Direct determination of lead in blood by electrothermal atomic absorption spectrometry with L'vov platform and matrix modification

An electrothermal atomic-absorption procedure with the L'vov platform and a simple five- or ten-fold sample dilution with a matrix-modifier solution containing diammonium hydrogenphosphate, Triton X-100 and nitric acid, is described for the direct determination of relatively low levels of lead in heparinized blood. The graphite-furnace parameters and matrix-modifier composition are optimized. Sensitivity, imprecision, accuracy and detection limit are reported. Results obtained by standard addition for ten human blood samples (30–400 μg l^?1 lead) were confirmed by an extraction/flame atomic-absorption reference method. Differences in mean lead values ranged from 2 to 31 μg l^?1 with 5.1% mean relative difference. The mean relative standard deviations for consecutive and between-day determinations were 4.6 and 9%, respectively. Accuracy was verified by analyzing six bovine-blood standards certified for lead in the range 70–1100 μg l^?1; deviations of found concentrations from expected values ranged from 0 to 44 μg l^?1 with 4.3% mean relative error. Recovery experiments done with human blood gave 104% (90–121%) of the added lead. The method offers several advantages for routine application in comparison with the extraction/flame atomic-absorption procedure.     

Minimization of matrix interferences in the determination of aluminium silicon by electrothermal atomic absorption spectrometry with the L'vov platform

The pyrolytic L'vov platform in a pyrolytically-coated graphite tube was successful in eliminating the suppressive interference by silicon (? 10 mg ml^?1) on the aluminium signal, thus allowing ? 0.2 μg Al g^?1 to be determined without preliminary separation.     

Determination of urinary arsenic by electrothermal atomic absorption spectrometry with the l'vov platform and matrix modification

Total arsenic can be determined rapidly and simply in urine by dilution with a matrix modifier containing nickel and magnesium nitrate in nitric acid. The background correction capability of Zeeman-effect electrothermal atomic absorption spectrometry effectively nullifies nonatomic absorption by urine concomitants. Accuracy and precision of the method were evaluated by the determination of total arsenic in the National Bureau of Standards' SRM 2670, Toxic Elements in Freeze-Dried Urine, and commercially available lyophilized urine material. Deviations of determined concentrations from expected values ranged from about 4 to 18 ng ml^?1 with standard deviations ranging from about 5 to 31 ng ml^?1.     

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.     

Reduction of interferences in graphite furnace atomic absorption spectrometry by multiple linear regression modelling

The multivariate effects of Na, K, Mg and Ca as nitrates on the electrothermal atomisation of manganese, cadmium and iron were studied by multiple linear regression modelling. Since the models proved to efficiently predict the effects of the considered matrix elements in a wide range of concentrations, they were applied to correct the interferences occurring in the determination of trace elements in seawater after pre-concentration of the analytes. In order to obtain a statistically significant number of samples, a large volume of the certified seawater reference materials CASS-3 and NASS-3 was treated with Chelex-100 resin; then, the chelating resin was separated from the solution, divided into several sub-samples, each of them was eluted with nitric acid and analysed by electrothermal atomic absorption spectrometry (for trace element determinations) and inductively coupled plasma optical emission spectrometry (for matrix element determinations). To minimise any other systematic error besides that due to matrix effects, accuracy of the pre-concentration step and contamination levels of the procedure were checked by inductively coupled plasma mass spectrometric measurements. Analytical results obtained by applying the multiple linear regression models were compared with those obtained with other calibration methods, such as external calibration using acid-based standards, external calibration using matrix-matched standards and the analyte addition technique. Empirical models proved to efficiently reduce interferences occurring in the analysis of real samples, allowing an improvement of accuracy better than for other calibration methods.     

Statistical investigations of interferences in graphite furnace atomic absorption spectroscopy

Summary In the first part different methods for studying interferences of the time dependent signal in flameless AAS are presented with emphasis on factorial designs in experimentation as opposed to the one-factor-at-a-time approach.An example of the statistical computations necessary for interpretation of a multifactor experiment is worked out and discussed in detail with special consideration of the explanation of first-order interactions.The influence of instrumentation upon determinations in the graphite furnace is dealt with in the second part: The temperature in the graphite furnace was measured with a pyrometer, a thermocouple and a Hg-thermometer. The results obtained with the pyrometer were in good agreement with the values given by the manufacturer. The stability of the AAS system was checked and found to be sufficient for the investigation of interferences.

