Thermal lens spectrometric determination of hexavalent chromium

The applicability of thermal lens spectrometry (TLS) for quantification and routine determination of hexavalent chromium was investigated by using a collinear dual beam thermal lens spectrometer. In aqueous solutions the LOD of 0.1 μg l⁻¹ was obtained for Cr(VI) by using 160 mW laser power. The performance of the technique was verified by the determination of hexavalent chromium in standard reference water samples (NIST SRM 1643a and NIST SRM 1643c) and comparing the results for Cr(VI) in CCA (Cr, Cu, As)-treated timber extracts to concentrations obtained by atomic absorption spectrometry (AAS). Good agreement between the TLS results and reported values for Cr(VI) in SRMs as well as AAS results for Cr(VI) in CCA-treated timbers confirmed that TLS is a reliable and accurate analytical technique applicable for the determination of Cr(VI) in aqueous solutions at concentration levels 0.5–100 μg l⁻¹.     

Speciation of chromium (VI) and total chromium determination in welding dust samples by flow-injection analysis coupled to atomic absorption spectrometry

We have studied the speciation of chromium (VI) in stainless-steel welding dusts. The approach used for the analysis of Cr(VI) and total Cr relies on a flow-injection analyzer (FIA) equipped with two different sequential detectors. The system measures Cr(VI). by colorimetry (with 1,5-diphenyl carbohydrazide) and total chromium content by flame atomic absorption spectroscopy (AAS). The extraction of the samples of welding-fume dusts is achieved in a buffer solution (acetic acid and sodium acetate at pH 4). This extraction procedure gives a 96% recovery of chromium (VI). The FIA-AAS system that has been described is also more sensitive, has a lower detection limit (0.005 mug ml(-1)) and gives a better precision (< 1%) than other equivalent systems that have been previously described.     

悬浊液直接进样非火焰原子吸收法测定蔬菜样品中微量铬的研究

本文通过用直接悬浊液进样原子吸收法对新鲜蔬菜中铬的测定,研究了各种实验条件,并建立了实际测定新鲜蔬菜中微量元素的方法。该法将可用于食品。     

Ultra‐performance liquid chromatography/tandem mass spectrometry in high‐throughput detection,quantification and confirmation of anabolic steroids in equine plasma

An ultra‐performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method for fast‐throughput analysis of eight anabolic and androgenic steroids (AAS) in equine plasma is reported. Analytes were recovered by liquid‐liquid extraction using methyl tert‐butyl ether, separated on a 1.9 µm C₁₈ reversed‐phase column, and analyzed in positive electrospray ionization mode on a triple quadrupole mass spectrometer with selected reaction monitoring (SRM) and full product ion scans. Two SRM ion transitions were monitored for each AAS during screening to obtain highly selective screening results. Full product ion spectra of excellent quality for AAS, at 100 pg/0.5 mL in plasma, devoid of interfering spectra from impurities in plasma, were obtained. To our knowledge, this is the first report on the acquisition of full product ion spectra at such a low analyte concentration and plasma volume using a triple quadrupole instrument. In addition to product ion intensity ratios obtained from three SRM scans for identifying AAS in equine plasma, full product ion spectra were used as supporting evidence for confirmation. For quantification, deuterium‐labeled testosterone and stanozolol were used as internal standards (ISs). The limits of detection, quantification and confirmation were 6.25–12.5 pg/0.5 mL, 25 pg/0.5 mL and 50–100 pg/0.5 mL, respectively. There was no significant matrix effect on the analysis of all eight AAS. Intra‐day precision and accuracy were 2–15% and 91–107%, respectively. Inter‐day precision and accuracy were 1–21% and 94–110%, respectively. Total analysis time was 5 min. To date, the method has been successfully used in the analysis of >12 000 samples for AAS in plasma samples from racehorses competing in the State of Pennsylvania. The method is fast, selective, reproducible, and reliable. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of molybdenum, chromium and vanadium by ion-pair high-pressure liquid chromatography based on precolumn chelation with 4-(2-pyridylazo)resorcinol

A reversed-phase ion-pair liquid chromatography-spectrophotometric detection system for the separation and simultaneous determination of molybdenum, chromium and vanadium is described. The chelates of the metal ions with 4-(2-pyridylazo)resorcinol are separated on a Zorbax CN column with 1 x 10(-3)M tetrabutylammonium iodide and 0.01M KH(2)PO(4)-Na(2)HPO(4) buffer (pH 7.50) in 30:70 v v methanol-water mixture as the mobile phase, at a flow-rate of 1.0 ml min . The chelates are detected spectrophotometrically at 540 nm.     

