Miloslav Vobecký

Silver chemical vapor generation for atomic absorption spectrometry: minimization of transport losses, interferences and application to water analysis.

A study of a transport process and interferences in the method of Ag chemical vapor generation (CVG) with AAS detection was performed. A modified externally heated quartz multiatomizer with a heated inlet arm was designed to minimize transport losses. Both transport efficiency and spatial distribution of a residual analyte in an apparatus were studied by means of 111Ag radioactive indicator. Compared to our previous study the apparatus design was significantly modified: removal of a spray chamber and heating of an inlet arm to 300 °C allowed us to reduce transport losses from 65% to 4% and thus to improve overall CVG efficiency up to 32.5%. Lower (ambient) or higher (700 °C) temperature was inferior to 300 °C due to either losses of Ag with aerosol droplets by deposition or trapping of decomposed Ag particles on a quartz surface, respectively. The interfering effect of hydride forming elements (As, Se) and some transition metals (Cu, Co, Ni, Au) was examined. No serious negative interference was observed up to 10 μg ml−1 level, with the exception of Au causing 18% signal depression already at 0.5 μg ml−1 level. Transmission electron microscopy and energy dispersive X-ray spectroscopy indicated mixed Ag and Au particles and formation of cross-linked structures was revealed. The upward calibration curvature was observed which was treated using power curve regression. The limit of detection under optimized conditions was 1.0 ng ml−1 and the method was also successfully tested using two proficiency testing samples of drinking water.

Gold volatile compound generation: optimization, efficiency and characterization of the generated form

The generation of an analytically useful volatile form of Au has been studied. The flow injection generation was performed in a dedicated generator consisting of a special mixing apparatus and gas–liquid separator design in the presence of surfactants (Triton X-100, Antifoam B) and diethyldithiocarbamate. The on-line atomization in the quartz tube multiatomizer for atomic absorption (AAS) detection has been employed as the convenient atomization/detection means. The optimization of generation and atomization conditions resulted in an analytical procedure yielding the detection limit of 17 ng ml−1 and a very good long range reproducibility of the analytical signal. A 198,199Au radioactive indicator of high specific activity together with AAS measurements was used to track quantitatively the transfer of analyte in the course of generation and transport to the atomizer and to determine the generation efficiency of 11.9 ± 0.1% at the Ar carrier flow rate optimized for the multiatomizer of 240 ml min−1. The efficiency was twice as high at the Ar carrier flow rate of 600 ml min−1. In situ trapping in GF for AAS was explored as an alternative to the on-line atomization. The detection limit of 3.0 ng ml−1 was achieved even though the Ar flow rate optimum for trapping (115 ml min−1) was too low for efficient generation: the overall efficiency of generation and trapping was 1.11 ± 0.03%. Transmission electron microscopy measurements proved the presence of Au nanoparticles of diameter of approximately 10 nm and smaller transported from the generator by the flow of carrier Ar.

Radioanalytical methods for the non-destructive analysis of lunar samples

The elemental compositions of Apollo 11 and Apollo 12 lunar soil samples 10084,141 and 12070,83 and Apollo 12 rock fragment 12063,73 were determined by non-destructive radioanalytical methods. Main mineral fractions and glasses separated from these samples were analyzed as well. Instrumental neutron activation analysis (INAA) was used to determine Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Cs, Ba La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Lu, Hf, Ta, W, Ir, Au, Th and U. A method of delayed neutron counting was used for the determination of uranium, and non-dispersive radioisotopic X-ray fluorescence analysis was applied to the determination of Ti, Fe, Sr, Y and Zr.

MULTIELEMENT STANDARDS IN ROUTINE REACTOR NEUTRON ACTIVATION ANALYSIS

The application of multielement standards (MES) in routine neutron activation analysis brings a whole range of advantages. This paper deals with the experience obtained during many years of application of these MES. Nine of these MES contain a total of 50 elements in suitable combinations and concentrations; thus, the determination of most of the common elements by NAA can be carried out simultaneously. This refers to the following elements: Na, Mg, Al, Cl, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Mo, Ag, Cd, In, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Re, Au, Hg, Th and U. For the determination of the remaining elements such as Zr, Ta, Ir etc., single element standards (SES) are used.

Multi-element standard for routine instrumental activation analysis of trace elements in rocks and tectites

The use of high-resolution Ge(Li) detectors in non-destructive instrumental neutron activation analysis (INAA) of mineral materials makes possible the simultaneous determination of a number of trace elements. In routine applications of INAA the use of a multi-element standard (MES) has proved to have advantages over a set of standards for each determined element. An MES has been prepared containing 8 trace elements mixed in a suitable proportion and giving, after neutron activation, long-lived γ-emitters, the γ-ray lines of which regularly occur in the γ-ray spectra of silicate mineral materials. This method has been used in the determination of Sc, Cr, Co, Rb. Cs, Eu, Hf and Th in samples of standard rocks and moldavites.

Radioactive decay of 49Sc

The radioactive isotope 49Sc was isolated from neutron irradiated natural calcium in a carrier-free form by means of chromatographic separation. It was found to decay with a half-life of 57·5±0·1 min mainly by 2010±5 keV β-transition to the ground state of 49Ti. A γ-line of 1780±40 keV was observed, indicating the presence of a soft beta component with transition energy of 230 keV and 0·03 per cent intensity. For the 1780 keV level the spin 52 was proposed.

