Resonance activation analysis of biological materials

An istrumental method is developed for the determination of As, Br, Cd, I, Mg, Mo, Sb, Si, Sn and Sr in biological materials based on resonance neutron activation analysis. Samples were irradiated inside cadmium and boron shields with reactor neutrons and counted on Ge(Li) detector after a delay of about 5 min. The interfering activities of²⁴Na,³⁸Cl and⁵⁶Mn were significantly reduced particularly in the boron shield. The advantage factors of the various elements are compared for boron and cadmium shields. The method is especially useful for the determination of As, Cd, I and Sn.     

Neutron activation analysis of iodine in soil

A simple pre-irradiation procedure for the separation of iodine from soil has been developed. A soil sample was heated in a quartz tube for 15 min at about 900 °C. The evaporated iodine was collected in activated charcoal, which was produced from phenol resin with low impurities. The charcoal, with sorbed iodine, was irradiated by neutrons and the¹²⁸I produced was measured. A successful elimination of the background radioactivity due to the matrix elements was possible with this separation procedure. The detection limit by this method for soil samples was about 0.1 mg/kg (dry). The method has been applied to analyze selected soil samples.     

Determination of iodine in reference materials by activation analysis

A rapid radiochemical procedure for the separation of iodine has been devised, which is characterized by extremely high decontamination factors so as to give pure¹²⁸I spectra with biological materials containing large concentrations of interferring elements such as sodium, bromine and chlorine. The method is based on ignition in oxygen followed by an oxidation-reduction and extraction-stripping cycle involving nitrite, sulfite and carbon tetrachloride. Results are presented for ten NBS and IAEA reference materials, frequently referred to in the literature. This work was done in partial fulfilment of the requirements for an M.Sc. degree (I. Gvardjančič).     

Fractionation analysis of iodine in bovine milk by preconcentration neutron activation analysis

Iodine is an essential trace element for human beings. The main source of iodine is generally food items such as fish and milk. Either the lack or the excess of iodine can cause health problems. There exists an increasing interest in the determination of total iodine as well as various species of iodine in milk. We have developed an epithermal neutron activation analysis method with a Compton suppression (ENAA-CS) counting system for the determination of ng mL⁻¹ levels of iodine. We have also employed chemical separation methods prior to ENAA-CS to measure the fraction-specific concentrations of iodine in bovine milk. We have measured the following iodine concentrations in homogenized milk (3.25%milk fat): 0.48 ± 0.02 μg mL⁻¹ of total iodine, 0.020 ± 0.003 μg mL⁻¹ of lipid-bound iodine, 0.039 ± 0.002, 0.019 ± 0.002 and 0.021 ± 0.004 μg mL⁻¹ of protein-bound iodine depending on the protein separation method and 0.45 ± 0.02 μg mL⁻¹ of inorganic species.     

Measurement uncertainty of iodine determination in radiochemical neutron activation analysis

The measurement uncertainty of iodine determination in NIST standard reference material (SRM) 1549 using radiochemical neutron activation analysis (RNAA) was studied. This method is based on ignition of the irradiated sample [¹²⁷I(n,)¹²⁸I, t_1/2=25 min, E=422.9 keV] in an oxygen atmosphere, followed by absorption of iodine in a reducing acid solution and its purification by a selective extraction–stripping–reextraction cycle. The purified solution of iodine in CHCl₃ was transferred to a well-type HPGe detector for -ray measurement of the induced radionuclide ¹²⁸I. The detection limit of the method employed under the conditions described was 1 ng/g. The reproducibility of iodine determination in the SRM was 3.6% (12 determinations within 1 month), calculated by the analysis of variance procedure. Using the commercially available software program GUM Workbench and the recommendations of the Eurachem/CITAC Guide, we evaluated the uncertainty budget for this RNAA method and the relative uncertainty obtained was 3.6%. The largest uncertainty contributions were due to the repeatability of the chemical yield determination, the count rate of the induced nuclide in the standard and sample, the mass of the carrier and the mass of the irradiation standard.     

Analysis of foods for iodine by epithermal neutron activation analysis

Epithermal-neutron activation analysis (ENAA) was applied to the analysis of foods for iodine. The procedure involves irradiation of wet foods in a boron nitride, vessel, followed by direct counting of the 442.9 keV gamma ray of¹²⁸I without any processing of the sample. Three research reactors were evaluated for use in determining iodine by ENAA. The University of Virginia reactor at Charlottesville was chosen for this study because the reactor facilities minimized thermal heating of the boron nitride vessel, enabling irradiation of larger, more representative analytical portions. Iodine concentrations ranging from <0.003 to 0.74 g/g are reported for 17 different food matrices.     

