Stanislav Musil

Speciation without chromatography using selective hydride generation: inorganic arsenic in rice and samples of marine origin.

Because of the toxicity of inorganic arsenic (iAs), only iAs needs to be monitored in food and feedstuff. This demands the development of easy and quick analytical methods to screen large number of samples. This work focuses on hydride generation (HG) coupled with an ICPMS as an arsenic detector where the HG is added as a selective step to determine iAs in the gaseous phase while organically bound As remains in the solution. iAs forms volatile arsine species with high efficiency when treated with NaBH4 at acidic conditions, whereas most other organoarsenic compounds do not form any or only less volatile arsines. Additionally, using high concentrations of HCl further reduces the production of the less volatile arsines and iAs is almost exclusively formed, therefore enabling to measure iAs without a prior step of species separation using chromatography. Here, we coupled a commercially available HG system to an ICPMS and optimized for determination of iAs in rice and samples of marine origin using different acid concentrations, wet and dry plasma conditions, and different reaction gas modes. Comparing this method to conventional HPLC-ICPMS, no statistical difference in iAs concentration was found and comparable limits of detections were achieved using less than half the instrument time.

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).

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.

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.

Loss of di- and trimethylarsine on Nafion membrane dryers following hydride generation

Complete loss of trimethylarsine upon passage through a Nafion membrane dryer was identified. Pronounced loss of dimethylarsine—19 and 66%, depending on dryer dimensions—was also observed; arsine and methylarsine did not exhibit significant losses. Arsines were generated from corresponding precursors at the 2 ng ml−1 level by tetrahydroborate reduction, after passing through the dryer separated by cryotrapping and thermal desorption and detected by atomic absorption spectrometry with a quartz multiatomizer. Since Nafion membrane dryers have been commonly used in analytical atomic spectroscopy, implications for trace and speciation analysis of arsenic are discussed. A dryer based on sodium hydroxide pellets is proposed as an alternative, safe for all arsines.

Hydride generation ICP-MS as a simple method for determination of inorganic arsenic in rice for routine biomonitoring

The inorganic arsenic (iAs) concentration was measured in 44 rice product samples, covering a wide range, using both hydride generation (HG) ICP-MS and HPLC-ICP-MS. Linear regression showed good linearity (R2 of 0.99) with a slope close to 1 (0.969 ± 0.015) and similar sensitivity showing that HPLC can robustly be replaced by a simple HG system, shortening the measurement time and resulting in easier data treatment as no manual integration of peaks is necessary. With upcoming regulations on the iAs concentration in rice in the EU, it is important that regulators do not prescribe only one standard method since it excludes new instrumental developments.

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.

Achieving 100% Efficient Postcolumn Hydride Generation for As Speciation Analysis by Atomic Fluorescence Spectrometry

An experimental setup consisting of a flow injection hydride generator coupled to an atomic fluorescence spectrometer was optimized in order to generate arsanes from tri- and pentavalent inorganic arsenic species (iAs(III), iAs(V)), monomethylarsonic acid (MAs(V)), and dimethylarsinic acid (DMAs(V)) with 100% efficiency with the use of only HCl and NaBH4 as the reagents. The optimal concentration of HCl was 2 mol L(-1); the optimal concentration of NaBH4 was 2.5% (m/v), and the volume of the reaction coil was 8.9 mL. To prevent excessive signal noise due to fluctuations of hydride supply to an atomizer, a new design of a gas-liquid separator was implemented. The optimized experimental setup was subsequently interfaced to HPLC and employed for speciation analysis of arsenic. Two chromatography columns were tested: (i) ion-pair chromatography and (ii) ion exchange chromatography. The latter offered much better results for human urine samples without a need for sample dilution. Due to the equal hydride generation efficiency (and thus the sensitivities) of all As species, a single species standardization by DMAs(V) standard was feasible. The limits of detection for iAs(III), iAs(V), MAs(V), and DMAs(V) were 40, 97, 57, and 55 pg mL(-1), respectively. Accuracy of the method was tested by the analysis of the standard reference material (human urine NIST 2669), and the method was also verified by the comparative analyses of human urine samples collected from five individuals with an independent reference method.

Hydride generation – in-atomizer collection of Pb in quartz tube atomizers for atomic absorption spectrometry – a 212Pb radiotracer study

Lead preconcentration on the quartz surface after plumbane generation was extensively studied in the separate quartz trap or in the compact trap-and-atomizer device by means of a laboratory prepared 212Pb radioactive indicator. Plumbane generation efficiency of 95% was found. A large surface area is required for sufficient analyte trapping as found by autoradiography. The lead trapping efficiency in the separate trap is around 85% at 300 °C whereas 100% trapping is reached in the trap-and-atomizer device at the same temperature due to its greater inner surface. Volatilization of the trapped lead species at 800 °C is efficient for both the separate quartz trap and the trap-and-atomizer device. The non-volatilized lead fraction was below 5% in the trap-and-atomizer device at 800 °C. The non-volatilized lead fraction increases substantially in the presence of Bi. This was proved to be the mechanism of the serious Bi interference. Although 1–10 ng of analyte is typically preconcentrated in ultratrace analysis the quartz trap is capable of efficient trapping and subsequent volatilization of up to 200 ng Pb.