G. M. Mizanur Rahman

Simultaneous extraction of arsenic and selenium species from rice products by microwave-assisted enzymatic extraction and analysis by ion chromatography-inductively coupled plasma-mass spectrometry.

A microwave-assisted enzymatic extraction (MAEE) method was developed for the simultaneous extraction of arsenic (As) and selenium (Se) species in rice products. The total arsenic and selenium content in the enzymatic extracts were determined by inductively coupled plasma mass spectrometry (ICP-MS), while the speciation analysis was performed by ion chromatography coupled to inductively coupled plasma-mass spectrometry (IC-ICP-MS). The main factors affecting the enzymatic extraction process were evaluated in NIST SRM-1568a rice flour. The optimum extraction conditions were 500 mg of sample, 50 mg of protease XIV, and 25 mg of alpha-amylase in aqueous medium during 40 min at 37 degrees C. The extraction recoveries of total As and Se reached 100 +/- 3 and 80 +/- 4%, respectively. The species stability study during the MAEE process did not show transformation of the target species in rice products. The results of As speciation obtained for SRM-1568a were in agreement with previous studies of As speciation performed on the same reference material. The proposed method was applied to the determination of As and Se species in rice and rice-based cereals. Arsenite [As(III)], arsenate [As(V)], dimethylarsinic acid (DMA), and selenomethionine (SeMet) were the predominant species identified in rice products.

Simultaneous determination of arsenic and selenium species in fish tissues using microwave-assisted enzymatic extraction and ion chromatography-inductively coupled plasma mass spectrometry.

A microwave-assisted enzymatic extraction (MAEE) method was developed for the simultaneous extraction of arsenic (As) and selenium (Se) species in fish tissues. The extraction efficiency of total As and Se and the stability of As and Se species were evaluated by analyzing DOLT-3 (dogfish liver). Enzymatic extraction using pronase E/lipase mixture assisted by microwave energy was found to give satisfactory extraction recoveries for As and Se without promoting interspecies conversion. The optimum extraction conditions were found to be 0.2 g of sample, 20 mg pronase E and 5mg lipase in 10 mL of 50 mM phosphate buffer, pH 7.25 at 37 degrees C. The total extraction time was 30 min. The speciation analysis was performed by ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS). The accuracy of the developed extraction procedure was verified by analyzing two reference materials, DOLT-3 and BCR-627. The extraction recoveries in those reference materials ranged between 82 and 94% for As and 57 and 97% for Se. The accuracy of arsenic species measurement was tested by the analysis of BCR 627. The proposed method was applied to determine As and Se species in fish tissues purchased from a local fish market. Arsenobetaine (AsB) and selenomethionine (SeMet) were the major species detected in fish tissues. In the analyzed fish extracts, the sum of As species detected was in good agreement with the total As extracted. However, for Se, the sum of its species was lower than the total Se extracted, revealing the presence of Se-containing peptides or proteins.

Comparison of methods with respect to efficiencies, recoveries, and quantitation of mercury species interconversions in food demonstrated using tuna fish

AbstractEight different analytical extraction procedures commonly used to extract mercury species from biological samples were evaluated by analyzing Tuna Fish Tissue Certified Reference Material (ERM-CE464) certified for the content of total mercury and methylmercury. Speciated isotope dilution mass spectrometry (SIDMS; US Environmental Protection Agency’s method 6800) was utilized to evaluate and effectively compensate for potential errors during measurement and accurately quantify mercury species using all the extraction methods. SIDMS was used to accurately evaluate species transformations during sample pretreatment, preparation and analysis protocols. The extraction methods tested in this paper were based on alkaline extraction with KOH or tetramethylammonium hydroxide; acid leaching with HCl, HNO3 or CH3COOH; extraction with l-cysteine hydrochloride; and enzymatic digestion with protease XIV. Detection of total mercury and mercury species from all extraction methods was carried out by inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography–ICP-MS, respectively. Microwave-assisted extraction and ultrasound-assisted extraction were found to be the most efficient alkaline digestion protocols that caused the lowest levels of transformation of mercury species (6% or less). Extraction with 5 M HCl or enzymatic digestion with protease resulted in the second-highest extraction efficiency, with relatively lower transformation of methylmercury to inorganic mercury (3 and 1.4%, respectively). Despite frequent use of acid leaching for the extraction of mercury species from tuna fish samples, the lowest extraction efficiencies and the highest mercury species transformation were obtained when microwave-assisted extraction with 4 M HNO3 or CH3COOH was used. Transformations as high as 30% were found using some literature protocols; however, all the extractions tested produced accurate quantitation when corrected in accordance with the SIDMS method standardized in the US Environmental Protection Agency’s method 6800. FigureDeterminative CRM Tuna Fish Tissue Methylmercury Calibration vs. Determinative Calculation.