Determination of iodine in biological materials by neutron activation analysis

A method of determination of iodine (total and PBI) in serum, urine and other biological materials has been developed. The method consists in a gamma-spectrometric measurement of¹²⁸I activity after its radiochemical separation. The radiochemical separation procedure includes wet decomposition of the samples in a nitric acid medium followed by a few separation steps, the essential step being the substoichiometric extraction of iodide with a chloroform solution of tetraphenylarsonium chloride. Owing to the application of the substoichiometric separation, a high radiochemical purity of the separated iodine is achieved and the determination of the yield of radiochemical separation is not necessary.     

Semi-automated determination of iodine in biological fluids by activation analysis

A simple automated system has been built that permits the selective separation of radioiodine by ion-exchange in eight samples simultaneously and the regeneration of the resin columns in fifteen minutes. Iodine is subsequently determined by γ-spectrometry.     

Resonance enhanced three-photon absorption of molecular iodine

D ← X resonance enhanced three-photon excitation spectrum of iodine was observed by a cw intracavity absorption technique. Vibrational quantum numbers of D ← X transitions are given for every major spectral feature. The corresponding one-photon enhancement from the B state is evident from the one-photon vibrational assignment. The spectroscopic constants for the D state are v₀₀ = 40 998 cm^?1 ω′₀ = 113 cm^?1 and ω′₀χ′₀ = 0.045 cm^?.     

Estimates of iodine in biological materials by epithermal neutron activation analysis

Iodine abundances in NBS biological SRMs and various organs of rats were evaluated by epithermal neutron activation analysis with a boron carbide filter. Detectability of iodine in different biological materials by this method is discussed.

     

Determination of iodine in human nails via epithermal neutron activation analysis

An epithermal instrumental neutron activation analysis (EINAA) method, using a boron nitride irradiation capsule compatible with use in the University of Missouri Research Reactor pneumatic-tube irradiation facility, has been developed for the analysis of iodine in human nails. The principal objective was to determine if the nail could be used as a means of monitoring dietary intake of iodine. The EINAA method was used to analyze nails from subjects having iodine intakes that could be qualitatively differentiated. Iodine concentrations in nails from these subjects were positively correlated with apparent iodine intake.     

Epithermal instrumental neutron activation analysis of biological reference materials for iodine

Epithermal instrumental neutron activation analysis (EINAA) methods have been optimized and applied to several biological reference materials and selected food items for the determination of iodine. The method involves irradiation of the samples for different periods in epi-cadmium and/or epi-boron flux of the Dalhousie University SLOWPOKE-2 reactor and direct counting without any pre-treatment on a 25-cm³ hyperpure Ge detector. The 443 keV photopeak of ¹²⁸I is used for assaying the iodine content. Precision of measurements, expressed as the relative standard deviation, is 10–15% at 200–500 ppb and 3–12% at 500–6000 ppb levels of iodine. Accuracy of iodine measurements is within 5%. The detection limits for iodine in several biological materials with cadmium and boron, either alone or a combination of the two, as thermal neutron shields have been found to vary between 0.1 and 0.4 mg · kg^–1 for different periods of irradiation, decay and counting. The results suggest that the EINAA methods can be successfully applied to biological materials for routine analysis of iodine at levels higher than 200 ppb.     

Photon activation analysis of iodine, thallium and uranium in environmental materials

Iodine, thallium and uranium were determined by photon activation analysis. Two electron linear accelerators were used for the analysis of several kinds of environmental, biological and geochemical reference materials under different irradiation conditions. Both analytical results for iodine were in good agreement with each other but not with literature values in the case of environmental samples. The results of thallium and uranium agreed well with their reference values. The detectable concentration levels of iodine, thallium and uranium were almost 0.3μg/g.     

A comparison of three activation analysis methods for iodine determination in foodstuffs

Activation analysis methods based on the nuclear reactions ¹²⁷ I(n, ) ¹²⁸ I, ¹²⁷ I(n,2n)¹²⁶I and ¹²⁷ I( ,n)¹²⁶ I were tested in terms ofdetection limits, accuracy and precision, and applicability for iodine determinationat various levels in foodstuffs. Both nondestructive and radiochemical modeswere employed using one of the two separation procedures developed (alkaline-oxidativefusion and iodine separation either by extraction of elemental iodine in chloroformor AgI precipitation). The lowest iodine detection limit of 1 ng . g ^—1 was achieved by employing the first nuclear reaction followedby separation of elemental iodine. Accuracy and precision of the proceduresdeveloped at largely different iodine levels were proved by analyses of biologicalreference materials having composition similar to that of various food items.     

