Thermal decomposition of PTFE in the presence of silicon,calcium silicide,ferrosilicon and iron

Simultaneous TG/DTA has been used to study the thermal decomposition of binary compositions containing polytetrafluoroethene (PTFE) with silicon (Si), calcium silicide (CaSi₂), ferrosilicon (FeSi) or iron (Fe) powders. In nitrogen and under dynamic heating program the thermal decomposition of Si/PTFE and CaSi₂/PTFE is an exothermic process. The other two compositions decompose endothermically. In each case the decomposition reactions show first-order kinetics but only iron does not change considerably the kinetics of PTFE depolymerization. The constants of the decomposition rate at 850 K for silicon containing reducers are about four times higher than those of PTFE and Fe/PTFE. This revised version was published online in July 2006 with corrections to the Cover Date.     

Separation and determination of uranium in phosphoric acid medium using high-performance ion chromatography

Journal of Radioanalytical and Nuclear Chemistry - A new method is presented for measuring of uranium at low levels in crude phosphoric acid without preconcentration or complexing agents using...     

Separation of uranium from iron in ground water samples using ion exchange resins

Uranium determination in environmental samples is faced with problems due to presence of iron and other major elements. Iron is also used many a times for pre-concentration of uranium and actinides. Separation of milligram quantity of Fe from microgram quantity of uranium becomes essential during the estimation step. A simple two step procedure has been standardized for separating uranium and iron using anion exchange in 0.025 M H₂SO₄. Quantitative recovery of uranium was obtained as well as good separation from iron. This method was applied for estimation of uranium in water samples.     

Determination of aluminium using high performance chelation ion chromatography

The suitability of high performance chelation ion chromatography (HPCIC) using postcolumn reaction for the separation and determination of dissolved aluminium in complex samples was investigated. Use of a chelating ion-exchanger allowed for differentiation between kinetically labile and kinetically stable species of aluminium. Separation through a combination of chelation and cation-exchange was achieved using a 200 x 4.0 mm id column packed with particles of silica functionalised with iminodiacetic acid, with nitric acid-potassium chloride eluents. A temperature anomaly causing a five-fold increase in column efficiency for aluminium is believed to be a result of localised temperature effects in the particular type of instrument used. Postcolumn reagents investigated for the photometric detection included Tiron, Pyrocatechol Violet, Chrome Azurol S, and Eriochrome Cyanine R. The lowest detection limit (2.7 microg/L for a 100 microL sample volume) was achieved using 0.25 mM Eriochrome Cyanine R in 0.2 M hexamine (pH 6.1) with 1 mM cetyltrimethylpyridium bromide (CTAB). The optimised HPCIC system was applied successfully to the quantification of labile aluminium in paper mill process water.     

Determination of tungstate in soils and sludges by using single-column ion chromatography

A procedure has been developed for the determination of tungstate at trace levels in aqueous extracts of soil and sludge by single-column ion chromatography (SCIC). Chromatographic parameters based on ion selectivity, time of determination and signal response were optimized for tungstate with the simultaneous detection of nitrate and sulfate. Chloride, phosphate, chromate, molybdate and vanadate were found not to interfere in the determination. A low-capacity resin-based column was used for the separation with p-hydroxybenzoic acid (5 mM) at pH 8.5 as the eluent. The limit of detection defined as three times the signal-to-noise ratio was 170 μg l^?1 (2-ml sample). The resolution between tungstate and sulfate was R_s=2.84. The results for aqueous extracts agree closely with those obtained by an accepted spectrophotometric method.     

离子色谱法测定饮用水中的5种卤代乙酸

利用IonPac AS19大容量阴离子交换色谱柱对水中的一氯乙酸、二氯乙酸、三氯乙酸、一溴乙酸、二溴乙酸5种卤代乙酸(HAAs)进行了分离,优化了分离条件.通过控制分离温度实现了二氯乙酸(DCAA)与NO2-的分离;通过梯度洗脱使三氯乙酸(TCAA)与SO42-得到较好、较快的分离;通过中和脱气法解决了在大量CO32-(HCO3-)存在时对实验的干扰.DCAA、TCAA的检出限(以3倍信噪比计)分别达到了2.50 μg/L和3.75 μg/L.5种HAAs在10.0～2 000.0 μg/L线性范围内线性相关系数在0.999以上.     

