Optimised method of coal digestion for trace metal determination by atomic absorption spectroscopy

Understanding the transport of trace elements through a coal-fired power plant requires reliable analytical methods for these elements in all the ingoing and outgoing mass streams. Coal and different kinds of ashes comprise the most abundant mass streams in such a plant. As a continuation of our previous work, we have optimised a digestion method for the AAS determination of heavy metals in coal samples. It has become evident that complete dissolution of metals in coal samples and accurate results in subsequent analysis can be obtained by means of applying pressurised digestion under microwave heating. The combination of HNO₃ (conc.) and HF (conc.) in the volume ratio of 50 : 1 attacked the sample well enough, and good recoveries for all the metals studied were obtained. Surprisingly good results were obtained also when HNO₃ alone was used as the digestion acid. Received: 18 June 1998 / Revised: 23 September 1998 / Accepted: 24 September 1998     

The determination of trace quantities of molybdenum by atomic absorption spectroscopy

A procedure is described for the determination of trace quantities of molyb denum by atomic absorption spectroscopy. Molybdenum is cornplexed with ammoni um pyrollidine dithiocarbamate or 8-hydroxyquinoline and extracted into n-amyl methyl ketone. Molybdenum is then determined by atomic absorption spectroscopy. Interferences have been eliminated and detection limits of 0.002 p.p.m, for water samples, 0.1 p.p.m. for samples of dried plant material, and 1 p.p.m. for silicate rock samples have been obtained.     

Validation of an analytical method to determine trace metal impurities in fluoride compounds by flame atomic absorption spectroscopy

 The development of an analytical method for the determination of some heavy metals (Fe, Cu, Co, Zn and Ni) in fluoride compounds [Cu(BF₄)₂, Sn(BF₄)₂, Pb(BF₄)₂ and HBF₄] by flame atomic absorption spectroscopy is described. This method is to be used as a routine analytical method in an industrial quality control laboratory. To this end the "performance characteristics" of an instrumental analytical method such as matrix effects, sensitivity, linearity, detection and quantitation limits, precision and accuracy were evaluated for every system under study. The results of these investigations showed that non-spectral interferences (due to the presence of large concentrations of major metals such as Cu, Sn and Pb) were observed. Nevertheless it was possible to define a matrix concentration interval where matrix effects were not statistically significant, and therefore a direct calibration approach could be used as the calibration tool whenever the major metal concentration was not higher than 40×10^–3 kg l^–1. A guide to the developement of an analytical method for trace metal determination is provided. General tools for quality control have been used in order to show how an analytical method can be tested daily and evaluated in a convenient manner. Received: 29 January 1997 Accepted: 11 March 1997     

The determination of palladium by atomic absorption spectroscopy

A commercial atomic absorption apectrophotometer was used without modification to establish the most suitable operating, conditions for the determination of palladium. A study of the effect of organic solvents miscible with water, and of acids was then carried out. In general, organic solvents led to increased sensitivity. With a complex of palladium, Pd(py)₂Cl₂, in 50% ethanol, the sensitivity was also enhanced and, with a hexone solution of the complex, Pd(py)₂(SCN)₂, amounts of palladium below 2 p.p.m. could be determined.     

原子吸收光度法间接测定甲基托布津的含量

用标准Cu^2 溶液和样品中的甲基托布津在氨碱性环境下作用，产生定量沉淀，离心分离未反应的Cu^2 ，用原子吸收分光光度计测定Cu^2 浓度可间接求得样品中的甲基托布津的含量。本法的检出限10mg/L；测定范围为10-120mg/L；RSD小于3．2％。本方法的测定结果与络合滴定法与分光光度法的结果能很好地符合。     

原子吸收法间接测定呋喃唑酮

运用原子吸收法间接测定了呋喃唑酮片剂中的呋喃唑酮。方法基于呋喃唑酮在N,N-二甲基甲酰胺（DMF）与乙醇的混合溶剂中与Zn-NH4Cl反应生成胲,胲与Tollens试剂按1：2的关系反应生成单质Ag沉淀,通过测定上清液中剩余Ag的原子吸收光度来间接测定呋喃唑酮。已用于呋喃唑酮片剂中呋喃唑酮的测定。     

The determination of aluminum by atomic absorption spectroscopy

A study of the determination of aluminum by atomic absorption spectroscopy has been made using a solution of aluminum cupferrate in 4-methyl-2-pentanone to feed oxy-acetylene or oxy-hydrogen flames. Investigations were made on the effect of the variables, viz., slit-width, flow rates, flow ratios and flame positions, on the intensity of aluminum absorption. The data were studied to determine the optimum conditions. These investigations brought out the comparative merits of the two flames for the determination of aluminum, and also elucidated the mechanism of aluminum absorption in an oxy-acetylene flame.     

