Negative thermal ionization mass spectrometry of selenium part 3.* Selenium trace determination in food samples

Summary Selenium traces are analysed in different animal tissue samples with isotope dilution mass spectrometry using the formation of negative Se^– thermal ions (NTI-IDMS) for isotope ratio measurements. An enriched⁸²Se spike is applied for the isotope dilution technique. After decomposition of the food samples with a HNO₃/HCIO₄ mixture selenium is separated by the formation of SeH₂ using a hydride generation system which is normally applied for atomic absorption spectrometry. Selenium hydride is absorbed in a cone. HNO₃ solution, from which sample mass spectrometric determinations are carried out. The recovery of selenium for the total sample treatment has been determined with a⁷⁵Se tracer to be about 62%. The precision of the IDMS method in the concentration range of 0.1–10 g/g lies between 1.8% and 4.1 %. The IDMS results agree well with the certified values of the analysed standard reference materials. A comparison of these results with those achieved by an isotope dilution method, using the formation of piazselenol and gas-chromatographic separation (GC-IDMS), and by hydride generation atomic absorption spectrometry (HGAAS) is given. Whereas the NTI-IDMS and GC-IDMS results are in very good agreement, HGAAS can be affected by interferences.

---

Negative Thermionen-Massenspektrometrie von Selen Teil 3. Selenspurenbestimmung in Lebensmittelproben

---

Part 2: see [131

---

Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

Selenium, chromium and zinc content of proposed SRM 1846 infant formula

A proposed infant formula SRM 1846 has been analyzed for zinc, selenium and chromium by isotope dilution mass spectrometry (IDMS). The precision of the IDMS methods has been sufficient to allow the estimation of the sample homogeneity with respect to these three analytes. Overall means of 60.9±0.9 g Zn/g (mean±standard deviation) and 76.1±1.9 ng Se/g have been found for 30 determinations. Values for chromium content have been found to depend on the sample preparation method, suggesting possible contamination. Accurary of the zinc, chromium and selenium values has been verified using a certified reference material, SRM 1549 Non-Fat Milk Powder.     

Trace analysis of chlorine in high-purity refractory metals with isotope dilution mass spectrometry

Summary A method for the determination of chlorine in high-purity molybdenum and tungsten with isotope dilution mass spectrometry (IDMS) has been developed using a ³⁷Cl enriched spike solution. After dissolution of the sample in H₂O₂, chlorine is separated by AgCl precipitation. Negative Cl^- thermal ions are produced in a double-filament ion source using an easy-to-handle and cost-efficient quadrupole thermal ionization mass spectrometer. The detection limit, which is mainly influenced by contaminations from the laboratory air, lies between 0.006 and 0.1 g/g depending on the variation of the blank values. Chlorine concentrations between 0.07 and 10.5 g/g are analysed in different tungsten and molybdenum samples. A comparison with other sensitive analytical methods shows the urgent necessity of developing alternative methods for the determination of chlorine traces in refractory metals.Dedicated to Professor Dr. V. Krivan on the occasion of his 60th birthday     

Determination of selenium in sediments by fluorimetry with 2,3-diaminonaphthalene after an improved pretreatment by tellurium coprecipitation

Summary An improved fluorimetric method for the determination of selenium in estuary sediments and sedimentary core samples is described. For the separation of selenium, coprecipitation with tellurium-ascorbic acid method gave satisfactory results. The status of the pollution caused by selenium in Nagoya area, which is one of the most industrially active areas in Japan, was estimated, based on the results obtained with this method. Several g/g of selenium were determined in the sediments. Interferences by foreign ions were eliminated by the coprecipitation procedure. Selenium added was recovered by 95–101%.

---

Selenbestimmung in Sedimenten mit Hilfe der Fluorimetrie mit 2,3-Diaminonaphthalin nach einer verbesserten Vorbehandlung durch Tellur-Mitfällung

Zusammenfassung Gehalte bis zu mehreren g/g Selen wurden nach dem verbesserten Verfahren in den Sedimenten des Hafens von Nagoya bestimmt. Störungen durch Fremdionen wurden durch das Mitfällungsverfahren mit Tellur/Ascorbinsäure verhindert. Zugesetztes Selen wurde zu 95 bis 101% wiedergefunden.