Determination of bromate in sea water using multi-dimensional matrix-elimination ion chromatography

A multi-dimensional matrix-elimination ion chromatography approach has been applied to the determination of bromate in seawater samples. Two-dimensional and three-dimensional configurations were evaluated for their efficacy to eliminate the interference caused by the high concentration of ubiquitous ions present in seawater, such as chloride and sulfate. A two-dimensional approach utilising a high capacity second dimension separation comprising two Dionex AS24 columns connected in series was applied successfully and permitted the determination of bromate in undiluted seawater samples injected directly onto the ion chromatography system. Using this approach the limit of detection (LOD) for bromate based on a signal to noise ratio of 3 was 1050 μg/L using a 500 μL injection loop. Good linearity was obtained for bromate with correlation coefficients for the calibration curves of 0.9981 and 0.9996 based on peak height and area, respectively. A three-dimensional method utilising two 10-port switching valves to allow sharing of the second suppressor and detector between the second and third dimension separations showed better resolution and detection for bromate and reduced the LOD to 60 μg/L for spiked seawater samples. Good linearity was maintained with correlation coefficients of 0.9991 for both peak height and area. Ozonated seawater samples were also analysed and exhibited a non-linear increase in bromate level on increasing ozonation time. A bromate concentration in excess of 1770 μg/L was observed following ozonation of the seawater sample for 120 min. Recoveries for the three-dimensional system were 92% and 89% based on peak height and area, respectively, taken over 5 ozonated samples with 3 replicates per sample.     

Anion analysis in uranium ore concentrates by ion chromatography

In the present exploratory study, the applicability of anionic impurities for attributing nuclear material to a certain chemical process or origin has been investigated. Anions (e.g., nitrate, sulphate, fluoride, chloride) originate from acids or salt solutions that are used for processing of solutions containing uranium or plutonium. The study focuses on uranium ore concentrates (“yellow cakes”) originating from different mines. Uranium is mined from different types of ore body and depending on the type of rock, different chemical processes for leaching, dissolving and precipitating the uranium need to be applied. Consequently, the anionic patterns observed in the products of these processes (the “ore concentrates”) are different. The concentrations of different anionic species were measured by ion chromatography using conductivity detection. The results show clear differences of anion concentrations and patterns between samples from different uranium mines. Besides this, differences between sampling campaigns in a same mine were also observed indicating that the uranium ore is not homogeneous in a mine. These within-mine variations, however, were smaller than the between-mine variations.     

Determination of 94Nb in radioactive waste using ion exchange chromatography

This paper describes a rapid method of ⁹⁴Nb pre-concentration, separation and purification by using cation and anion exchange resins. The method is suitable for analyzing highly contaminated radioactive waste samples in a relatively short time and high decontamination factors. The use and effectiveness of the method was successfully tested by analysis of samples from nuclear reactor parts such as control rod drive shaft, shielding cassettes, neutron in-core measurement channels (KNI), pressure vessel construction material and fuel cassette construction material samples.     

Determination of sodium,potassium, calcium and magnesium cations in biodiesel by ion chromatography

This work reports an ion chromatographic (IC) method for the quantitative determination of inorganic cations (Na⁺, K⁺, Mg²⁺ and Ca²⁺) in biodiesel samples that were synthesized from different vegetable oils and fat. The proposed method uses water extraction, heating and ultrasound. The limits of detection (LOD) for each ion, in milligrams of the analyte per kilogram of biodiesel (mg kg⁻¹), were respectively: 0.11 (Na⁺); 0.42 (K⁺); 0.23 (Ca²⁺); and 0.36 (Mg²⁺). The accuracy of the method was studied through recovery tests. For comparison, two samples were also analyzed using an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) procedure. The paired Student t test and the Snedecor F test showed that both methods offer equivalent results in terms of accuracy and precision. The operational simplicity, accuracy and precision of the proposed method suggest that it can be a good alternative for the determination of inorganic cations in biodiesel samples.     

