Günter Knapp

Elementquerstörungen bei der spurenanalytischen Selen-Bestimmung nach dem Hydrid-AAS-Verfahren

SummaryThe sodium boro hydride-reduction method for the liberation of selenium from acid sample solutions in connection with its determination by AAS using a heatable optical cell made of quartz (hydride system MHS-1, Bodenseewerk Perkin-Elmer, Überlingen, F.R.G.) is interfered with by numerous concomitant elements occurring even in the trace range in the sample solution.In the determination of 5–100 ng of selenium in 20 ml sample solution 0.3 N in HCl, 0.7 μg of Ag+; 1.5 μg of Sb3+; 3 μg of Au3+; 5 μg of Cu2+; 6 μg of As3+;25 μg of Sb5+; 30 μg of As5+; 60 μg of Ni2+; 200 μg of Pt4+ and Mn7+; 700 μg of Co+; 1.5 mg of Pb2+; 3 mg of Cr6+ and 5 mg Hg2+ cause a depression of the Se-signal of 50%. 4 μg of Sn2+/Sn4+ and 6 μg of Bi3+ cause a depression of 30%. Fe2+ /Fe3+ interfere only if present in quantities ≥400 μg. Te4+ in quantities ≤300 μg, alkali metals and alkaline earths ≤25 mg, and Al3+, Cr3+, Mn2+ and Zn2+ ≤5 mg do not affect the selenium hydride formation.The interferences depend very strongly on the used HCl concentration in the sample solution. Further sources of systematic errors are investigated and partly eliminated. The hydride-AAS procedure cannot be recommended for the determination of traces of selenium (ng/g-range) directly in metallic, geological or biological matrices, if the levels of the interfering concomitants reach above a certain threshold concentration, which numerically depend strongly on the apparatus and the parameters of the analysis.ZusammenfassungDie Natriumborhydrid-Reduktionsmethode zur Austreibung des Selens aus sauren Probenlösungen in Kombination mit einer AAS-Bestimmung des Selens in einer geheizten Quarzküvette (Hydridsystem MHS-1 der Firma Bodenseewerk Perkin-Elmer, Überlingen) wird durch die Gegenwart zahlreicher Begleitelemente selbst im Spurenbereich gestört. Bei der Bestimmung von 5–100 ng Se in 20 ml 0,3 N salzsaurer Probenlösung verursachen ca. 0,7 μg Ag+;1,5 μg Sb3+;3 μg Au3+; 5 μg Cu2+; 6 μg As3+; 25 μg Sb5+; 30 μg As5+; 60 μg Ni2+; 200 μg Pt4+ bzw. Mn7+; 700 μg Co2+; 1,5 mg Pb2+; 3 mg Cr6+ und 5 mg Hg2+ jeweils Erniedrigungen des Se-Signals um 50%. 4 μg Sn2+/Sn4+ bzw. 6 μg Bi3+ führen zu einer 30 %igen Erniedrigung.Fe2+/Fe3+ stören ab Mengen ≥400 μg. Te4+ ≤ 300 μg, Alkali- und Erdalkalimengen≤25 mg sowie Mengen ≤ 5mg Al3+, Cr3+, Mn2+ und Zn2+ waren ohne Einfluß auf die Ausbeute der Selenhydrid-Bildung. Die Störungen sind stark abhängig von der vorgegebenen HCl-Konzentration in der Probenlösung. Weitere Quellen für systematische Fehler des Verfahrens wurden untersucht und teilweise behoben. Das Hydrid-AAS-Verfahren kann nicht zur direkten Bestimmung von Selenspuren (ng/g-Bereich) in metallischen, geologischen und biologischen Matrices empfohlen werden, wenn die Gehalte der störenden Begleitelemente in der Probe bestimmte Grenzkonzentrationen überschreiten, die numerisch stark von der apparativen Anordnung und den Versuchsparametern abhängen.

Evaluation of sample preparation methods for polymer digestion and trace elements determination by ICPMS and ICPOES

In this work, sample preparation methods for polymer digestion based on microwave-induced combustion (MIC) and microwave-assisted acid digestion (MW-AD) were evaluated for further As, Bi, Cd, Co, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Sr, Ti, V and Zn determination by inductively coupled plasma mass spectrometry (ICPMS) and inductively coupled plasma optical emission spectrometry (ICPOES). Samples of low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET, colorless and green), polyetheretherketone (PEEK) and nylon 6,6 were digested using MIC and MW-AD in closed quartz vessels. The type and concentration of acids used for MIC were investigated and better results were achieved using a 4 mol l−1 HNO3 + 4 mol l−1 HCl solution. Microwave-assisted acid digestion was also evaluated for polymer digestion using concentrated acids. Both sample preparation methods were considered suitable for polymer digestion but MIC was preferable in view of the possibility of using diluted acids as absorbing solution and allowing higher sample mass to be digested and consequently better limits of detection. Residual carbon content in digests of polymers obtained by MIC was lower in comparison with the values obtained after MW-AD. Accuracy for all the analytes determined by ICPOES and ICPMS after MIC digestion was better than 95% (analysis of certified reference materials and by neutron activation analysis). It was possible to digest up to 8 samples by MIC in less time (in 25 min) in comparison with MW-AD (more than 50 min) and also using diluted acids (4 mol l−1 HNO3 and HCl) instead of concentrated acids.

