微波溶解光度法测定茶叶中痕量锗

采用微波加热和双层聚四氟乙烯密闭容器，以HNO3－HClO4为消解试剂、MgO为外层吸收剂，用CCl4萃取，光度法快速测定茶叶中痕量锗。研究了消化茶叶的最佳条件。萃取锗的最佳酸度及其它影响因素。该方法具有选择性高，成本低等特点，其精密度和准确度令人满意。     

Radiochemical separation methods for the determination of some toxic elements in biological reference materials

The present paper describes radiochemical separation procedures developed for the determination of the elements As, Cr, Hg, Sb and Se in biological reference materials. The methods chosen utilize ion exchange, retention on inorganic exchangers and solvent extraction techniques for the isolation of the elements of interest. These procedures are more rapid than previously used methods, such as distillation and precipitation. As to the sample dissolution, the following procedures were tested using radioactive tracers and reference materials: treatment of the materials in teflon bombs with a mixture of HNO₃+H₂SO₄ or HNO₃ only in a normal oven, and with HNO₃ in a microwave oven using specially designed digestion bombs.     

Aufschluß biologischer Matrices für die Bestimmung sehr niedriger Spurenelementgehalte bei begrenzter Einwaage mit Salpetersäure unter Druck in einem Teflongefäß

For the determination of trace elements (< 10^?4%) in biological materials (e.g. tissue, food, sewage muds) in samples ≤ 500 mg a pressure decomposition with nitric acid or a mixture of nitric and hydrofluoric acid in a teflon tube is described. The recoveries for the volatile elements, e.g. Hg, Se and I, in the ng-range were investigated by the tracer method and were found to be ≥ 98%.     

H3PW12O40/CNTs吸附-分解NOx及微波作用效果

将碳纳米管(CNTs)载体分别经混酸与硝酸蒸气预处理并在不同温度下煅烧, 然后分别采用浸渍法及机械研磨法负载磷钨酸(HPW), 制备出HPW/CNTs催化剂, 对比考察了上述催化剂对NOx的吸附与分解效果. 在空速为10000 h-1、 吸附温度为200℃的条件下, 用0.5 g催化剂对1696 mg/m3的NOx进行吸附实验, 结果表明, 以硝酸蒸气预处理且经300℃煅烧后的CNTs为载体, 采用机械研磨负载法制备的催化剂HPW/CNTs对NOx的吸附率与吸附能力最高, 分别为54%与16.6 mg NOx/(g\5h). 对吸附NOx后的催化剂体系进行了催化分解NOx的程序升温脱附-质谱(TPD-MS)研究, 结果表明, 所吸附的NOx在快速升温过程中发生分解, 在此过程中有氧产生, 分解产物包括N2, O2及N2O. 采用电阻炉快速加热与微波辐射2种方式分别对吸附的NOx进行催化分解, 结果表明, 微波功率为700 W时, NOx分解为N2的收率为33.3%, 高于电阻炉以150℃/min快速升温的N2收率. 使用过的催化剂通水蒸气后可实现再生, 对再生后的催化剂进行循环使用研究, 结果表明, 再生后的催化剂吸附与催化分解NOx的性能未有明显下降.     

Analysis of standard reference materials after microwave-oven digestion in open vessels using graphite furnace atomic absorption spectrophotometry and Zeeman-effect background correction

Summary Heating-covered teflon digestion vials located inside a reheatable container in the presence of different acid mixtures with microwave oven dissolve the metals from biological and environmental certified reference materials. Pb, Cd, Cu, Mn and Fe from the dissolved samples are determined by graphite furnace atomic absorption spectrophotometry and Zeeman-effect background correction. The method allows the treatment of about 100 samples per operation.     

Atomic Emission Analysis of Human Nails for the Content of Trace Elements

To obtain data on the concentrations of trace elements in a human body, different biological samples are used; however, nails have some advantages. An optimized procedure is developed for the acid mineralization of human nails for the subsequent determination of trace elements therein by arc atomic emission spectrometry with excitation of a spectrum of a dry mineralization residue from the end of a carbon electrode. A mixture of conc. HNO₃ (1 mL) and conc. H₂O₂ (0.1 mL) was shown to be an optimum reagent for the decomposition of a nail sample with a weight of 0.1 g. The efficiency and process features of acid decomposition upon heating on a plate and in a microwave oven were compared. Seventy three nail samples were analyzed for the contents of Ag, Al, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, and Zn according to the developed procedure. The calculated statistically average contents and concentration ranges of the above-mentioned elements were compared with data of other publications.     

