Samuel S. de Souza

Speciation of arsenic in rice and estimation of daily intake of different arsenic species by Brazilians through rice consumption

Rice is an important source of essential elements. However, rice may also contain toxic elements such as arsenic. Therefore, in the present study, the concentration of total arsenic and five main chemical species of arsenic (As(3+), As(5+), DMA, MMA and AsB) were evaluated in 44 different rice samples (white, parboiled white, brown, parboiled brown, parboiled organic and organic white) from different Brazilian regions using high-performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The mean level of total arsenic was 222.8 ng g(-1) and the daily intake of inorganic arsenic (the most toxic form) from rice consumption was estimated as 10% of the Provisional Tolerable Daily Intake (PTDI) with a daily ingestion of 88 g of rice. Inorganic arsenic (As(3+), As(5+)) and dimethylarsinic acid (DMA) are the predominant forms in all samples. The percentages of species were 38.7; 39.7; 3.7 and 17.8% for DMA, As(3+), MMA and As(5+), respectively. Moreover, rice samples harvested in the state of Rio Grande do Sul presented more fractions of inorganic arsenic than rice in Minas Gerais or Goiás, which could lead to different risks of arsenic exposure.

Methylmercury and inorganic mercury determination in blood by using liquid chromatography with inductively coupled plasma mass spectrometry and a fast sample preparation procedure.

Despite the necessity to differentiate chemical species of mercury in clinical specimens, there are a limited number of methods for this purpose. Then, this paper describes a simple method for the determination of methylmercury and inorganic mercury in blood by using liquid chromatography with inductively coupled mass spectrometry (LC-ICP-MS) and a fast sample preparation procedure. Prior to analysis, blood (250microL) is accurately weighed into 15-mL conical tubes. Then, an extractant solution containing mercaptoethanol, l-cysteine and HCl was added to the samples following sonication for 15min. Quantitative mercury extraction was achieved with the proposed procedure. Separation of mercury species was accomplished in less than 5min on a C18 reverse-phase column with a mobile phase containing 0.05% (v/v) mercaptoethanol, 0.4% (m/v) l-cysteine, 0.06molL(-1) ammonium acetate and 5% (v/v) methanol. The method detection limits were found to be 0.25microgL(-1) and 0.1microgL(-1) for inorganic mercury and methylmercury, respectively. Method accuracy is traceable to Standard Reference Material (SRM) 966 Toxic Metals in Bovine Blood from the National Institute of Standards and Technology (NIST). The proposed method was also applied to the speciation of mercury in blood samples collected from fish-eating communities and from rats exposed to thimerosal. With the proposed method there is a considerable reduction of the time of sample preparation prior to speciation of Hg by LC-ICP-MS. Finally, after the application of the proposed method, we demonstrated an interesting in vivo ethylmercury conversion to inorganic mercury.

Mercury speciation in seafood samples by LC-ICP-MS with a rapid ultrasound-assisted extraction procedure: Application to the determination of mercury in Brazilian seafood samples.

This paper describes a simple method for mercury speciation in seafood samples by LC-ICP-MS with a fast sample preparation procedure. Prior to analysis, mercury species were extracted from food samples with a solution containing mercaptoethanol, l-cysteine and HCl and sonication for 15min. Separation of mercury species was accomplished in less than 5min on a C8 reverse phase column with a mobile phase containing 0.05%-v/v mercaptoethanol, 0.4%m/v l-cysteine and 0.06molL(-1) ammonium acetate. The method detection limits were found to be 0.25, 0.20 and 0.1ngg(-1) for inorganic mercury, ethylmercury and methylmercury, respectively. Method accuracy is traceable to Certified Reference Materials (DOLT-3 and DORM-3) from the National Research Council Canada (NRCC). With the proposed method there is a considerable reduction of the time of sample preparation. Finally, the method was applied for the speciation of mercury in seafood samples purchased from the Brazilian market.

A simple method for methylmercury, inorganic mercury and ethylmercury determination in plasma samples by high performance liquid chromatography–cold-vapor-inductively coupled plasma mass spectrometry