     

Die polarographische Bestimmung kleiner Selenmengen

Zusammenfassung Zur polarographischen Bestimmung sehr kleiner Selenmengen sind vor allem angesäuerte Natriumkaliumtartrat- oder Lithiumcitratlösungen brauchbar. Bei Selenkonzentrationen von mehr als etwa 10–15 g/ml sind schwach alkalische Grundlösungen, z.B. NH₃ + NH₄Cl, vorzuziehen.

---

Summary Useful supporting electrolytes for the polarographic determination of very small quantities of selenium are chiefly acidified solutions of sodium potassium tartrate or lithium citrate. For selenium concentrations higher than 10–15 g/ml, weakly alkaline solutions, e.g. NH₃ + NH₄Cl, are to be preferred.

---

---

Wir danken den Vereinigten Aluminium-Werken AG. für die Überlassung des Radiometer-Polarographen.     

Determination of cadmium, lead, and thallium in materials of the environmental specimen bank using mass spectrometric isotope dilution analysis (MS-IDA)

Summary An analytical procedure for the simultaneous determination of cadmium, lead, and thallium in the mg/kg- and g/kg-range in biological materials and sewage sludge by mass spectrometric isotope dilution analysis (MS-IDA) is described.Cadmium, lead, and thallium were separated by electrolytical deposition after low temperature ashing (LTA) of the samples in oxygen plasma and dissolution of the ashes in HNO₃ or HNO₃/HF. Measurement of the isotopic ratio was carried out with a thermal ionization mass spectrometer using the silica gel technique. Cadmium contents ranging from 1.03 to 4.60 mg/kg with relative standard deviations from 0.3 to 1.3%, lead contents ranging from 75 g/kg to 25 mg/kg with relative standard deviations from 0.6 to 3.5%, and thallium contents ranging from 2.9 to 247.7 g/kg with relative standard deviations from 0.1 to 1.7% were determined in the materials of the environmental specimen bank analyzed.

---

Bestimmung von Cadmium, Blei und Thallium in Materialien der Umweltprobenbank mit der massenspektrometrischen Isotopenverdünnungsanalyse

Zusammenfassung Ein Analysenverfahren zur simultanen Bestimmung von Cadmium, Blei und Thallium im mg/kg- und g/kg-Bereich in biologischen Materialien und Klärschlamm mit der massenspektrometrischen Isotopenverdünnungsanalyse (MS-IDA) wird beschrieben.Nach Niedertemperaturveraschung (LTA) der Proben im Sauerstoffplasma und Lösen der Aschen in HNO₃ oder HNO₃/HF-Gemisch werden Cadmium, Blei und Thallium durch elektrolytische Abscheidung abgetrennt. Die Isotopenverhältnismessung erfolgt mit der Silicageltechnik in einem Thermionen-Massenspektrometer. In den analysierten Probenbankmaterialien werden Cadmiumgehalte im Bereich von 1,03 bis 4,60 mg/kg mit relativen Standardabweichungen von 0,3 bis 1,3%, Bleigehalte im Bereich von 75 g/kg bis 25 mg/kg mit relativen Standardabweichungen von 0,6 bis 3,5 % und Thalliumgehalte im Bereich von 2,9 bis 247,7 g/kg mit relativen Standardabweichungen von 0,1 bis 1,7% bestimmt.

---

---

Dedicated to Prof. Dr. W. Fresenius on the occasion of his 70th birthday     

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on ⁷⁶Se, ⁷⁷Se, and ⁷⁸Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H₂ gas. We developed a novel simple optimization routine for the H₂ gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H₂ flow was 2.9 mL min^–1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO₃ and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 g L^–1 for ⁷⁶Se and ⁷⁸Se and 0.13 g L^–1 for ⁷⁷Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 g L^–1 and the range was 73.4–305.5 g L^–1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145±3 g L^–1 (n=36) and the certified value of 136±9 g L^–1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911±75 g L^–1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920±60 g L^–1.     