Determination of trace amounts of scandium by atomic absorption spectroscopy

Optimum instrumental conditions were investigated for the determination of trace quantities of scandium by atomic-absorption spectroscopy. Enhancement effects by organic solvents and by complex extractions were also studied. (46)Sc was used to establish the optimum extraction conditions. A sensitivity of 0.06 ppm of Sc was observed when using extraction into oxine-butanol and atomic absorption was measured with an acetylene-nitrous oxide flame.     

The determination of metal content in biochemical products by atomic absorption spectroscopy. I

Summary Atomic absorption spectroscopy has been used to determine the copper content of commercial chlorophyllins and of the iron in Cytochrome-C. The procedure is rapid and direct as preparation involves only weighing and dissolution of the sample. The precision of the methods is excellent. The values obtained compare favorably with those obtained by the standard colorimetric methods.

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Zusammenfassung Mit Hilfe der Atomabsorption wurde der Kupfergehalt in käuflichem Chlorophyllin und der Eisengehalt in Cytochrom C bestimmt. Da zur Vorbereitung nur die Einwaage und die Auflösung der Probe nötig sind, führt das Verfahren rasch ans Ziel. Seine Genauigkeit ist ausgezeichnet und seine Resultate entsprechen den Ergebnissen der kolorimetrischen Standardmethoden.

     

原子吸收光谱法间接测定碘解磷定

研究了原子吸收光谱法间接测定碘解磷定。在pH5．0溶液中,当四苯硼钠过量时可完全沉淀碘解磷定,在滤液中加入过量的KCl沉淀剩余的四苯硼钠．再测定滤液中的过量的钾,可以计算得到碘解磷定的量。方法的回收率在98％～103％之间．相对标准偏差为1．8％。     

Low volume microwave digestion for the determination of selenium in marine biological tissues by graphite furnace atomic absorption spectroscopy

A microwave digestion method for the determination of marine biological tissues has been developed to allow determination of selenium in small sample sizes (< 0.1 g). The benefits of this technique include maintaining concentrates in extracts without the subsequent over dilution encountered when using larger vessels, increased sample throughput and reduced loss of volatile material. Freeze dried biological material (< 0.1 g) and nitric acid (1 ml) were placed into 7 ml screw top Teflon vessels which are completely sealed on capping. Two 7 ml vials were placed into larger 120 ml vessels fitted with a Teflon spacer and 10 ml of distilled water. The effects of microwave power and time, and sample mass on selenium recovery from three marine standard reference materials (NIST SRM 1566a Oyster Tissue, NRCC DORM-1 Dogfish Muscle and NRCC TORT-1 Lobster Hepatopancreas) were examined. The optimum conditions: 600 W, 2 min; 0 W, 2 min; 450 W, 45 min, allowed quantitative recoveries of selenium from these and three other standard reference materials (NRCC DOLT-1 Dogfish liver, NIST RM-50 Albacore tuna and IAEA MA-A-2 fish flesh). Studies on sample mass showed that the analysis of sample masses from 0.025 to 0.1 g gave selenium concentrations within the certified range. Six species of selenium: selenite, selenate, selenomethionine, selenocysteine, selenocystamine, and trimethyl selenonium were added to oyster, dogfish, and lobster tissues. Recoveries were near quantitative for all species (94–105%) except trimethyl selenonium (90–101%).     

The determination of aluminum and beryllium by atomic absorption spectroscopy

The use of atomic absorption spectroscopy for the determination of aluminum and beryllium has been studied. The nitrous oxide-acetylene flame was found to be useful for the determination of trace amounts of either aluminum or beryllium. Beryllium can also be determined in an oxy-acetylene flame at the 1 p.p.m. level and upwards if the aqueous solution contains 10% of diethylene glycol diethyl ether. The determinations were essentially free from interferences.     