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Statistische Untersuchungen über Störungen bei der flammenlosen AtomabsorptionsspektralphotometrieI. Methoden und Apparaturen

Zusammenfassung Im ersten Abschnitt werden die verschiedenen Möglichkeiten zur Untersuchung von Störungen des zeitabhängigen Signals bei der flammenlosen AAS aufgezeigt, wobei besondere Bedeutung den faktoriellen Versuchsplänen im Gegensatz zu einparametrigen Untersuchungen beigemessen wird.Ein Beispiel der statistischen Auswertung zur Interpretation eines Experiments mit mehreren Faktoren wird gebracht, und dabei besonderes Gewicht auf die Erklärung von Wechselwirkungen zwischen zwei Faktoren gelegt.Im zweiten Abschnitt werden die apparativen Einflüsse auf Messungen in der Graphitrohrküvette behandelt. Dazu wurde die Temperatur im Graphitrohr mit einem Pyrometer, einem Thermoelement und einem Quecksilberthermometer gemessen. Die Temperaturen, die mit der pyrometrischen Methode gefunden wurden, stimmen gut mit den vom Hersteller angegebenen Werten überein. Die Stabilität des AAS-Gerätes wurde überprüft: sie reicht für die Durchführung von Interferenzstudien aus.

     

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].     

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.     

Use of hydrogen for the elimination of matrix interferences in the determination of lead by graphite furnace atomic absorption spectrometry

Summary Comparatively high sulphur contents in brown algae (Fucus vesiculosus) cause interferences in the determination of lead by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). These cannot always be eliminated by the application of the L'vov platform, matrix modifiers recommended for lead as (NH₄)₂HPO₄ and Mg(NO₃)₂, Zeeman-effect background correction and peak area evaluation.The behaviour of the lead absorbance signal obtained from the L'vov platform inserted into an uncoated as well as a pyrolytically coated graphite tube was examined in the presence of sodium and magnesium sulphate and (NH₄)₂HPO₄ and Mg(NO₃)₂ matrix modifiers.Accurate lead determinations could only be performed if hydrogen was used as alternate gas during drying and charring steps since this eliminated the interferences caused by sulphates.

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Verwendung von Wasserstoff zur Eliminierung von Matrixstörungen bei der Bleibestimmung durch Graphitofen-AAS

Zusammenfassung Vergleichsweise hohe Schwefelgehalte in Braunalgen (Fucus vesiculosus) verursachen Störungen bei der Bestimmung von Blei mit Grahitrohrofen-AAS. Diese können nicht immer durch Anwendung der L'vov-Plattform und den für Blei empfohlenen Matrix-Modifizierer (NH₄)₂HPO₄ und Mg(NO₃)₂, Zeeman-Effekt-Untergrundkorrektur und Peakflächenauswertung behoben werden.Das Verhalten des Blei-Absorbance-Signals, das von einer L'vov-Plattform, die sowohl in ein unbeschichtetes wie in ein mit Pyrokohlenstoff beschichtetes Graphitrohr eingebracht wurde, erzeugt wird, wurde in Gegenwart von Natrium- und Magnesiumsulfat sowie (NH₄)₂HPO₄ und Mg(NO₃)₂-Matrix-Modifizierern untersucht.Richtige Bleibestimmungen konnten nur durchgeführt werden, wenn Wasserstoff als Alternativgas während des Trocknens und der thermischen Zersetzung verwendet wurde, was die durch Sulfat hervorgerufenen Störungen eliminierte.

     

Reduction of temperature variation in the atomic absorption graphite furnace

The temperature variation that is experienced along the length of the graphite furnace tube of the Massmann design can be reduced by the use of a contoured tube. An analytical model of the steady-state temperature distribution along the graphite tube has been developed and has been shown to agree quite well with experimental data. Steady-state and time-dependent measurements along the length of the graphite tube are reported for different conditions. With conventional tubes at thermal equilibrium, there is a temperature difference exceeding 1000°C between the center and the ends when the center of the tube is at 2500°C. With a contoured tube this temperature gradient has been reduced to 100°C.     

