Investigation of aluminum interferences using the stabilized temperature platform furnace

Al was determined in the stabilized temperature platform furnace with very few interferences. No interferences were found for several metal nitrates, sulfates or phosphates, or for NaCl. The Al absorbance signal was delayed in the presence of MgCl₂ but there was no interference. This led to the use of 50 μg Mg(NO₃)₂ as a matrix modifier for Al. There were no interferences for CaCl₂ but it was particularly important to use new pyrolytically coated tubes to avoid “aging” effects. CuCl₂ provided a very persistent interference that was reduced when the Mg(NO₃)₂ matrix modifier was used that permitted a char temperature of 1700°C. Perchloric acid interferences were severe with improperly coated graphite tubes but did not exist up to 0.5 M HClO₄ when the new pyrolytically coated tubes were used. A serum Al method was tested briefly and no problems were found. Al was determined in seawater with no influence from the salinity of the sample and less than 0.6 μg/1 Al in seawater could be detected.     

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.     

Kinetics and mechanism of the oxidation of 2-furancarbox-aldehyde by thallium(III) in perchloric acid solutions

The kinetics of the oxidation of 2-furancarboxaldehyde by thallic perchlorate at 50°C obeys the rate law

Kinetics and mechanism of reduction of thallium(III) by hydrogen peroxide in perchloric acid medium

The kinetics and mechanism of reduction of thallium(III) by hydrogen peroxide has been studied in 1.0 mol dm^–3 perchloric acid medium. The reaction is first order with respect to thallium(III) and second order with respect to hydrogen peroxide. A negative hydrogen ion and chloride ion catalysis is observed. Bromide ion is found to catalyze the reaction in low concentration. There is no effect of ionic strength on the rate of the reaction. A plausible mechanistic pathway for the reaction is suggested which leads to the following rate law: Rate=–d[T1(III)]/dt=kK[T1(III)][H₂O₂]²/[H⁺] where K is the formation constant of the complex between thallium(III) and hydrogen peroxide and k is the rate constant of the reaction between that complex and hydrogen peroxide. The computed values of E_a and S^# are 44.8±6.5 kJ mol^–1 and –107.8±22.2 JK^–1 mol^–1, respectively.

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(III) - - . - (III) . - - . . -- . , - :=–[T1(III)]/dt=kK[T1(III)][H₂O₂]²/[H⁺], - (III) - . E_A S^# 44,8±6,5 / –107,8±22,1 /·, .

     

Determination of phosphorus in steel with a stabilized-temperature graphite furnace and zeeman-corrected atomic absorption spectrometry

The determination of phosphorus in steel by graphite furnace a.a.s. is plagued by a spectral interference from the iron matrix which results in overcompensation when a continuum-source background corrector is used. Zeeman background correction using an alternating transverse magnetic field at the furnace eliminates this problem and allows a routine determination of phosphorus down to 0.002% in steel. Lanthanum is an effective matrix modifier for the phosphorus determination, but its enhancing effect depends largely upon the tube material used and the sample matrix. A 0.2% lanthanum solution was found to be optimum. The stabilized-temperature platform furnace concept allows an interference-free determination of phosphorus in steel, down to 0.002%, directly against aqueous standards. Atomizing the sample from a pyrolytic graphite platform in an uncoated graphite tube provides the optimum environment for a phosphorus determination.     

Statistical investigations of interferences in graphite furnace atomic absorption spectroscopy

Summary Interferences in the flameless determination of cadmium using the HGA 72 were studied for HCl, HNO₃, H₂SO₄, HClO₄ and HF and found to be depending on different thermal pretreatment. The interferences of cations were much smaller than for anions. The results are discussed with respect to thermal stability as well as atomization rate of the compositions under investigation. Special emphasis is put upon the presence of interactions between interferents, which in some cases can be used to eliminate interferences.

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Statistische Untersuchungen über Störungen bei der flammenlosen AtomabsorptionsspektralphotometrieII. Cadmium

Zusammenfassung Interferenzen, die bei der flammenlosen Bestimmung von Cadmium in der HGA 72 auftreten, wurden bei HCl, HNO₃, H₂SO₄, H₃PO₄, HClO₄ und HF studiert; die AbhÄngigkeit ihres Auftretens von der thermischen Vorbehandlung wird gezeigt. Interferenzen von Kationen sind kleiner. Die Ergebnisse werden im Hinblick auf die thermische StabilitÄt und die Atomisierungsgeschwindigkeit der Proben diskutiert. Besonders betont wird die Gegenwart von Wechselwirkungen zwischen Störungen, die manchmal auch benützt werden können, um Interferenzen auszuschalten.

Part I: Z. Anal. Chem. [10]     

Statistical investigations of interferences in graphite furnace atomic absorption spectroscopy

Summary Interferences in the flameless determination of lead using the HGA 72 were studied for HCl, HNO₃, H₂SO₄, H₃PO₄, HClO₄, HF and for a number of cations. In certain instances interferents in just 1000-fold concentration over lead are shown to cause deviations in the lead signal. Many of the interferences are matrix-dependent themselves and can be reduced by matrix variations. Optimization of the thermal pretreatment can be used effectively to reduce random error and/or systematic errors. The thermal stability of lead compounds in the graphite furnace was sufficient for charring procedures up to 900° C for 20 s.