Novel method for the decomposition of organic and biological materials in an oxygen plasma excited at high frequency for elemental analysis

ZusammenfassungEin neues leistungsfähiges Aufschlußverfahren für die Elementbestimmung in organischen bzw. biologischen Proben wird vorgestellt. In einem mit Hochfrequenz (27,12 MHz) angeregten Sauerstoffplasma kann mehr als 1 g Probenmaterial bei niedriger Temperatur abgebaut werden. Der Aufschluß erfolgt in einem Quarzgefäß mit aufgesetztem Kühlfinger. Flüchtige Elemente, wie As, Sb, Se u. a. werden dadurch quantitativ zurückgehalten. Ein eingebauter Magnetrührer sorgt für ein stetiges Umwälzen der Probe während des Aufschlußvorganges. Die Aufschlußzeit stark mineralhaltiger organischer Proben wird dadurch sehr verkürzt.Die in der Asche verbliebenen, bzw. an der Oberfläche des Aufschlußgefäßes und des Kühlfingers kondensierten Elemente werden durch Rückflußkochen in 1 bis 2 ml hochreiner Säure gelöst. Die Wiederfindung der Elemente Al, As, Cd, Cr, Cu, Fe, Mn, Pb, Se, Zn, Co, Sb, Ni und V mit Hilfe von 6 NBS-SRMs wurdeje nach Element und Konzentrationsbereich mit der ETA-AAS, Flammen-AAS und Hydrid-AAS überprüft. Die Übereinstimmung der Ergebnisse mit den zertifizierten Werten ist sehr gut.Das beschriebene Aufschluß verfahren zeichnet sich durch universelle Anwendbarkeit, sehr geringe Blindwerte und quantitative Wiedergewinnung der meisten Elemente aus. Auch schwer aufschließbare organische Materialien wie Kohle, Graphit, jede Art von Kunststoffen (auch PTFE), Zucker usw. können mit Hilfe dieses Verfahrens problemlos mineralisiert werden.SummaryA new efficient decomposition method for the determination of elements in organic or biological samples is introduced. Within an oxygen plasma excited at high frequency (27.12 MHz), more than 1 g of sample material can be ashed at low temperature. Decomposition is performed in a quartz vessel equipped with a cooling finger. Volatile elements like As, Sb, Se, etc. can be quantitatively recovered in this way. A built-in magnetic stirrer provides for steady sample circulation during the decomposition process. This results in minimum decomposition time for organic samples with high mineral content. All ashing residues and elements condensed on the surface of the decomposition vessel or cooling finger are collected within 1 to 2 ml of high-purity acid by refluxing. The recoveries of the elements were checked using 6 NBS-Standard Reference Materials for the elements Al, As, Cd, Cr, Cu, Fe, Mn, Pb, Se, Zn, Co, Sb, Ni, and V with either the ETA-AAS, flame-AAS, or hydride-AAS, dependent on the respective element and range of concentration.Very good agreement with the certified values was observed. The decomposition method described in the current paper stands out for universal applicability, quantitative recovery of most of the elements, and is characterized by low blanks. Even difficultly decomposable organic materials like charcoal, graphite, all plastics (also PTFE), sugar, etc. can be ashed without any problems.

Mechanized techniques for sample decomposition and element preconcentration

High performance decomposition techniques for organic and inorganic samples are discussed. Wet decomposition in closed vessels with conventional and microwave heating enables the decomposition of a wide variety of sample materials. A complete mineralization of organic samples with nitric acid is just possible by means of the High Pressure Asher®. After microwave digestion 2–20% of the carbon of the introduced sample remains in the digestion solution. Trace elements in aqueous samples or in digestion solutions can be determined with high sensitivity and free of systematic errors by means of a combined analytical method consisting of a computer controlled preconcentration device (TraceCon®) and a simultaneous ICP emission spectrometer.

Atomic emission gas chromatographic detection—chemical and spectral interferences in the stabilized capacitive plasma (SCP)

Abstract The stabilized capacitive plasma (SCP) is a 27 MHz discharge in helium at atmospheric pressure used as atomic emission source for element specific detection (ESD) in gas chromatography. The discharge is sustained in a liquid-cooled fused-silica tube surrounded by two annular electrodes. The introduction of small amounts of various gases (H 2 , O 2 , N 2 , CO 2 , Ar) into the helium plasma leads to significant changes in the spectral emission pattern and the emission intensity of important analyte lines. The analytes were introduced into the plasma at constant flow using a diffusion device and by chromatographic separation of test mixtures. Both a monochromator and a polychromator system were used to detect spectral emission in the near-infrared region.