Detection of sub-micro quantities of thorium by solocnrome azurine B. S.

Summary Solochrome Azurine B. S. has been introduced as a new colour reagent for the detection of thorium in sub-micro quantities. Thorium gives a bluish violet colour with the dye at p_H 4. The limit of identification is 0.22g of thorium.

---

Zusammenfassung Solochrom Azurin B. S. wird als neues Farbreagens für den Nachweis von Thorium in Mikrogrammengen vorgeschlagen. Thorium gibt mit dem Farbstoff bei p_H 4 eine blauviolette Farbe. Die Erfassungsgrenze beträgt 0,22g Thorium.

---

Résumé On a introduit la Solochrome Azurine B. S. comme nouveau réactif colorimétrique pour déceler les quantités submicro de thorium. Celui-ci donne une couleur violet bleuâtre avec le colorant à p_H 4. La limite de dilution est de 0,22g de thorium.

     

Systematische Fehler bei der Selenbestimmung im ng/g-Bereich in biologischen Matrices nach dem Hydrid-AAS-Verfahren

Zusammenfassung Vier biologische Standardreferenz-substanzen (NBS und IAEA) werden mit zwei unterschiedlichen Aufschlußmethoden, einem Naßaufschluß mit einem HNO₃/HClO₃/HClO₄-Gemisch nach optimiertem Temperatur-Zeit-Programm sowie einer Verbrennungsmethode im Sauerstoffstrom (Trace-O-Mat), mineralisiert und die Selengehalte der Aufschlußlösungen nach der Hydrid-AAS-Methode bestimmt. Dabei treten gegenüber den zertifizierten Selengehalten mit zunehmender Einwaage Minusbefunde auf, die — von den Aufschlußmethoden unabhängig — auf sich addierende Querstörungen durch Begleitelemente im g/g-Bereich bei der Selenhydridbildung zurückzuführen sind, wie bereits an anderer Stelle [3] beschrieben wurde.

---

Systematic errors in the determination of selenium in the ng/g-range in biological matrices by the hydride-AAS method

Summary Four biological standard-reference materials (NBS and IAEA) were mineralized with two independent decomposition methods — a wet decomposition with a mixture of HNO₃/HClO₃/HClO₄ using an optimized temperature-time programme, and a combustion method in an oxygen stream (Trace-O-Mat). The selenium contents of the decomposition solutions were determined by the hydride-AAS method. The selenium concentrations were in agreement with the certified values at low sample weights, but decreased as the sample weights were increased. This effect is independent of the decomposition method, but is caused by interferences of concomitant elements in the g/g-range with the formation of selenium hydride, as has been previously discussed [3].

Diese Arbeit wurde in dankenswerter Weise von der Fa. Sandoz AG, Basel, unterstützt.     

Atomic-absorption spectrophotometric determination of ultramicro amounts of selenium(IV) and total selenium in sulphuric acid

Summary Ultramicro amounts of selenium in sulphuric acid are determined by a new atomic absorption spectrophotometric method. Selenium(IV) is directly determined ater extraction into toluene with an aromatic o-diamine and addition of nickel(II) prior to atomization; the determination of total selenium (0, IV and VI) needs a treatment of the sample with selected oxidizing and reducing agents.In the studied samples, total selenium (0.003–0.022 g of Se in 1 ml sulphuric acid) is present only in the tetravalent state. The detection limit of the method is 0.003 g of selenium.

---

Atomabsorptions-spektralphotometrische Bestimmung von Ultramikromengen Selen(IV) und Gesamtselen in Schwefelsäure

Zusammenfassung Selen(IV) kann direkt bestimmt werden nach Toluolextraktion der mit einem aromatischen o-Diamin behandelten Lösung und Zusatz von Nickel(II). Die Bestimmung von Gesamtselen (0, IV, VI) erfordert eine Vorbehandlung mit Perchlor- bzw. Salpetersäure und Wasserstoffperoxid. Die Nachweisgrenze des Verfahrens beträgt 0,003 g Se. In den untersuchten Proben war das Gesamtselen (0,003–0,022 g/ml) nur als Se(IV) vorhanden.

