Microdetermination of carbon and hydrogen in organofluorine compounds

A simple method is described for the elimination of the interferences of fluorine in carbon and hydrogen determination of fluorinated organic compounds. Samples are burnt in a rapid flow of oxygen using the cobalto-cobaltic oxide, rapid straight empty tube, rapid empty tube of Belcher-Ingram, and flash combustion methods.The combustion products are passed through Anhydrone, silica gel-thorium nitrate, and soda asbestos absorption tubes, respectively. Carbon and hydrogen are determined gravimetrically. Acceptable results are generally obtained for a wide range of partially and highly fluorinated organic compounds.     

Elemental analysis of organo-metallic compounds The simultaneous determination of carbon, hydrogen and other elements in one weighed sample

A method is described for simultaneous gravimetric microdetermination of carbon, hydrogen and one or more heteroelements in one weighed sample of organic substances. The method is based on pyrolytic combustion of the sample in a quartz container placed in an empty combustion tube. The carbon and hydrogen determination is completed as usual. Hetero-elements, in the form of volatile compounds, are retained in special previously weighed tubes inside the combustion tube. Hetero-elements forming non-volatile residues can be determined by the change in weight of the quartz sample-container. Volatile elements or compounds are determined by weighing the quartz insert tube. More than 40 elements in various combinations can be determined simultaneously with carbon and hydrogen.     

The determination of selenium by atom-trapping atomic absorption spectrometry

The application of atom-trapping atomic absorption spectrometry to the determination of selenium has been studied in detail. The optimum experimental parameters were established and the interference of major elements on the determination of selenium was studied using collection on a cold silica tube. The atom-trapping atomic absorption technique gives a detection limit of 0.03 ppm after 2-min collection on silica in an air—acetylene flame. This compares with ca. 1 ppm by the conventional absorption technique at the same 196.1-nm line. Methods to minimize interferences were examined, including the use of a double tube arrangement, an aluminium oxide-coated silica tube and ion-exchange separation. A combination of combustion in an oxygen flask and collection from an air—acetylene flame on the aluminium oxide-coated silica tube yielded satisfactory results in the analysis of four plant tissue samples.     

Determination of carbon, hydrogen and nitrogen in inorganic compounds by means of an automatic organic elemental microanalyzer

The Hewlett Packard Model 185 CHN Analyzer, which is based on an automated modified Dumas combustion technique and was designed for the analysis of organic materials, has been applied to the determination of carbon, nitrogen and hydrogen in inorganic compounds.With minor modifications to the procedure routinely used for the organic analysis, the instrument has proved to be able to broaden its original application field giving in general good performances in the inorganic domain.A particular emphasis has been put in testing nitrates, carbonates, ammonium salts and different kinds of carbon. Till now it appears that the only materials really difficult to analyze are the refractory nitrides, carbides and carbonitrides.Finally some considerations have been made in respect of the determination of the percent weight composition of mixtures through their carbon, nitrogen and hydrogen content.     

Microdetermination of carbon and hydrogen Automatic combustion in a dynamic system

An automatic combustion method has been developed for organic and organo-metallic compounds (5-10 mg samples), based on "wide tube" dynamic combustion in a turbulent oxygen atmosphere. Hydrocarbons, carboranes, transition metal carboran complexes, highly fluorinated compounds, silanes, siloxanes and cyclosilazanes, fluoroderivatives of alkyl phosphinic acids, high polymers, etc. have been analysed by it. Silver-plated pumice, magnesium oxide, fibrous asbestos and crushed quartz were used to absorb interfering elements. Advantages over the manual procedure are simplicity of procedure, rapid combustion of difficultly combustible or highly volatile compounds, and better reproducibility of the results. The overall combustion cycle takes 15 min. The standard deviation for hydrogen is 0.01-0.15 % and for carbon is 0.10-0.23 % (carbon content 20-95 %).     

