Determination of tungsten by calcium atomization inhibition titration

A method for the determination of tungsten utilizing inhibition effect on calcium emission in hydrogen-air flame is described. The technique is based on atomization inhibition titration (AIT) and subsequent release by means of lanthanum. The signal enhancement following the lanthanum addition is proportional to the tungsten concentration up to 0.8 ppm W. A detection limit of 0.013 ppm and a determination limit of 0.12 ppm were found. The effect of 13 foreign ions on the tungsten determination was investigated.     

Determination of indium by graphite furnace atomic absorption spectrometry after coprecipitation with chitosan.

A sensitive and simple method for the determination of trace amounts of indium in water samples by graphite furnace atomic absorption spectrometry (GFAAS) after coprecipitation with chitosan was investigated. Indium was quantitatively preconcentrated from water samples by coprecipitation with chitosan at pH 7.0-9.0. The coprecipitant was easily dissolved with acetic acid, and indium in the resulting solution was determined by GFAAS. The addition of lanthanum as a chemical modifier was more effective for the atomic absorbance of indium. The detection limit (S/N > or = 3) for indium was 0.04 microg dm(-3), and the relative standard deviations (n = 5) were 3.5-4.5% at 1.0 microg/100 cm3. The results obtained in this study indicate that the proposed method can be successfully applied to the determination of trace indium in water samples.     

Determination of chromium in river waters by electrothermal atomic absorption spectrometry with preconcentration on a tantalum wire

The preconcentration of chromium on tantalum wire followed by electrothermal atomic absorption spectrometry with a tungsten tube atomizer is described. The preconcentration is accomplished by adsorbing chromium on a tantalum wire. The optimal immersion time was 3 mm. The best pH for chromium adsorption was 3. Under optimal conditions, the detection limit was 15 pg mU1 (3 x SIN). The effects on the preconcentration of chromium by large amounts of contaminants were evaluated. Even though matrix elements existed in 10(3)-10(4)-fold excess in water, the chromium absorption signal was not affected by the matrix elements. The method with preconcentration on tantalum wire was applied to the determination of chromium in river water.     

微波等离子体炬原子发射光谱法测定铁增敏效应

针对在低功率下工作的微波等离子体炬原子发射光谱法(MPT-AES)存在对一些元素检测灵敏度较低和抗基体干扰能力弱的问题,以氩气为载气和工作气,研究了表面活性剂及镧盐对MPT-AES测定铁的增敏效应,考察了铁测定的工作条件和共存元素对铁测定的影响.实验结果表明,非离子表面活性剂对铁的测定有抑制作用,而阳离子表面活性剂和镧盐对铁的测定有增敏作用,其中镧盐增敏效果最好.以镧盐为增敏剂,不仅可提高MPT-AES测定铁的灵敏度,还可增加共存元素的允许量.当体系中镧浓度为0.500 mg/m L时,至少可使40倍的锌,30倍的钴,20倍的镍、锰,15倍的钙,10倍的镁、铜和钠不影响铁的测定.与不加镧时相比,铁的发射强度提高了2.4倍,检出限由原来的27.5×10~(-3)μg/m L下降为8.5×10~(-3)μg/m L.将本方法应用于原油样品中铁的测定,所得结果与火焰原子吸收光谱法测定结果一致.     

A new atomization cell for trace metal determinations by tungsten coil atomic spectrometry

A new metallic atomization cell is used for trace metal determinations by tungsten coil atomic absorption spectrometry and tungsten coil atomic emission spectrometry. Different protecting gas mixtures are evaluated to improve atomic emission signals. Ar, N₂, CO₂ and He are used as solvents, and H₂ and C₂H₂ as solutes. A H₂/Ar mixture provided the best results. Parameters such as protecting gas flow rate and atomization current are also optimized. The optimal conditions are used to determine the figures of merit for both methods and the results are compared with values found in the literature. The new cell provides a better control of the radiation reaching the detector and a small, more isothermal environment around the atomizer. A more concentrated atomic cloud and a smaller background signal result in lower limits of detection using both methods. Cu (324.7 nm), Cd (228.8 nm) and Sn (286.3 nm) determined by tungsten coil atomic absorption spectrometry presented limits of detection as low as 0.6, 0.1, and 2.2 μg L⁻¹, respectively. For Cr (425.4 nm), Eu (459.4 nm) and Sr (460.7 nm) determined by tungsten coil atomic emission spectrometry, limits of detection of 4.5, 2.5, and 0.1 μg L⁻¹ were calculated. The method is used to determine Cu, Cd, Cr and Sr in a water standard reference material. Results for Cu, Cd and Cr presented no significant difference from reported values in a 95% confidence level. For Sr, a 113% recovery was obtained.     