     

Zur Verteilung von Dotierungsstoffen in Selengleichrichterplatten

Zusammenfassung Zur schichtweisen Analyse von Tellurmengen im ppm-Bereich in Selengleichrichterplatten wird das Selen mit wäßriger Alkalicyanidlösung in etwa 1 starken Schichten von diesen abgelöst. Für die Abtrennung der darin befindlichen Tellurspuren eignet sich die gemeinsame reduzierende Fällung durch Hydrazindichlorid mit Selen als Spurenfänger. Die quantitative Analyse des Tellurs erfolgt in Gegenwart eines maximal 10⁵fachen Selenüberschusses mit Hilfe der durch Chrom katalysierten Redoxreaktion zwischen Tellur(IV) und Tri-1, 10-eisen(III)-phenanthrolin (Ferriin). 20 Proben können in 2 Tagen analysiert werden. Es betragen die Standardabweichung im Bereich von 3–50 g Tellur etwa 0,6 g, der Streubereich für 99%ige Sicherheit ±42% resp. ±12%, die Erfassungsgrenze 1,5 g in 25 ml und die Grenzkonzentration 0,06 g/ml. Ein Beispiel für die Tellurverteilung in einer Selengleichrichterplatte ist wiedergegeben.

---

On the distribution of doping elements in selenium rectifier cellsII. Method for the determination of the distribution of tellurium in selenium rectifier cells

The dissolution of the selenium in ca. 1 layers is realised by aqueous solutions of alkali cyanides. The separation of the ppm amounts of tellurium from this solution is possible in acid medium by a reducing coprecipitation of the traces of tellurium by hydrazine dichloride with selenium as trace catcher. In the presence of an excess up to 10⁵ of selenium tellurium is determined quantitatively by means of the Cr-catalysed redox reaction between tellur(IV) and tri-1,10-phenanthroline-iron(III) (ferriin). 20 samples can be completed in 2 days. The standard deviation in the range from 3 g to 50 g is about 0.6 g; the limit of error for 99% security is ±42%, respectively ±12%; the limit of detection is 1.5 g tellurium in 25 ml according to 0.06 g/ml. An example for the distribution of tellurium in a selenium rectifier cell is given.

---

---

I. Mitteilung: D. Baresel u. K. Jaetsch: diese Z. 249, 234 (1970).

---

Jetzt: Robert Bosch GmbH, Forschungsinstitut Berlin.

---

Der Fa. Siemens AG danken wir für die Genehmigung zur Veröffentlichung der Ergebnisse, Herrn Dr. Iwantscheff und Herrn Ernst im Forschungszentrum der Siemens-Schuckert-Werke in Erlangen sowie Herrn Dr. Eggert im Schaltwerk Berlin für die anregenden Diskussionen.     

Thallium determination in reference materials by Isotope Dilution Mass Spectrometry (IDMS) using thermal ionization

Summary Using Isotope Dilution Mass Spectrometry (IDMS) with thermal ionization, thallium concentrations were determined in reference materials from NIST and BCR, from other sources, and reference materials from the German Environmental Specimen Bank. ²⁰³Tl spike solution is applied for the isotope dilution technique. Thallium concentrations in the investigated materials range from 2.67 g Tl·kg^–1 to 963 g Tl·kg^–1 with a relative standard deviation from 0.14 to 10%. The detection limit was 0.1 ng thallium for this work.     

