Jiří Dědina

Multiple microflame quartz tube atomizer — further development towards the ideal hydride atomizer for atomic absorption spectrometry ☆

Abstract The development of an improved type of hydride atomizer for atomic absorption spectrometry — multiple microflame quartz tube atomizer (MMQTA) — is presented. The main feature of this atomizer is recurrent analyte atomization proceeding over its whole optical tube length, which is achieved by production of H-radicals at multiple points within the tube by oxygen microflames burning in the hydrogen-containing atmosphere. The MMQTA design optimization leading to a complete filling of the observation volume with H-radicals is described. The influence of individual atomization parameters is discussed. Optimum H-radical producing oxygen intake into the MMQTA was found to correspond to a H 2 :O 2 stoichiometric (3:1) ratio. The performance of the individual MMQTA tube designs is evaluated and compared to a typical externally heated quartz tube atomizer (EHQTA) — the linearity of calibration graphs for As, Se and Sb is significantly improved in all MMQTA tubes, without compromising the sensitivity, simplicity, low cost and easy operation. In fact, the free atom reactions within the tube causing calibration curvature are avoided up to an analyte concentration of at least 200 ng ml −1 for Se and Sb and 100 ng ml −1 for As. Tolerance limits of 0.7, 1.4, 0.2 and 0.2 μg ml −1 are achieved for the atomization interferences of As on Se, Se on As, Sb on Se and Se on Sb, respectively, which is an improvement by 1–2 orders of magnitude in comparison to the conventional EHQTA with the same hydride generation system.

Multiple microflame—a new approach to hydride atomization for atomic absorption spectrometry

A novel hydride atomizer, called a multiple microflame quartz tube atomizer, is described. A preliminary evaluation of its performance based on a comparison with the commonly employed externally heated quartz tube atomizer is presented. Selenium hydride is used as the analyte and arsine as the interferent. It is demonstrated that the multiple microflame quartz tube atomizer retains the most important advantage of the commonly employed externally heated quartz tube atomizer, the high sensitivity, and substantially reduces its fundamental disadvantages: the poor resistance to atomization interferences and unsatisfactory linearity of the calibration graphs.

Quartz tube atomizers for hydride generation atomic absorption spectrometry: mechanism for atomization of arsine. Invited lecture

The mechanism for the atomization of arsine was studied in externally heated quartz tube atomizers of various designs. A continuous flow of arsine was generated either by reaction with sodium tetrahydroborate or by direct arsine sampling from a cylinder. The latter, together with precautions taken to ensure that inadvertent addition of oxygen to the system was minimized, made possible full control of the composition of the atmosphere in the atomizer. The effect of atomizer design, purge gas type, purge gas flow rate and atomizer temperature on the oxygen supply required for optimum sensitivity and on the curvature of the calibration graph was investigated. An extremely low supply of oxygen is required for efficient atomization of arsine in heated atomizers with narrow inlet arms. At sub-optimum oxygen supply flow rates, calibration graphs are curved significantly, and gradually approach a limiting absorbance, which depends on the flow rate of the oxygen if hydrogen is the main component in the purge gas. If there is an excess of argon over hydrogen in the purge gas, the calibration exhibits a roll-over. At least a slight stoichiometric excess of hydrogen over oxygen is essential for the atomization. The results of the experiments gave a deeper insight into the mechanism of radical formation involved in atomization of the hydride in quartz tube atomizers. The influence of various experimental parameters on the cross-sectional density of hydrogen radicals in a radical cloud, which controls atomization efficiency, was established. Possibilities for improvement of analytical performance, as a consequence of the results, are discussed.

