Spectral interferences and background overcompensation in zeeman-corrected atomic absorption spectrometry : Part 1. The effect of iron on 30 elements and 49 element lines

The background compensation performance of a Zeeman corrector with the magnetic field acting on the graphite atomization cell was assessed for 30 elements and 49 element lines in an iron matrix. Two of the elements studied, gallium and zinc, are influenced by background overcompensation which introduces serious negative systematic errors. The overcompensation is due to the presence of iron lines close to the 287.4-nm gallium line and the 213.9-nm zinc line; when the magnetic field is on, the σ-components of the adjacent iron lines overlap at the position of the analyte line and a background, which is not present when the magnetic field is off, is recorded. When gallium and zinc are measured under the same conditions but with deuterium arc background correction, the adjacent iron lines cause positive systematic errors. These spectral interferences for gallium in the presence of iron can be avoided by doing the measurements at the 294.4-nm gallium line; the two lines have about the same sensitivity. When zinc is to be measured at the 213.9-nm line, with either type of background correction, the spectral interferences from iron can be avoided by careful selection of the graphite-furnace parameters. In addition to spectral interferences, iron also affects the sensitivity for both gallium and zinc.     

Spectral interferences and background overcompensation in inverse zeeman-corrected atomic absorption spectrometry Part 3. Study of eighteen cases of spectral interference

Atomic line tables were surveyed in order to select pairs of elements which have contiguous lines and so are likely to suffer from spectral interference. Spectrometric measurements of these element pairs revealed eighteen cases of spectral interference. Four of these cases occurred at the recommended wavelengths for the analyte: the 459.4-nm europium line (interference form vanadium and cesium), the 247.6-nm palladium line (interference from lead) and the 265.9-nm platinum line (interference from europium).     

Determination of manganese,iron, cobalt and nickel in air and water by atomic absorption spectroscopy

Flames of 4 different kinds and of various compositions were studied for their suitability for atomic absorption spectroscopy for the determination of manganese, iron, cobalt and nickel. The effects of various other factors such as lamp current, slit-width and position of the burner were also investigated. Interference effects of a large number of ions and compounds were studied. Very few ions were found to interfere and means of eliminating the interferences noted are described. As a result of the investigation, sensitive and selective procedures for the determination of manganese, iron, cobalt and nickel are reported. Sensitivities are Mn, 0.01 mg/l; Fe, 0.05 mg/l; Co, 0.03 mg/l and Ni, 0.02 mg/l for 1% absorption.     

The determination of metals in petroleum samples by atomic absorption spectrometry : Part II. Determination of nickel

Some atomic absorption characteristics of xylene solutions of eight organometallic compounds of nickel in air—acetylene and nitrous oxide—acetylene flames are described. Different absorbances from various nickel organometallic compounds were observed; these differences were not eliminated by using the nitrous oxide—acetylene flame. Serious errors may arise when different organometallic compounds are used for calibration in the determination of nickel in xylene solutions of various petroleum samples. These errors are much less pronounced when nickel is determined by a standard addition technique. The effects of different sample matrices are discussed.     

Determination of cobalt and nickel by graphite-furnace atomic absorption spectrometry after coprecipitation with scandium hydroxide.

Trace amounts of cobalt and nickel in a water sample were quantitatively coprecipitated with scandium hydroxide at pH 8.0-10.5. Because the coprecipitant could be easily dissolved with 1 mol dm(-3) nitric acid, and the presence of up to 10 mg cm(-1) of scandium did not interfere with the graphite-furnace atomic absorption spectrometric determination of cobalt and nickel, the volume of the final solution prepared for the determination could be minimized down to 0.5 cm3. The concentration factor was 400-fold and the detection limits (signal to noise = 2) were 5.0 pg cm(-3) of cobalt and 10.0 pg cm(-3) of nickel in 200 cm3 of the initial sample solution. The 27 diverse ions investigated did not interfere with the determination in at least a 500-fold mass ratio to cobalt or nickel. The proposed method was successfully applied to the determination of trace amounts of cobalt and nickel in river-water samples.     