Development of mycotoxin reference materials

Summary The analytical difficulties in mycotoxin determination have given rise to the development of mycotoxin reference materials by the European Community Bureau of Reference (BCR) in cooperation with several European Laboratories, among them the National Institute of Public Health and Environmental Protection. The first project undertaken concerned four milk powders certified for their aflatoxin M₁ content (concentrations 0, 0.1, 0.3 and 0.8 g/ kg). Projects that are well-advanced include two peanut meals (aflatoxin B₁ contents 0 and ca. 200 g/kg) and two compounded animal feedingstuffs (aflatoxin B₁ contents 0 and 10 g/kg). Mycotoxin reference materials are also under development for zearalenone in wheat and maize, and for ochratoxin A in wheat.The general approach followed in the development and certification of mycotoxin reference materials (preparation, testing for homogeneity and stability, intercomparisons of methods and certification exercise) will be discussed and exemplified with the help of the completed project on aflatoxin M₁ in milk powder.

---

Entwicklung von Mycotoxin-Referenzmaterialien

     

Rapid electrothermal atomic absorption method for arsenic and selenium in geological materials via hydride evolution

Summary A rapid semi-automated hydride evolution-electrothermal atomic absorption spectrophotometric method has been developed for the determination of arsenic and selenium in geological materials. A representative sample of a rock, soil or sediment is digested with a mixture of HNO₃-HClO₄. The nearly dry digestate is taken up in HCl. The arsenic (or selenium) in the hydrochloric acid solution is converted to its hydride with sodium borohydride. The hydride is decomposed and atomized in an electrically heated quartz furnace, and the atomic absorption signal is measured at the appropriate resonance wavelengths of arsenic and selenium. Both the elements can be reliably determined in geochemical samples in the range of 0.05–2.00 g/g. The method has wide tolerance for variation in reagent concentrations and possible interferences, and when tested on some certified rocks having a wide range of arsenic and selenium values is found to be satisfactorily accurate and precise. The procedure is now routinely used in our laboratories. At least 10 samples can be analyzed per hour.

---

Schnelles elektrothermisches AAS-Verfahren zur Bestimmung von Arsen und Selen in geologischem Material über die Hydridbildung

Zusammenfassung Bei dem beschriebenen Verfahren wird die Probe mit einem Salpetersäure-Perchlorsäure-Gemisch aufgeschlossen, der Rückstand in Salzsäure aufgenommen und Se bzw. As mit Hilfe von Natriumborhydrid in Hydrid übergeführt. Die Atomisierung zur Messung erfolgt in einem elektrisch beheizten Quarzofen. Beide Elemente können im Bereich von 0,05–2,00 g/g zuverlässig in geologischem Material bestimmt werden. Die Methode hat einen weiten Toleranzbereich für Änderungen der Reagenskonzentration sowie für mögliche Begleitelemente und zeigte bei Referenz-Gesteinsproben zufriedenstellende Ergebnisse. Sie wird in den Laboratorien des Autors routinemäßig eingesetzt. Wenigstens 10 Proben können innerhalb von 1 h analysiert werden.

     

Negative Thermionen-Massenspektrometrie von Selen

Summary Negative thermal ionization is used to determine the selenium isotope ratios in a double-filament ion source. A thin film of barium hydroxide on the rhenium ionization filament is applied to increase the Se^– thermal ion current. The produced Se^– ion beam is by a factor of about four higher when selenious acid instead of barium selenite or sodium selenate is used. A strong dependence of the ion current on the temperature of the ionization filament is found showing the maximum ion intensity at temperatures of 970–1000 C. The different selenium isotope ratios of samples with natural isotopic abundance can be determined with relative standard deviations of 0.3–0.6%. This reproducibility is a good basis to improve the accuracy of the selenium atomic weight in the future by a calibrated measurement. An enriched ⁸²Se spike is used to analyse selenium traces in aquatic systems with isotope dilution mass spectrometry down to the pg/g level. In the concentration range of 4–23 ng/g the selenium content is determined with relative standard deviations of 0.1–5%. The results agree well with those obtained with a hydride generation atomic absorption system. It is shown that the described method of isotope dilution mass spectrometry analyses the sum of the inorganic species selenate, selenite and selenide, but not volatile organic selenium compounds.

