Application of 140La and 24Na as intrinsic radiotracers for investigating catalyst dynamics in FCCUs.

Instrumental neutron activation analysis (INAA) of fluid catalytic cracking (FCC) catalyst samples was carried out with an objective to identify activable elements and evaluate its suitability for use as an intrinsic radiotracer for tracing catalyst itself in Fluid Catalytic Cracking Units (FCCUs) used in petroleum refining. Two catalyst samples obtained from two different refineries were analyzed. Twelve different elements were identified in each catalyst sample and their respective concentrations were determined. From the recorded gamma-ray spectra, it was found that lanthanum-140 ((140)La) and sodium-24 ((24)Na) were the predominantly present and suitable radionuclides that could be used as radiotracers for tracing catalyst in FCCUs. Lanthanum being present in much higher concentration forms the major component of the radiotracer after irradiation. Based on the results of INAA, appropriate quantities of the catalyst samples were irradiated with neutrons to produce the desired amount of activity of lanthanum-140 and sodium-24 to be used as radiotracers for tracing the catalyst itself in a pilot as well as an industrial-scale FCCU. The residence time distribution (RTD) of catalyst was measured and analyzed to determine mean residence time (MRT). The axial dispersion model (ADM) was used to simulate the measured RTD data and investigate the degree of axial mixing. The results of the experiments were used to improve the design of pilot-scale FCCU and optimize the performance of the industrial-scale FCCU.

Molecular iodine preconcentration and determination in aqueous samples using poly(vinylpyrrolidone) containing membranes.

Membranes for preconcentration of molecular iodine were developed by two different routes: (i) UV-grafting of 1-vinyl-2-pyrrolidone in the pores of microporous poly(propylene) host membrane (grafted membrane), and (ii) physical immobilization of preformed poly(vinylpyrrolidone) (PVP) in a plasticized cellulose triacetate matrix to form the polymer inclusion membrane (PVP-PIM). The UV-grafted PVP-membrane was found to be hydrophilic (water uptake capacity=166 wt.%), while the PVP-PIM was found to be highly hydrophobic ( approximately 2 wt.%). PVP-PIM was found to uptake only I(2) from aqueous sample whereas I(2) and I(3)(-) were sorbed in the grafted membrane. This selectivity of PVP-PIM towards I(2) was attributed to its hydrophobicity that allows only neutral I(2) to interact with PVP in the membrane matrix. Thus, the selective preconcentration and quantitative determination of I(2) in aqueous sample was carried out using PVP-PIM. As PVP-PIM was optically transparent, the characteristic absorbance of PVP-I(2) complex (lambda(max)=361 nm) could be used for quantitative determination of I(2) in the membrane. The instrumental neutron activation analysis (INAA) of the I(2)-loaded PIM samples indicated that 82% could be sorbed into the PIM samples from the solution within 10 min of equilibration time. This membrane was applied to I(2) determinations in the samples of (131)I radiotracer. The concentration level of iodine species in these samples were in sub-ppb level. Therefore, these samples were ideal for testing the preconcentration efficiency of the membrane towards I(2) by monitoring the radioactivity of (131)I. The amounts of I(2) in the aqueous samples were standardized by conventional solvent extraction of I(2) with the chloroform for validating the preconcentration efficiency of PVP-PIM. The detection limit of I(2) in aqueous samples by INAA hyphenated with PVP-PIM was found to be 0.3ppb for a sample size of 25mL.

Development and applications of the k0-based internal mono standard INAA method.

The k0-based internal monostandard instrumental neutron activation analysis (IM-INAA) method, developed and standardized in our laboratory, is capable of analyzing both small and large samples of different sizes and shapes. Use of in-situ relative efficiency makes the method geometry independent. In this paper, we present the development of this methodology and applications to two types of alloys namely, stainless steel and brass. A stainless steel certified reference material, BCS 466 was also analyzed to evaluate the accuracy of the method. Absolute concentrations in these alloys were arrived by a standard-less method. The method has also been applied for the analysis of large-size wheat samples (0.45-1 kg) and the results were compared with the data obtained for selected elements in sub-samples (50-1000 mg).

Selective preconcentration and determination of iodine species in milk samples using polymer inclusion sorbent.

A method to determine low levels of iodine species namely I(-) and IO(3)(-) in aqueous samples was developed and applied to milk and milk powder samples. It is based on selective preconcentration of I(-) in polymer inclusion sorbent (PIS) and neutron activation analysis (NAA) of I(-) sorbed in PIS. The PIS was found to be highly selective for I(-) in presence of IO(3)(-) and other anions commonly present in the milk samples. In order to preconcentrate total I(-)+IO(3)(-) content in the PIS, IO(3)(-) was reduced to I(-) using a mixture of acetic acid and ascorbic acid. It was found that total iodine content in milk could be determined with epithermal neutron activation analysis (ENAA). A scheme was developed to determine I(-), IO(3)(-) and total iodine. The developed method was applied to milk reference materials (NIST SRM-1549 and IAEA-RM-153 milk powder) and a commercially available milk powder. The scheme for estimation of iodine in different forms was validated by using reference material NIST SRM-1549.

Bhasmas: unique ayurvedic metallic-herbal preparations, chemical characterization.