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.     

Some interferences in the atomic absorption spectrophotometry of calcium

The effects of anions, cations and complexing agents on the absorbance of calcium in the air-propane flame are investigated. Mechanisms for the various enhancing and depressive effects are suggested.     

石墨炉原子吸收光谱法测定锌基体物料中微量铊

采用B-HNO3-A溶解样品,硝酸钯作基体改进剂,通过优化仪器分析条件,灰化温度为500℃,原子化温度为1 800℃,成功实现了石墨炉原子吸收光谱法测定湿法冶炼锌基体物料锌精矿、锌焙砂、氧化锌、锌粉等物料中微量铊。方法对照实验结果与电感耦合等离子体质谱法(ICP-MS)测定值基本一致。方法的相对标准偏差(RSD,n≤8)为1.7%~7.8%,加标回收率为99%~103%。     

The role of metallic matrix modifiers in graphite furnace atomic absorption spectrometry

The role of metallic matrix modifiers in AAS is considered; for elements reduced, together with modifier elements, during ashing and the beginning of the atomization process, the thermodynamic activity and melting points of the alloys formed are important. For Mg²⁺, prevention of the effects of halide ions is considered, as is also the behaviour of buffer and/or carrier in emission spectrometric analysis of the other alkali and alkaline earths.     

The direct determination of cadmium in urine by electrochemical atomic absorption spectrometry with the L'vov platform

A simple, direct procedure for the measurement of cadmium in urine is described. Graphite-furnace atomic absorption spectrometry is used in conjunction with selective atomisation at 800°C from a L'vov platform. Urine samples are diluted with an equal volume of deionised water and 20-μl aliquots are injected. Calibration is done by standard additions. The sensitivity is 0.016 μg Cd l^?1 for 1% absorption for a 20-μl sample. Within-run precision is 4.9% at 0.84 μg l^?1. The detection limit is 0.06 μg l^?1, which allows normal unexposed levels of cadmium in urine to be determined. The method is applicable to the determination of urinary cadmium levels of both occupationally non-exposed and exposed populations.     

Organophosphorus acid interferences in flame atomic absorption spectrometry

The interference of the organophosphorus acids, 1-hydroxyethane-1,1-bisphosphonic acid, aminotris(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid) and hexamethylenediaminetetrakis(methylenephosphonic acid) on the determination of eighteen metal ions by flame atomic absorption spectrometry is reported. Comparisons with the effect of orthophosphoric acid reveal similarities and distinct differences in their interfering effects. In the air/acetylen flame, depressive interferences are attributed to the formation of phosphates, M₃(PO₄)₂, or hydroxynpatite-like compounds, M₅(OH)(PO₄)₃, in the flame aerosol particles for Mg, Ca, Sr, Ba, Mn, Co and Ni. Iron(III) and chromium(III) appear to form stable oxide phosphates, M₂O₃?MPO₄ or M₃O₄?MPO₄. Evidence for the formation of stable molybdenum carbides, MoC and MoC₂, is also presented. In the nitrous oxide/acetylene flame, serious interferences perssisted only for molybdenum but were eliminated by the addition of sodium sulphate.     

Determination of palladium by graphite furnace atomic absorption spectroscopy without matrix matching

A graphite furnace atomic absorption spectroscopy method for the analysis of the palladium (Pd) content in bulk pharmaceutical drug substances and their intermediates prepared in aqueous solutions is extended to samples prepared in acetonitrile (ACN) and ACN-water mixtures as well to samples prepared in dimethyl sulfoxide (DMSO) and DMSO-water mixtures. The Pd content in samples solubilized in these solvents can be accurately determined with calibration established with standards prepared in aqueous solutions without matrix matching or using the method of standard additions. The validity of this method is demonstrated by spike recovery studies and by the agreement with results for the same samples prepared in these solvents, in concentrated nitric acid, and prepared by a microwave digestion system.     

Time resolution of interferences in electrothermal atomic absorption spectrometry

A fast detector-amplifier-readout system is used for studying interferences in electrothermal graphite atomizers. The effects of different matrix components (K, B, Ca, Mg, and Cl), and graphite tube surfaces significantly alter the atomization processes of lead.     

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.