Alkali metal fluoride matrix modifiers for the determination of trace levels of silicon by graphite furnace atomic absorption spectrometry

A method is described for the determination of silicon by graphite-furnace atomic absorption spectrometry with alkali metal fluorides as matrix modifiers. Alkali metal fluorides react with silicon to produce metal hexafluorosilicates, which are stable at temperatures as high as 1120– 1300°C, depending on the particular metal used. At higher temperatures, alkali metal hexafluorosilicates decompose into the metal fluoride and silicon tetrafluoride. The subsequent gas-phase atomization of silicon tetrafluoride occurs rapidly, and produces clean, sharp absorption peaks. When used in conjunction with a zirconium-treated graphite tube, this method has a sensitivity of 50 pg Si at a confidence interval of 95%. There is no evidence of silicon carbide formation in the graphite tube, and very little evidence of any deterioration of the zirconium-treated surface, as demonstrated by the fact that more than 200 samples can be processed on a single graphite tube without a decrease in sensitivity or change in the baseline.     

The determination of magnesium in silicates by atomic absorption spectroscopy

The determination of magnesium in silicates by atomic absorption spectroscopy using a hot flame is discussed. Interference by aluminium observed, in the air-acetylene flame is overcome by using the hotter nitrous oxide-acetylene flame. There is some evidence to suggest that the alkali metals interfere in this determination but this is not confirmed in the results obtained on standard rock samples. Values for magnesium are given for some new rock standards recently distributed by the U.S. Geological Survey.     

The determination of titanium in alloys by atomic absorption spectroscopy

A method is described for the determination of 0.1–1.2 % of titanium in steels, permanent magnet alloys and cast iron using atomic absorption spectroscopy with hydrofluoric acid solutions and a nitrous oxide-acetylene flame. No preliminary separations are required. When the correct conditions are employed there is no interference from the other elements commonly found in these alloys.     

An improved method for the determination of trace levels of arsenic and antimony in geological materials by automated hydride generation—atomic absorption spectroscopy

An improved, automated method for the determination of arsenic and antimony in geological materials is described. After digestion of the material in sulfuric, nitric, hydrofluoric and perchloric acids, a hydrochloric acid solution of the sample is automatically mixed with reducing agents, acidified with additional hydrochloric acid, and treated with a sodium tetrahydroborate solution to form arsine and stibine. The hydrides are decomposed in a heated quartz tube in the optical path of an atomic absorption spectrometer. The absorbance peak height for arsenic or antimony is measured. Interferences that exist are minimized to the point where most geological materials including coals, soils, coal ashes, rocks and sediments can be analyzed directly without use of standard additions. The relative standard deviation of the digestion and the instrumental procedure is less than 2% at the 50 μg l^-1 As or Sb level. The reagent-blank detection limit is 0.2 μg l^-1 As or Sb.     

Slurry sampling graphite furnace atomic absorption spectrometry: determination of trace metals in mineral coal

A procedure for lead, cadmium and copper determination in coal samples based on slurry sampling using an atomic absorption spectrometer equipped with a transversely heated graphite tube atomizer is proposed. The slurries were prepared by weighing the samples directly into autosampler cups (5-30 mg) and adding a 1.5 ml aliquot of a diluent mixture of 5% v/v HNO(3), 0.05% Triton X-100 and 10% ethanol. The slurry was homogenized by manual stirring before measurement. Slurry homogenization using ultrasonic agitation was also investigated for comparison. The effect of particle size and the use of different diluent compositions on the slurry preparation were investigated. The temperature programmes were optimized on the basis of pyrolysis and atomization curves. Absorbance characteristics with and without the addition of a palladium-magnesium modifier were compared. The use of 0.05% m/v Pd and 0.03% m/v Mg was found satisfactory for stabilizing Cd and Pb. The calibration was performed with aqueous standards. In addition, a conventional acid digestion procedure was applied to verify the efficiency of the slurry sampling. Better recoveries of the analytes were obtained when the particle size was reduced to <37 mum. Several certified coal reference materials (BCR Nos. 40, 180, and 181) were analyzed, and good agreement was obtained between the results from the proposed slurry sampling method and the certificate values.     

A low-cost flame atomic absorption spectrometry method for determination of trace metals in aqueous samples

A simple and fast method for the extraction into xylene of sub mug l(-1) concentrations of metals using ammonium diethyldithiophosphate (DDTP) as a complexing reagent and their subsequent determination by flame atomic absorption spectrometry is described. The method was tested in sea water spiked with Au at a concentration of 3.0 mug l(-1). The extraction was carried out until the aqueous to organic phase ratio achieved a 1000-fold preconcentration of metal. Optimisation of extraction parameters and the effect of Fe interference was investigated. Sea water samples spiked with Au produced an average recovery of 95% and the detection limit (3sigma) in deionized water was 2.9 ng l(-1). High enrichment factors could be obtained due to the small final volume (mul) of organic solvent.