Mechanical degradation of filter polymer materials: Polyphenylene sulfide

Polyphenylene sulfide (PPS) is known as a material resistant to high temperature and chemicals; however, there are arguments on the durability of PPS non-woven fabrics to chemicals, such as nitric acid (HNO₃), sulfuric acid (H₂SO₄), and hydrochloric acid (HCl). Therefore, this work aims at investigating the degradation of PPS non-woven fabrics in HNO₃, H₂SO₄ and HCl, and at confirming acid durability of PPS non-woven fabrics. In addition, this paper also studies the interaction among these three acids by measuring the retention of strength in binary or tertiary mixtures of these three acids. A discussion has been made on the acceleration/retardation of PPS degradation by the interactive effects, and also on the chemistry related to the degradation by these acids. Furthermore, there is a linear relationship between the nitric acid concentration and the proportion of carbon in the remaining PPS structures after 100 h of acid exposure. Also, this proportion of carbon is a good indicator of the retained strength in PPS fabrics.     

Kinetics of sodium ethylenediaminetetraacetate mineralization by cerium(IV) in nitric acid medium

The process of sodium ethylenediaminetetraacetate (EDTA) mineralization by cerium(IV) in nitric acid medium was studied in batch and continuous feeding modes. In the batch mode EDTA solution was fed into the reactor in one stroke and in the continuous mode it was fed with a constant flow rate during a definite time interval. Cerium(IV) concentration was kept at high and constant level by selecting correct relation between cerium(IV) production in the electrochemical cell and the EDTA added. During the organic mineralization process cerium(IV) is reduced to cerium(III). The process was carried out at different temperatures, concentrations of nitric acid and cerium(IV). To obtain the limiting factors in the batch mode reaction, the dependence of CO₂ evolution with time and carrier gas blowing rate was studied. Application of the model previously developed by us to the continuous process gave us the possibility to calculate pseudo first order kinetic constant on the basis of CO₂ evolution data of both EDTA destruction regimes during feeding mode and after stopping organic addition. The efficiency of organic destruction estimated on the basis of CO₂ evolved was in the range 75–95% and on the basis of liquid phase residual organic carbon analysis 95–99%.     

Determination of calcium, magnesium and strontium in soils by flow injection flame atomic absorption spectrometry

Several procedures for the determination of Ca, Mg and Sr in soils have been compared on the basis of the accuracy of analysis of two NIST reference materials (Montana Soils SRM 2710 and SRM 2711). Samples were dissolved in a mixture of hydrofluoric and nitric acids in sealed vessels in a microwave oven and in teflon beakers on a hot plate. The digests obtained from both dissolution methods were evaporated to dryness in an attempt to remove silicon. Boric acid was added to prevent the precipitation of the lanthanum releasing agent (as lanthanum fluoride) and potassium was added as an ionization buffer. Determinations were made by flame atomic absorption spectrometry with both the nitrous oxide-acetylene flame and the air-acetylene flame, with calibration either by standard additions or against external standards matrix matched with respect to nitric acid, boric acid, lanthanum and potassium. The silicon remaining in the solution was also determined by external calibration. A single-line flow injection manifold was used to overcome any problems due to the presence of high dissolved solids. A volume of 300 mul was injected into a water carrier stream flowing at 8 ml min(-1). To determine Ca in the air-acetylene flame, it was necessary to remove silicon. Magnesium was determined in either flame without complete removal of the silicon, however, for the determination of Sr, it was necessary to remove the silicon and use the nitrous oxide-acetylene flame. The indicative value for Sr in SRM 2710 was too low: the value determined was 360+/-30 mug g(-1).     

Determination of aluminium and chromium in slurried baby food samples by electrothermal atomic absorption spectrometry

Electrothermal atomic absorption spectrometry was used to determine aluminium and chromium in different types of baby foods. Samples without previous treatment were introduced into the atomizer as suspensions, which were prepared in a medium containing 0.1% (w/v) Triton X-100 (for chromium) or 10% (v/v) ethanol (for aluminium), 5% (v/v) concentrated hydrogen peroxide, and 0.5% (v/v) concentrated nitric acid. The slurries were homogenized with a potter and introduced directly into the furnace. The presence of nitric acid allowed a substantial amount of analyte to be extracted to the liquid phase. No matrix effect was observed and aqueous standard solutions were used for calibration. The detection limits were 4 and 50 pg for chromium and aluminium, respectively; characteristic masses were 3.8 pg for chromium and 18 pg for aluminium. Reliability of the procedures was checked by statistically comparing the results with those obtained with a previous microwave oven mineralization stage and by analyis of several certified reference materials. Values for the aluminium content ranged between 0.4 and 3.0 microg/g, and for chromium between 0.003 and 0.06 microg/g.     

