Comparative study of pretreatment methods for the determination of metals in atmospheric aerosol by electrothermal atomic absorption spectrometry

A comparative study of pretreatment methods for the determination of 10 elements (As, Cd, Pb, V, Ni, Mn, Cr, Cu, Fe, Al) in atmospheric aerosols by electrothermal atomic absorption spectrometry (ETAAS) was conducted. For the digestion of the particulates collected in filters, six methods were compared using a mixture of HNO₃ and HF with or without the addition of various oxidative agents (HClO₄ or H₂O₂) or acids (HCl). The comparative study was performed using loaded cellulose filter samples, which were digested in Parr bombs and heated in a conventional oven at 170 °C for 5 h. The extraction efficiency and blanks were compared and it was proved that the digestion method using only HNO₃–HF extracted most of the metals and gave the lowest blanks. The HNO₃–HF mixture was selected for the development of an improved microwave digestion method specific for aerosol-loaded filters. The operating parameters were optimized, so that quantitative recovery of the reference materials NIST 1649a urban dust and NIST 1648 urban particulate matter was achieved. The blank of cellulose and teflon filters were also determined and compared. Teflon filters present the lowest blanks for all the elements. The obtained limits of detection for each type of filters were adequate for environmental monitoring purposes. ETAAS instrumental operation was also optimized for the compensation and the elimination of interferences. The temperature optimization was performed for each metal in every type of filter and optimized parameters are proposed for 10 elements.     

A flow injection-ETAAS system for the on-line determination of total and dissolved silica in waters

In this work total (Si-tot) and ‘soluble’ or reactive (Si-sol) concentrations of silicon in natural and tap waters were sequentially determined by electrothermal atomic absorption spectrometry (ETAAS). First, samples were on-line diluted based on the merging-zone principle in order to allow the determination of Si-tot within the 300–1000 μgSi l⁻¹ range. After the dilution process, a sub-sample was collected in the capillary of a sampling arm assembly (SAA). Thereafter, samples were subject to a precipitation/dissolution process in order to allow the determination of Si-sol within the 280–850 μgSi l⁻¹. Si-sol was precipitated with ammonium chloride and collected on the walls of a knotted coil. The precipitate was dissolved with ammonium molybdate in an acidic medium (HNO₃) and a sub-sample was then collected in the SAA. In both cases, 10 μl volumes of the sub-sample were injected into the atomizer with the previous introduction of 20 ng of Eu as chemical modifier (10 μl) by the spectrometer autosampler. The recovery values obtained with natural waters spiked samples were over 46% and the agreement between observed and certified samples values was good. The proportion of Si-sol in comparison with the Si-tot was high (85–95%) in most natural waters. The precision of the method was 2.4–3.5 and 4.5–6.2% (n=10) for the determination of Si-tot and Si-sol, respectively.     

Determination of arsenic in mussels by slurry sampling and electrothermal atomic absorption spectrometry (ETAAS)

A method for the determination of arsenic in slurries of mussel tissue using palladium-magnesium nitrate as modifier was optimized. The slurry was stabilized by a 0.015% (v/v) of Triton X-100. To achieve complete mineralization the slurries were ashed at 480 °C for 10s in an air flow (50 ml/min) and at 1200 °C for 15s in an argon flow (300 ml/min) in the presence of Pd—Mg(NO₃)₂ as modifier. The optimum atomization temperature was 2200 °C. The precision and accuracy of the method were studied using the Reference Material BCR n ° 278 Mussel Tissue (Mytilus edulis). The detection limit (LOD) of the final slurry solution was 1 g/l of arsenic corresponding to an arsenic level in the mussel of 1.3 g/g, for a 0.5% (m/v) slurry. Results of calibration using aqueous standards and the standard additions method were compared. The method was applied to the determination of arsenic in mussels from the Galician coast. The levels found lie between 2 and 9.3 g/g of arsenic.     