---

---

Herrn Prof. Dr. W. Fresenius zum 75. Geburtstag gewidmet     

Semiquantitative estimation of the mycotoxins citrinin, Ochratoxin A, Aflatoxin M1 and penicillic acid on thin-layer chromatograms with a grey scale

Summary Spots of citrinin, ochratoxin A, aflatoxin M₁ and penicillic acid on thin-layer chromatograms can be semi-quantitatively estimated by using a grey scale, commonly used in photo laboratories. The detection limits are 0.01 g for citrinin, 0.006 g for ochratoxin A, 0.002 g for aflatoxin M₁ and 0.01 g for penicillic acid. Standard curves for these mycotoxins are given.

---

Halbquantitative Bestimmung der Mycotoxine Citrinin, Ochratoxin A, Aflatoxin M₁ und Penicillinsäure auf Dünnschicht-Chromatogrammen mit Hilfe eines Graukeils

Zusammenfassung Mit Hilfe eines in Photolabors gebräuchlichen Graukeils können dünnschicht-chromatographische Flecke der obengenannten Mycotoxine halbquantitativ bestimmt werden. Die Nachweisgrenzen betragen 0,01 g für Citrinin, 0,006 g für Ochratoxin A, 0,002 g für Aflatoxin M₁ und 0,01 g für Penicillinsäure. Eichkurven werden angegeben.

     

Production of reference material

Summary Carbon has been determined in the certified reference sample Euro CRM Pure Iron 097-1 to 3.98 g C/g (R = 0.15 at P = 95%) by combustion of the sample portion with subsequent indication of the CO₂ by coulometry. A calibration material based on primary sources of carbon was used with a sufficient small interval of uncertainty of the accuracy and an adequate weighing system. The blank could be kept sufficiently small with a fraction of 23% of the total analytical signal. The surface carbon of the 097-1 was determined to approximately 50% of the total carbon. This result of total carbon is considerably lower than the values in the certificate reading up to 20 g/g. This reflects the strong tendency to too high values in the certificates of reference steels with contents of carbon up to 100 g/g. Examples are given.

---

Herstellung von Referenzmaterial — Bestimmung von Kohle in Stählen und reinem Eisen im Bereich von 1–100 g/g mit primärer Kalibrierung

     

Differential pulse polarographic determination of nickel(II) as water-soluble dithiocarbamate

Summary A differential pulse polarographic determination of nickel(II) in the lower ppb region is possible by the addition of a dithiocarbamate, N-(dithiocarboxy)sarcosine, which forms water-soluble complexes with metal ions. An enhanced reduction current, due to adsorption of the complex, is obtained in an electrolysis solution composed of 0.1 M KCl and 0.015 M (NH₄)₂oxalate/0.02 M NaOH buffer in the presence of dithiocarbamate. The nickel(II) content in standard reference materials was accurately determined after separation of Fe(III) and Zn(II) by an anion-exchange technique. 0.89 and 1.36 (1.39) g/g have been recovered from the certified values of 1.03 and 1.3 g/g, respectively.

---

Differential-pulspolarographische Bestimmung von Nickel(II) als wasserlösliches Dithiocarbamat

Zusammenfassung Durch Zusatz eines Dithiocarbamates, N-(Dithiocarboxy)sarcosin, das mit Metallionen wasserlösliche Komplexe bildet, wird die differential-pulspolarographische Bestimmung von Nickel(II) im unteren ppb-Bereich ermöglicht. In der Dithiocarbamat enthaltenden Grundlösung aus 0,1 M KCl und 0,015 M (NH₄)₂-Oxalat/0,02 M NaOH-Puffer erhält man wegen der Adsorption des Komplexes einen erhöhten Reduktionsstrom. Nach Abtrennung des Fe(III) und Zn(II) durch Ionenaustausch konnte der Nickel(II)-Gehalt in Standardreferenzproben mit guter Genauigkeit bestimmt werden. Von den zertifizierten Werten 1,03 bzw. 1,3 g/g konnten 0,89 bzw. 1,36 (1,39) g/g wiedergefunden werden.