Determination of metals in small samples by atomic absorption and emission spectrometry with discrete nebulization

Eight elements in NBS-SRM 1577 bovine liver and other biological standards are determined by flame atomic absorption (Ca, Cu, Fe, Mg, Mn and Zn) and emission (K and Na) spectrometry. Samples (2 mg) weighed into a 3.8-ml teflon vessel are decomposed with 40 μl of (5 ÷ 1) nitric—perchloric acids in a sealed teflon vessel. A 75-μl or 100-μl aliquot of the diluted sample solution is injected into a small teflon funnel coupled directly to the nebulizer needle of the spectrometer. The results obtained agree well with certified values: the standard deviation is about 2%.     

The mechanism of the sonochemical degradation of benzoic acid in aqueous solutions

The sonolytic degradation of benzoic acid in aqueous solution was investigated at an ultrasonic frequency of 355 kHz. The degradation rate was found to be dependent upon the solution pH and the surface activity of the solute. The degradation rate was favoured at a solution pH lower than the pK _a of benzoic acid. At pH < pK _a, HPLC, GC and ESMS analysis showed that benzoic acid could be degraded both inside the bubble by pyrolysis and at the bubble/solution interface by the reaction with OH radicals. At higher pH (> pK _a) benzoic acid could only react with OH radicals in the bulk solution. During the sonolytic degradation of benzoic acid, mono-hydroxy substituted intermediates were observed as initial products. Further OH radical attack on the mono-hydroxy intermediates led to the formation of di-hydroxy derivatives. Continuous hydroxylation of the intermediates led to ring opening followed by complete mineralization. Mineralization of benzoic acid occurred at a rate of < 40μM/h.     

Preparation and chain extension of C100dicarboxylic acid

The selective degradation of polyethylene crystals with fuming nitric acid has been used to prepare a C₁₀₀ chain with terminal functional groups. After treating this product with concentrated sulphuric acid, it is shown by average molecular weight, titration and infra-red spectroscopy measurements that each molecule contains two carboxylic acid groups. This C₁₀₀ dicarboxylic acid is chain extended with several low molecular weight difunctional coupling agents. Block copolymers of this acid and poly(propylene glycol) have been prepared.     

Evolved Gas Analysis of Some Solid Fuels by TG-FTIR

FTIR spectrometry combined with TG provides information regarding mass changes in a sample and permits qualitative identification of the gases evolved during thermal degradation. Various fuels were studied: coal, peat, wood chips, bark, reed canary grass and municipal solid waste. The gases evolved in a TG analyser were transferred to the FTIR via a heated teflon line. The spectra and thermoanalytical curves indicated that the major gases evolved were carbon dioxide and water, while there were many minor gases, e.g. carbon monoxide, methane, ethane, methanol, ethanol, formic acid, acetic acid and formaldehyde. Separate evolved gas spectra also revealed the release of ammonia from biomasses and peat. Sulphur dioxide and nitric oxide were found in some cases. The evolution of the minor gases and water parallelled the first step in the TG curve. Solid fuels dried at 100°C mainly lost water and a little ammonia. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optimization of digestion methods for sewage sludge using the Plackett-Burman saturated design

The Plackett-Burman saturated factorial design was used to select optimized dissolution conditions for sewage sludge samples. Three different digestion methods were applied: i) microwave oven digestion in a domestic oven with Parr-type reactors; ii) microwave oven digestion with controlled-pressure reactors; iii) pressure bomb reactor heated on a hot plate. The three methods were validated by statistically comparing the metal contents found with the certified ones of the sewage sludge sample (BCR 145R). No significant differences were obtained and the RSD values were lower than 3% in all cases. The metals were determined by flame-AAS. The variables studied were the following: microwave power; digestion time; predigestion; volume of hydrochloric acid; volume of hydrofluoric acid; volume of nitric acid. The operative advantages offered by microwave digestion with controlled-pressure reactors were also considered. Received: 23 July 1997 / Revised: 31 October 1997 / Accepted: 5 November 1997     

Optimization of digestion methods for sewage sludge using the Plackett-Burman saturated design

The Plackett-Burman saturated factorial design was used to select optimized dissolution conditions for sewage sludge samples. Three different digestion methods were applied: i) microwave oven digestion in a domestic oven with Parr-type reactors; ii) microwave oven digestion with controlled-pressure reactors; iii) pressure bomb reactor heated on a hot plate. The three methods were validated by statistically comparing the metal contents found with the certified ones of the sewage sludge sample (BCR 145R). No significant differences were obtained and the RSD values were lower than 3% in all cases. The metals were determined by flame-AAS. The variables studied were the following: microwave power; digestion time; predigestion; volume of hydrochloric acid; volume of hydrofluoric acid; volume of nitric acid. The operative advantages offered by microwave digestion with controlled-pressure reactors were also considered. Received: 23 July 1997 / Revised: 31 October 1997 / Accepted: 5 November 1997     

Digestion of plastic materials for the determination of toxic metals with a microwave oven for household use.