Determination of nickel, chromium and cobalt in wheat flour using slurry sampling electrothermal atomic absorption spectrometry

The slurry technique was applied to the determination of Ni, Cr and Co in wheat flour by electrothermal atomic absorption spectrometry (ETAAS). The influence of the graphite furnace temperature programme was optimized. Optimum sensitivity was obtained by using a mixture of 15% HNO₃–10% H₂O₂ as suspended medium for a 3% w/v slurry in the determination of Ni; lower concentrations of HNO₃ were necessary for the determination of Co and Cr (viz. 5 and 10%). The precision of direct analyses of the slurries was improved by using mechanical agitation between measurements; thus, the RSD of the measurements was ca. 5% for repeatability. The direct slurry sampling (SS) technique is suitable for the determination of Ni and Cr in wheat flour samples at levels of 150–450 and 30–72 ng g⁻¹, respectively, as it provides results similar to those obtained by ashing the sample. However, the typically low level of Co in these samples precluded its determination by the proposed method (the study was made in an SRM spiked wholemeal flour), at least in those samples that were contaminated with elevated concentrations of the metal (viz. more than 90 ng of Co per g of flour). The method provides a relative standard deviation of 6, 8, and 4% for Ni, Cr, and Co, respectively.     

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.     

Effect of hydrogen on atomic absorption of iron,cobalt and nickel

Addition of hydrogen to the argon purge gas used for the electrothermal atomic absorption spectrometry of iron, cobalt and nickel in a molybdenum tube provided narrower and more sensitive peaks than those obtained in pure argon. Reproducibility and background were also improved and atomizer lifetime was prolonged. Optimal gas flow rates are reported.     

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.     

Halide interferences in an electrothermal graphite furnace atomic absorption spectrometry with group IIIB elements as studied by atomic and molecular absorption signal profiles

Molecular absorptions of monohalides (MX; X = F, Cl and Br) of alkali metals, alkaline-earth metals and Group IIIB elements produced in a conventional electrothermal graphite furnace atomizer have been observed by a rapid measurement system. Their characteristic data are summarized as appearance and peak temperatures and the analytical sensitivities. Furthermore, molecular absorptions ofAlF and InF are utilized to study the interference of fluoride with aluminum and indium atomic absorptions. Although the formations of AlF and InF suppress the atomic absorptions ofAl and In, respectively, the time-overlap in signal appearance of atomic absorptions of these two elements and molecular absorptions of their monofluorides is not observed. This is contradictory to pure “vapor phase mechanism”, and indicates that processes occurring on the graphite surface are also important. Usefulness of strontium nitrate as a matrix modifier for the determination of indium was also demonstrated.     

Spectral interferences from phosphate matrices in the determination of arsenic, antimony, selenium and tellurium by electrothermal atomic absorption spectrometry

The spectral interferences of phosphorus species originating from the thermal decomposition of calcium phosphate on Sb, As, Se and Te resonance lines, and the influence of increasing amounts of Ce, Ni, W, Pd, Pt, Zr and other elements on non-correctable signals generated by calcium phosphate and on selenium and phosphorus sensitivity have been studied. The results indicate that spectral interference is caused by P₂ absorption and that the extent of interference depends on the wavelength and the spectral band width. The generation of P₂ is masked by large amounts of all the tested reagents. There is a significant reduction in selenium sensitivity in the presence of high concentrations of Ce, Pd and Pt while no decrease in sensitivity is caused by the presence of even 1% nickel and tungsten solutions. All the reagents tested provided enhanced phosphorus sensitivity, thorium being the best.     

Acid interferences in atomic spectrometry: analyte signal effects and subsequent reduction

When considering elemental analysis by atomic spectrometry techniques (e.g. flame atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry), the sample is normally introduced as a solution. In many instances an acid is present in that solution, as a result of previous sample preparation steps, analyte stabilization procedures, etc. Therefore, acids are among the most common matrices involved in spectroscopic analysis. The effect of the acid on the different stages taking place during the whole analytical process has been reviewed. Attention has been paid to the three techniques mentioned above. The results summarized here reveal the crucial role that acids play in atomic spectrometry, being one of the most important sources of interferences suffered by these techniques. In the last part of this bibliographic survey, the methods found for correction of the acid effect are mentioned and briefly described.     