A simple and sensitive method with a fast sample preparation procedure is proposed for the determination of mercury species in plasma/serum. The method combines online high-performance liquid chromatography separation, Hg cold-vapor formation and inductively coupled plasma mass spectrometry detection. Prior to analysis, plasma (250 μL) was accurately pipetted into 15 mL conical tubes. Then, an extractant solution containing mercaptoethanol, L-cysteine and HCl was added to the samples following sonication for 10 min. Quantitative mercury extraction was achieved with the proposed procedure. Separation of mercury species was accomplished in less than 8 min on a C8 reverse phase column with a mobile phase containing 3% v/v methanol + 97% v/v (0.5% v/v 2-mercaptoethanol + 0.05% v/v formic acid). The method detection limits were found to be 12 ng L(-1), 5 ng L(-1) and 4 ng L(-1) for inorganic mercury, ethylmercury and methylmercury, respectively. Method accuracy is traceable to Standard Reference Material (SRM) 966 Toxic Metals in Bovine Blood from NIST. Additional validation was provided by the analysis of a secondary reference serum sample from the INSQ-Canada. Finally, the method was successfully applied for the speciation of mercury in plasma samples collected from volunteers exposed to methylmercury through fish consumption. For the first time to our knowledge, levels of different species of Hg in plasma samples from riverside populations exposed to MeHg were determined.

A fast sample preparation procedure for mercury speciation in hair samples by high-performance liquid chromatography coupled to ICP-MS

A simple method for mercury speciation in hair samples with a fast sample preparation procedure using high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry is proposed. Prior to analysis, 50 mg of hair samples were accurately weighed into 15 mL conical tubes. Then, an extractant solution containing mercaptoethanol, L-cysteine and HCl was added to the samples following sonication for 10 min. Quantitative mercury extraction was achieved with the proposed procedure. Separation of inorganic mercury (Ino-Hg), methylmercury (Met-Hg) and ethylmercury (Et-Hg) was accomplished in less than 8 min on a C18 reverse phase column with a mobile phase containing 0.05% v/v mercaptoethanol, 0.4% m/v L-cysteine, 0.06 mol L−1 ammonium acetate and 5% v/v methanol. The method detection limits were found to be 15 ng g−1, 10 ng g−1 and 38 ng g−1, for inorganic mercury, methylmercury and ethylmercury, respectively. Sample throughput is 4 samples h−1 (duplicate). A considerable improvement in the time of analysis was achieved when compared to other published methods. Method accuracy is traceable to Certified Reference Materials (CRMs) 85 and 86 human hair from the International Atomic Energy Agency (IAEA). Finally, the proposed method was successfully applied to the speciation of mercury in hair samples collected from fish-eating communities of the Brazilian Amazon.

Determination of total and inorganic mercury in whole blood by cold vapor inductively coupled plasma mass spectrometry (CV ICP-MS) with alkaline sample preparation

A simple method with a fast sample preparation procedure for total and inorganic mercury determinations in blood samples is proposed based on flow injection cold vapor inductively coupled plasma mass spectrometry (FI-CV ICP-MS). Aliquots of whole blood (500 µL) are diluted 1 + 1 v/v with 10.0% v/v tetramethylammonium hydroxide (TMAH) solution, incubated for 3 h at room temperature and then further diluted 1 + 4 v/v with 2.0% v/v HCl. The inorganic Hg was released by on-line addition of L-cysteine and then reduced to elemental Hg by SnCl2. On the other hand, total mercury was determined by on-line addition of KMnO4 and then reduced to elemental Hg by NaBH4. Samples were calibrated against matrix-matching. The method detection limit was found to be 0.80 µg L−1 and 0.08 µg L−1 for inorganic and total mercury, respectively. Sample throughput is 20 samples h−1. The method accuracy is traceable to Standard Reference Material (SRM) 966 Toxic Metals in Bovine Blood from the National Institute of Standards and Technology (NIST). For additional validation purposes, human whole blood samples were analyzed by the proposed method and by an established CV AAS method, with no statistical difference between the two techniques at 95% confidence level on applying the t-test.

Cryogenic sample grinding for copper, lead and manganese determination in human teeth by slurry sampling GFAAS

A simple method is proposed for copper, lead and manganese determination in deciduous teeth by graphite furnace atomic absorption spectrometry (GFAAS) using slurry sampling introduction and cryogenic sample preparation. Teeth samples were ground in a cryogenic mill in two steps: pre-cooling (5 min) and cryogenic grinding (2 min) in liquid nitrogen. After grinding, 90% of the sample particles were lower than 150 µm. The minimum mass necessary for slurry preparation as an indicator of sub-sample homogeneity was evaluated by weighting masses between 5 and 20 mg directly in autosampler cups, followed by addition of 1 mL of a solution containing 0.04% Triton® X-100 and 0.2% v/v HNO3. Samples (20 µL) were sonicated during 20 s, before delivering into a W–Rh coated platform. Detection limits based on integrated absorbance were 34.0 ng g−1 Pb, 7.4 ng g−1 Mn and 18.0 ng g−1 Cu for 2% m/v slurries. W–Rh permanent modifier permitted calibration against aqueous standards. The Certified Reference Material (H-5 animal bone) from the International Agency of Atomic Energy (IAEA) was analyzed to determine lead for method validation. For copper, lead and manganese, 12 human teeth samples were analyzed using the proposed method with calibration against aqueous solution and using a comparative Pd/Mg method with the same digested samples, and standard addition calibration, with no statistical difference at 95% level on applying the t-test.