Determination of calcium in uranium by X-ray fluorescence

Summary An X-ray fluorescence method for the analysis of calcium in uranium in the range of 20 to 500 ppm is described. U₃O₈ samples are mixed with boric acid binder and double-layer pellets are prepared. The pellets are analysed using Philips PW 1220 semi-automatic X-ray spectrometer. Calculated lower limits of detection are better than 5 ppm for calcium in uranium.

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Bestimmung von Calcium in Uran durch Röntgenfluorescenz

Zusammenfassung Ein Verfahren für den Bereich von 20–500 ppm wird beschrieben. Die U₃O₈-Proben werden mit BorsÄure als Bindemittel vermischt zu Doppelschicht-Tabletten gepre\t, die mit Hilfe eines halbautomatischen Philips PW 1220 Röntgenspektrometers analysiert werden. Die untere Nachweisgrenze liegt bei 5 ppm Ca.

     

离子色谱法检测高纯硅微粉中痕量铁和氧化铁杂质

建立了柱后衍生-紫外检测-离子色谱法同时测定高纯硅微粉中痕量铁和氧化铁杂质含量的方法。方法选用具有阴阳离子交换基团的高选择性Thermo Scientific Dionex^TM IonPac^TM CS5A色谱柱,选择与铁形成单一络合形态、中等络合能力的2,6-吡啶二羧酸（PDCA）为淋洗液,在线柱后添加普适性的4-2-吡啶偶氮苯二酚（PAR）金属显色剂,于530 nm波长下准确完成了二价和三价铁离子的分离测定。结果表明,本方法对二价铁离子和三价铁离子的检出限分别为0.013 mg/kg和0.006 mg/kg,线性相关系数r²均大于0.999,实际样品中二价铁和三价铁的加标回收率分别为79%~90%和92%~105%,具有较高的灵敏度、准确度和选择性。该方法可以准确测定高纯硅微粉中痕量二价铁和三价铁的含量,以此结果反馈高纯硅微粉产品中铁杂质含量的不同来源,为其生产工艺的持续优化和改进提供重要的参考数据。     

Determination of anions by non-suppressed ion chromatography using an amine column

Summary The Synchropak AX300 column has been used to separate a wide range of anions. A standard solution containing F^–, Cl^–, NO ₂ ^– , NO ₃ ^– , HPO ₄ ^2– , SO ₄ ^2– ions can be analysed in 8–14 minutes using a phthalate or phthalate/citrate eluent at pH 6–7. Addition of citrate to a phthalate eluent has a pronounced effect on the times of analysis. Detection by direction and indirect UV absorption enables the analysis of a wide range of anions. Application of the technique range from rain water to ash pond liquor analysis.     

Determination of protein-free and protein-bound calcium and magnesium in biological samples by use of ultrafiltration and ion chromatography

Protein-free and protein-bound calcium and magnesium are determined selectively in biological samples by use of ultrafiltration followed by ion chromatography. A commercial ultrafiltration kit is used to remove proteins of molecular weight > 10 000. The content of protein-bound cation is calculated by subtracting the value of protein-free from that of total cation. A protein-free cation filtrate is prepared by ultrafiltration of a diluted sample; a total cation filtrate is prepared by adding EDTA to the sample and filtering. Calcium and magnesium are determined in each filtrate by single-column ion chromatography with 1 mM EDTA (pH 6.5) as eluent and a conductivity detector. The use of a u.v. detector, in series with the conductivity detector, is useful for monitoring small molecules in the filtrates. The proposed method has been successfully applied to the determination of calcium and magnesium in blood serum, milk and egg white.     

Determination of cadmium in uranium by ion exchange and square-wave polarography

Traces of cadmium in uranium and its compounds can be determined by ion-exchange separation and square-wave polarography. With a small column of anion-exchange resin, cadmium can be separated from uranium and recovered quantitatively from hydrochloric acid solution, Separations of cadmium from uranium are not perfect but are sufficient for the determination of traces of cadmium by square-wave polarography. The lower limit of the method is 0.01 p.p.m. of cadmium.