Determination of selenium in human milk by electrothermal atomic absorption spectrometry and chemical modification

A method was developed for the determination of selenium in human milk using electrothermal atomic absorption spectrometry. The use of chemical modifiers as well as their implications during the pyrolysis step was examined. The chemical modifiers that were studied were Zr, Ir as well as the mixed modifier Zr-Ir. The Ir modifier stabilized selenium at 1000 °C, Zr at 800 °C, while the mixed modifier at 1200 °C. The effect of modifier mass was studied and was found that better results are achieved with addition of 2 μg Zr and 2 μg Ir. The characteristic masses of selenium in the presence of Zr, Ir and the mixed modifier were found to be 73.3, 18.0 and 14.7 pg, respectively, while the corresponding limits of detection were found 2.0, 0.50 and 0.41 μg l⁻¹. Consequently better results were obtained with the mixed modifier. The developed method was applied for the determination of selenium in human milk, which was digested with a HNO₃ + H₂O₂ mixture in a microwave oven. The limit of detection of the method was 1.37 μg l⁻¹, the characteristic mass, m₀, was 48.8 pg and the repeatability was less than 5% as R.S.D.(%). Matrix matched calibration was used. Recoveries were estimated to be 93-105%. The method was applied to breast milk of Greek women (n = 9) and the Se content was found to be in the range 16.7-42.6 μg l⁻¹ with mean value 27.4 ± 5.5 μg l⁻¹.     

Practical aspects of the uncertainty and traceability of spectrochemical measurement results by electrothermal atomic absorption spectrometry

The determination of trace elements concentration in water by electrothermal atomic absorption spectrometry (ETAAS) is a common and well established technique in many chemical testing laboratories. However, the evaluation of measurement uncertainty results is not systematically implemented. The paper presents an easy step-by-step example leading to the evaluation of the combined standard uncertainty of copper determination in water using ETAAS. The major contributors to the overall measurement uncertainty are identified due to amount of copper in water sample that mainly depends on the absorbance measurements, due to certified reference material and due to auto-sampler volume measurements. The practical aspects how the traceability of copper concentration in water can be established and demonstrated are also pointed out.     

Slurry sampling for determination of lead in marine plankton by electrothermal atomic absorption spectrometry

A slurry sampling method has been developed for the determination of Pb in marine plankton by ETAAS using a freshwater plankton certified reference material (CRM 414). Slurries were prepared in 1–3% m/v range with 1% v/v HNO₃ by ultrasonic agitation for 5 min. The effects of several chemical modifiers, including Ir(NO₃)₂, Mg(NO₃)₂, Pd(NO₃)₂, Pd(NO₃)₂ + Mg(NO₃)₂, and Mg(NO₃)₂ + NH₄H₂PO₄, were investigated for the stabilization of Pb during thermal pretreatment. Lead in slurries was effectively stabilized up to 1000 °C with Ir, Pd and Pd + Mg modifiers among which Pd + Mg provided the best results with complete atomization at 1850 °C. Firings in the presence of Ir were, problematic due to ash formation inside the atomizer. Water, dilute HNO₃ and HF were examined as suspension medium. Dilute HNO₃ (1–2% v/v) proved to be advantageous over water as it afforded extraction of Pb from plankton almost quantitatively in 5 min agitation. Hydrofluoric acid was the least suitable medium. Increasing HF concentration up to 5% v/v resulted in inaccuracy and substantial background absorption. Fast-heating furnace method provided comparable accuracy and precision to that of conventional-heating in slurries of CRM 414. Detection limits and characteristic masses were, respectively, 0.49 μg L^− 1 and 32 pg for the conventional method and 0.62 μg L^− 1 and 37 pg for the fast-heating method. However, fast-heating approach suffered from distorted peaks at high temperatures and incomplete pyrolysis of matrix at lower temperatures. Analysis of marine plankton samples for Pb was performed by using the conventional furnace program. The results showed a high correlation with those obtained by solution ICP-MS. Differences were statistically insignificant within 95% confidence interval.     

Determination of Lead, Chromium, Manganese and Zinc in Slurries of Botanical and Biological Samples by Electrothermal Atomic Absorption Spectrometry Using Tungsten-Containing Chemical Modifiers

Lead, Cr, Mn and Zn in slurries of botanic and biological samples were determined by electrothermal atomic absorption spectrometry (ETAAS) using W, Ir, NH₄H₂PO₄, W and NH₄H₂PO₄, Ir and NH₄H₂PO₄, W and Ir, and W + Ir + NH₄H₂PO₄ chemical modifiers in an 0.2% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture. Zeeman effect background correction was performed and platforms inserted into graphite tubes were used. Comprehensive comparative studies were carried out with respect to pyrolysis and atomization temperatures, atomization and background absorption profiles, characteristic masses, detection limits and accuracy of the determinations in the presence and absence of modifiers. The mixture of W + Ir + NH₄H₂PO₄ was found to be preferable for the determination of Pb, Cr, Mn and Zn in slurry samples. The pyrolysis temperatures of the analytes were increased up to 1250 °C for Pb, 1000 °C for Zn, 1400 °C for Cr and Mn by using W + Ir + NH₄H₂PO₄ with an 0.2% (v/v) Triton X-100 plus 0.2% (v/v) nitric acid mixture used as diluent solution. The optimum masses of the mixed modifier components were found to be 20 µg W + 4 µg Ir + 50 µg NH₄H₂PO₄. The characteristic masses of Pb, Cr, Mn and Zn obtained are 16.3, 5.6, 0.1 and 1.1 pg, respectively. The detection limits of Pb, Cr, Mn and Zn based on integrated absorbance for 0.5% (m v⁻¹) slurries were found to be 0.14, 0.06, 0.02 and 0.01 µg g⁻¹, respectively. The slurries of botanic and biological certified and standard reference materials were analyzed with and without the modifiers. Depending on the sample type, the percent recoveries increased from 63 up to 104% for analytes when using the proposed modifier mixture.     

