Robert Alvarez

Determination of trace elements in zinc by isotope dilution spark source mass spectrometry

Abstract The applicability of the isotope dilution technique in spark source mass spectrometry has been investigated for the determination of Pb, Cu, Cd, Ag, Tl, and Sn in zinc metal. In the procedure developed, a solution of the zinc is spiked with known amounts of stable isotopes of the elements to be determined, and the elements are electrodeposited onto gold wires that subsequently serve as electrodes for the mass spectrographic isotopic analysis. Chemical operations, including isothermal distillation of reagents, dissolution of the zinc, and the electro-deposition step are conducted in a closed system to minimize contamination. The results of the analysis of two NBS zinc standard reference materials include determinations ranging from 11 ppm (11 μg g ) for Pb to as low as 0.02 ppm (20 ng g ) for Sn. It is concluded that this method is of general utility for simultaneous multi-element trace analysis and is especially applicable in providing much needed standardization in spark source mass spectrometry.

Trace Element Determinations in a Low-Alloy Steel Standard Reference Material by Isotope Dilution, Spark Source Mass Spectrometry

A stable isotope dilution procedure using the spark source mass spectrograph was developed for the simultaneous determination of cerium, copper, neodymium, selenium, silver, tellurium, and zirconium in a low-alloy steel material. Except for copper, the elements were present at trace concentrations that are difficult to determine by most analytical methods. In the procedure, known amounts of the isotopically enriched elements were added to 100-mg samples, which were dissolved in perchloric and hydrofluoric acids. After evaporation of the solutions almost to dryness, dissolution of the residues, and addition of hydrofluoric acid to complex the iron, the resulting solutions were electrolyzed in polytetrafluoroethylene cells. The electrodeposit on high purity, gold cathode wires was sparked in the mass spectrograph and the isotope ratios of the isotopically equilibrated elements were measured. The concentrations, ranging from 0.041% for copper to 3.1 µ/g (ppm) for neodymium, were calculated from the general isotope dilution equation. The low-alloy steel is available from NBS as Standard Reference Material 1261.

Sub-microgram per gram concentrations of mercury in orchard leaves determined by isotope dilution and spark-source mass spectrometry

Abstract A stable isotope dilution procedure in conjunction with the spark source mass spectrograph was developed for determining sub-μg g -1 concentrations of mercury in orchard leaves. A 5-g sample was spiked with a solution of mercury, isotopically enriched in 201 Hg and 198 Hg. The 198 Hg served as a carrier. After wet-ashing the sample with nitric and perchloric acids under reflux and distilling most of the acid, the isotopically equilibrated mercury was electrodeposited onto high-purity gold wires for sparking in the mass spectrograph. The concentration was calculated from the altered isotope ratio, 201 Hg/ 202 Hg, and other data. The results were compared with those obtained by atomic absorption spectrometry and neutron activation, leading to a certified value of 0.155 ± 0.015 μg g -1 for the mercury content of Orchard Leaves, SRM 1571 of the National Bureau of Standards.

Recently developed NIST food related standard reference materials

SummaryNIST issues food related, chemical composition standard reference materials for validating food analyses. SRMs certified for inorganic constituents are: Non-Fat Milk Powder (SRM 1549), Oyster Tissue (SRM 1566a), Bovine Liver (SRM 1577a), Wheat Flour (SRM 1567a), Rice Flour (SRM 1568a), and Total Diet (SRM 1548). The certificate of analysis for the total diet SRM also provides a certified concentration for cholesterol. Oyster tissue, a renewal SRM, is certified for 25 elements including 6 (Al, Cl, I, P, S, and V), that had not been certified in the previously issued SRM 1566. The elemental certified concentrations are based on concordant results of two or more independent analytical methods. The chemical compositions of the six food matrix SRMs are tabulated. Three food matrix SRMs certified for organic constituents are: Cholesterol and Fat-Soluble Vitamins in Coconut Oil (SRM 1563), Cholesterol in Whole Egg Powder (SRM 1845) and Organics in Cod Liver Oil (SRM 1588). Serum and urine matrix SRMs are also available that may be useful for metabolic and bioavailability studies.

Certified reference materials for validating spectroscopic methods and experimental data

