Multielement photon activation analysis of biological materials.

A non-destructive photon activation procedure with 30-MeV bremsstrahlung followed by high-resolution γ-spectrometry is proposed for multielement analysis of biological materials. The materials tested were the NBS SRM Orchard Leaves and Bovine Liver, Bowen′s kale and Kentucky 1R1 tobacco standards. Simultaneous irradiation of the sample with synthetic multielement standards containing 25 elements showed that up to 12 elements can be determined in a single sample. The method is quite simple and gives good reproducible results. Agreement of the results with published data is excellent.     

National Bureau of Standards coal flyash (SRM 1633a) as a multielement standard for instrumental neutron activation analysis

The (U. S.) National Bureau of Standards standard reference material 1633a (coal flyash) was standardized for the concentrations of 29 elements against chemical standards by instrumental neutron activation analysis. United States Geological Survey basalt standard BCR-1 was analyzed concurrently as a check. SRM 1633a is a good multielement comparator standard for geochemical analysis for 25 of the elements analyzed and is a better standard than rock-powder SRMs commonly used. Analytical data for USGS DTS-1, PCC-1, GSP-1, BIR-1, DNC-1, and W-2; NBS SRMs 278 and 688; and GIT-IWG (French) anorthosite AN-G are also presented.     

The Synergic Extraction of Uranium(VI) with Bis(octylsulfinyl)ethane (BOSE) and Petroleum Sulfoxides (PSO)

The biological standard reference materials Orchard Leaves SRM 1571 and Oyster Tissue SRM 1566a was analysed by instrumental neutron activation analysis (INAA) at the International Centre for Environmental and Nuclear Sciences, Jamaica at (ICEN) and at the Instituto de Pesquisas Energeticas e Nucleares (IPEN-CNEN/SP), Brazil. The comparison of the results with those obtained with the more powerful reactor are used to evaluate the possibilities of INAA for the analysis of biological samples at ICENS. The detection limits, the precision and accuracy of the results obtained in both laboratories are compared. The advantages and disadvantages of the different irradiation facilities are discussed. Some results obtained for Jamaican biological samples are also presented.     

Accuracy in standards preparation for neutron activation analysis

Errors in preparing standards, especially multielemental standards, are extremely important if accurate results are desired from neutron activation analysis (NAA). It is often convenient to prepare standards for NAA from single or multi-element solutions which are then deposited onto (or into) a suitable matrix, such as filter paper or quartz vials. There are many potential sources of error in preparing single-element standards including: impurities and non-stoichiometric composition of the element or compound used to prepare the standard solutions; evaporative losses of solvent; inaccuracy of calibration, and imprecision of the pipettes used; moisture content of elements or compounds used; contamination from reagents, equipment, laboratory environment, or final matrix of the standard; instability of standard solutions (i.e., to losses via precipitation or adsorption), and losses of volatile elements during dissolution and/or irradiation. Additional sources of error in preparing multielement standards includes: instability of mixed, multielement solutions, and cross-contamination of one element by the addition of a second element. Procedures previously used by the author at NIST to prepare multielement standards with concentrations accurate to about one percent are described. Additional techniques needed to prepare multielement standards with accuracies better than 1 percent will be discussed.     

Determination of trace level mercury in biological and environmental samples by neutron activation analysis

Sorptivity studies with Chelex 100 column indicated chloride to be the best medium for the sorption of mercury. A radiochemical separation procedure has been developed for the determination of mercury by neutron activation analysis utilizing sorption of mercury on Chelex 100. The method was checked with Orchard Leaves and Tuna Fish standards from the National Institute of Standards and Technology.     

Usefulness of thermal and epithermal cyclic activation analysis with a reactor system

A new cyclic activation system (CAS) has recently been installed at the University of London Reactor and is briefly described. It has the unique feature that it allows choice as to whether irradiations are to be carried out under cadmium or in a bare tube and thus both epithermal and thermal cyclic activation analysis can be performed. Measurements in this work, have been carried out using a Ge(Li) detector but the facility allows other detectors to be used and an additional return line from the central distributive mechanism of the system (not yet installed) will allow samples to be cycled to and from a neutron detector thus providing the possibility of measuring radionuclides emitting delayed neutrons. By way of illustration of the theory of cyclic activation analysis, since the paper is to serve as an introduction to other papers in the conference using the technique, the results of a calculation for the detection of uranium under thermal and epithermal conditions are presented and compared to conventional activation. The usefulness of cyclic neutron activation analysis (CNAA) is also demonstrated in cases where identification of an isotope through its gamma-ray energy alone is not sufficient and conformation is achieved through determination of the half-life of the activity of interest, without resort to further experimental work or additional instrumentation. This leads on the thorny problem as to whether Poisson statistics should continue to be used in cases where the period of observation is of the same order as the decay constant of the activity of interest and it is pointed out how CNAA can be employed to extract the information required if a binomial-type statistical density function is used. Finally in order to prove the system and the cyclic method and as a preliminary to a larger project, prepared single element standards and standard reference materials [NBS Orchard Leaves, NBS Bovine Liver, IAEA Animal Blood, IAEA Hair standard and Bowen's Kale] are analysed under the two cyclic irradiation conditions. Sensitivities and cadmium ratios are obtained for the twelve elements from the elemental standards (Na, Al, Sc, Ge, Se, Rh, Pd, Ag, Ce, Er, Hf and Pb) and detection limits for a number of elements of interest presented for the standard reference materials.     