Flotation separation and electrothermal atomic absorption spectrometric determination of lead in water samples

Abstract

The application of macro- and micro-electrodes constructed using the new ionophore were tested in a range of solution compositions reflecting concentrations found in fresh waters, and containing Cl^?, NO₃ ^?, SO₄ ^2-, HCO₃ ^2-, H₄SiO₄ and a natural humic acid. The inhibition of the electrode responses to these ions was quantified using a mixed-solution method by optimising the agreement between the measured potentials and predictions from the Nicolsky-Eisenman equation. In addition, measurements were made in separate solutions of KC1 to enable results to be compared with the literature. Apart from the results obtained for humic acid, mean selectivity coefficients for 16 macro- and 21 micro-electrode experiments are given. The results indicate inhibition of the electrode response to phosphate for all the anions in the concentration ranges of 0.05–1 mM Cl^?, 0.1–1.0 mM NO₃ ^?, 0.1–10.0 mM HCO₃ ^? and 0.1–1.5 mM SO₄ ^2- with high selectivity for HPO₄ ^2- in the presence of both dissolved silicon and a standard humic acid. This means that the application of the electrodes to hard waters is impracticable although studies of soft waters and laboratory studies in controlled conditions, e.g. calcium phosphate precipitation experiments, are feasible.     

Evaluation of different rhodium modifiers and coatings on the simultaneous determination of As, Bi, Pb, Sb, Se and of Co, Cr, Cu, Fe, Mn in milk by electrothermal atomic absorption spectrometry

Different kinds of modifiers and coatings on the integrated platform of transversely heated graphite atomizer (THGA) have been tested for the simultaneous determination of two group of elements: the first, the more volatile, formed by arsenic, bismuth, lead, antimony and selenium; the second, the less volatile, formed by cobalt, chromium, cupper, iron and manganese in milk by electrothermal atomic absorption spectrometry. Different Rh-modifiers were studied, such as Rh-coated platforms (Rh), carbide plus rhodium coated platforms (W-Rh, Zr-Rh), carbide-coated platforms (W and Zr) with co-injection of RhCl₃, solutions and uncoated platforms with injection of solutions of Pd(NO₃)₂, Mg(NO₃)₂, and RhCl₃. Milk samples were diluted 1:10 in 1.0% HNO₃ and injected into the tube. The mass of modifier deposited and co-injected in the tube and the use of end capped tubes were also evaluated in order to improve the electrothermal behavior of analytes. Integrated platform pretreated with W plus co-injection RhCl₃ for first group and pretreated with W-Rh for second group were elected. For 20 μL injected samples the analytical curves in the 5.0–20.0 μg L⁻¹ concentration range have good linear correlation coefficients (r > 0.998). Relative standard deviations (n = 12) are <6% and the calculated characteristic masses are between 5 pg and 62 pg. Correspondence: Gian Paulo G. Freschi, Faculdade de Ciências Exatas e Tecnologia, Universidade Federal da Grande Dourados, PO Box 332, 79.804-970, Dourados-MS, Brazil; Instituto de Química, Universidade Estadual Paulista, PO Box 355, 14801-970 Araraquara-SP, Brazil     

电热原子吸收法测定人发中硒时不同改进剂的研究

对于生物体中硒的测定,国内外已有大量报道,所用方法也相当广泛。本文利用石墨炉原子吸收对人发中硒的测定进行了研究;对使用较多的两种硒的基体改进剂:铜与镍的作用与效果进行了研究,发现铜较镍在某些方面更为优越。当选用100 μg/mL的铜作改进剂时,硒的特征浓度为0.13 ng/1％abs,测定精度为3.4％～5.4％;线性范围达400 ng。