Evaluation of electrodeposited tungsten chemical modifier for direct determination of chromium in urine by ETAAS

The direct determination of chromium in urine by electrothermal atomic absorption spectrometry (ETAAS) using graphite tubes modified with tungsten is proposed. Modification of the graphite is made by tungsten electrodeposition over the whole surface atomizer followed by carbide formation by heating the tube inside its own furnace. For tungsten electrocoating, the graphite tube and a platinum electrode were connected to a power supply as cathode and anode, respectively, and immersed in a solution containing 2 mg of W in 0.1% v/v HNO₃. Then, 5 V was applied between the electrodes during 20 min for tungsten electrodeposition over the whole atomizer. A SpectrAA 220 Varian atomic absorption spectrometer equipped with a deuterium background corrector was used throughout. Undiluted urine (20 μl) was delivered over the tungsten-treated tube and the chromium-integrated absorbance was measured after applying a suitable heating program with maximum pyrolysis at 1300 °C and atomization at 2500 °C. With electrodeposited tungsten modifier, the tube lifetime increased up to four times when compared to previous published methods for Cr determination in urine by ETAAS, reaching 800 firings. Method detection limit (3 S.D.) was 0.10 μg l⁻¹, based on 10 integrated absorbance measurements of a urine sample with low Cr concentration. Two reference materials of urines (SRM 2670) from National Institute of Standards and Technology (NIST) were analyzed for method validation. For additional validation, results obtained from eight human urine samples were also analyzed in a spectrometer with Zeeman effect background correction.     

On-line coupling of ion chromatography and atomic spectrometry for ultra trace analysis in high purity molybdenum- and tungsten-silicide

The well-established technique of on-line coupling ion chromatography and atomic spectrometry for ultra trace analysis in high purity molybdenum and tungsten is extended to include the silicides MoSi(x) and WSi(x). An additionally included matrix elimination step allows an almost interference-free trace analysis in the silicide matrices. Reproducibility and accuracy of the on-line method were checked by comparison with several other methods, such as isotope dilution, radiochemical neutron activation analysis, direct determination by atomic absorption analysis and not at least with glow discharge mass spectrometry. The results show the high potential of the on-line method for reaching detection limits in the pg g(-1) range, but they show also remaining problems with contamination and system calibration.     

Application of edta to direct graphite-furnace atomic absorption analysis for cadmium in sea water

A method is described for the direct determination of cadmium in undiluted sea water by graphite-furnace atomic absorption spectrometry. The addition of EDTA ( 1 mg ml^-1) reduces the temperature of atomization of cadmium to far below that of volatilization of other matrix components. The need for very careful temperature control and accurate background compensation is thus minimized. Sea water was analyzed by the method of standard additions. A detection limit of 0.01 μg l^-1, a sensitivity of 0.034 μg l^-1 and a precision of ±10% at the 0.05 μg l^-1 level were obtained for 20-μl injections.     

Determination of Ultratrace Amounts of Copper(Ⅱ) in Water Samples by Electrothermal Atomic Absorption Spectrometry After Cloud Point Extraction

A novel approach was developed for the determination of ultratrace amounts of copper in water samples by using electrothermal atomic absorption spectrometry (ETAAS) after cloud point extraction (CPE). 1-( 2-Pyridylazo)-2-naphthol was used as the chelating reagent and Triton X-114 as the micellar-forming surfactant. CPE was conducted in a pH 8.0 medium at 40 ℃ for 10 min. After the separation of the phases by centrifugation, the surfactant-rich phase was diluted with 1 mL of a methanol solution of 0. 1 mol/L HNO3. Then 20 μL of the diluted surfactant-rich phase was injected into the graphite furnace for atomization in the absence of any matrix modifier. Various experimental conditions that affect the extraction and atomization processes were optimized. A detection limit of 5 ng/L was obtained after preconcentration. The linear dynamic range of the copper mass concentration was found to be 0-2.0ng/mL, and the relative standard deviation was found to be less than 3.1% for a sample containing 1.0 ng/mL Cu(Ⅱ). This developed method was successfully applied to the determination of ultratrace amounts of Cu in drinking water, tap water, and seawater samples.     

