Non-chromatographic screening procedure for arsenic speciation analysis in fish-based baby foods by using electrothermal atomic absorption spectrometry

A procedure for the speciation analysis of arsenic in fish-based baby foods is presented. Inorganic arsenic, methylarsonic acid (MA), dimethylarsinic acid (DMA) and arsenobetaine (AB) were determined by electrothermal atomic absorption spectrometry (ETAAS) using suspensions prepared in a 0.01 mol L⁻¹ tetramethylammonium hydroxide (TMAH) solution. Speciation is based on the use of three different chemically modified ETAAS atomizers to obtain the analytical signals. Using a palladium salt as the chemical modifier, the signal corresponding to the total arsenic concentration is obtained. When palladium is replaced by Ce(IV), the signal is solely due to inorganic arsenic (III and V) + MA. If no signal is obtained in this latter case, it is possible to distinguish between DMA and AB using a zirconium coated atomizer. The signal obtained in this way is due solely to DMA, and the concentration of AB can be obtained by the difference with the total arsenic content. Determinations by ETAAS require the use of the standard additions method. The limits of detection for the determination of AB, DMA and inorganic arsenic (+MA) are 15, 25 and 50 ng g⁻¹ expressed as arsenic, respectively. These detection limits are good enough for the procedure to be appropriate for the rapid determination of these compounds, avoiding extraction processes and/or chromatographic separations. Data for commercial samples, as well as for four standard reference materials, are given.     

Multivariate optimization of the synthesis and of the microwave dissolution of biomorphic silicon carbide ceramics

Biomorphic silicon carbide ceramics are a new class of materials that are used for various industrial applications owing to its attractive properties. The efficiency of the synthesis and the partly extreme properties of the biomorphic ceramic depend decisively on the synthesis parameters and on the impurities of the final ceramic. In the present article the synthesis as well as the decomposition of these materials is optimized using a multivariate methodology for the design of experiments. Three variables (initial amount of Si, infiltration temperature and reaction time) were considered as factors in the synthesis optimization and six variables (digestion time, ramp time, microwave power, volumes of concentrated HF, HNO₃ and H₂SO₄) in the microwave dissolution optimization. Interactions, between analytical factors and their optimised levels were investigated using full factorial, Plackett–Burman and central composite designs. The synthesis parameters that found higher percentage of SiC (quantified by FTIR) and the digestion procedure that found higher concentrations of metals (Co, Cr and Ni, determined by FI-ETAAS) were considered the optimum.     

A study of the direct determination of Cd, Cr, Cu, Pb and Zn in certified reference materials of soils by solid sampling electrothermal atomic absorption spectrometry

A simple and rapid method for the direct determination of Cd, Cr, Cu, Pb and Zn in soil was developed. The method was developed using three certified reference materials of soil: Eutric Cambisol, Orthic Luvisols and Rendzina, which differed in their matrix composition. Chemical modifiers were essential to achieve reproducible and interference-free signals for the analytes studied. The best results were obtained with a Pd/Mg(NO₃)₂ admixture for the determination of Cd, Pb and Zn and NH₄F for Cu. The combination of W (as a permanent modifier) and Mg(NO₃)₂ provided well-defined signal profiles for Cr. The following spectral lines were used: Cd 228.8 nm, Cr 520.6 nm, Cu 218.2 nm, Pb 205.3 nm and Zn 307.6 nm. The limit of detection was 4.2 ng g^− 1 for Cd, 1.1 μg g^− 1 for Cr, 0.5 μg g^− 1 for Cu, 1.3 μg g^− 1 for Pb and 8.6 μg g^− 1 for Zn for the maximum sample mass used. Under optimized conditions, the analyte and matrix were separated effectively in situ, and aqueous standards could be used for calibration.     

Behavior of Volatile Elements in the Graphite Furnace in the Presence of Silver as Matrix Modifier

The effect of silver, as an aqueous solution of AgNO₃, on the pretreatment and atomization behaviour of As, Cd, Bi, Hg, Pb, Sb, Se, Sn and Tl during electrothermal atomic absorption spectrometry has been investigated. The presence of silver in the graphite furnace leads to thermal stabilisation of all investigated volatile elements to allow higher pyrolysis temperatures. The maximum, loss‐free, pretreatment temperatures (°C) in the presence of 100 µg Ag by atomization from the wall or from a platform are respectively: As (1500°C, –); Cd (800°C, 800°C); Bi (700°C, 700°C); Hg (250°C, –); Pb (600°C, 900°C); Sb (1200°C, 1200°C); Se (1400°C, 1400°C); Sn (1100°C, 1100°C) and Tl (1000°C, 1100°C). Also, silver facilitates a relatively low atomization temperature (°C) from the wall for Cd (1300°C), Bi (1700°C), Pb (1400°C), Se (1900°C) and Tl (1400°C). In addition, silver enhances the measurement sensitivity by a factor of 1.2–1.8.     