Capillary gas chromatography of metal chelates of diethyl dithiocarbamates

Summary Capillary GC of metal chelates of diethyl dithiocarbamate (DDTC) was examined on a methylsilicone DB-1 column, (25 meter, 0.2 mm. i.d) with a film thickness of 0.25 μm. Elution was carried out at the initial column temperature of 180°C and programmed at 5°C min⁻¹ to 260°C. Detection was by FID or ECD. Symmetrical peaks with base line separation were obtained with the metal chelates of copper(II), nickel(II), cobalt(III), manganese(II) and chromium(III). The ECD gave better sensitivity than the FID with a linear calibration range of 5–50 μg mL⁻¹ and detection limits 2.0–6.0 μg mL⁻¹, corresponding to 111–333 pg of metal ion reaching the detector. The method was applied to the determination of metal ions in water and pharmaceutical preparations with a coefficient of variation (CV) within 4.0%. When compared with a standard flame AAS method the results revealed no significant difference.     

Atomic absorption spectrometric determination of mercury in soil standard reference material following microwave sample pretreatment

Several decomposition procedures and their influence on the determination of mercury by electrothermal (ET) and cold vapour (CV) atomic absorption spectrometry (AAS) have been studied. Soil samples were decomposed by microwave digestion in closed and open vessels as well as by digestion under reflux according to German standard. The use of different acids (HNO₃, HCl or aqua regia) was evaluated and compared in respect to their influence on the determination of mercury by ET AAS and CV AAS. The digestion solutions were analyzed by ET AAS with a palladium modifier and by CV AAS using SnCl₂ or NaBH₄, as reducing agents. The detection limits obtained with different procedures were also evaluated. For the soil containing 6.25 g/g of Hg the ET AAS measurements were possible. In the case of lower concentration of mercury the CV AAS determination following the microwave digestion procedure with HCl or aqua regia is recommended. The accuracy of the proposed procedure was confirmed by the determination of total mercury in SRM 2711 Montana Soil.On leave from: Institut für Analytische Chemie, Technische Universitat Wien, Getreidemarkt 9, A-1060 Wien, Austria     

Phase separation in semi-interpenetrating polymer networks based on crosslinked poly(urethane) and linear poly(methyl methacrylate) containing iron,copper, and chromium chelates

Phase separation that occurs during formation of semi-interpenetrating polymer networks of various compositions based on crosslinked poly(urethane) and linear poly(methyl methacrylate) containing 1 wt % iron, copper, and chromium chelates has been studied by the methods of DSC and DMA. It has been shown that, in contrast to chromium chelates, the incorporation of iron and copper β-diketonates into the semi-interpenetrating polymer networks (PU : PMMA = 50 : 50) causes retardation of phase separation owing to high rates of poly(urethane) and poly(methyl methacrylate) formation and the appearance of chelate complexes with both blend components at the interface. A more complete phase separation in metal-containing semi-interpenetrating polymer networks (PU : PMMA = 70 : 30) is associated with the fact that chemical kinetics and complexation processes act in opposite directions. The latter processes prevail, and the influence of the type of metal ion in a chelate that predominantly interacts with PU in the blend is diminished.     

Studies towards understanding the mechanism of organic reagent enhancement in flame and plasma atomic absorption spectrometry

A series of organic reagents have been tested in atomic absorption measurement for signal enhancement of metal elements. Organic reagents like tetrabutylammonium bromide are demonstrated to enhance the absorption sensitivity to some specific elements such as calcium and chromium. A group of amines were found to have significant enhancement for chromium and calcium measurements. The function of organic reagents in flame and plasma atomic absorption spectrometry (AAS) was investigated in this work with emphases on mechanism of signal enhancement and interference suppression. An alternative mechanism of organic reagent enhancement in flame and plasma AAS has been suggested based on the experimental results obtained in this work. The reduction environments in flame and plasma produced by the organic reagents are considered as major reason for the signal enhancement.     

Selenium, chromium and zinc content of proposed SRM 1846 infant formula

A proposed infant formula SRM 1846 has been analyzed for zinc, selenium and chromium by isotope dilution mass spectrometry (IDMS). The precision of the IDMS methods has been sufficient to allow the estimation of the sample homogeneity with respect to these three analytes. Overall means of 60.9±0.9 g Zn/g (mean±standard deviation) and 76.1±1.9 ng Se/g have been found for 30 determinations. Values for chromium content have been found to depend on the sample preparation method, suggesting possible contamination. Accurary of the zinc, chromium and selenium values has been verified using a certified reference material, SRM 1549 Non-Fat Milk Powder.     