Robust microwave-assisted extraction protocol for determination of total mercury and methylmercury in fish tissues

A rapid and efficient closed vessel microwave-assisted extraction (MAE) method based on acidic leaching was developed and optimized for the extraction of total mercury (Hg), inorganic mercury (Hg(2+)) and methylmercury (CH(3)Hg(+)) from fish tissues. The quantitative extraction of total Hg and mercury species from biological samples was achieved by using 5molL(-1) HCl and 0.25molL(-1) NaCl during 10min at 60 degrees C. Total Hg content was determined using inductively coupled plasma mass spectrometry (ICP-MS). Mercury species were measured by liquid chromatography hyphenated with inductively coupled plasma mass spectrometry (LC-ICP-MS). The method was validated using biological certified reference materials ERM-CE464, DOLT-3, and NIST SRM-1946. The analytical results were in good agreement with the certified reference values of total Hg and CH(3)Hg(+) at a 95% confidence level. Further, accuracy validation using speciated isotope-dilution mass spectrometry (SIDMS, as described in the EPA Method 6800) was carried out. SIDMS was also applied to study and correct for unwanted species transformation reactions during and/or after sample preparation steps. For the studied reference materials, no statistically significant transformation between mercury species was observed during the extraction and determination procedures. The proposed method was successfully applied to fish tissues with good agreement between SIDMS results and external calibration (EC) results. Interspecies transformations in fish tissues were slightly higher than certified reference materials due to differences in matrix composition. Depending on the type of fish tissue, up to 10.24% of Hg(2+) was methylated and up to 1.75% of CH(3)Hg(+) was demethylated to Hg(2+).

Development of a microwave-assisted extraction method and isotopic validation of mercury species in soils and sediments

An efficient and rapid closed vessel microwave-assisted extraction method based on an acidic extractant has been developed to determine inorganic mercury and methylmercury in soils and sediments. Parameters optimized during this study were nitric acid concentration, amount of sample, extraction temperature and irradiation time. The results suggest that the nitric acid concentration and the irradiation temperature are statistically significant both for extraction efficiency and for stability of mercury species. A processed topsoil (Hg < 0.01 ng g−1) spiked with inorganic mercury and methylmercury and SRM 2711 (spiked with methylmercury) were used during the method development. The sample preparation was optimized in a closed-vessel system by heating 1.0 g of sample in 10.0 ml of 4.0 mol l−1 HNO3 for 10 min at 100 °C with magnetic stirring. Analyses of the extracts were carried out by using three types of instruments, Direct Mercury Analyzer-80 (DMA-80), inductively coupled plasma mass spectrometer (ICP-MS) and high-performance liquid chromatograph coupled with inductively coupled plasma mass spectrometer (HPLC-ICP-MS). The results obtained from each of these detection techniques agreed significantly at the 95% confidence level. The method was validated by the analyses of two types of specifically prepared reference soil samples and four certified reference materials (BCR 580, SRM 2704, SRM 2709 and SRM 1941a). The inorganic mercury and methylmercury concentrations found were in good agreement at the 95% confidence level with the certified or “made-to” value. The method was also validated using EPA Method 6800 as a diagnostic tool to check whether interconversion of inorganic mercury to methylmercury or vice versa took place during or after extraction; the amount of such interconversions was found to be statistically negligible. The method is in the process of consideration and adopted by the United States Environmental Protection Agency (US EPA) as a primary mercury species extraction protocol from soils and sediments in EPA draft Method 3200.