Interferences in hydride atomization studied by atomic absorption and atomic fluorescence spectrometry

Abstract A hydride atomizer able to operate in the flame-in-tube mode and in the miniature diffusion flame mode was used to investigate interferences of arsenic in selenium atomization. A twin-channel continuous flow hydride generator was utilized to eliminate liquid phase interferences. Both atomic absorption and atomic fluorescence detectors (EDL sources) were employed. The miniature diffusion flame can tolerate interferent concentrations up to 70 μg ml −1 . The magnitude of interferences in the flame-in-tube atomizer is controlled by the distance between the atomization and detection zones. The best tolerance to interferents, comparable with that in the miniature diffusion flame, was obtained for the minimum distance of the zones. The figures were deteriorated by two orders of magnitude when increasing the distance between the observation and the atomization zones to 50 mm. Also a curvature and rollover of calibration graphs was observed when increasing the distance. The presence of the interferent enhanced substantially the curvature and rollover, so that the magnitude of observed interferences was dependent on the analyte concentration. All the observed interferences and the calibration graph curvature are due to the decay of free analyte atoms by reactions in the free space. The nature of the species formed is discussed. No significant depletion of hydrogen radicals was observed. As demonstrated by measurements in the miniature diffusion flame, the species formed can be reatomized by interaction with hydrogen radicals with an efficiency better than 90%.

Speciation analysis of arsenic by selective hydride generation-cryotrapping-atomic fluorescence spectrometry with flame-in-gas-shield atomizer: Achieving extremely low detection limits with inexpensive instrumentation

This work describes the method of a selective hydride generation-cryotrapping (HG-CT) coupled to an extremely sensitive but simple in-house assembled and designed atomic fluorescence spectrometry (AFS) instrument for determination of toxicologically important As species. Here, an advanced flame-in-gas-shield atomizer (FIGS) was interfaced to HG-CT and its performance was compared to a standard miniature diffusion flame (MDF) atomizer. A significant improvement both in sensitivity and baseline noise was found that was reflected in improved (4 times) limits of detection (LODs). The yielded LODs with the FIGS atomizer were 0.44, 0.74, 0.15, 0.17 and 0.67 ng L–1 for arsenite, total inorganic, mono-, dimethylated As and trimethylarsine oxide, respectively. Moreover, the sensitivities with FIGS and MDF were equal for all As species, allowing for the possibility of single species standardization with arsenate standard for accurate quantification of all other As species. The accuracy of HG-CT-AFS with FIGS was verified by speciation analysis in two samples of bottled drinking water and certified reference materials, NRC CASS-5 (nearshore seawater) and SLRS-5 (river water) that contain traces of methylated As species. As speciation was in agreement with results previously reported and sums of all quantified species corresponded with the certified total As. The feasibility of HG-CT-AFS with FIGS was also demonstrated by the speciation analysis in microsamples of exfoliated bladder epithelial cells isolated from human urine. The results for the sums of trivalent and pentavalent As species corresponded well with the reference results obtained by HG-CT-ICPMS (inductively coupled plasma mass spectrometry).

Direct analysis and stability of methylated trivalent arsenic metabolites in cells and tissues

Chronic ingestion of water containing inorganic arsenic (iAs) has been linked to a variety of adverse health effects, including cancer, hypertension and diabetes. Current evidence suggests that the toxic methylated trivalent metabolites of iAs, methylarsonous acid (MAs(III)) and dimethylarsinous acid (DMAs(III)) play a key role in the etiology of these diseases. Both MAs(III) and DMAs(III) have been detected in urine of subjects exposed to iAs. However, the rapid oxidation of DMAs(III) and, to a lesser extent, MAs(III) in oxygen-rich environments leads to difficulties in the analysis of these metabolites in samples of urine collected in population studies. Results of our previous work indicate that MAs(III) and DMAs(III) are relatively stable in a reducing cellular environment and can be quantified in cells and tissues. In the present study, we used the oxidation state-specific hydride generation-cryotrapping-atomic absorption spectroscopy (HG-CT-AAS) to examine the presence and stability of these trivalent metabolites in the liver of mice and in UROtsa/F35 cells exposed to iAs. Tri- and pentavalent metabolites of iAs were analyzed directly (without chemical extraction or digestion). Liver homogenates prepared in cold deionized water and cell culture medium and lysates were stored at either 0 °C or -80 °C for up to 22 days. Both MAs(III) and DMAs(III) were stable in homogenates stored at -80 °C. In contrast, DMAs(III) in homogenates stored at 0 °C began to oxidize to its pentavalent counterpart after 1 day; MAs(III) remained stable for at least 3 weeks under these conditions. MAs(III) and DMAs(III) generated in UROtsa/F35 cultures were stable for 3 weeks when culture media and cell lysates were stored at -80 °C. These results suggest that samples of cells and tissues represent suitable material for the quantitative, oxidation state-specific analysis of As in laboratory and population studies examining the metabolism or toxic effects of this metalloid.