Mercury determination in soil by CVG-ICP-MS after volatilization using microwave-induced combustion

Microwave-induced combustion (MIC) was applied for mercury volatilization from soil with subsequent determination by cold vapor generation coupled with inductively coupled plasma mass spectrometry (CVG-ICP-MS). Samples of soil were mixed with microcrystalline cellulose (300 mg), pressed as pellets and combusted in closed quartz vessels pressurized with 20 bar of oxygen. Mercury was volatilized from the sample matrix during combustion and quantitatively absorbed in a suitable solution. The type and concentration of absorbing solution (diluted or concentrated nitric or hydrochloric acids, or even water) as well as the use of a reflux step after combustion were studied. Accuracy was evaluated using soil certified reference materials. Using 0.25 mol L−1 HNO3 as absorbing solution with a reflux step of 5 min the agreement with reference values was better than 95%. The limit of detection was 0.006 μg g−1 Hg (using 300 mg of sample mass) and the residual carbon content for MIC digests was always below 1%. The main advantage of the proposed method is related to the complete separation of the analyte from the sample matrix. Up to eight samples could be simultaneously combusted in only 25 min. Taking into account that only 6 ml of very diluted nitric acid solution (0.25 mol L−1) were used, the proposed MIC method coupled with CVG-ICP-MS can be considered in good agreement with green analytical chemistry recommendations.

Application of an on-line preconcentration system in simultaneous ICP-AES

A PC-controlled on-line preconcentration system (TRACECON) developed by Knapp et al. [11], was connected to a JY-70 Plus simultaneous ICP spectrometer to preconcentrate on-line seven trace elements (Cu, Fe, Zn, Cr, Ni, Mn, V) in biological and environmental samples. EDTrA-cellulose was used as column material. The elemental concentrations were determined by simultaneous ICP-AES. The effect of pH of the sample solution on the enrichment was studied. It was found that the recoveries of chromium and iron depend strongly on the pH of the sample solution. All the elements mentioned were recovered quantitatively at pH 4.0±0.1. The flow rates of sample solution and element solution were optimized. The enrichment factors for seven elements at 5 ml loading volume range from 3.9 for Cu to 7.9 for Zn. The detection limits of all seven elements were improved. The accuracy of the method was tested by the analysis of a number of CRMs of NIST, BCR and NIES. Most results are in good agreement with the certified values.

Determination of halides by microwave induced plasma and stabilized capacitive plasma atomic emission spectrometry after on-line continuous halogen generation

This paper describes a comparative study of the microwave induced plasma (MIP) and the stabilized capacitive plasma (SCP) for halide determinations. The MIP is generated in a Beenakker cavity TM(010) using a tangential flow torch and the SCP consists of a 27.12 MHz discharge sustained in a liquid-cooled, fused silica tube surrounded by two annular electrodes. Both discharges are operated in helium at atmospheric pressure and detection was carried out by Atomic Emission Spectrometry (AES). The halides (I(-), Br(-), Cl(-)) are converted to volatile halogens by continuous flow generation based on chemical oxidation and on-line separation from the aqueous phase, via a gas-liquid separator, to be finally introduced into the plasma. The different factors affecting the emission intensity of the volatile halogens generated are compared for both discharges and the analytical performance characteristics are also evaluated. Detection limits of 17 ng ml(-1), 24 ng ml(-1) and 55 ng ml(-1) are obtained for the determination of Cl(-), Br(-), and I(-), respectively, in the ultraviolet-visible (UV-VIS) region using the MIP-AES and 45 ng ml(-1), 135 ng ml(-1) and 400 ng ml(-1) for Cl(-), Br(-), and I(-) with the SCP-AES. Lines in the near infrared (NIR) region were also evaluated for the SCP-AES detection; improvements in detection limits higher than 30 times were observed in the NIR region as compared with the UV-VIS with detection limits in the NIR of 1.4 ng ml(-1) for Cl(-), 3 ng ml(-1) for Br(-) and 13 ng ml(-1) for I(-).

Preparation of Chemically Modified Cellulose Exchangers and their use for the Preconcentration of Trace Elements

I. INTRODUCTION Analytical chemistry at trace levels frequently requires special techniques and precautions to avoid systematic errors. Preconcentration of the analyte elements is one of these special steps that can be favorably applied to the sample prior to analysis.

Multi-elemental analysis in biological samples by on-line preconcentration on 8-hydroxyquinoline-cellulose microcolumn coupled to simultaneous ICP-AES

SummaryThe analytical performance of an on-line oxine-cellulose microcolumn preconcentration system coupled to simultaneous ICP was investigated. Different factors including the pH of the sample solution, the flow rates of sample loading and eluation, the acidity of eluent and different eluents were investigated and optimized. In comparison with continuous aspiration, the signal enhancement factors of eleven elements (Zn, Cu, Ni, V, Cr, Fe, Mn, Co, Pb, Cd and Al) were in the range of 6.4 to 13.5 for peak height (0.5 s) and 3.7 to 5.8 for peak area (15 s), respectively. The influences of matrix ions, such as Ca, Mg, Fe, Cu and NaCl were studied. Performance was demonstrated by simultaneous determination of seven (Zn, Cu, Ni, V, Cr, Fe, Mn) elements in a number of CRMs. Most results were satisfactory, except for iron and chromium. The possible reasons were discussed. Co, Pb, Cd and Al were not available in the simultaneous instrument. Therefore, only the analytical performance was measured for these elements by the sequential instrument.