Chemical modification of graphite surfaces for the determination of chromium by electrothermal atomic absorption spectrometry

Different kinds of graphite surfaces (electrographite, pyrolytic graphite, zirconium and tungsten carbide-coated) have been tested for optimization of analytical conditions for the determination of chromium using electrothermal atomic absorption spectrometry. The effect of mineral acids on the peak absorbance signal of chromium has been investigated. Considering pyrolysis temperature and sensitivity, atomization from pyrolytic graphite coated surface showed the best performance.     

Hydride generation for the direct determination of trace and ultra-trace level of arsenic and antimony in waters using derivative atomic absorption spectrometry

A new method is developed for the direct determination of trace and ultra-trace level of arsenic and antimony in waters by hydride generation derivative atomic absorption spectrometry (DHGAAS). The signal model and fundamentals of DHGAAS are described. The effects of atomization temperature, argon flow rate, acidity and concentration of KBH(4)and KI were investigated and analytical conditions were optimized. The sensitivities for arsenic and antimony were increased 36.4 and 27.6 times better than those of conventional hydride generation atomic absorption spectrometry (HGAAS). For a 2 mV min(-1) sensitivity range setting, the characteristic concentration was 0.003 microg L(-1) for arsenic and 0.004 microg L(-1)for antimony, and the detection limits (3sigma) were 0.015 micro g L(-1) for arsenic and 0.020 microg L(-1) for antimony. The proposed method was applied to the determination of arsenic and antimony in several water samples with satisfactory results.     

Determination of thallium by furnace atomic absorption spectrometry

The analytical conditions for the determination of thallium by graphite furnace atomic absorption spectrometry were studied and optimized using the peak-height mode. The charring-atomization curves for thallium from different atomization surfaces were constructed and the optimum charring and atomization conditions were established. These atomization surfaces included pyrolytic graphite-, tantalum-, zirconium- and tungsten-coated graphite tubes. The effects of different inorganic acids on the absorbance of thallium from different surfaces were studied. Using tungsten carbide-coated tubes, the interference effects due to hydrochloric and perchloric acids were eliminated. The matrix modification technique was also investigated for increasing the maximum permissible charring temperature for thallium. The matrix modifiers used included tungsten, zirconium, nickel and tantalum. The effect of adding these modifiers were studied in the presence of different acids. Tungsten increased the maximum permissible charring temperature from 400 to 1000 °C.     

Evaluation of tungsten coil electrothermal vaporization-Ar/H2 flame atomic fluorescence spectrometry for determination of eight traditional hydride-forming elements and cadmium without chemical vapor generation

A tungsten coil electrothermal vaporizer (W-coil ETV) was coupled to an Ar/H(2) flame atomic fluorescence spectrometer for the determination of eight traditional hydride-forming elements (i.e., As, Bi, Ge, Pb, Sb, Se, Sn, and Te) as well as cadmium without chemical vapor generation. A small sample volume, typically 20muL, was manually pipetted onto the W-coil and followed by a fixed electric heating program. During the vaporization step, analyte was vaporized off the coil surface and swept into the quartz tube atomizer of AFS for further atomization and excitation of atomic fluorescence by a flow of Ar/H(2) gas, which was ignited to produce the Ar/H(2) flame. The tungsten coil electrothermal vaporizer and Ar/H(2) flame formed a tandem atomizer to produce reliable atomic fluorescence signals. Under the optimal instrumental conditions, limits of detection (LODs) were found to be better than those by flame atomic absorption spectrometry (FAAS) or inductively coupled plasma optical emission spectrometry (ICP-OES) for all the nine elements investigated. The absolute LODs are better or equivalent to those by hydride generation atomic fluorescence spectrometry (HG-AFS). Possible scattering interferences were studied and preliminary application of the proposed method was also reported.     

Preconcentration of trace lead by adsorption onto a tantalum wire for electrothermal atomization atomic absorption spectrometry with a tungsten tube atomizer

A preconcentration method of lead in waters by adsorption on a tantalum wire was developed for electrothermal atomization atomic absorption spectrometry with a tungsten tube atomizer. After the preconcentration, the tantalum wire was directly inserted into the tungsten tube atomizer. In the preconcentration (adsorption) process for lead, the optimal immersing time was 90 s and the best pH was 4. Under the optimal conditions, the detection limit for lead by the tantalum wire preconcentration method was 6.0 pg mL^− 1 (3S/N) and the relative standard deviation was 6.1%. The influences of large amounts of concomitants on the preconcentration of lead were evaluated. Even though 10³ to 10⁴-fold excess of matrix elements existed in aqueous solution, the lead absorption signal was not significantly affected by the matrix elements. The method with preconcentration on a tantalum wire was applied to the determination of lead in river waters and proved to be sensitive, simple, and convenient. Because this preconcentration method can be utilized in the in-situ treatment of trace lead in environmental water samples, it was unnecessary to carry the water samples to the analytical work place. The present technique was shown to be useful for the determination of lead in environmental water samples at 0.1−1 μg L^− 1.     