In situ trapping of bismuthine in externally heated quartz tube atomizers for atomic absorption spectrometry

A modification of the externally heated quartz tube atomizer, making possible in situ trapping of bismuthine, is described. The very simple experimental set-up is thus capable of lossless collection at a high preconcentration ratio. The collection/volatilization efficiency is 100 ± 2.5%. For a collection time of 300 s (sample volume of 20 ml), the preconcentration ratio and detection limit (3σ), respectively, are 530 and 3.9 pg ml−1. The same approach is analytically useful also for stibine but not for arsine.

Stibine preconcentration in a quartz trap with subsequent atomization in the quartz multiatomizer for atomic absorption spectrometry

A preliminary evaluation of a simple (bare) quartz tube trap for collection of SbH3 and for volatilization of trapped analyte with subsequent atomization in a multiple microflame quartz tube atomizer (multiatomizer) for atomic absorption spectrometry is presented. The influence of relevant experimental parameters on the collection/volatilization efficiency was investigated. The parameters studied were: collection temperature and time, volatilization temperature and flow rates of air and hydrogen for the volatilization. Under optimized conditions, the collection/volatilization efficiency was 65%. For the collection time of 120 s (sample volume of 8 ml), the detection limit was 3.9 pg ml−1, and the analytical plot was linear up to 1.25 ng ml−1. Possible ways of improving the performance of the set-up as well as the collection/volatilization efficiency are suggested.

Selective hydride generation-cryotrapping-ICP-MS for arsenic speciation analysis at picogram levels: analysis of river and sea water reference materials and human bladder epithelial cells

An ultra sensitive method for arsenic (As) speciation analysis based on selective hydride generation (HG) with preconcentration by cryotrapping (CT) and inductively coupled plasma- mass spectrometry (ICP-MS) detection is presented. Determination of valence of the As species is performed by selective HG without prereduction (trivalent species only) or with L-cysteine prereduction (sum of tri- and pentavalent species). Methylated species are resolved on the basis of thermal desorption of formed methyl substituted arsines after collection at -196°C. Limits of detection of 3.4, 0.04, 0.14 and 0.10 pg mL-1 (ppt) were achieved for inorganic As, mono-, di- and trimethylated species, respectively, from a 500 μL sample. Speciation analysis of river water (NRC SLRS-4 and SLRS-5) and sea water (NRC CASS-4, CASS-5 and NASS-5) reference materials certified to contain 0.4 to 1.3 ng mL-1 total As was performed. The concentrations of methylated As species in tens of pg mL-1 range obtained by HG-CT-ICP-MS systems in three laboratories were in excellent agreement and compared well with results of HG-CT-atomic absorption spectrometry and anion exchange liquid chromatography- ICP-MS; sums of detected species agreed well with the certified total As content. HG-CT-ICP-MS method was successfully used for analysis of microsamples of exfoliated bladder epithelial cells isolated from human urine. Here, samples of lysates of 25 to 550 thousand cells contained typically tens pg up to ng of iAs species and from single to hundreds pg of methylated species, well within detection power of the presented method. A significant portion of As in the cells was found in the form of the highly toxic trivalent species.

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.