Liquid-liquid extraction with 2-acetylpyridinebenzoylhydrazone in the determination of traces of copper,nickel, cobalt and zinc by atomic absorption spectrometry

Trace amounts of Cu, Ni, Co and Zn in aqueous solutions are determined by their simultaneous extraction with 2-acetylpyridinebenzoylhydrazone followed by flame atomic absorption spectrometry. Isoamyl alcohol is the preferred solvent. Calibration graphs are linear, usually over the range 0–0.2 mg 1^?1 of aqueous phase. There are few interferences from other ions present in 500–1000-fold amounts.     

Direct and simultaneous determination of arsenic, manganese, cobalt and nickel in urine with a multielement graphite furnace atomic absorption spectrometer

A simple method was developed for the direct and simultaneous determination of arsenic (As), manganese (Mn), cobalt (Co), and nickel (Ni) in urine by a multi-element graphite furnace atomic absorption spectrometer (Perkin-Elmer SIMAA 6000) equipped with the transversely heated graphite atomizer and longitudinal Zeeman-effect background correction. Pd was used as the chemical modifier along with either the internal furnace gas or a internal furnace gas containing hydrogen and a double stage pyrolysis process. A standard reference material (SRM) of Seronorm™ Trace Elements in urine was used to confirm the accuracy of the method. The optimum conditions for the analysis of urine samples are pyrolysis at 1350 °C (using 5% H₂ v/v in Ar as the inter furnace gas during the first pyrolysis stage and pure Ar during the second pyrolysis stage) and atomization at 2100 °C. The use of Ar and matrix-free standards resulted in concentrations for all the analytes within 85% (As) to 110% (Ni) of the certified values. The recovery for As was improved when mixture of 5% H₂ and 95% Ar (v/v) internal furnace gas was applied during the first step of a two-stage pyrolysis at 1350 °C, and the found values of the analytes were within 91-110% of the certified value. The recoveries for real urine samples were in the range 88-95% for these four elements. The detection limits were 0.78 μg l⁻¹ for As, 0.054 μg l⁻¹ for Mn, 0.22 μg l⁻¹ for Co, and 0.35 μg l⁻¹ for Ni. The upper limits of the linear calibration curve are 60 μg l⁻¹ (As); 12 μg l⁻¹ (Mn); 12 μg l⁻¹ (Co) and 25 μg l⁻¹ (Ni), respectively. The relative standard deviations (R.S.D.s) for the analysis of SRM were 2% or less. The R.S.D.s of a real urine sample are 1.6% (As), 6.3% (Mn), 7.0% (Ni) and 8.0% (Co), respectively.     

Extraction-flame atomic absorption determination of microtraces of copper, zinc, nickel, cobalt, manganese and iron in some alkali salts

Summary The microtrace content of Cu, Zn, Ni, Co, Mn and Fe in NaClO₄, KCl, KOH and KAl(SO₄)₂ · 12 H₂O is determined by flame atomic absorption spectrometry after preceding preconcentration of the traces using the extraction system PMBP/MIBK. It is proved that the salt matrix does not affect the quantitative extraction of the traces. The method permits the determination of the traces in the concentration range of 10^–3–10^–6% with good precision (variation coefficient 2–8%) and accuracy.

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Extraktions-Flammenatomabsorptions-Bestimmung von Mikrospuren von Cu, Zn, Ni, Co, Mn und Fe in Alkali-Salzen

Zusammenfassung Der Mikrospurengehalt von Cu, Zn, Ni, Co, Mn und Fe in NaClO₄, KCl, KOH, und KAl(SO₄)₂ · 12H₂O wurde durch Flammenatomabsorption nach Extraktionsanreicherung mit einer 1-Phenyl-3-methyl-4-benzoylpyrazolon-5 (PMBP)-Lösung in MIBK bestimmt. Die Salz-Matrix weist keinen störenden Einflu\ auf die quantitative Extraktion der Elementspuren auf. Die Bestimmung der Spuren im Konzentrationsgebiet von 10^–3–10^–6% erfolgt mit guter PrÄzision (Variationskoeffizient 2–8%) und Richtigkeit.

