to methodology and instrumentation. The technique has been essentially improved by the introduction of e.g., automatic sample devices, the L'vov platform technique, matrix modifications, pyrolytically coated graphite, automatic background correctors, adequate signal evaluation and rapid controlled heating of the atomizers. In spite of this progress there still remain problems in connection with the vaporization/atomization of samples. In conventional Massmann-type furnaces, the temperature at which an element is vaporized depends on its volatility and usually effective atomization temperatures are often too low for complete atomization. An additional disadvantage comprises difficulties in relating absorbance signals, which may originate from different atomization intervals, to true amounts of an element. Many of these problems inherent in Massmann-type furnaces can be eliminated by vaporizing samples into atomizers which are kept at a constant temperature. This concept was employed in the first graphite furnace ever built for analytical AAS [l], but due to the technical complexity of the isothermal approach, it has only been realized on a minor scale and therefore little is known about its limitations.By vaporizing samples from a platform [2,3] inserted into Massmann-type furnaces, the problems arising from non-isothermal atomization can often be minimized in a relatively simple way. In particular for volatile elements it is possible to approach conditions of constant temperature atomizers by the combined use of the platform technique with an element stabilizing modifier solution [4,5].The aim of this paper is to characterize isothermal as well as Massmann-type atomizers (equipped with and without platforms) with respect to sensitivity and susceptibility to interference effects as well as identifying future needs in order to develop the graphite furnace technique further.     

Effect of ions on the vibrational relaxation of liquid water

We study the relaxation of the O-H stretch vibration of water in aqueous salt solutions using femtosecond two-color pump-probe spectroscopy. The vibrational lifetimes are measured for a series of salts consisting of the anions Cl(-), Br(-), and I(-) and the cations Li(+), Na(+), and Mg(2+), for a range of concentrations from 0.5 M up to 6 M (chloride salts), 9 M (bromide salts), and 10 M (iodide salts). In addition to the previously found dependence of the vibrational lifetime on the nature of the anion, the lifetime is found to depend on concentration and is observed to show a small but significant dependence on the nature of the cation. We present a model in which all the effects of ions on the vibrational relaxaton of liquid water are accounted for.