Determination of lead in hair and its segmental analysis by solid sampling electrothermal atomic absorption spectrometry

A rapid and practical solid sampling electrothermal atomic absorption spectrometric method was described for the determination of lead in scalp hair. Hair samples were washed once with acetone; thrice with distilled-deionized water and again once with acetone and dried at 75 °C. Typically 0.05 to 1.0 mg of dried samples were inserted on the platforms of solid sampling autosampler. The effects of pyrolysis temperature, atomization temperature, the amount of sample as well as addition of a modifier (Pd/Mg) and/or auxiliary digesting agents (hydrogen peroxide and nitric acid) and/or a surfactant (Triton X-100) on the recovery of lead were investigated. Hair samples were washed once with acetone; thrice with distilled-deionized water and again once with acetone and dried at 75 °C. Typically 0.05 to 1.0 mg of dried samples were inserted on the platforms of solid sampling autosampler. The limit of detection for lead (3σ, N = 10) was 0.3 ng/g The addition of modifier, acids, oxidant and surfactant hardly improved the results. Due to the risk of contamination and relatively high blank values, the lead in hair were determined directly without adding any reagent(s). Finally, the method was applied for the segmental determination of lead concentrations in hair of different persons which is important to know when and how much a person was exposed to the analyte. For this purpose, 0.5 cm of pieces were cut along the one or a few close strands and analyzed by solid sampling.     

X-ray photoelectron spectroscopy study of pyrolytically coated graphite platforms submitted to simulated electrothermal atomic absorption spectrometry conditions

The present work is part of an ongoing project aiming to a better understanding of the mechanisms of atomization on graphite furnace platforms used for electrothermal atomic absorption spectrometry (ETAAS). It reports the study of unused pyrolytic graphite coated platforms of commercial origin, as well as platforms thermally or thermo-chemically treated under simulated ETAAS analysis conditions. X-ray photoelectron spectroscopy (XPS) was employed to study the elements present at the surfaces of the platforms. New, unused platforms showed the presence of molybdenum, of unknown origin, in concentrations up to 1 at.%. Species in two different oxidations states (Mo⁶⁺ and Mo²⁺) were detected by analyzing the Mo 3d spectral region with high resolution XPS. The analysis of the C 1s region demonstrated the presence of several signals, one of these at 283.3 eV related to the presence of Mo carbide. The O 1s region showed also various peaks, including a signal that can be attributed to the presence of MoO₃. Some carbon and oxygen signals were consistent with the presence of CO and C-O- (probably C-OH) groups on the platforms surfaces. Upon thermal treatment up to 2900 °C, the intensity of the Mo signal decreased, but peaks due to Mo oxides (Mo⁶⁺ and Mo⁵⁺) and carbide (Mo²⁺) were still apparent. Thermo-chemical treatment with 3 vol.% HCl solutions and heating up to 2900 °C resulted in further diminution of the Mo signal, with complete disappearance of Mo carbide species. Depth profiling of unused platforms by Ar⁺ ion etching at increasing time periods demonstrated that, upon removal of several layers of carbonaceous material, the Mo signal disappears suggesting that this contamination is present only at the surface of the pyrolytic graphite platform.     

钯涂层石墨炉原子吸收热处理分离测定环境水样中的As~（3＋）／As~（5＋）

本文提出了一种较为简便的测定环境水体中Ａｓ３＋和Ａｓ５＋的方法。在研究了钯涂层石墨管性能的基础上，利用ＡｓＣｌ３的低沸点、高挥发性，在石墨炉升温过程中，使Ａｓ３＋在灰化阶段分离；改变灰化温度可以测定总Ａｓ含量。从而对Ａｓ３＋／Ａｓ５＋分别定量     

Determination of hexavalent chromium in exhaled breath condensate and environmental air among chrome plating workers

Chromium speciation has attracted attention because of the different toxicity of Cr(III), which is considered relatively non-toxic, and Cr(VI), which can cross cell membranes mainly as a chromate anion and has been classified as a class I human carcinogen. The aims of the present study were to measure soluble Cr(VI) levels in environmental samples, to develop a simple method of quantifying Cr(VI) in exhaled breath condensate (EBC), and to follow the kinetics of EBC Cr(VI) in chrome plating workers.Personal air samples were collected from 10 chrome platers; EBC was collected from the same workers immediately after the work shift on Tuesday and before the work shift on the following Wednesday. Environmental and EBC Cr(VI) levels were determined by means of colorimetry and electrothermal absorption atomic spectrometry, respectively.The method of detecting Cr(VI) in environmental air was based on the extraction of the Cr(VI)-diphenylcarbazide (Cr(VI)-DPC) complex in 1-butanol, whereas EBC Cr(VI) was determined using a solvent extraction of Cr(VI) as an ion pair with tetrabutylammonium ion, and subsequent direct determination of the complex (Cr(VI)-DPC) in EBC.Kinetic data showed that airborne Cr(VI) was reduced by 50% in airway lining fluid sampled at the end of exposure and that there was a further 50% reduction after about 15 h. The persistence of Cr(VI) in EBC supports the use of EBC in assessing target tissue levels of Cr(VI).     

Hydride generation-headspace single-drop microextraction-electrothermal atomic absorption spectrometry method for determination of selenium in waters after photoassisted prereduction

A headspace single-drop microextraction (SDME) method has been developed in combination with electrothermal atomic absorption spectrometry for determination of total inorganic Se and Se(IV). SeH₂ is generated in a 40 mL volume closed-vial and trapped onto a Pd(II)-aqueous containing drop that is supported at the needle tip of a high-precision chromatographic syringe. Sample pre-treatment by UV irradiation prior to hydride generation allowed converting Se(VI) into Se(IV), hence, facilitating total Se determination. A fractional factorial design was employed for characterising the effect of relevant variables over SeH₂ trapping. The variables showing the most significant effect were Pd(II) concentration in the drop and extraction time. A preconcentration factor of about 25 is achieved. The limit of detection of Se was 0.15 ng/mL using trapping onto a 3-μL drop and the precision expressed as relative standard deviation was about 3%. The limit of detection could be improved further using repeated sampling of the headspace.