Automation of the gas analysis of14C-labelled compounds utilizing a piston-type counter tube

In this paper an automatic apparatus designed for the radioactivity measurement of¹⁴C-labelled organic compounds in the gaseous phase is described. The labelled organic compounds are combusted in a mixture of argon and oxygen. After combustion the oxygen content of the gas is eliminated by passing it through a copper packing. The water and heteroelements present are also removed and the radioactive carbon dioxide gas is swept by argon carrier gas into a piston-type counter tube. In the counter tube the piston forming a dividing wall moves forward in accordance with the rate of combustion and sweeping, and thus sucks the gases leaving the combustion tube into the effective tube volume. The anode wire is carried by a reel located in the piston and a spring device ensures its stretched state. At the end of the sweeping period methane is fed into the counter tube and the activity of the argon—methane—carbon dioxide mixture is measured in the limited proportional region. Manual and automatic operation is possible. The piston-type counter tube provides possibility for strandardization by means of extrapolation and for measurement of absolute activities.     

The First Synthesis of Organic Diselenolates: Application to the Synthesis of Diorganyl Diselenides

The addition of elemental selenium to organolithium compounds 1 or organic selenates 2 gives organic diselenolates 3 . The reactions proceed by the insertion of two selenium atoms into the carbon–metal bonds or of one selenium atom into a selenolate. Evidence for the existence of n-butyldisilenol has also been obtained.     

Atom-trapping absorption spectrometry with water-cooled metal collector tubes

Water-cooled metal collector tubes for atom-trapping atomic absorption spectrometry in air—acetylene flames are discussed, particularly for the more volatile elements such as cadmium and selenium which may be less efficiently trapped at the hotter surface of a silica tube. It was found that a nickel tube gave 3 times greater sensitivity than silica for the determination of cadmium but was oniy half as sensitive for the determination of selenium. No atomic absorption signal for copper could be obtained with a nickel collector tube. A copper tube was 3–4 times more sensitive than nickel for cadmium and selenium. Similar effects were observed for cadmium solutions containing 1000 ppm copper or nickel, and for selenium solutions containing 1000 ppm copper, with silica atom-trap tubes, but in both cases better results were obtained when the analyte solution of cadmium or selenium contained the co-element (1000 ppm) than when the cadmium or selenium was measured with a silica tube previously metallized with the co-element.     

The submicro determination of carbon,hydrogen and nitrogen by a gas-chromatographic method

A method for the determination of carbon, hydrogen and nitrogen in organic samples weighing 40–80 μg is described. The sample is decomposed conventionally in a helium stream and the water formed is converted to acetylene. Nitrogen, carbon dioxide and acetylene are then separated on a silica-gel column, and the acetylene is burned to carbon dioxide by passage through copper oxide at 900° because the acetylene peak itself is not easily measured. Water from the second combustion is removed on silica gel and the three peaks emerging are measured by means of a micro thermistor cell. The standard deviations obtained for acetanilide are 0.31% for carbon, 0.28% for hydrogen and 0.11% for nitrogen. Results for other compounds are given and the parameters relevant to precision are discussed.     

Simultaneous determination of carbon,hydrogen, and nitrogen

Summary It was shown that carbon, hydrogen, and nitrogen can be determined simultaneously by the pyrolytic decomposition of the organic substance in a stream of oxygen in an empty combustion tube. Carbon and hydrogen are determined in the usual way, and nitrogen is determined from the sum of the amounts present as nitrogen oxides and as elementary nitrogen.     

Microdetermination of carbon and hydrogen in organic compounds using flushed-oxygen combustion tube

A rapid method of microanalysis for carbon and hydrogen in organic compounds using an empty combustion tube fused with two nozzles for flushing oxygen and employing reduced copper for the reduction of nitrogen oxide was investigated. A sample was decomposed rapidly in a sample heater for 2 min, and the gasified vapor was transported to the stationary combustion zone heated at 850 °C, where oxygen was flushing from two nozzles, the oxygen flow was then replaced with nitrogen for 3 min until all the combustion products were swept out towards the absorption train. The sample size was suggested to be around 1 mg for this rapid method, using a Mettler UM6, or an electrobalance having equal precision for the sampling.     