Neutron activation analysis of biological materials by the monostandard method

Instrumental neutron activation analysis by the monostandard method has been applied to the analyses of biological NBS standard reference materials; 1571 Orchard Leaves and 1577 Bovine Liver. Aluminum foils containing 0.100% gold or 2.00% cobalt were used as the monostandards. The gamma-ray spectral data were recorded on punched paper tape and were analyzed by a computer assisted data processing. The following 25 elements were determined: Al, Ca, Cl Cu, Mg, Mn, V (by short period irradiation), As, Ba, Br, Co, Cr, Cs, Eu, Fe, Hg, K, La, Na, Rb, Sb, Sc, Se, Sm and Zn (by long period irradiation). The results were compared with the certified values by NBS and the reported values in literatures to prove the reliability and accuracy of the monostandard method.     

Evaluation of botanical reference materials for the determination of vanadium in biological samples

Three botanical reference materials prepared by the National Bureau of Standards have been studied by neutron activation analysis to evaluate their suitability with respect to the determination of vanadium in biological samples. Various decomposition methods were applied in connection with chemical or radiochemical separations, and results for vanadium were compared with those found by purely instrumental neutron activation analysis. Significantly lower results indicate losses or incomplete dissolution, which makes SRM 1575 Pine Needles and SRM 1573 Tomato Leaves less satisfactory than SRM 1570 Spinach. A reference value of 1.15 mg/kg of this material is recommended, based on results from 3 different methods. All three materials are preferable to SRM 1571 Orchard Leaves, while Bowen's Kale remains the material of choice because of its lower concentration.     

Elemental analysis of water and air solids by neutron activation analysis

Instrumental neutron activation analysis was used to determine the elemental concentrations in water and air solid samples collected on Nuclepore and Whatman filters from the Walker Branch Watershed. The results from this study show that the trace element concentrations removed by water from the watershed vary seasonally, as well as geographically. The data point up the usefulness and versatility of absolute neutron activation analysis. The NBS Standard Orchard Leaves was assayed in a similar manner, and good agreement was obtained between results here and standard values.     

Use of l-cysteine for minimization of inorganic Hg loss during thermal neutron irradiation

Thermal neutron irradiation experiments performed with cellulose-based l-cysteine-treated and untreated Hg standards showed Hg losses of 59–81% for untreated standards but only about a 0.2% loss for treated standards. These results and others for multielement standards showed that Hg loss is highly dependent on total mass and placement of materials in the irradiation vessel and that distribution of volatilized Hg was fairly uniform throughout the sample-containing region of the vessel. Polyethylene trapped volatile Hg much more efficiently than cellulose and a multielement standard containing inorganic Se selectively trapped Hg lost from a co-irradiated multielement standard containing Hg.     

Vanadium determination in rat tissues and biological reference materials by neutron activation analysis

Vanadium was determined in adrenal gland, brain, ileum, kidney, liver, lung, muscle, myocard, skin, spleen, gonads, thyroid, and tibia of rats fed with normal diet and exposed to high vanadium doses in drinking water. Both radiochemical neutron activation analysis (RNAA) and instrumental neutron activation analysis (INAA) were employed. The RNAA procedure consisted in dry ashing samples prior to irradiation and vanadium separation from the irradiated samples by extraction with N-benzoyl-N-phenylhydroxylamine (BPHA) in toluene from 5 mol·l^–1 HCl. Vanadium accumulation as a function of a type of the tissue, exposure time, sex of rats, and administration of V(IV) or V(V) was studied. For quality assurance purposes, the biological (standard) reference materials NBS SRM 1571 Orchard Leaves, NBS SRM 1577a Bovine Liver, IAEA H-4 Animal muscle, and Bowen's Kale were analyzed.Presented at the 2nd Balkan Conference on Activation Analysis and Nuclear-Related Analytical Techniques, Bled, 4–6 October, 1989.     