Stibine and bismuthine trapping in quartz tube atomizers for atomic absorption spectrometry. Part 2: a radiotracer study

A trap-and-atomizer device based on a multiatomizer has been described recently. This compact and universal device enables the preconcentration of As, Sb, Bi and Se hydrides on-line prior to their AAS detection. Up to date only optimization of the method and its analytical applications have been described. In this work, 125Sb and 205,206Bi radioactive indicators were used to quantify the efficiency of the individual steps of preconcentration procedure as well as to investigate the spatial distribution of the analytes. The investigation proved the complete trapping and volatilization of Sb and Bi. The trapping efficiency of Sb was better than 93% (RSD < 6%) between 200 and 800 °C. The trapping efficiency of Bi was above 96% (RSD < 5%) between 100 and 800 °C whereas it fell to 83% at 900 °C. The area of the trapping spot increased with increasing trapping temperature. The trap is capable of trapping up to 400 ng of Bi and 2 µg of Sb, respectively. Typically, 1–10 ng of analyte is preconcentrated in ultratrace analysis. No change in either trapping efficiency, or in the spatial distribution of analyte was observed with increasing trapped analyte mass. Also the volatilization step proved to be efficient – only (1.8 ± 1.6)% and (2.9 ± 0.9)% of original Bi and Sb activity, respectively, was found in the traps after the volatilization at 900 °C.

In situ collection of volatile silver species in a new modular quartz tube atomizer for atomic absorption spectrometry

Collection of volatile Ag species on a quartz surface has been successfully achieved for the first time, improving substantially the analytical performance of a previously reported on-line atomization procedure. Ag volatile species were formed during the reaction with tetrahydroborate in the presence of chemical modifiers (Triton X-100 and Antifoam B) in a special generator, collected and atomized in a quartz tube atomizer and detected by atomic absorption spectrometry. A novel modular design of the quartz tube atomizer was employed to allow trapping of volatile Ag species inside the optical tube heated to 1000 °C in excess of O2 over H2. Fast revolatilization and atomization of Ag species were subsequently realized by the change of the gas composition to H2 excess over O2. Collection efficiency under optimized conditions reached 94.1 ± 3.2%. The limit of detection was 0.11 ng ml−1 for a 250 μl sample, nine times better than in the on-line atomization mode. Precision expressed as the relative standard deviation of measured trapping peak areas was 3% at the 4 ng ml−1 level. The method was tested using water reference materials. The present shortcomings of this approach such as quartz devitrification at the collection area are discussed and feasible solutions are suggested.

Long-term action of potassium bromide on the rat thyroid gland

Male rats fed by a standard diet with determined of bromine and iodine content were exposed to a 133-day oral administration of KBr (100, 200, 400 mg Br-/l drinking water). Their thyroid glands showed increased growth of the epithelial cells reflected by a microfollicular rearrangement of the parenchyma due to proliferation of very small follicles with a low or zero content of colloid. Morphometric analysis of thyroids of Br(-)-exposed animals revealed a significant decrease in the volume of intrafollicular colloid and marked increase in the number of the smallest follicles (areas up to 100 and 100-300 micron 2). In addition, the nuclei of thyrocytes showed an increased number of mitoses. The vascularization was increased as well. In the blood plasma of the Br(-)-exposed animals the T4 concentration was significantly decreased in dependence on the bromine concentrations. Thyroglobulin immunoreactivity in the colloid of Br(-)-exposed animals decreased after administration of 400 mg Br-/l drinking water. Increasing concentrations of Br- in the drinking water caused an increased bromine concentration in the thyroid, a decreased iodine content and a decreased I/Br molar ratio. The changes in the rat thyroid caused by long-term administration of 100 mg Br-/l were similar to hyperplastic parenchymal goitre and were comparable to those induced in previous experiments by the same bromine concentration administered over a 16- and 66-day period respectively.

Potassium bromide and the thyroid gland of the rat: morphology and immunohistochemistry, RIA and INAA analysis

The increasing environmental concentration of bromine has resulted in attempts to obtain information on its possibly deleterious effect on humans, particularly on a major target organ of this halogen i.e. the thyroid gland. In order to establish the morphological and functional effects of bromine on the thyroid, we have performed experiments on male rats which, in addition to a standard diet with an estimated iodine/bromine content, were fed for periods of 16 and 66 days with the small quantities of bromide expected to be encountered in the environment (10, 50 and 100 mg of Br-/l in drinking water). This treatment induced growth of the follicular epithelial component and microfollicular tissue rearrangement, a reduction of intrafollicular colloid, an increase in the height of the follicular cells and the number of mitoses, and it enhanced vascularization. Image analysis revealed a significant reduction in the volume of colloid, despite the accompanying rise in the number of minute follicles. The immunohistochemical positivity of the thyroglobulin fell in the microfollicular colloid of the exposed animals, although this was affected to a lesser extent in the larger follicles. The concentration of bromine in the thyroid increased with the amount of bromine intake, while at the same time the molar ratio of iodine/bromine decreased. The plasma level of T4 was lowered after both 16 and 66 days of treatment, but the T3 level only after 66 days treatment. The level of TSH did not exhibit any significant change. The observed changes, which have a parenchymatous goitre-like character, may have a direct relevance for human medicine, since the concentrations of bromide chosen in these experiments are readily encountered in the environment.