Automatic isotope gas analysis of tritium labelled organic materials

An analytical procedure and an automatic apparatus are described for the determination of tritium in organic compounds by gas counting. The sample is pyrolysed in hydrogen atmosphere at 1000°C, then, with hydrogen, the decomposition products are rinsed through a column of molecular sieve-5A heated to 550°C. Tritium in water, hydrogen sulphide, ammonia and hydrogen cyanide is transferred into the hydrogen stream by isotope exchange completed on the column. The inactive water vapor, hydrogen sulphide, ammonia and hydrogen cyanide as well as carbon dioxide are removed from the gas stream by appropriate absorbents, and the radioactive hydrogen together with tritiated methane, carbon monoxide and nitrogen included in the pyrolytic products is led into an internal proportional counter tube for radioactivity measurement. The method provides quantitative recovery, it is free of memory effect and suitable for the rapid assay of a wide variety of organic compounds containing C, H, N, O, S in addition to tritium.     

燃煤电厂砷、硒、铅的排放与控制技术研究进展

煤炭是中国重要的能源资源，而中国煤中重金属砷、硒、铅含量较高，燃煤电厂已经成为重要的砷、硒、铅排放源之一。针对电厂燃煤带来严峻的砷、硒、铅污染问题， 本文首先介绍了燃煤释放的砷、硒、铅排放量大且危害性强，概述了世界各国关于重金属排放控制的相关政策法规，指出中国对燃煤重金属砷、硒、铅的排放控制势在必行；其次从煤中赋存形态、燃烧过程中的形态转化和质量分布三个方面阐释了燃煤过程中砷、硒、铅的迁移转化规律，重点描述了砷、硒、铅在颗粒物上的形态特征和尺度分布；最后综述了燃烧前、燃烧中和燃烧后对砷、硒、铅的排放控制技术，详述了吸附剂捕集和烟气净化装置协同脱除的研究进展，并论述了低低温除尘器和团聚技术对砷、硒、铅的强化脱除潜力。以期为燃煤电厂重金属砷、硒、铅超低排放的实现提供参考和指导。     

Influence of volatile hydride-forming elements on antimony determination by atomic-absorption spectrometry with hydride-generation

A study was undertaken to determine the interfering effects of arsenic, bismuth, germanium, lead, selenium, tin and tellurium on trace determination of antimony by atomic-absorption spectrometry with hydride-generation. A 1% NaBH(4) solution was used as reductant and a small amount of oxygen was added to the hydrogen produced, to support the combustion and atomization of SbH(3). The interference from selenium in the determination of antimony is removed if potassium iodide-ascorbic acid solution or copper sulphate is added to the sample solution. The interference of tin and tellurium can also be avoided by adding potassium iodide-ascorbic acid solution. A possible interference mechanism is discussed.     

Assessment of Additives for Nitrogen, Carbon, Hydrogen and Sulfur Determination by Organic Elemental Analysis

 A survey is reported on the use of additives in organic elemental analysis of compounds containing functional groups that may compromise the combustion process. 28 substances containing the following functional groups were selected: organic fluorine, hexafluorophosphate, tetrafluoroborate, tetraphenylborate, sulfonate, phosphine, nitrile, carbide, organometallic. Six additives (powdered silver, silver tungstate with magnesium oxide, silica oxide, tungsten (VI) oxide with magnesium oxide, powdered tin, cerium (IV) oxide) in various sample:additive ratios were assayed. Silver tungstate with magnesium oxide (mixture 1:1, w/w) turned out to be most efficient for the analysis of nitrogen, carbon, hydrogen and sulfur for almost all the compounds assayed. Author for correspondence. Received August 2, 2002; accepted December 12, 2002 Published online May 19, 2003     

