Tomáš Matoušek

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.

Methylated trivalent arsenicals are potent inhibitors of glucose stimulated insulin secretion by murine pancreatic islets

Epidemiologic evidence has linked chronic exposure to inorganic arsenic (iAs) with an increased prevalence of diabetes mellitus. Laboratory studies have identified several mechanisms by which iAs can impair glucose homeostasis. We have previously shown that micromolar concentrations of arsenite (iAs(III)) or its methylated trivalent metabolites, methylarsonite (MAs(III)) and dimethylarsinite (DMAs(III)), inhibit the insulin-activated signal transduction pathway, resulting in insulin resistance in adipocytes. Our present study examined effects of the trivalent arsenicals on insulin secretion by intact pancreatic islets isolated from C57BL/6 mice. We found that 48-hour exposures to low subtoxic concentrations of iAs(III), MAs(III) or DMAs(III) inhibited glucose-stimulated insulin secretion (GSIS), but not basal insulin secretion. MAs(III) and DMAs(III) were more potent than iAs(III) as GSIS inhibitors with estimated IC(50)≤0.1 μM. The exposures had little or no effects on insulin content of the islets or on insulin expression, suggesting that trivalent arsenicals interfere with mechanisms regulating packaging of the insulin transport vesicles or with translocation of these vesicles to the plasma membrane. Notably, the inhibition of GSIS by iAs(III), MAs(III) or DMAs(III) could be reversed by a 24-hour incubation of the islets in arsenic-free medium. These results suggest that the insulin producing pancreatic β-cells are among the targets for iAs exposure and that the inhibition of GSIS by low concentrations of the methylated metabolites of iAs may be the key mechanism of iAs-induced diabetes.

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.

Speciation of arsenic in exfoliated urinary bladder epithelial cells from individuals exposed to arsenic in drinking water.

Background The concentration of arsenic in urine has been used as a marker of exposure to inorganic As (iAs). Relative proportions of urinary metabolites of iAs have been identified as potential biomarkers of susceptibility to iAs toxicity. However, the adverse effects of iAs exposure are ultimately determined by the concentrations of iAs metabolites in target tissues. Objective In this study we examined the feasibility of analyzing As species in cells that originate in the urinary bladder, a target organ for As-induced cancer in humans. Methods Exfoliated bladder epithelial cells (BECs) were collected from urine of 21 residents of Zimapan, Mexico, who were exposed to iAs in drinking water. We determined concentrations of iAs, methyl-As (MAs), and dimethyl-As (DMAs) in urine using conventional hydride generation-cryotrapping-atomic absorption spectrometry (HG-CT-AAS). We used an optimized HG-CT-AAS technique with detection limits of 12–17 pg As for analysis of As species in BECs. Results All urine samples and 20 of 21 BEC samples contained detectable concentrations of iAs, MAs, and DMAs. Sums of concentrations of these As species in BECs ranged from 0.18 to 11.4 ng As/mg protein and in urine from 4.8 to 1,947 ng As/mL. We found no correlations between the concentrations or ratios of As species in BECs and in urine. Conclusion These results suggest that urinary levels of iAs metabolites do not necessarily reflect levels of these metabolites in the bladder epithelium. Thus, analysis of As species in BECs may provide a more effective tool for risk assessment of bladder cancer and other urothelial diseases associated with exposures to iAs.

Selenium hydride atomization, fate of free atoms and spectroscopic temperature in miniature diffusion flame atomizer studied by atomic absorption spectrometry

The mechanism of hydride atomization and the fate of free atoms was investigated in the miniature diffusion flame. Selenium hydride was used as a model for the other hydrides. Mercury vapor was employed as an analyte to study physical processes, such as macroscopic movements and free atom diffusion, controlling the distribution of free analyte atoms in the observation volume, separately from chemical reactions of the free atoms. Free atoms were detected by atomic absorption spectrometry. Spectroscopic temperature measurements based on atomic absorption at 196.1 and 204.0 nm Se lines were used to determine the temperature distribution. The spatial temperature distribution was highly inhomogeneous ranging from 150°C to 1300°C. The whole flame volume is actually a cloud of hydrogen radicals maintaining analyte in the free atom state since hydrogen radicals formed in outer zone of the flame diffuse to its cooler inner parts.

Surfactant assisted chemical vapour generation of silver for AAS and ICP-OES: a mechanistic study

A chemical vapour generation (CVG) procedure for the production of volatile species of Ag was developed and studied using AAS and ICP-OES detection. A characteristic mass of 0.12 ng was achieved using a miniature diffusion flame atomizer-AAS system, whereas a 38-fold higher sensitivity (as cps per ng of introduced analyte) compared with conventional liquid nebulization was obtained with ICP-OES. The overall efficiency of introduction of Ag to the plasma was verified to be over 20%. More than one order of magnitude enhancement of efficiency was obtained by the addition of a surfactant (Triton X-100 in combination with an antifoaming agent), the effect of which, however, cannot be ascribed to the formation of organized media. Experiments concerning the mechanism of the CVG, transport and memory effect are discussed: Ag CVG is not a simple one-step process as is the case for CVG of selenium, but rather a two-step procedure. Transport properties of the volatile Ag species resemble more the transport of the liquid aerosol than a simple gaseous species such as H2Se. Possible alternatives concerning the identity of the volatile metal species are presented.

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.

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.

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.