Critical evaluation of analytical performance of atomic absorption spectrometry and inductively coupled plasma mass spectrometry for mercury determination

The analytical performance of cold vapor atomic absorption spectrometry (CV AAS), graphite furnace atomic absorption spectrometry (GF AAS) and inductively coupled plasma mass spectrometry (ICP-MS) for mercury determination have been investigated with the use of two reference materials SRM 2710 Montana I Soil and BCR-144R (sewage sludge from domestic origin). The digestion conditions and their influence on determination of mercury have been studied. Samples were decomposed by microwave digestion in closed vessels with the use of HCl alone or mixture of HCl+HNO₃+HF. The digestion solutions were analyzed by CV AAS using NaBH₄ as a reducing agent, by GF AAS with Pd or mixture of Pd/Rh as modifiers and by ICP-MS with Rh as internal standard. In the case of CV AAS, results were not dependent on digestion conditions. In the case of GF AAS and ICP-MS, results depended significantly on digestion conditions; in both cases, the use of the mixture of acids as defined above suppressed the signal of mercury. Therefore, in those cases, the microwave digestion with HCl is recommended. Detection limits of 0.003, 0.01 and 0.2 μg g⁻¹ were achieved by ICP-MS, CV AAS and GF AAS, respectively.     

Solubility of metal chelates and their extraction from an aqueous environment via supercritical CO(2)

Solubility of nickel(II), copper(II), and chromium(III) hexafluoroacetylacetone and chromium(III) acetylacetone chelates was measured in supercritical CO(2) at two different pressures (200 and 400 atm) and 60 degrees C. Solubility of fluorinated acetylacetone chelates was at least an order of magnitude higher than the non-fluorinated complexes. These pre-formed metal chelates as well metal diethyldithiocarbamate (DDC) and metal bis(trifluoroethyl)dithiocarbamate (FDDC) have also been extracted from aqueous environment using pure supercritical CO(2). It was demonstrated that metal HFA chelates while exhibiting higher solubility in supercritical CO(2) compared with metal FDDC chelates, exhibited lower extraction efficiency using the same extraction conditions. This behavior of metal HFA chelates is related to their stability in an aqueous environment. Direct extraction of Ni(+2) and Cu(+2) from an aqueous matrix was also achieved via in-situ chelation using diethyldithiocarbamate and bis(trifluoroethyl)dithiocarbamate as the ligands. Bis(trifluoroethyl)dithiocarbamate proved to be a more effective ligand for direct extraction of metal ions from aqueous environment using supercritical CO(2).     

Frequency-modulated simultaneous multielement atomic absorption spectrometry using electrothermal atomizer and deuterium background correction

Characteristic data of the frequency-modulated simultaneous multielement atomic absorption spectrometry (FREMSAAS) using electrothermal atomizer with deuterium background correction, have been determined. The data obtained have been processed by using several statistical tests recommended for quality control purposes. The instrumentation has been presented as well as procedures of separating elements into measure groups and fixing of variable conditions. Detection limits, characteristic masses and working ranges have been given for the eleven elements examined. The data have been in good agreement to results obtained with conventional one-channel AAS instruments. The eleven elements have been simultaneously determined in a standard reference material (SRM) and all results are compatible with a 95% certainty with the certified values. FREMSAAS has been applied to a real sample.Dedicated to Professor Dr. Dieter-Klockow on the occasion of his 60th birthday     

Chromium speciation and preconcentration using zirconium(IV) and zirconium(IV) phosphate chemically immobilized onto silica gel surface using a flow system and F AAS

A procedure for chromium speciation by F AAS using a flow system has been proposed. In this system, Cr(III) and Cr(VI) ions were adsorbed sequentially onto a mini-column packed with silica gel modified with zirconium phosphate and a mini-column packed with silica gel modified with zirconium oxide, respectively. The elution of Cr(III) and Cr(VI) was made with, respectively, nitric acid solution and tris(hydroxymethyl)methylamine (THAM) solution in reverse mode and determination by flame atomic absorption spectrometry without interference of the matrix. Chemical and flow variables as well as concomitant ions were studied in the developed procedure. The enrichment factor for Cr(III) and Cr(VI) was 20.8 and 24.9, respectively, using a preconcentration time of 3.75 min. The limit of detection for Cr(III) and Cr(VI) was 1.9, and 2.3 μg l⁻¹, respectively. The precision of the method, evaluated as the relative standard deviation in solutions containing 100 μg l⁻¹ of chromium species, by analyzing a series of seven replicates, was lower than 3.0%. The accuracy was assessed through recovery experiments of water samples and using another methodology.     