     

Suspensions of biological tissues in alkaline medium for the determination of copper, manganese and cobalt by electrothermal atomic absorption spectrometry

Electrothermal atomic absorption spectrometry was applied to the determination of copper, manganese and cobalt in biological tissues of which small amounts are available only. The samples (10 mg of mice tissue) were suspended in 1 mL of water containing tetramethylammonium hydroxide, Triton X-100 and silicone antifoam. The sample was homogenized by heating to 60 °C for 5 min, submitted to dilution if necessary, and injected into the atomizer. Wall atomization was used for Cu and Mn, and platform atomization for Co. Calibration was carried out using aqueous standards for copper and manganese determination. The determination of cobalt suffered from a matrix effect and, in this case, calibration was enabled by using a suspension of a cobalt-free muscle sample. The detection limits are 25, 20 and 62 ng?g^?1. The results obtained for five certified reference materials demonstrated the reliability of the procedures for the determination of the three analytes in normal and dystrophic mice tissue.     

Correction for background absorption and stray radiation in a.c. modulated Zeeman atomic absorption spectrometry

Analytical results are presented obtained with Zeeman atomic absorption (ZAA) using a modified sine wave magnetic field. The measurement at zero field strength is lengthened to 0.5 ms for a 50 Hz magnetic field of 10 kG.The a.c. Zeeman system is extended with an additional intensity measurement performed at an intermediate field strength. The three field Zeeman system (3FZAA) permits simultaneous correction for background absorption and stray radiation at the expense of halved analytical sensitivity. The background correction capabilities of ZAA and 3FZAA are the same. However, the 3FZAA signals show increased noise in comparison to ZAA.In the three field system the roll-over problem, inherent in existing Zeeman systems, is shifted to higher concentration and to higher absorbance. The height and the position of the maximum in ZAA and 3FZAA analytical curves do not depend on the amount of background absorption.A method for the extension of analytical curves in AA is presented. Utilizing an a.c. modulated magnetic field any sensitivity between zero and ordinary AA sensitivity can be obtained.     

Hydrogen effects on copper,zinc and nickel atomic emission lines in argon radiofrequency glow discharge optical emission spectrometry

The effect of hydrogen (0.5%, 1% and 10% v/v) added to the argon plasma gas on the emission spectra of selected atomic lines for copper, zinc and nickel has been studied by radiofrequency glow discharge optical emission spectrometry (rf-GD-OES). Conductive homogeneous samples containing different concentrations of the elements under study in different matrices have been investigated. Results show different trends of the emission intensity lines with increasing hydrogen concentration in the rf-GD, depending on the line characteristics. In most cases, the emission yields of the lines under study did not change or increased when hydrogen was added to the discharge (no decreases were observed). The emission yields of certain lines showed much higher increases than other lines of the same element (for example, lines 213.86 nm of Zn and 231.10 nm of Ni). Our experiments indicate that such notorious increases could be related with the possible decrease of the self-absorption when hydrogen is added to the discharge. Overall, the results obtained for the emission yield changes of certain lines of a given element in different matrices (with different analyte content) showed that while for resonance emission lines very notorious increases are observed, the values for non-resonance lines do not change significantly (specially if the matrices employed are similar).     

The use of dithizone extraction and atomic absorption spectrometry for the determination of cadmium,zinc, copper,nickel and cobalt in rocks and sediments

A method is presented for the determination of cadmium, zinc, copper, nickel and cobalt in sediments. The sediments are digested with hydrofluoric, sulphuric and perchloric acids. The metals are extracted into dithizone. Cadmium and zinc are back-extracted into dilute hydrochloric acid, but the other metals are determined in a solution prepared after the destruction of the organic extract. The method has been applied to USGS rock reference samples and to estuarine sediments.     

Mutual interactions of elements in the hydride technique in atomic absorption spectrometry: Part 1. Influence of selenium on arsenic determination

The interference from selenium(IV) on the determination of arsenic(III) and -(V) by hydride-generation atomic absorption spectrometry is removed if copper is added to the sample solution. This prevents the evolution of selenium hydride but has no influence — up to certain copper concentrations — on the formation of arsine. The possible interference mechanism is discussed. Interferences on selenium determinations are also described.