The determination of iodine in biological and environmental standard reference materials

Iodine is an element with excellent intrinsic sensitivity when determined by thermal neutron activation. However, in most real samples, the preponderance of chlorine and bromine, relative to iodine, makes the direct determination of iodine virtually impossible. Over the past 20 years, there probably have been as many publications on the separation of iodine as there have been for any other radionuclide. Upon review, however, the methods are essentially the same. After irradiation, the samples are subjected to a rapid destructive process to free the iodine from the matrix and then the iodine is separated from the other halides either by liquid-liquid extraction or by liquid ion exchange. Both of these procedures are, however, rather complex and do not effect a complete separation of the halides in one pass. In the work presented here, a simple procedure is described for the quantitative separation of iodine from chlorine. The procedure utilizes a gas phase separation on hydrated manganese dioxide with iodine collected on silvered quartz wool. The described procedure has been used for the determination of iodine in numerous new and old SRM's at the NBS.     

Input of missing trace elements in some IAEA/NBS biological certified reference materials using INAA

IAEA and NBS biological certified reference materials have been analyzed by instrumental neutron activation analysis and concentration of 17 elements was determined. The elements determined were either completely missing or their certified values were not given in the original compilations. For quality assurance of our work, a comparison of data on missing trace elements in some of the CRMs has been presented. It seems that second round of analysis for the certification of these elements would be useful.     

The preparation of biological and environmental reference materials

The facilities of the Institute for Reference Materials and Measurements for the preparation of biological and environmental reference materials are discussed under the aspect of satisfying important parameters for the preparation of candidate reference materials. The choice of transformation methods and their possible influences on quality and long-term conservation, the need for automation as well as the importance of quality control are particularly emphasized.     

IAEA Programme of natural matrix reference materials for the determination of radionuclides

Summary The International Atomic Energy Agency has been providing analytical quality control services (AQCS) to its Member States since the 1960's. The AQCS programme distributes reference materials (RMs), organizes intercomparison runs, and provides training courses for quality assurance in chemical analysis and radioactivity measurements of food, biological, environmental and marine materials. This paper focusses on those aspects of the subject dealing with reference materials and intercomparison runs for the determination of radionuclides. Nineteen natural matrix reference materials are available for the determination of radionuclides. Twelve new intercomparison and reference materials are in preparation or under consideration. The radionuclides of interest include: K-40, Mn-54, Co-60, Sr-90, Tc-99, Ru-106, Ba-133, Cs-134, Cs-137, Pb-210, Ra-226, Th-228, Th-232, Pu-238, Pu-239+240.     

Preparation of biological and environmental reference materials at CBNM

Summary Since 1984, CBNM has been officially responsible for supporting the BCR programme for CRM storage, distribution and sale activities for the development of methods for preparation, conditioning and packing for reference materials, as well as actually preparing candidate CRMs. This has allowed CBNM to set up a new laboratory with unique facilities for the preparation of biological and environmental reference materials, in particular for organic and inorganic trace analysis. The main technical facilities developed at CBNM and additional equipment built to CBNM specifications by external companies are described. They have been used for the preparation of a variety of reference materials including cod fish, pig liver, offal, spiked milk, curd, orange juice, clover, lettuce, paprika, tomato, fly ash, soils and sediments.     

Methyl mercury determination in environmental and biological reference and other materials by quality control with certified reference materials (CRMs)

Summary Two concentration methods — HCl extraction and extraction followed by water vapour distillation — prior to anion exchange separation and cold-vapour atomic absorption spectrometry were used for the quantification of methyl mercury in a number of reference materials of biological and environmental origin with reference or certified total mercury contents. The applied methods were validated by the analysis of three marine reference materials, certified for methyl mercury. The results obtained in the materials with methyl mercury contents ranging from less than 1 g/kg to a few hundred g/kg showed good agreement between both methods for biological materials, whereas extraction/anion exchange resulted in somewhat too high values for a number of environmental materials. These findings, however, require further confirmation by additional methods and by other laboratories.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Selenomethionine contents of NIST wheat reference materials

Values of the total selenium and selenomethionine (Semet) content of four wheat-based reference materials have been obtained by gas chromatography-stable isotope dilution mass spectrometry methods. The total Se method is an established one, and the results obtained with it are consistent with previously-assigned values. The Semet method (previously reported by our laboratory) is based on reaction with CNBr. Our data indicate that the four wheat samples (wheat gluten, durum wheat, hard red spring wheat, and soft winter wheat), though having a 30-fold range in total Se content, all have about 45% of their total Se values in the form of selenomethionine. Investigation of the CNBr-based method suggests that additional experiments are needed to verify that all selenomethionine in the wheat samples is accounted for, but also indicates that the values obtained are within 15% of the true values. As the form in which Se occurs in foods and dietary supplements is important from a nutritional perspective, adding information about Se speciation to total Se values in appropriate reference materials makes these materials more valuable in relevant analytical work.     

Radiochemical separation methods for the determination of some toxic elements in biological reference materials

The present paper describes radiochemical separation procedures developed for the determination of the elements As, Cr, Hg, Sb and Se in biological reference materials. The methods chosen utilize ion exchange, retention on inorganic exchangers and solvent extraction techniques for the isolation of the elements of interest. These procedures are more rapid than previously used methods, such as distillation and precipitation. As to the sample dissolution, the following procedures were tested using radioactive tracers and reference materials: treatment of the materials in teflon bombs with a mixture of HNO₃+H₂SO₄ or HNO₃ only in a normal oven, and with HNO₃ in a microwave oven using specially designed digestion bombs.     