Oxygen determination in organic fluorine compounds by means of a glassy-carbon pyrolysis tube

A conventional apparatus for determination of oxygen in organic compounds has been improved for application to organic fluorine compounds. A feature of the apparatus is the use of a pyrolysis tube made of glassy carbon instead of quartz, which eliminates effects due to hydrogen fluoride produced in pyrolysis of the sample. Ten analyses of dexamethasone with the apparatus gave a mean value of 20.44% for oxygen (theory, 20.38%), with a standard deviation of 0.16%. Oxygen in 9 organic fluorine compounds was accurately determined by using the apparatus, with an average error of +0.1%. One analysis by a gravimetric or a coulometric method took about 40 or 25 min, respectively.     

Direct introduction of volatile carbon compounds into the spray chamber of an inductively coupled plasma mass spectrometer: Sensitivity enhancement for selenium

The effect of signal enhancement of elements with ionization potentials in the range from 9 to 11 eV by carbon-containing compounds is a well-known phenomenon in inductively coupled plasma mass spectrometry (ICPMS). It has traditionally been exploited through the addition of organic solvents to the sample matrix or to the mobile phase to improve sensitivity. In the present work, aqueous solutions of volatile carbon compounds (acetone, methanol and acetic acid) were directly introduced into the thermostatted spray chamber rather than being added to the sample matrix. It is presumed that no aerosol is produced from these solutions and only vapors of organic compounds are swept into the plasma together with the sample aerosol. When a 0.40 mol l^− 1 aqueous solution of acetone was introduced directly into the spray chamber, the signals for arsenic and selenium were enhanced by a factor of 4.2. The usefulness of this approach was demonstrated through the achievement of lower instrumental detection limits for selenium at m/z 82 (0.1 ng ml^− 1) compared to the system without direct introduction of volatile carbon compounds (0.5 ng ml^− 1). The method was successfully applied in the determination of traces of selenium in natural water, urine and bovine liver reference material.     

微波消解–原子荧光光谱法测定植物样品中的砷和硒

建立微波消解-原子荧光光谱法测定植物样品中砷和硒的含量。微波消解后残留的有机颗粒和硝酸等会对测定结果造成影响,因此需要将硝酸除尽。在驱除硝酸过程中加入高氯酸,加热至溶液冒白烟,避免硒挥发损失。该方法砷、硒的检出限分别为6.8,4.0 ng/g(稀释因子40),测定结果的相对标准偏差分别为3.65%,3.52%(n=12),加标回收率分别为94.5%~104.6%,92.2%~98.9%。经过国家一级标准物质验证,该方法准确可靠。     

The Submicrodetermination of Carbon and Hydrogen in organic Compounds by A Gas-Chromatographic Method

Abstract

Preliminary studies on the development of a method for the determination of carbon and hydrogen in 50–100 μg samples of organic compounds are described. The sample is burned over copper oxide in a helium stream and the water formed is converted to acetylene. Separation of CO₂ and acetylene on a silica gel column is followed by combustion of acetylene to carbon dioxide; the two peaks remain separate and are measured by a highly sensitive katharometer.     

A simple and rapid hydride generation—atomic absorption method for the determination of arsenic in biological,environmental and geological samples

An inexpensive 50-ml disposable (hypodermic) syringe is used as the arsine generation vessel. The arsine is passed into a 10-cm long. 10-mm i.d. electrically heated silica tube atomizer with nitrogen carrier gas. Excess of hydrogen is burned off in a hydrogen diffusion flame at the ends of the tube. Samples containing appreciable silica are fused with KOH—MgO_XXX while organic samples are digested with H₂SO₄—H₂O₂. Parameters affecting the determination of arsenic as arsine have been investigated. Collaborative results on a variety of standard reference materials agree well with literature values. The advantages of the proposed method are that it is sensitive, selective, fast, simple, inexpensive, precise and accurate.