Determination of bismuth in river sediment by electrothermal atomic absorption spectrometry with low-temperature atomization in argon/hydrogen

A method is described for the direct determination of bismuth (1–5 μg g^?1) in river sediments by graphite-furnace atomic absorption spectrometry in 90% argon/10% hydrogen with low-temperature atomization. The presence of 10% hydrogen in the argon sheath gas promotes atomization; the bismuth absorption reaches a maximum at 850–950°C, which allows better discrimination of the atomic signal from the background absorption. The use of trisodium phosphate as the matrix modifier further decreases the interference effects from the matrix components and increases the sensitivity. The results, obtained by direct calibration with aqueous standards, are in good agreement with certified values.     

Atomization of Al in a tungsten coil electrothermal atomic absorption spectrophotometer

Electrothermal atomic absorption spectrophotometry of Al in a tungsten coil atomizer was evaluated and applied for its determination in hemodialysis fluid. The system was mounted on a Varian Spectra AA-40 spectrophotometer with continuum background correction and all measurements, in peak height absorbance, were done at 309.3 nm. The purge gas was a mixture of 90% Ar plus 10% H(2). Observation height, gas flow, drying, pyrolysis and atomization steps were optimized. The heating program was carried out by employing a heating cycle in four steps: dry, pyrolysis, atomization and clean. The determination of Al in hemodialysis solutions was performed by using a matrix-matching procedure. Al in hemodialysis solutions was determined by TCA and by electrothermal atomization with a graphite tube atomizer. There is no differences between results obtained by both methods at a confidence level of 95%. The characteristic mass of Al by using the TCA was 39 pg and the detection limit was 2.0 mug l(-1).     

Sequential injection analysis of lead using time-based colorimetric detection and preconcentration on an anionic-exchange resin.

The development of a sequential injection analysis manifold for the colorimetric determination of lead in water samples is described The concentration of lead was assessed from its catalytic effect on the reaction of resazurine reduction caused by sulfide in an alkali medium. To that effect, the reaction zone was stopped at the detector, and the time interval required for the attainment of an absorbance decrease of 0.800 at the wavelength of 610 nm was estimated. Interference of other transition metals of the samples was minimized by adding potassium iodide to the sample and retaining the iodocomplexes formed in an on-line anionic resin (AGI X8). Elution was made with a 2 mol/L sodium hydroxide solution. The relationship [SIA] microg/L = 0.99 (+/- 0.11) x [ETAAS] microg/L + 0 (+/- 4) was obtained upon comparing the results given by the proposed system and by electrothermal atomization atomic absorption spectrometry (ETAAS) after the analysis of ten water samples.     

Determination of cadmium in paint samples by graphite furnace atomic absorption spectrometry with optical temperature control

A graphite furnace atomic absorption spectrometry (GFAAS) method with optical temperature control for the determination of trace cadmium in paint samples is described. Optical temperature control was superior in many respects to current temperature control. The sensibility increased by 60%, the linear range widened by 60%, and the life of graphite tube showed a 200–300% increase because atomization temperature was lowered distinctly and atomization time was shortened. Use of lanthanum chloride as a matrix modifier was investigated. The linear range of calibration curve was 0–24 ng mL⁻¹. The detection limit was 9.6 ng L⁻¹. The characteristic mass was 3.0 pg. The method also resulted in excellent reproducibility (≤2.5% R.S.D.) at such low levels, and the recovery of added cadmium in paint samples was from 94.6% to 102%. This method is readily applicable to the determination of cadmium in paint samples.     

关于影响镧、钐与铕测定灵敏度原因的探讨

实验证明，在石墨表面上原子化时，镧、钐或铕与炽热的石墨反应生成难解离的碳化物是导致镧、钐和铕测定灵敏度低与严重记忆效应的原因。用钽探针原子化测定钐样品时，钐物种与钽氧化物之间发生反应，生成复合物SmTaO4、镶嵌于钽探针表面的裂痕内，阻碍了钐原子化，导致测定钐的灵敏度下降。