S. R. Kayasth

Proconcentration of trace elements from high-purity thorium and uranium on Chelex-100 and determination by graphite furnace atomic absorption spectrometry with Zeeman-effect background correction

Abstract Preconcentration of trace impurities form large-sized samples of uranium metal and thorium oxide using a small column of Chelex-100 followed by their determination using graphite furnace atomic absorption spectrometry (GFAAS) is reported. A 0.5–10-g amount of the sample (uranium metal or thorium oxide) was dissolved, complexed with ammonium carbonate and subjected to the ion-exchange procedure. The retained analytes were eluted with 2–4 M nitric acid and brought to a small volume for a final dilution to 10-25 ml for their determination using GFAAS. The validity of the separation procedure and recoveries at μg kg −1 levels was checked by standard addition; the recoveries were > 95%.

A sequential multielement separation scheme for determination of As, Mn, Mo, Cu and Zn in human milk by neutron activation analysis

A simple separation scheme for the analysis of As, Mn, Mo, Cu and Zn using neutron activation is described. It has been checked using three standard reference materials, A-11 milk powder (IAEA) and bovine liver and orchard leaves (USNBS) and found to give acceptable results. This scheme was applied for determination of these trace elements in mature human milk samples. The concentrations of As, Mn, Mo, Cu in samples obtained from two socio-economic groups—low and middle incomes—were not significantly different. However, Zn levels in samples obtained from the poor income group were significantly lower than in those obtained from the other group.

Daily requirements of Fe, Co and Se during infancy

The daily intakes of trace elements by infants showing optimal pattern of growth are used as the basis to estimate the requirements of Fe, Co and Se during infancy. Since milk is the only food and source of nutrition in the first few months of life, the requirements of these elements are calculated from their average concentrations in human milk and the volume of milk required to supply sufficient amount of energy for maintenance and healthy growth of infants. The concentrations of the three elements in human milk were determined, using the technique of neutron activation followed by radiochemical separation.

Determination of traces of rare earth elements in high-purity uranium by ion-exchange separation and neutron activation γ-spectrometry

Abstract Neutron activation γ-spectrometry is sufficiently sensitive for the determination of traces of rare earth elements but quantitative separation from uranium is essential. The rare earth elements in 0.2 M ammonium carbonate medium are quantitatively retained on Chelex-100, and are quantitatively separated from uranium by recycling the eluate. When 10-g samples are used, neutron activation provides detection limits of 1–20 μg kg −1 . Recoveries of rare earths, checked by spiking with radiotracers, are essentially complete.

Radiochemical neutron activation analysis of individual rare earth elements in monazites from different geological environments

Radiochemical neutron activation analysis /RNAA/ has been applied for the determination of individual rare earth elements /REE/, except Tm, in 8 Indian monazites and one each from Malaysia and Thailand. Because of the very low amounts of heavy rare earths /HREE/ compared to light rare earths /LREE/ in monazite, HREE from Ho onwards have been determined only after the separation of the heavy and light rare earth fractions in the irradiated monazite samples. The results indicate significant variations in REE contents from Eu to Lu among different monazite samples. The chondritic normalized REE patterns of all the samples show a prominent negative Eu anomaly with different slopes at the heavy rare earth end. All the individual REE, except Tm, have been reported for the first time in various Indian monazites.

Preconcentration and determination of mercury in high purity arsenic

Abstract An analytical procedure for the determination of trace amounts of mercury in high purity arsenic metal/oxide, widely used in electronic devices, is presented in this manuscript. Pre-concentration of mercury from a large amount of the matrix on a small amount of anion exchanger in hydrochloric acid medium was used to enrich the analyte concentration, followed by its determination using neutron activation analysis (NAA). A detailed study was carried out for the quantitative separation of the analyte from the matrix along with the precautions to be considered for the accurate determination of this volatile element. The separation of the analyte was quantitative and the validity of the procedure was confirmed by tracer studies, standard addition of the analyte to the matrix and by analyzing high purity arsenic for which certified values are available. The overall reproducibility of the separation procedure was 2–10%.

Determination of Traces of Uranium and Thorium in Environmental Matrices by Neutron Activation Analysis

Radioactive elements like 232Th and 238U along with their daughter products, form part of all environmental matrices and are getting transferred to living beings by different pathways, leading to a continuous radiation exposure and need to be monitored. This paper presents an analytical methodology, highlighting the need to separate interfering beta- and gamma-emitters from the analytes, when neutron activation analysis is employed for the determination of traces of uranium and thorium in soil and plant materials. The method has been applied to the soil and plant materials from selected regions of India, along with standard reference materials to verify the validity of the proposed separation scheme. The overall reproducibility of the procedure was 2–10%. The concentration values of uranium and thorium so obtained, have been used to calculate transfer factors from soil to various parts of wheat plant.

Differential-pulse anodic-stripping voltammetric determination of traces of lead in high-purity copper after its separation by ion exchange

Abstract Trace amounts of lead in copper can be determined by differential-pulse anodic-stripping voltammetry after separating it from the matrix. Lead was quantitatively retained on a small Dowex 1-X4 ion-exchange column, without retaining copper when present as a copper-amine complex in solutions containing 0.2 M sodium hydroxide. Subsequent desorption was done with 2 M nitric acid. After deposition for 1 min on a hanging mercury drop electrode and subsequent stripping, the limit of detection was 2 ng ml−1 and the limit of quantification was 6.6 ng ml−1. Recoveries of lead were checked by standard addition to copper solution.

Trace element characterization of high purity gallium

Abstract An ion exchange method is described for the quantitative separation of ca. twenty trace elements from high purity gallium metal. 0.5–2 g of matrix is dissolved and subjected to a separation procedure using an anion exchanger in hydrochloric acid followed by sodium hydroxide medium to preconcentrate the analytes. Desorbed analytes are then available for their quantification depending upon the availability of the technique and its sensitivity. Graphite furnace atomic absorption spectrometry and neutron activation analysis techniques have been used for their final determination during this work. Most of the analytes found were in the ng g −1 range. Depending on the blank values, the reproducibility of the overall procedure is 2–10%. Separation of the matrix and recovery of the analytes were essentially complete as confirmed by standard addition of the analytes to the matrix and also by tracer studies.

LOSS OF ELEMENTS IN THE OXYGEN FLASK DECOMPOSITION OF BIOLOGICAL MATERIALS: A STUDY BY NEUTRON ACTIVATION ANALYSIS

Partial loss of elements in the oxygen flask method for the decomposition of biological materials is described. The irradiated sample is placed in a platinum wire gauze or quartz cup and burnt in an oxygen atmosphere in the presence of carrier solutions. The results obtained by radiochemical neutron activation analysis for the elements like Mn, As, Cu, Sb and Zn in different standard reference materials are presented with a discussion of the possible causes for the lower values.