ZusammenfassungChemische Laboratorien erhalten häufig signifikant verschiedene Ergebnisse, wenn sie das gleiche homogene Material untersuchen. Die unterschiedlichen Ergebnisse können verursacht sein durch ungeeignete Methoden, falsche Geräteeichung, fehlerhafte experimentelle Techniken, unreine Reagentien oder eine Kombination dieser Faktoren. Für die Spurenbestimmung sind Größe und Auswertung des Blindwertes der Methode oft die Hauptbeschränkungen bei der Erzielung genauer Ergebnisse.Ein Schritt in Richtung auf Verbesserung der Genauigkeit von analytischen Bestimmungen ist die Benutzung zertifizierter Referenzmaterialien (CRMs), die von Organisationen überall in der Welt ausgegeben werden. Ein CRM ist ein homogenes, stabiles Material mit zertifizierten chemischen und/oder physikalischen Eigenschaften, das benutzt wird, um Geräte zu eichen, experimentelle Daten zu bewerten, zuverlässige Methoden zu entwickeln und Daten verschiedener Laboratorien auf eine gemeinsame Basis zu beziehen. In den Vereinigten Staaten ist das „National Bureau of Standards“ (NBS) gesetzlich autorisiert, CRMs auszugeben, die aus historischen Gründen Standardreferenzmaterialien (SRMs) genannt werden. In dem heute gültigen NBS-Katalog sind mehr als 900 SRMs aufgelistet, wovon die meisten in bezug auf ihre chemische Zusammensetzung zertifiziert sind. Sie umfassen eine Vielzahl von Matrices mit Bestandteilen anorganischer und organischer Art und sind von großem Interesse für Spektrochemiker. Diese SRMs finden Anwendung auf derart verschiedenen Gebieten wie klinische analytische Chemie, Umweltanalytik, Nahrungsmittelchemie, landwirtschaftliche und industrielle analytische Chemie. Auch SRMs zur Beurteilung der Leistungsfähigkeit von Geräten, wie die, die entwickelt wurden, um die Leistungsfähigkeit von Gas-Chromatograph-Massenspektrometern zu bewerten, sind für Spektrochemiker von Interesse.SummaryChemical laboratories frequently obtain significantly different results when analyzing the same homogeneous material. The different results may be caused by poor methodology, improper instrument calibration, faulty experimental techniques, impure reagents, or a combination of these factors. For trace constituent determinations, the magnitude and evaluation of the method blank are often the main limitations toward obtaining accurate results.One approach towards improving the accuracy of analytical determinations is by the use of Certified Reference Materials (CRMs) issued by organizations throughout the world. A CRM is a homogeneous, stable material with certified chemical and/or physical properties used in calibrating instruments, validating experimental data, developing methods of known reliability, and referring data from different laboratories to a common base. In the United States, the National Bureau of Standards (NBS) has legal authority to issue CRMs, which for historical reasons are called Standard Reference Materials (SRMs). There are more than 900 SRMs listed in the current NBS SRM catalog, the greatest number of these SRMs are certified for chemical composition. Chemical composition SRMs, which comprise a variety of matrices and constituents, inorganic and organic, are of greatest interest to spectrochemists. These SRMs have applications in such diverse areas as clinical, environmental, nutritional, agricultural, and industrial analytical chemistry. Instrument-performance SRMs, such as the one developed for validating the performance of gas chromatograph-mass spectrometers, will also be of interest to spectrochemists.

NBS plant tissue standard reference materials certified for trace elements

Abstract NBS issues six Standard Reference Materials that are useful for the determination of nutrient and contaminant trace elements in plant tissues and agricultural food products. They are: SRM 1571 Orchard Leaves, SRM 1573 Tomato Leaves, SRM 1575 Pine Needles, SRM 1570 Spinach, SRM 1567 Wheat Flour, and SRM 1568 Rice Flour. These SRMs are used to calibrate instrumentation, to determine the accuracy of existing analytical methods, and to develop more accurate methods. The Certificate of Analysis for each SRM contains such information as the homogeneity of the powdered material, the minimum sample size to be used, the certified values for the elements with their uncertainties, and the non‐certified values. A certified value is based either on concordant results by independent analytical methods or on results by a definitive method, i.e., an accurate method having negligible, systematic errors. These certified values can serve as cannon reference points for comparison of data acquired over a long period...

Standard Reference Materials for dioxins and other environmental pollutants.

The National Institute of Standards and Technology issues approximately 1100 Standard Reference Materials (SRMs) certified for chemical composition or physical properties. A number of these SRMs has been developed to assist chemists in analyzing environmental samples more reliably for chlorinated dioxins and other organic pollutants. Certification of the pollutant concentration in a natural matrix SRM is based on concordant analyses by the NIST Organic Analytical Research Division using at least two independent methods. For a calibration solution, such as SRM 1614, Dioxin (2,3,7,8-TCDD) in Isooctane, certification is based on agreement of the calculated concentration based on the gravimetric preparation and the concentration as determined experimentally. SRM 1614 also includes a 13C-labeled 2,3,7,8-TCDD for use as an internal standard in methods based on gas chromatography/mass spectrometry. The certified concentrations (ng g-1) are 98.3 +/- 3.3 for the unlabeled dioxin and 95.6 +/- 1.5 for the labeled dioxin. The certificates for SRM 1588, Organics in Cod Liver Oil, and SRM 1589, Polychlorinated Biphenyls (as Aroclor 1260) in Human Serum, provide noncertified concentrations of dioxins. Concentrations of chlorinated dioxins in two urban particulate SRMs have been reported in the literature.

NBS Standard Reference Materials for Food Analysis

In recent years, the chemical composition of foods has received increased national attention. Foods are being scrutinized by scientists in the food industry, government agencies, professional societies, and academic institutions. One of the more important aims in nutrition is to determine the effects of food nutrients on health and disease.