A rapid sample-digestion method for the determination of toxic metals, cadmium, chromium, and lead, in polyethylene and polyvinyl chloride has been developed by using a microwave oven for household use. An appropriate amount of the sample taken in a PTFE decomposition vessel was mixed with nitric acid or nitric and sulfuric acids. The vessel was heated in a microwave oven by a predetermined operating program. The digested sample was diluted to a definite volume with water after evaporating most of the nitric acid. The precipitate, if formed, was filtered off by a membrane filter. The metals were determined by ICP-AES. The sample digestion required 5 min (for 20-mg sample) to 25 min (for 60-mg sample). The analytical results obtained for cadmium, chromium, and lead in a polyethylene certified reference material, BCR-680, digested with nitric acid, were in good agreement with the certified values.     

The surface characterization and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr ODS steels for nuclear fuel reprocessing application

In spent fuel nuclear reprocessing plant, nitric acid is the main medium used in PUREX method. The passive film compositions and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr oxide dispersion strengthened steels in different nitric acid concentrations were studied. The open circuit potential is shifted toward more noble potential as the concentrations increased from 1 M HNO₃ to 9 M HNO₃ in all the investigated alloy steels. The results of the potentiodynamic polarization plots also exhibited a shift in corrosion potential as the concentrations increased from 1 M to 9 M HNO_3. This shift is undesirable because of risk of overshooting the potential beyond passive region and may result into transpassive corrosion. The X-ray photoelectron spectroscopy results of the passive film analysis are composed mostly of Fe₂O₃, Cr₂O₃, and Y₂O₃, and the depth profile of Fe and Cr concentrations vary depending upon the nitric acid concentration. The surface morphology after the corrosion test does not show intergranular corrosion attack at the nitric acid concentrations studied. It is desirable that materials for use in nitric acid service are resistant to such corrosion induced degradation.     

Ion exchange behavior of plutonium(IV) on imidazolium nitrate immobilized resin

Imidazolium nitrate anchored on poly(styrene-divinylbenzene) co-polymer, Im-NO₃, has been synthesized and evaluated for plutonium purification. The results are compared with those obtained using Dowex 1 × 4 anion exchange resin. The distribution coefficient (K_d) of Pu(IV) increased with increase in concentration of nitric acid, reached a maximum at 8 M, followed by decrease in K_d values. Rapid ion exchange of Pu(IV) followed by the establishment of equilibrium occurred within 100 min of equilibration and the data was fitted in to first order rate equation. Variation of distribution coefficient of Pu(IV) as a function of exchange capacity and nitrate ion concentration suggest the involvement of anion exchange mechanism is responsible for extraction. The apparent ion exchange capacity was 310 mg/g at 8 M nitric acid. The performance of the Im-NO₃ under dynamic condition was assessed by column breakthrough experiments. Radiolytic degradation of Im-NO₃ resin in presence and absence of nitric acid (8 M) was studied and the results are reported in this paper.     

A study of sample mineralization methods for arsenic analysis of blood and urine by hydride generation and graphite furnace atomic absorption spectrometry

Mineralization procedures for blood and urine suitable for the determination of arsenic by Hydride Generation Atomic Absorption Spectrometry (HGAAS) are studied on model samples, and the results are utilized in biological monitoring investigations. The objective of this work is to obtain good total As recoveries for both matrices regardless of added As species (As(III), As(V), DMA, MMA, AsB, or AsC). Prior to the HGAAS analyses, preparation procedures were controlled under optimised conditions by graphite furnace atomic absorption spectrometry (GFAAS). Two preparation procedures for urine give As recoveries close to 100% by HGAAS: a) dry ashing at 420°C with Mg(NO₃)₂ on a hot plate, and b) microwave oven decomposition with (NH₄)₂S₂O₈. For blood samples, As recoveries by HGAAS range between 95 and 108% for all species when using dry ashing after a pretreatment of samples with HNO₃ and H₂O₂ in a microwave oven. Wet digestion with (NH₄)₂S₂O₈ in a microwave oven gives recoveries very near 100% for As _inorg. and MMA. For other As species in spiked blood samples, recoveries of less than 20% As are found. Precision and detection limits obtained by both techniques are evaluated as well. For arsenic concentrations of 20 μg dm⁻³ or more in blood and urine, a chemical modifier is recommended for GFAAS analysis; it may or may not be proceeded by a mineralization step. For low As levels encountered in the unexposed population, the HGAAS technique provides reliable results only if a very complete mineralization procedure is used.