Determination of 237Np by k0 RNAA

The determination of very low concentrations of ²³⁷Np is of key-interest for environmental monitoring. The application of the k ₀-method to neutron activation analysis was not possible so far, since the k ₀-parameters were lacking. The parameters required for the k ₀-method are: the effective resonance energy r, the resonance integral (1/E) to 2200 m^.s^-1 cross section ratio Q ₀, and the k ₀ values. In this work, the experimental values of these parameters were determined by using two nuclear reactors with very different flux characteristics.     

Position of RNAA in trace-element analysis

An overview is presented of the characteristic features of RNAA (radiochemical neutron activation analysis). Criteria are given for comparison of RNAA with other trace-element analytical techniques. Appropriate fields of application of RNAA are indicated as well as approaches to secure the future position of the technique. Finally, some trends for further development of chemical separations in RNAA are outlined.     

Simultaneous determination of Rb and Cs by RNAA method

A RNAA method has been developed for the simultaneous determination of Rb and Cs in geological samples. The method is based on precipitation with sodium tetraphenylborate followed by NaI(Tl) gamma spectrometry. Three mica dust particulate samples and two USGS standard rocks, BCR-1 and W-1 were analyzed. Dipicrylamine (DPA) and 2-thenoyl-trifluoroacetone (TTA) in nitrobenzene were also used for solvent extraction. The precipitation method is better than solvent extraction.     

Determination of Ultratrace Levels of Mercury in Three SRMs by Combustion RNAA

A radiochemical neutron activation analysis (RNAA) combustion method coupled with a neutron exposure normalization technique was used to determine low g/kg mercury levels in three National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs). Two coals (sub-bituminous and bituminous) and a diet material were analyzed. The results obtained provided recommended values of approximately 5 g/kg for SRM 1548a Typical Diet, 24 g/kg for SRM 1635 Trace Elements in Coal (sub-bituminous), and 100 g/kg for SRM 1632b Trace Elements in Coal (bituminous).     

Determination of sub-PPB contents of uranium and thorium in high-purity aluminium by RNAA

Aluminium samples, irradiated in a reactor, are dissolved in nitric acid²³³Pa and²³⁹Np are adsorbed on an anion exchange column and then separately eluted. The neptunium fraction is very pure and can be counted in a liquid scintillation counter with 100% efficiency. From the other fraction protactinium is extracted by trioctylphosphine oxide and measured by -ray spectrometry. With samples of 3 g, a thermal flux of 3·10¹³ n cm^–2s^–1 and an irradiation time of 24 hours detection limits are 0.0005 ng/g for U and 0.01 ng/g for Th.     

Determination of cobalt in biological materials by RNAA via induced short-lived 60mCo

A chemiluminescence (CL) micro-flow system is presented for rapid determination of chemical oxygen demand (COD) in water at room temperature. In this system, potassium dichromate is reduced to Cr³⁺ in 2 mol L⁻¹ H₂SO₄ during the chemical oxidation of COD substances in the sample, and Cr³⁺ can be measured with the help of the luminol-H₂O₂ CL system. The polymethyl methacrylate micro-flow chip with discrete microdroplet sampling was used here. Effects on COD determination (such as pH, concentrations, the channel length, and interference) were investigated. The linear range for COD determination was 0.27–10 g L⁻¹, and the detection limit was 100 mg L⁻¹. The method was successfully applied to the determination of COD in wastewater samples. The data obtained with the present method were in fairly good agreement with those obtained by the titrimetric method. Correspondence: Zhujun Zhang, Key Laboratory of Analytical Chemistry for Life Science of Shaanxi Province, School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, P.R. China; Department of Chemistry, Institute of Analytical Science, Southwest University, Beibei, Chongqing 400715, P.R. China     

RNAA of trace iridium in Precambrian-Cambrian boundary samples by thiourea type chelate resin separation

A RNAA procedure is described for the determination of trace Ir in Precambrian-Cambrian boundary samples. After irradiation, the powdered sample is transferred to a graphite crucible to expel the massive silicon with mixed acid (HF–HCl–HNO₃) by heating. The residue is then fused with mixed fusion (Na₂O₂–NaOH) in a muffle furnace at 700°C for 15 minutes. After cooling, the fused mixture is leached with hot water. The final solution is adjusted to pH 1.5–2.0 and then passed through a column filled with thiourea type chelate resin. The resin absorbed with¹⁹²Ir is measured for 4000–10 000 s by means of SCORPIO-3000 multi-channel computer — Ge(Li) detector system. Experiments with radioactive tracer are carried aout for checking radiochemical separation yield. The accuracy and precision of the method are evaluated by the analysis of U.S. geological SRMs DTS-1 and AG-Bohor-1. The method is used for the determination of trace Ir in several sets of Precambrian-Cambrian boundary samples collected from Yunnan province in China and the Ir anomaly is observed.     

Phosphorus Ylides in the Coordination Sphere of Transition Metals: An Inventory

Phosphorus ylides are not only classical reagents in organic chemistry, but also play an increasingly important role as novel components in organometallic compounds. These metallic “ylide complexes” are either synthesized from “preformed ylides” and coordination compounds by addition or substitution, on the building block principle, or they are formed, in sometimes complicated reactions, from phosphanes, metal complexes, and C₁ substrates in the coordination sphere of the metals. The resulting metal-carbon bonds are greatly modified in their properties by the immediate presence of the phosphonium center and often belong to the most stable of M-C structural units. The metal can come from any group of the periodic table, including the lanthanoids and actinoids. Numerous preparative and structural studies are gradually enabling us to gain an overall picture of the scope of this area of research.     