Bhasmas are unique Ayurvedic metallic preparations with herbal juices/fruits, known in the Indian subcontinent since the seventh century BC and widely recommended for treatment of a variety of chronic ailments. Twenty bhasmas based on calcium, iron, zinc, mercury, silver, potassium, arsenic, copper, tin, and gemstones were analyzed for up to 18 elements by instrumental neutron activation analysis, including their C, H, N, and S contents. In addition to the major constituent element found at % level, several other essential elements such as Na, K, Ca, Mg, V, Mn, Fe, Cu, and Zn have also been found in microg/g amounts and ultratrace (ng/g) amounts of Au and Co. These seem to remain chelated with organic ligands derived from medicinal herbs. The bhasmas are biologically produced nanoparticles and are taken along with milk, butter, honey, or ghee (a preparation from milk); thus, this makes these elements easily assimilable, eliminating their harmful effects and enhancing their biocompatibility. Siddha Makaradhwaja, a mercury preparation is found to be stoichiometrically HgS without any traces of any other element. Similarly, Swet Parpati is stoichiometrically KNO3 but is found to have Mn, Cu, Zn, Na, P, and Cl as well. An attempt has been made to correlate the metallic contents with their medicinal importance. Na and K, the two electrolytic elements, seem to be well correlated, although K/Na varies in a wide range from 0.06 to 95, with specifically low values for Ca-, Fe-, and Zn-based bhasmas. K/P also varies in a wide range from 0.23 to 12, although for most bhasmas (n = 12), it is 2.3 +/- 1.2. Further, Fe/Mn is linearly correlated (r = 0.96) with Fe in nine noniron bhasmas.

Analysis of essential elements in Pragya-peya--a herbal drink and its constituents by neutron activation.

Ayurvedic herbal formulations are a good source of several nutrient elements essential for metabolic processes. Pragya-peya, a herbal drink and its 12 herbal constituents have been analyzed for 7 minor (Al, Ca, Cl, Mg, Na, K, P) and 15 trace (Ba, Br, Co, Cr, Cs, Fe, Hg, La, Mn, Rb, Sc, Se, Th, V, Zn) elements by instrumental neutron activation analysis (INAA). The method involves thermal neutron irradiation in a reactor followed by counting at several intervals. Also Cd, Cu, Ni and Pb contents were determined by atomic absorption spectrometry (AAS). Elemental data were validated by simultaneously analysing reference materials (RMs) such as mixed Polish herbs (INCT-MPH-2) and peach leaves (SRM-1547). Sample homogeneity was tested by analysing samples from three different batches collected at different intervals. Pragya-peya has been found to be especially rich in several nutrient elements such as Ca, K, V, Fe, Mn, Se and Zn whereas no single constituent is enriched in all the nutrient elements. Concentrations of elements are discussed vis-a-vis their medicinal/therapeutic uses. Several elements such as Na, K, P, Ca, Fe, Co, and Zn seem to be well correlated in 12 constituent herbs.

Development of an internal monostandard instrumental neutron activation analysis method based on in situ detection efficiency for analysis of large and nonstandard geometry samples.

A k0-based internal monostandard instrumental neutron activation analysis method for determination of relative elemental concentration in samples of large size and irregular geometry has been developed. In this method, one of the elements present in the sample is used as comparator. A priori knowledge of the concentration of one of the constituents is required to convert the relative concentration into absolute values. The problems of gamma-ray self-attenuation and geometrical effects that arise in the assay of large and nonstandard geometry samples were overcome by an in situ relative detection efficiency calibration procedure, which requires one or more activation products emitting gamma-rays over a wide range of the spectrum. To minimize the problem of neutron flux perturbations that may arise in large samples, irradiations were carried out using a thermal column with thermal neutron component of more than 99.9%. The method has been standardized with samples of silica (approximately 0.5 kg) and water (0.5 L) spiked with known amounts of different elements and has been advantageously applied to some alloy and metal samples of irregular geometry, where complete compositional characterization was carried out using mass balance. This approach is highly valuable for analysis of large, irregularly shaped samples if not too high demands are set to the degree of accuracy.

Validation of a neutron activation analysis method using k0-standardization.

A neutron activation analysis method using k0-standardization has been adopted for multielement analysis using our research reactors. Gold has been used as the comparator. The input parameters, used for calculation of elemental concentration, such as subcadmium to epithermal neutron flux ratio (f), the epithermal neutron flux shape factor (alpha), and the absolute efficiency of the detector (epsilon) have been determined. The values of k0-factors and Q0 (the ratio of resonance integral to thermal neutron cross section) have been taken from the literature. The validity of applying this method in our laboratory is evaluated by analyzing the elemental concentrations with respect to the certified values in eight reference materials of different origin obtained from USGS, IAEA and NIST. The percent deviation of the measured elemental concentrations are found to be within +/- 15% to that of the certified values whereas the percent relative standard deviation ranged from 2% to 10% for most of the elements analyzed.

Heavy metal concentration and distribution in a dated sediment core of Nainital Lake in the Himalayan region.

The concentrations and distribution of the elements, including heavy metals such as As, Ba, Br, Co, Cr, Cs, Fe, Ga, K, Mn, Na, Rb, Sc, Sr, Th and Zn, were investigated in dated sediment cores of Nainital Lake located in the Himalayan region, in Uttar Pradesh state of India, which is considered as a remote background area. The concentrations of the elements were measured by instrumental neutron activation analysis using the k0 method. The International Atomic Energy Agency certified reference material SL-3 was used to evaluate the accuracy of the method. The normalized data for a series of elements were used to understand the source of loading. Elements like Br, Co, Cr, Fe, K, Mn and Zn show a negative correlation with increasing depth whereas elements like As, Ba, Cs, Na and Rb show a positive correlation with increasing depth. By considering the concentration for the bottom segments of the core as close to the baseline concentration, recent flux values for different elements were calculated. An increase in the flux value was observed for Br, Cr, Fe, K, Mn and Zn, which can be attributed to anthropogenic contribution in recent years.