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.     

Irreversible adsorption of triple-helical soluble collagen monomers from solution to glass and other surfaces

The adsorption from various solutions of triple-helical soluble collagen monomers to solid surfaces was studied by labeling the collagen with ¹²⁵1. Adsorption to glass, siliconized glass, and Teflon, from aqueous solutions at various pH and ionic strength, was determined at collagen concentrations from 2 to 25 μg/ml. Adsorption was shown to be irreversible and little dependent on pH and ionic strength but increasing enormously as the surface is made more hydrophobic. Surface denaturation of the collagen by heat results in a substantial loss of material. The kinetics of adsorption suggest that the adsorption process may be selective and that not all collagen molecules which reach the surface are immediately adsorbed. Checking these results with earlier measurements of adsorbed layer thickness, a model for collagen adsorption is proposed.     

Laboratory studies on the adsorption behavior of americium

With increasing global nuclear activities, there is a growing interest in understanding the migration behavior of transuranic elements in the terrestrial environment. The laboratory investigations on the adsorption behavior of AM(III) (10^–7M) in aqueous solutions showed that there was not adsorption of Am(III) on glass or polyethylene vials from aqueous solutions at pH<3. The rate of adsorption was found to be inversely related to the (H⁺) in the pH range 4–7. It was also found to be strongly influenced by stirring/shaking as well as by the presence of particulate matter in the aqueous phase. The presence of particulate matter (>0.6 m) in the aqueous solutions significantly inhibits the adsorption rate. Attempts to fit the kinetic data (collected on filtered [particle size >0.6 m] or unfiltered distilled water at pH 6) to the reversible or irreversible first order rate equation did not successfully indicate the complexity of the adsorption process. The presence of 20mg/liter of humic acid at pH 6.3 completely inhibits the adsorption of Am on glass surfaces.     

Trace element analysis of waters by X-ray emission spectroscopy

X-ray emission spectroscopy is a rapid, simple and accurate method for multielement trace analysis of water. This is accomplished by trace elements precipitation with a nonspecific chelating agent APDC (ammonium-1-pyrollidine dithiocarbamate) and filtration through a Millipore filter. In that way the uniform targets suitable for X-ray analysis were made and elements in concentrations as low as few ppb could be determined. APDC chelation over broad pH ranges for different elements in seawater is discussed. The best pH range for simultaneous determination of these elements is found. Results of analysis of seawater samples taken near the island Krk in the Adriatic sea are presented.     

Preconcentration of trace chalcophile elements by a zincon--loaded resin and its application to neutron activation analysis (author's transl)]

A chelating agent-loaded resin consisting of an anion exchange resin and zincon which has widely been employed as a specific reagent for zinc(II) and copper(II) in spectrophotometry was prepared. The adsorption behavior of some chalcophile elements was studied in detail, with respect to pH, flow rate and exchange capacity. From the results, it was confirmed that the zincon-loaded resin reacts selectively with copper(II), zinc(II), mercury(II) and lead(II) at lower pH region, and the above reaction is stoichiometric as in the case of the reaction of zincon with metal ions in aqueous solution. Furthermore, the zincon-loaded resin was applied to the selective concentration of trace amounts of chalcophile elements in natural water samples prior to neutron activation analysis. Water samples taken from the Watarase River were filtered and the pH of each filtrate was adjusted to ca. 5.5. After preconcentration was made by the column method (zincon-loaded resin: 2 x 10-4 mol/g resin, 1.0 g, 7 mm phi x 35 mm), the resin in the column was washed and dried in a desiccator. The standard material was also prepared according to the above mentioned scheme. The sample and the standard materials packed in polyethylene vials were irradiated for 40 min by a neutron flux of 5 x 10(13 n.cm-2.sec-1 in the JRR-4 of the Japan Atomic Energy Research Institute. After cooling the materials, activity measurements were made. The results were 53 ppb for copper, 0.25 ppb for mercury.     

The role of210Pb in evaluating container adsorption of Pb(II) from dilute aqueous solutions

Solutions of Pb²⁺ at ppb to ppm levels were tagged with²¹⁰Pb and then counted from time to time over a period of one year to measure the extent of container adsorption. All count rates for samples which were acidified with HNO₃ were at least 90% of their initial values, even after one year of storage. Amber glass containers proved to be superior to polypropylene for 0.1 and 1.0 ppm Pb²⁺ solutions; but below 0.1 ppm, polypropylene was superior. For non-acidified samples, the count rate dropped rapidly within the first two months, and then declined more gradually thereafter, with polypropylene generally superior.     

Untersuchungen zur adsorptiven Anreicherung von Elementspuren an Adsorberharzen

Summary Because of the purity and of the adsorption properties, the Amberlite XAD-4 resin is an adsorbent suitable for multielement preconcentration from aqueous solutions. Adsorbed trace compounds can easily be eluted from the resin by use of 1 M HNO₃ in acetone and subsequently be determined by AAS. In this paper the adsorptivity of complexes of 15 elements with different chelate forming reagents was investigated. Besides of multielement preconcentration, selective trace separation procedures are possible by suitable selection of complex reagents and pH-adjustment of the sample solution. In many cases the resin XAD-4 can advantageously be used as a trace collector instead of activated carbon. The advantages and disadvantages in the application of the two adsorbents are discussed.     

Adsorption behaviour of microamounts of cesium on manganese dioxide

The adsorption of cesium on manganese dioxide from aqueous solutions has been studied in relation to pertinent variables such as shaking time, pH, composition of aqueous solutions, mass of adsorbent (10 mg–1 g) and concentration of adsorbate (10^–6–5·10^–3 M), using a radiotracer technique. The influence of various anions and cations on cesium adsorption was examined. The distribution coefficient of a variety of other elements was determined under similar conditions. The adsorption of cesium obeys a Freundlich-type isotherm over the entire concentration range investigated, whereas the Langmuir-type isotherm is followed only at moderate concentrations.     

Flow-injection extraction and gas-chromatographic determination of terodiline in blood serum

Adsorption losses of terodiline (N-t-butyl-1-methyl-3,3-diphenylpropylamine) from aqueous and organic solutions in the different parts of a flow-injection extraction system are described. Terodiline base adsorbs strongly on PTFE and polypropylene tubing from aqueous solution; 60–80% is lost from low concentration samples during its passage through the tubing (2 m long, 0.7 mm i.d.). For nickel, stainless steel and glass, the adsorption losses were slight. Terodiline in organic solution did not adsorb on any of the tested materials. Based on these results, an extraction manifold was designed for mechanized work-up of human blood serum. The samples were injected from a valve with a steel loop (0.5 ml) at a rate of 30 h^?1 into n-heptane + 2% n-pentanol, made alkaline, segmented with the organic phase and extracted. After phase separation, portions of the extract stream were collected in vials and analyzed for terodiline by using capillary gas chromatography with a nitrogen-selective detector.     

Adsorption and desorption studies of radiocesium on Al2O3 from aqueous solutions

The adsorption and the desorption of radiocesium from aqueous solutions containing NaNO₃ or CaCl₂ on Al₂O₃ were studied over a wide range of background electrolyte concentration and solution pH by using batch techniques in polyethylene and glass test tubes. It was found that the wall of the glass test tubes has a great effect on the adsorption and desorption data, and the adsorption-desorption hysteresis on the same time scale is negligible by using the same aqueous solutions for both adsorption and desorption in the polyethylene test tubes. The dependences of the distribution coefficient on the pH and background electrolyte concentration and the adsorption mechanism were discussed.