Multielement standards for instrumental neutron activation analysis of biological materials

Standards for instrumental neutron activation analysis (INAA) of biological materials are proposed. The standards are multielement solid solutions in phenol-formaldehyde resole resin (PFR) moulded as pellets weighing 30 to 50 mg. The concentrations of trace elements in the standards are selected so that, firstly, they are commensurable with their concentrations in the biological materials and, secondly, that the analytical lines of each of the elements incorporated in PFR are resolved with the aid of modern equipment. The principal standard contains 21 trace elements from among those of greatest interest for INAA of biological materials. This standard is recommended for work on high-resolution equipment. At the same time, standards of simpler trace element composition have been prepared and studied which can be used in work on simpler equipment or in solving particular problems in determination of certain groups of chemical elements.     

Application of NAA standardization methods using a low power research reactor

Two widely used neutron activation analysis (NAA) standardization methods (relative and k ₀) have been validated at the Ghana Research Reactor-1 (GHARR-1) Centre using environmental and biological standard reference materials (SRMs). The samples were IAEA Soil-7 as an environmental sample, and NIST Orchard Leaves 1571 as a biological sample. The qualitative and quantitative analyses were done using a high resolution Canberra N-type high purity germanium (HPGe) detector. The accuracy and precision were evaluated for the elements analysed. The concentrations of most of the elements were found to be within 10% of the certified values. Precision was calculated from six replicate measurements and was found to be within 15%.     

Neutron activation analysis without multielement standards

To carry out neutron activation analysis without using multielement standards requires knowledge of (i) the absolute photopeak efficiency as a function of energy of the gamma-ray detector, (ii) nuclear data for each reaction used, and (iii) neutron flux parameters for the irradiation position. The present paper discusses each of these topics and shows an example of the determination of flux parameters and improved nuclear data.     

Possibilities of low-level determination of silicon in biological materials by activation analysis

The capabilities of neutron and photon activation analysis (NAA and PAA, respectively) for low-level determination of silicon in biological materials have been examined. Sensitivities of a variety of modes of NAA and PAA with radiochemical separation have been evaluated. Results are presented for silicon in reference materials CSRM 12-2-03 Lucerne, Bowen's Kale, NIST SRM-1571 Orchard Leaves, and NIST SRM-1515 Apple Leaves. The results were obtained by employing the 29Si(n,p)29Al reaction with fast reactor neutrons and the radiochemical procedure developed for aluminium separation. Possibilities of further improvement of the silicon determination limit down to the microg g(-1) level by employing NAA and PAA with radiochemical separation are outlined.     

Simultaneous determination of arsenic and antimony in environmental samples by radiochemical neutron activation analysis

A radiochemical separation procedure using an inorganic exchanger, tin dioxide (TDO), for the separation of arsenic from antimony is reported here. This separation avoids the interference of 564 keV gamma-ray of¹²²Sb in the measurement of the 559 keV gamma-ray of⁷⁶As in neutron activation analysis. Environmental samples, after neutron irradiation and digestion, are taken up in 1M HCl–0.1M HF and passed through a TDO column which selectively retains arsenic. The effluent from the TDO column, after proper conditioning, is passed through an anion exchange column for quantitative retention of antimony. The procedure has been utilized for arsenic and antimony determination in NBS Orchard Leaves and NBS Albacore Tuna.     

Determination of chromium in biological matrices by neutron activation: Application to standard reference materials

Chromium is recognized to be an essential trace element in several biological systems. It exists in many biological materials in a variety of chemical forms and very low concentration levels which cause problems for many analytical techniques. Both instrumental and destructive neutron activation analysis were used to determine the chromium concentration in Orchard Leaves, SRM 1571, Brewers Yeast, SRM 1569, and Bovine Liver, SRM 1577. Some of the problems inherent with determining chromium in certain biological matrices and the data obtained here at the National Bureau of Standards using this technique are dicussed.     

A comparison of synthetic irradiation-resistant multielement standards for activation analysis

An aluminium matrix and a phenolformaldehyde polymer were tested as base materials for multielement standards resistant to high neutron doses in activation analysis. Interlaboratory analyses showed that these standards can be certified for the concentrations of the majority of introduced elements.     

Multielement determination in tobacco leaves by photon activation analysis

A nondestructive photon activation procedure with 30 MeV bremsstrahlung followed by high-resolution gamma-spectrometry has been applied to the multielement determination in tobacco leaves and commercial cigarettes. The elements determined by this method included essential minor elements such as Ca, Cl, K and Mg, essential trace elements such as Fe, Mn and Zn, and possibly toxic elements such As and Sb. The NBS Orchard Leaves could successfully be used as a comparative standard. The method is quite simple and gives good reproducible results for at least 12 elements.