Measurement of mercury species in whole blood using speciated isotope dilution methodology integrated with microwave-enhanced solubilization and spike equilibration, headspace-solid-phase microextraction, and GC-ICP-MS analysis.

A biomonitoring method was developed for the determination of inorganic-, methyl-, and ethylmercury (Hg(2+), CH3Hg(+), and C2H5Hg(+), respectively) in whole blood by triple-spiking speciated isotope dilution mass spectrometry (SIDMS) using headspace (HS) solid-phase microextraction (SPME) in combination with gas chromatographic (GC) separation and inductively coupled plasma mass spectrometric (ICP-MS) detection. After spiking the blood sample with isotopically enriched analogues of the analytes ((199)Hg(2+), CH3(200)Hg(+) and C2H5(201)Hg(+)), the endogenous Hg species were solubilized in 2.0 mol L(-1) HNO3 and equilibrated with the spikes using a microwave-enhanced protocol. The microwaved sample was treated with a 1% (w/v) aqueous solution of sodium tetrapropylborate (buffered to pH 5.2), and the propylated Hg species were sampled in the HS using a Carboxen/polydimethylsiloxane-coated SPME fiber. The extracted species were thermally desorbed from the fiber in the GC injection port and determined by GC-ICP-MS. The analytes were quantified, with simultaneous correction for their method-induced transformation, on the basis of the mathematical relationship in triple-spiking SIDMS. The method was validated using a bovine blood standard reference material (SRM 966, Level 2). Analysis of human blood samples demonstrated the accuracy and reproducibility of the method, which can detect the Hg species down to 30 pg g(-1) in blood. The validity of the analytical results found for the blood samples was demonstrated using mass balance by comparing the sum of the concentrations of the individual Hg species with the total Hg in the corresponding samples; the latter was determined by isotope dilution mass spectrometry (IDMS) after decomposing the blood using EPA Method 3052 with single-spiking.

Application of speciated isotope dilution mass spectrometry to evaluate methods for efficiencies, recoveries, and quantification of mercury species transformations in human hair

Nine different analytical extraction methods commonly used for mercury speciation in human hair samples were evaluated by analyzing hair certified reference material (IAEA-085) certified for the content of monomethyl mercury and total mercury. Extraction efficiencies, recoveries, as well as their potential of species transformations during sample processing, were evaluated by applying speciated isotope dilution mass spectrometry (SIDMS) as both a quantitative and diagnostic tool. The extraction methods evaluated in this study were based on acid leaching with HCl and HNO3. Detection of total mercury and mercury species from all extraction methods were carried out by inductivley coupled plasma mass spectrometry (ICP-MS) and high performance liquid chromatography-ICP-MS, respectively. Microwave-assisted extraciton (4 mol l−1 HNO3, at 100 °C for 10 min) and mechanical shaking (2 mol l−1HCl, at room temperature for 24 h) were found to be the most efficient protocols that demonstrated approximately 100% mecury recovery with less species transformations (6% or less). Ultrasound-assisted extraction (2% HCl + 10% ethanol, at 60 °C for 7 min) or extraction with 2 mol l−lHCl in a water bath (at 100 °C for 5 min) resulted in the second highest extraction efficiency (∼90%) with little or no mercury species transformations. Demethylation as high as 22% using 5 mol l−1 HNO3 in a water-bath heating (at 100 °C for 2 h) and 90% with cold acid digestion using concentrated HNO3 and H2O2 (room temperature for 24 h) were observed, however, all the extraction methods tested produced accurate quantitation when corrected in accordance with the SIDMS method standardized in the US Environmental Protection Agencys method 6800.