Elemental concentrations in nbs biological and environmental standard reference materials

Elemental concentrations reported by 325 investigators in 16 NBS SRM's are summarized. Mean values, standard deviations and comparative data from NBS and other reviews are provided.     

Recently developed NIST food related standard reference materials

Summary NIST 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.     

Non-destructive determination of zinc in biological certified reference materials

Non-destructive neutron activation analysis was employed to determine zinc in ten biological standard reference materials from the National Bureau of Standards and the National Research Council of Canada. The use of a 4 h. irradiation at a medium neutron flux allows excellent accuracies, precision and sensitivities to be attained for all the samples analyzed. It is suggested that neutron activation analysis be one of the benchmark methods for the determination of zinc in biological reference materials for concentrations as low as the one part per million level.     

Low level determination of thallium in biological and environmental reference materials by RNAA using several counting methods

A new RNAA procedure was developed capable of low level determination of thallium in biological and environmental samples. After high fluence neutron irradiation in a nuclear reactor, wet ashing of samples and T1(I) separation by solvent extraction with sodium diethyldithiocarbamate at pH 13, several types of counting were employed to compare their detection limits and to utilize the self-validation principle of NAA. The following measurement modes were used: High efficiency counting of -rays of²⁰²T1 and Hg X-rays produced on decay of²⁰⁴T1 using a well-type HPGe detector, combined ^– ray and ^–-counting of²⁰⁴T1 with the aid of a HPGe planar detector, and liquid scintillation counting and counting of Cerenkov radiation of ^–-particles of²⁰⁴T1. The lowest detection limit of 0.034 ng of T1 was achieved on liquid scintillation counting of²⁰⁴T1. The method was applied for the analysis of biological NIST SRMs 1515, 1573a, 1577b and environmental NIST SRM 1633a. Good agreement was found between the thallium certified value in SRM 1633a and values determined in this work by all counting modes. For SRM 1573a, results in agreement were obtained by two counting modes, while counting of Hg X-rays of²⁰⁴T1 was only used for SRMs 1515 and 1577b.     

Low uncertainty determination of manganese and vanadium in environmental and biological reference materials by instrumental neutron activation analysis

The elements Mn and V were determined by INAA in about 5 mg and 100 mg aliquots of NIST SRM 1648 to elucidate discrepancies between our previous results for the 0.5 mg to 15 mg aliquots and the NIST certified and/or information values. Simultaneously, other NIST SRMs 1633a, 2704, and BCR CRMs 038, 101 and 143 were also analyzed. Special attention was given to evaluating and minimizing uncertainties of all steps of analysis. Our results compared very well with the respective certified and/or information values (if available) of all SRMs and CRMs studied, except for NIST SRM 1648. For this SRM we have found significantly lower results than the NIST values which suggests that the NIST values are positively biased by about 10%. A new value for V in BCR CRM 143 was also obtained.     

The updated IAEA database of natural matrix reference materials

The International Atomic Energy Agency (IAEA) maintains a database of biological and environmental reference materials of natural origin (human and animal tissues, foods, plants, soils, sediments, etc.) for trace elements, radionuclides, stable isotopes, organic contaminants and other related measurands. The purpose is to help analysts to select reference materials for quality assurance purposes that match as closely as possible (i.e., with respect to matrix type and concentrations of the measurands of interest) the real samples that are to be analyzed. Former versions of this database were prepared in co-operation with the United Nations Environment Programme (UNEP), and provided as hardcopies free of charge. The latest version was from 1995. More recently the database has been updated by the IAEA so that it now contains more than 22,500 values (mass fraction or concentration) for 660 different measurands and 1,705 reference materials developed by 56 producers from 22 countries. This paper gives an overview of the structure and content of the database and of the two ways it may be browsed. Emphasis is given to reference materials that are intended to verifying analysis for radioanalytical measurements. The database is soon accessible on-line, cost-free, via the internet.     

NIST reference materials to support accuracy in drug testing

Substance abuse is a major problem worldwide. There is considerable emphasis placed upon testing individuals for evidence of use of controlled substances. Because the consequences of a positive test can be quite severe, laboratories conducting such tests must rigorously follow a carefully designed quality assurance program. Such a QA program should include use of reference materials to assure that the methods used to detect and quantify drugs are providing accurate results. The National Institute of Standards and Technology (NIST) supports accuracy in drugs of abuse testing by providing Standard Reference Materials (SRMs) with certified concentrations of drugs of abuse in urine- and hair-based reference materials. NIST, working in collaboration with the College of American Pathologists (CAP), has developed urine-based SRMs for marijuana metabolite, cocaine metabolite, morphine and codeine, and morphine glucuronide and CAP Reference Materials for amphetamines and phencyclidine. Certification measurements performed at NIST involve two independent methods for each analyte, one of which always uses GC/MS with the other usually being an LC method with either MS or UV detection. Work has recently been completed on a seven component drug in urine SRM. In addition NIST conducts research in the analysis of hair for drugs of abuse. To assist laboratories testing hair for that purpose, NIST has developed two drugs in hair reference materials.College of American Pathologists Research Associate at NIST