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Statistische Untersuchungen über Störungen bei der flammenlosen Atomabsorptionsspektralphotometrie

Zusammenfassung Interferenzen, die bei der flammenlosen Bestimmung von Blei in der HGA 72 auftreten, wurden bei HCl, HNO₃, H₂SO₄, H₃PO₄, HClO₄, HF und einigen Kationen studiert. In gewissen Fällen reicht ein nur 1000 facher Überschuß des Störions, um Abweichungen vom Signal des Bleistandards hervorzurufen. Da das Auftreten von Interferenzen auch oft matrixabhängig ist, können Matrixvariationen zur Unterdrückung von Interferenzen eingesetzt werden. Die Optimierung des Temperaturprogrammes wird erfolgreich zur Beeinflussung des Zufallsfehlers und/ oder systematischer Fehler herangezogen. In der Graphitrohrküvette reichte die Stabilität der Bleiverbindung aus, um beim Veraschungsschritt die Temperatur bis auf 900° C (20 s) zu steigern.

Part I: Z. Anal. Chem. [13].Part II: Z. Anal. Chem. [14].     

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.     

Influence of graphite furnace tube design on vapour temperatures and chemical interferences in ETA-AAS

A two-line atomic absorption method for determination of lead was used for calculation of the temperatures experienced by analyte atoms in the gas phase after wall atomization with modified Philips SP-9 graphite tubes. For each tube, the influence of the temperature gradient on the vapour phase temperature and chemical interferences experienced by Cd, Mn and Pb in ETA-AAS was investigated. A higher vapour temperature and lower chemical interference by chlorides were observed when the tube temperature gradient was reversed through a reduction in the wall thickness towards the ends of the tube.     

Spectral interferences using the Zeeman effect for furnace atomic absorption spectroscopy

Using a transverse, a.c. Zeeman system, with the magnet on the analyte, background correction is performed at the exact analyte wavelength. As a result, nearly all of the spectral interferences associated with continuum correction are eliminated. Errors may occur, though, using Zeeman correction if coincident or nearby absorption lines or molecular absorption bands exhibit Zeeman splitting.We have found an example of overcorrection in the determination of Cd at the alternate 326.1-nm line that we believe is due to splitting of PO bands. We have also confirmed errors from Ft in the determination of Fe at the alternate 271.9-nm line and from Co in the determination of Hg at 253.6 nm.     

Reaction between nitrous acid and hydrogen peroxide in perchloric acid medium

A kinetic investigation on the reaction has been carried out in HClO₄ medium under different conditions. A spectrophotometric method of estimation of nitrous acid at various time intervals has been employed. The results are interpreted on the basis ofthe following mechanism: The absolute rate constant value of 39.7 M^?1 plusmn; s^?1 for k₄ and the equilibrium constant K_eq = 116M^?1 for reaction (2) have been evaluated. The activation energy of the overall reaction has also been determined as E_a = 13.2 kcal/mol.     

Acetylation of methylindoles in the presence of perchloric acid

Under the action of acetic anhydride in the presence of equimolecular amounts of 70% perchloric acid, methylindoles form perchlorates of the 3H-indole form of 3-acetylindoles and these are converted by treatment with bases into the corresponding 3-acetylindoles in high yields.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 8, pp. 1058–1059, August, 1970.     

Hydrolysis mechanisms for indomethacin and acemethacin in perchloric acid

The acid-catalyzed hydrolysis reactions of the antiinflammatory drugs indomethacin and acemethacin were investigated at 25.0 degrees C in a number of strongly concentrated perchloric acid media. The reaction rates were evaluated by UV measurements, and the intermediate species were detected by UV-vis, 1H NMR, 13C NMR, and mass spectroscopy measurements. A switchover from an A-2 to an A-1 mechanism as a function of the medium acidity is reported for the acid-catalyzed hydrolyses of the amide group of both indomethacin and acemethacin. In the A-2 hydrolysis, two water molecules are involved in the rate-determining step. An analysis of the kinetic data collected for acemethacin by the different techniques used reveals a complex mechanism, indomethacin being a metabolite intermediate species in the hydrolysis of acemethacin. The rate constants for the hydrolysis of the acemethacin ester group were considerably larger compared to those of the amide group.     

Kinetics and mechanism of the oxidation of acetaldehyde by chromic acid in perchloric acid

Summary The oxidation of MeCHO by chromium(VI) has been studied in HClO₄ medium over a wide range of experimental conditions and has been found to obey the rate law;v=k[MeCHO][HCrO ₄ ^– ][H⁺]. The calculated H and-S values for the reaction are 30±2kJ mol^–1 and 171±7J mol^–1deg^–1, respectively. The mechanism is discussed in terms of carbon-hydrogen bond cleavage.     

The reduction and elimination of matrix interferences in graphite furnace atomic absorption spectrometry

The approaches to reduction or elimination of matrix interferences encountered in graphite furnance atomic absorption spectrometry is reviewed. These techniques include matrix modification, application of active gas, and coating tubes with metallic compounds. The research work carried out in the author's laboratory is emphasized. A more universal matrix modifier, palladium, is proposed for the determination of mercury, lead, tellurium, bismuth, arsenic, thallium and indium in environmental samples.     

Radiation induced electron exchange reaction of thallium/I/-thallium/III/ at low sulfate ion concentration in perchloric acid solution

To understand the behaviour of Tl/II/ and the bridging group SO ₄ ^2– in radiation induced electron exchange reactions we have investigated the rate constants and mechanisms of reaction of Tl/II/ with Tl/I/ and Tl/III/ in perchloric acid solutions. The results indicated that Tl/II/ is an intermediate in the -ray induced electron exchange process of T1/I/–T1/III/. Sulfate ions at [SO ₄ ^2– ]>-0.02M serve as bridging groups and play an important role in accelerating the T1/II/–T1/I/ reaction. A cooperative effect was found between hydrogen peroxide and sulfate ion at low sulfate ion concentration, [SO ₄ ^2– ]0.02M in perchloric acid solution.