Determination of Chromium Species in Dietary Supplements Using Speciated Isotope Dilution Mass Spectrometry with Mass Balance

In order to determine the health impact of chromium in dietary supplements, the Cr(III) and Cr(VI) must be independently measured and verified with mass balance (sum of both species equaling independent measurements of total chromium), as both may be present in finished products. Because Cr(III) is stable in acidic conditions and Cr(VI) in alkaline conditions, interconversions between species may occur in complex matrices and during analytical extraction, increasing the difficulty of quantification. A study was conducted to determine Cr(VI) and Cr(III) in dietary supplements. EPA Method 3060A extraction protocol was performed to extract Cr(VI), and EPA Method 3052 was performed on the extracted residue to digest the remaining Cr(III). Speciated isotope dilution mass spectrometry (SIDMS), as described in the EPA Method 6800 (update V), was implemented with ion-exchange chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS). Method 6800 uniquely enables tracking and correcting for the bidirectional chromium interspecies conversions that occur during extraction and sample handling prior to instrumental analysis. Mass balance results indicated that the off-the-shelf dietary supplements analyzed during this study contained hexavalent chromium ranging from <DL (detection limit) to 122.4 ± 13.0 μg/g, which corresponds to concentrations from below detection levels to up to 16% of the total chromium content. This type of variation in the final products raises public health issues and points to a need to use a robust method that can accurately and reliably make species measurements including correcting for species conversions.

Speciation analysis of arsenic in prenatal and children's dietary supplements using microwave-enhanced extraction and ion chromatography-inductively coupled plasma mass spectrometry.

A study was conducted to develop a microwave-enhanced extraction method for the determination of arsenic species in prenatal and childrens dietary supplements prepared from plant materials. The method was optimized by evaluating the efficiency of various solutions previously used to extract arsenic from the types of plant materials used in the dietary supplement formulations. A multivitamin standard reference material (NIST SRM 3280) and a prenatal supplement sample were analyzed in the method optimization. The identified optimum conditions were 0.25 g of sample, 5 mL of 0.3 mol L(-1) orthophosphoric acid (H3PO4) and microwave heating at 90 °C for 30 min. The extracted arsenic was speciated by cation exchange ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS). The method detection limit (MDL) for the arsenic species was in the range 2-8 ng g(-1). Ten widely consumed prenatal and childrens dietary supplements were analyzed using the optimized protocol. The supplements were found to have total arsenic in the concentration range 59-531 ng g(-1). The extraction procedure recovered 61-92% of the arsenic from the supplements. All the supplementary products were found to contain arsenite (As(3+)) and dimethylarsinic acid (DMA). Arsenate (As(5+)) was found in two of the supplements, and an unknown specie of arsenic was detected in one product. The results of the analysis were validated using mass balance by comparing the sum of the extracted and non-extracted arsenic with the total concentration of the element in the corresponding samples.

Determination and evaluation of hexavalent chromium in power plant coal combustion by-products and cost-effective environmental remediation solutions using acid mine drainage

The chromium species leaching from a coal combustion fly ash landfill has been characterized as well as a novel approach to treat leachates rich in hexavalent chromium, Cr(VI), by using another natural waste by-product, acid mine drainage (AMD), has been investigated during this study. It is observed that as much as 8% (approximately 10 microg g(-1) in fly ash) of total chromium is converted to the Cr(VI) species during oxidative combustion of coal and remains in the resulting ash as a stable species, however, it is significantly mobile in water based leaching. Approximately 1.23 +/- 0.01 microg g(-1) of Cr(VI) was found in the landfill leachate from permanent deposits of aged fly ash. This study also confirmed the use of AMD, which often is in close proximity to coal combustion by-product landfills, is an extremely effective and economical remediation option for the elimination of hexavalent chromium in fly ash generated leachate. Speciated isotope dilution mass spectrometry (SIDMS), as described in EPA Method 6800, was used to analytically evaluate and validate the field application of the ferrous iron and chromate chemistry in the remediation of Cr(VI) runoff.