Study of a system for introducing metal chelate complexes in AAS

Summary The possibility of extending the sampling of volatile phases in AAS by use of metal beta-diketonates is considered. An electrically heated system was designed in which the chelate was injected, volatilized and then carried by a nitrogen stream to a silica tube, which was heated with an air-acetylene flame. The method was investigated for Cr, Zn and Mn using acetylacetone as chelating agent. The introduction of volatile chelates gives an increase in sensitivity with respect to the nebulization and atomization of solutions in the flame. This sampling system is limited to metallic chelates which are thermally stable and sufficiently volatile. The partial decomposition, which Zn acetyl-acetonate and, particularly Mn acetylacetonate undergo, causes a reduction in the sensitivity and precision of the determination.

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Untersuchung eines Probeeingabesystems für Metallchelatkomplexe in der AASEinfluß der Chelatstabilität

     

采用吸附树脂Amberlite XAD-4从水溶液中富集痕量元素

本文采用短吸附柱(10×60mm,充填高度24mm)研究了非离子性吸附树脂AmberliteXAD-4从水溶液中对16种金属元素的氢氧化物,二硫代氨基甲酸衍生物的配合物和二甲酚橙配合物的吸附行为。难溶金属化合物在树脂上的吸附率与溶液pH值的关系与采用活性碳作吸附剂的情况十分相似。而含有亲水基团的二甲酚橙螯合物不被树脂吸附。对吸附于树脂上的痕量元素的洗脱以及采用火焰原子吸收光谱法测定丙酮富集液中的金属元素问题也进行了讨论。     

A multicommuted flow system for the determination of copper, chromium, iron and lead in lubricating oils with detection by flame AAS

In this work, a flow analysis procedure for the determination of copper, chromium, iron and lead in lubricating oils using flame AAS as detection technique is described. The flow manifold was designed to implement the multicommutation approach and it comprised three 3-way solenoid valves controlled by a personal computer. The flow system presented allowed to process the oil samples to determine wear metals without any prior preparation. Aiming to assess accuracy the results were compared with those obtained by manual procedure using flame AAS. Applying the joint-confidence ellipse test, no significant difference at the 95% confidence level was observed. Other profitable features such as a sample throughput of 50 determinations per hour; relative standard deviations (n = 5) below 2% for Cu, and below 8% for Cr, Fe and Pb; and linear responses in the range 0–40 ppm (w/w) (Cu, Fe) and 0–15 ppm (w/w) (Cr, Pb) were also achieved.     

Determination of chromium in biological matrices by neutron activation: Application to standard reference materials

Chromium is recognized to be an essential trace element in several biological systems. It exists in many biological materials in a variety of chemical forms and very low concentration levels which cause problems for many analytical techniques. Both instrumental and destructive neutron activation analysis were used to determine the chromium concentration in Orchard Leaves, SRM 1571, Brewers Yeast, SRM 1569, and Bovine Liver, SRM 1577. Some of the problems inherent with determining chromium in certain biological matrices and the data obtained here at the National Bureau of Standards using this technique are dicussed.     

Determination of trace elements in gallium arsenide by graphite-furnace atomic absorption spectrometry after pretreatment in gas streams

Atomic absorption spectrometry (AAS) with a resistively-heated graphite furnace is used for the determination of chromium (0.3–1 atom/10⁶ atom) in chromium-doped gallium arsenide after pretreatment in a separate furnace in a stream of argon to remove arsenic, and of manganese and silver (0.03 and 0.04 atom/10⁶ atoms, respectively) by a similar procedure after pretreatment with argon and chlorine, the latter to remove both gallium and arsenic as volatile chlorides. Results for chromium were in agreement with those obtained by furnace AAS after dissolution and by spark-source mass spectrometry (SSMS) but AAS after dissolution is more precise. Results for manganese and silver obtained by both gas pretreatments were in good agreement, but were higher than those obtained for presparked material by SSMS, indicating that surface contamination of gallium arsenide was not completely removed by the etching methods used. The procedures established that the concentrations of bismuth, indium and lead in the gallium arsenide sample were below the limits of detection of 3 × 10^?3, 10 × 10^?3 and 1 × 10^?3 atom/10⁶ atoms, respectively. In all cases, calibration graphs were constructed from data obtained with aqueous solutions of appropriate salts.     

Application of zone melting techniques to metal chelate systems-I Concentration of trace amounts of aluminium in tris(acetylacetonato)chromium(III)

The possibilities of applying the zone melting technique to metal chelates are described and discussed. The technique has been applied to the system of tris(acetylacetonato)chromium(III)-tris-(acetylacetonato)aluminium(III). The concentrating effect is not dependent upon the initial concentration of the minor component, but on the rate of zone movement. When the rate is set at 15 mm hr , the value of the distribution coefficient, 0.55-0.64, is at a minimum, and may be assumed to be the equilibrium distribution coefficient under the conditions described.