Determination of Cd,Mo, Cr and Co in biological materials by RNAA

A method for the determination of trace amounts of Mo, Cd, Co and Cr in biological materials by neutron activation analysis with radiochemical separation is presented. The method is based on the ion-exchange scheme developed by SAMSAHL, where Co and Cr are trapped on BioRad Chelex-100 and Cd and Mo on BioRad AG2X8. The elements Mo, Cd and Co can be determined without systematic errors. For the element chromium the situation is less clear, partially due to lack of sufficient certified reference materials for Cr. The method has been used in the characterization of candidate reference materials. Detection limits in these materials range from 1.5 g/kg for Co to 10 g/kg for Cr. Actual levels as low as 8 g/kg for Cd and 7 g/kg for Co were measured.     

Multi-element analysis of biological material by RNAA using HPLC with on-line yield determination

The idea to use high performance liquid chromatography with continuous UV detection for multi-element radiochemical separation and simultaneous multi-element on-line yield determination is introduced. The validity of the concept was evaluated by demonstrating the constancy of the ratio of the signals for a main isotope (⁶⁰Co) and a carrier (⁵⁹Co) as a function of the elemental mass processed in the separation. The suitability of the method for practical purposes is demonstrated by its application to the RNAA determination of cobalt in biological materials. It is concluded that the method, although not yet completely developed, bears the potential of improving both accuracy and precision of multi-element RNAA.     

Determination of vanadium in biological and environmental samples by RNAA with emphasis on quality control

Summary In the present work an improvement of radiochemical neutron activation analysis for determination of nanogram levels of vanadium is described. The method is based on post-irradiation wet ashing and solvent extraction of vanadium with N-benzoyl-N-phenyl-hydroxylamine (BPHA) forming a violet chelate complex in strongly acidic medium. For quality assurance purposes a procedure for determination of the overall chemical yield using spectrophotometry of the V-BPHA complex is described, and possible interferences are evaluated. The procedure was applied to the determination of vanadium in reference materials and selected food samples from Slovenia.     

Competitive Coordination of Metals by Phosphorus and Sulfur in Complexes with Polydentate Ligands Containing P(III)-S Bonds

A series of complexes of thiophosphites with transition metals has been studied by X-ray single crystal diffraction: CuHalLP(SR)₃, CuHalLP(SR)₃LNCMe, CuBrLP(SEt)₂NEt₂, CuSCNLP(SR)₃, CpMn(CO)₂LP(SR)₃, ArCr(CO)₂LP(SR)₃, with Hal = Cl, Br, I and R = Me, Et, Pr, i-Pr, Bu, Ph. Depending on the metal center, substituents R at sulfur, the conditions of reactions and crystal growth, different coordination modes have been observed: “classical” monodentate binding via phosphorus, unusual bidentate mode with participation of both P and S donor atoms of the ambident P – S system, as well as both monodentate and bidentate modes in one complex.     

Limit of detection for the determination of Pt in biological material by RNAA using electrolytic separation of gold

Neutron activation analysis based on the¹⁹⁹Au indicator for platinum requires the separation of gold at high radiochemical purity. The limit of detection is strongly affected by the presence of gold; with a gold content of 50 pg/g, irradiating for 5 days at 5·10¹³ n/cm²s is needed to achieve a limit of detection of approximately 30 pg/g. In this case the nuclear interference from gold will exceed the level of platinum by several orders of magnitude and has to be determined with exceedingly high precision. Preliminary results for SRM 1577 Bovine Liver with 95% yield gave consistent results for Au, but Pt could not be detected.     

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.     

RNAA in metrology: A highly accurate (definitive) method

The idea of highly accurate (definitive) methods by radiochemical neutron activation analysis (RNAA) is presented and illustrated with several examples of methods worked out in this Laboratory over the past several years. Definitive methods by RNAA are constructed by combining reactor neutron activation with very selective and quantitative post-irradiation separation of the indicator radionuclide by column chromatography followed by γ-ray spectrometric measurement. All conditions for the determination of the individual element are optimized and uncertainties associated with every step of the analytical procedure are minimized. Even after the method has been thoroughly elaborated and validated through the analysis of appropriate certified reference materials (CRMs), the results obtained in each series of measurements are acknowledged as obtained by definitive method only when a series of previously formulated criteria is simultaneously fulfilled. The examples of definitive methods for the determination of cadmium, cobalt and molybdenum, respectively, in biological materials are presented. Each of these methods has detection limit of the order of ng g⁻¹ or better, and yields accurate and precise results. The expanded standard uncertainty is of the order of 2.6% for the case of single-element determination (Co) and 3.4-5.2% for the less favourable case (Mo) where there is necessity for simultaneous determination of uranium to correct for interference due to fission reaction. Definitive methods by RNAA may constitute an option or alternative with respect to ID-MS as methods of “guaranteed accuracy” being also a perspective solution in the case of monoisotopic elements, for which ID-MS cannot be used.     

Determination of selenium in biological materials by means of RNAA and comparison of spectrophotometric and81mSe radiotracer recovery

Two methods for chemical yield measurement of Se in biological samples after radiochemical neutron activation analysis when using the⁷⁵Se nuclide are described, namely a Spectrophotometric technique and a radiotracer technique employing^81mSe. These two approaches were compared and evaluated by applying them to the analysis of Se in various certified reference materials.