Determination of iodine in human brain by epithermal and radiochemical neutron activation analysis

Despite the role of iodine for proper development of the brain and the functions of the element, the accurate data on its concentration in brain tissue are largely lacking, the main reason being analytical difficulties associated with determination of the element especially at low levels. In this work, samples from human brain regions from Hungarian patients were analyzed using epithermal and radiochemical neutron activation analysis (ENAA and RNAA, respectively). The RNAA procedure is based on alkaline-oxidative fusion followed by extraction of elemental iodine in chloroform. The results were checked by the analysis of biological standard reference materials, namely bovine liver, bone meal and diet, and by comparison with previous results obtained by a different RNAA procedure.     

Determination of iodine in Asian diets by epithermal and radiochemical neutron activation analysis

Samples of diets from China, Japan, Korea, India, Pakistan and Philippines were analyzed using epithermal and radiochemical neutron activation analysis (ENAA and RNAA, respectively) within the framework of the IAEA project “Reference Asian Man”. The RNAA procedure was based on alkaline-oxidative fusion followed by extraction of elemental iodine in chloroform. The analytical methods employed are discussed in terms of detection limits and uncertainties of the results obtained. For quality control purposes a number of NIST biological reference materials, namely diets and foods were analyzed. Results for the diet samples indicate that achieving the WHO recommended daily allowance for iodine may be a problem in most of the above given countries. This revised version was published online in August 2006 with corrections to the Cover Date.     

Neutron activation analysis of iodine in blood serum or other biological materials by substoichiometric precipitation of iodine as silver iodide

Several modifications are proposed of the established methods of iodine determination in serum. Prior to the actual analysis, the serum is lyophilized. This preliminary treatment permits the use of large samples. Through lyophilization human blood serum samples can easily be reduced to one-tenth of the original weight. Reduction is even more dramatic with materials from other than human origin. After irradiation the samples are subjected to chemical treatment in the presence of an iodine carrier and¹³¹I-labelled thyoxine. This procedure has been adopted for the determination of the iodine content and the chemical yield in one and the same radioactive measurement. The analysis technique itself consists of an open system Schöniger combustion. The open combustion allows the use of large samples; the gases evolved are absorbed upon their subsequent passage through potassium hydroxide and hydrochloric acid; the mineralization requires less than two minutes. After the addition of a substochiometric amount of silver nitrate, silver iodide is precipitated from an ammoniacal solution as a flat sample, which has been found ideally suited for high efficiency counting with a Ge(Li) detector. The spectrum gives evidence of an excellent decontamination from the³⁸Cl,⁸⁰Br and⁸²Br activities. The iodine content can be calculated from the ratio of the photopeak areas at 364.5 keV and 442.7 keV corresponding to¹³¹I and¹²⁸I, respectively. The chemical procedure requires a mere 15 min, and the recording of the γ-ray spectrum takes no longer than 30 min. The technique is not limited to serum only. It proved well suited for the analysis of many other types of biological material, e.g. human skin tissues.     

Evaluation of minimum detectable amounts of iodine in biological samples by neutron activation analysis

Evaluation of minimal detectable amounts (MDA) of iodine in various or specified irradiation and measurement conditions is described. Interfering contributions due to Na and Cl to the spectral background as well as the dead time of detection system were calculated in details based on an experimental approach. The MDA of iodine for some important biological samples with various Na and Cl concentrations can be evaluated and predicted according to the specified irradiation and measurement arrangements to meet the requirement of analytical purposes.     

Simultaneous determination of iodine and selenium in biological samples by radiochemical neutron activation analysis

Summary Regarding the favourably sensitive nuclear characteristics of iodine and of selenium but the very different half lives of their induced nuclides ¹²⁸I and ⁷⁵Se, a radiochemical neutron activation analysis method for simultaneous determination of these elements in a single sample was developed. It is based on the double irradiation LICSIR technique — Long Irradiation for Se (40h), Cooling (a week or more), Short Irradiation for iodine (1–15 min) with following Radiochemistry. After the second short irradiation, the sample is ignited in an oxygen flask and iodine and selenium are sequentially and selectively extracted as elemental iodine and 5-nitro-2,1,3 benzoselena diazole chelate. With the described method biological samples were analysed and the reliability of the results was checked by the analyses of different standard reference materials. Good agreement with certified values and high radiochemical purity of the spectra show the applicability of the radiochemical separation developed.