A fast method for the determination of 16 elements in hair samples by inductively coupled plasma mass spectrometry (ICP-MS) with tetramethylammonium hydroxide solubilization at room temperature

This paper describes a simple and fast method for the determination of Se, Pb, Cd, Mn, Co, Zn, Cu, Pt, U, Tl, As, Mg, Cr, Be, Ag and Ni in hair by using inductively coupled plasma spectrometry (ICP-MS). Prior to analysis, 50–100 mg of hair samples were accurately weighed into (15 mL) conical tubes. Then, 1 mL of 25% m/v tetramethylammonium hydroxide (TMAH) solution was added to the samples, incubated at room temperature overnigh and then further diluted to 10 mL with 1% v/v HNO3. After that, samples were directly analyzed by ICP-MS (ELAN DRC II). Rhodium was used as internal standard. Calibration was performed with standards containing 1.0 mg mL−1 of L-cysteine. The method detection limits were 4.0; 0.8; 0.06; 0.8; 0.02; 3.5; 2.3; 0.005; 0.03; 0.02; 0.4; 0.03; 0.09; 0.07; 0.09; 2.0 ng g−1 for Se, Pb, Cd, Mn, Co, Zn, Cu, Pt, U, Tl, As, Mg, Cr, Be, Ag and Ni, respectively. Method accuracy is traceable to Certified Reference Materials (CRMs) 85 and 86 human hair from the International Atomic Energy Agency (IAEA). Additional validation data are provided based on the analysis of hair samples from the trace elements intercomparison program operated by the Institut National de Sante Publique du Quebec, Canada. With the proposed method at least 500 hair samples can be solubilized and analyzed in 3–4 days.

Direct determination of selenium in whole blood by electrothermal atomic absorption spectrometry using W–Rh-coated platform and co-injection of Rh as thermal stabilizer

Abstract A W–Rh coating on the integrated platform of a transversely heated graphite atomizer (platform modifier) and a RhCl3 solution (analyte/matrix modifier) were combined for the direct determination of selenium in whole blood by electrothermal atomic absorption spectrometry. Samples were diluted 1+4 v/v with a mixture of 0.2% v/v HNO3 and 0.5% v/v Triton X-100. For the analysis, 12 μl of the resulting sample plus 6 μl of the Rh solution were delivered into the transversely heated graphite atomizer (THGA) platform modified with W–Rh. The combined use of Rh solution with the W–Rh coating was decisive in increasing the maximum pyrolysis temperature of blood selenium up to 1300 °C. Use of W–Rh as a platform modifier increased the tube useful lifetime up to 200% when compared to an untreated platform using a conventional [Pd+Mg(NO3)2] modifier. The accuracy and precision of the method proposed were verified by analyzing serum certified reference material (Seronorm™) and 20 whole blood samples using Pd/Mg(NO3)2 modifier in untreated platforms; no statistical differences were found between methods by applying the t-test at the 95% level.

In situ trapping of selenium hydride in rhodium-coated tungsten coil electrothermal atomic absorption spectrometry

A flow injection hydride generation manifold was coupled to a tungsten coil electrothermal atomizer for in situ collection of selenium. This strategy exploits selenium hydride trapping onto a double-layer coiled tungsten filament coated with rhodium. The hydride flows through a capillary quartz tube (20 mm long × 1.3 mm od × 0.5 mm id) positioned 1 mm from the modified tungsten coil surface. The capillary can be either inserted in the tip of the autosampler arm by replacing the last section of the PTFE sample delivery tube, or can be fixed in a silicone stopper. Signal stability and repeatability were observed over 300 atomization cycles using 300 µg Rh thermally reduced over the tungsten coil surface. The coil lifetime was extended to at least 2000 firings at 2300 °C. An enrichment factor of 200 was obtained for selenium after 60 s of hydride trapping for a sample flowing at 2.5 ml min−1. The detection limit, based on three times the standard deviation of the blank, was 50 ng l−1 Se with a sample throughput of 40 h−1. Method accuracy was evaluated by analysing ordinary mineral water using the proposed method and hydride generation atomic fluorescence spectrometry and water reference materials from the National Institute of Standards and Technology (SRM 1640 Trace Elements in Natural Water) and from High-purity Standards (Trace Metals in Drinking Water). No statistical differences were found between the values encountered by both techniques and the certified values by applying a t-test at the 95% confidence level.