非色散原子荧光光度法测定二氧化锰中砷

砷作为有害元素之一 ,在二氧化锰中的含量对碱性电池的质量产生直接的影响。因此 ,测定二氧化锰中砷含量显得十分重要。传统的方法测砷有直读光谱法、示波极谱法和银盐法。但这些方法的灵敏度低 ,且测定二氧化锰中的砷干扰大 ,随着原子荧光光度计技术的发展 ,为测定砷提供了一种便于使用的方法。在酸性条件下 ,五价砷被硫脲 +抗坏血酸还原为三价砷 ,硼氢化钠与酸作用生成大量的新生态氢 ,与三价砷生成气态的砷化氢 ,被载气载入石英管炉中 ,受热后即分解为原子态砷 ,在特制砷空心阴极灯发射光谱的激发下产生原子荧光 ,其荧光强度与砷含量成正…     

Use of cholesterol reference materials in a nation wide study of the cholesterol content of eggs

Summary National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1563-2, Cholesterol and Fat-Soluble Vitamins in Coconut Oil, and SRM 1845, Cholesterol in Whole Egg Powder, were used to monitor the accuracy and precision of analyses in a recent nationwide study of cholesterol in eggs. A two-phase study was conducted between June, 1988 and May, 1989 by USDA in collaboration with the egg industry to update the USDA nutrient data for eggs. Determination of cholesterol levels received special emphasis since dietary cholesterol is monitored as part of the assessment of the relationship between diet and coronary disease. During each phase of the study eggs were collected from 122 of the top 200 US egg handlers in six regions of the country, representing 67% of the nation's monthly egg production. During Phase I egg yolks were composited into 24 analytical samples. As a result of low variance in cholesterol values for Phase I, egg yolks in Phase II were composited into 6 samples. The selection of the analytical contractor was based on results of analyses of SRM 1563-2, a USDA frozen egg material, and a whole egg powder material (SRM 1845, candidate status) submitted by several laboratories. In all cases the results by the selected contractor were within 1% of the certified or recommended values. The contractor used SRM 1563-2 as well as an in-house cholesterol-spiked oil research material to validate the modified AOAC method which incorporated ethanolic potassium hydroxide saponification followed by gas chromatography. During the analysis of nationwide samples the contractor analyzed SRMs 1563-2 and 1845, as well as the cholesterol-spiked oil and the USDA frozen egg material to monitor accuracy and precision. Over the course of the study coefficients of variation for all materials were less than 5%. As a result of rigorous quality control the cholesterol results for eggs have been regarded with confidence and used to update various public and private data bases used to monitor dietary cholesterol levels.     

Direct evidence for chemically distinct regions within nation films on electrodes

Electrochemical and spectroelectrochemical experiments on the complexes [(bpy)₂(py)Ru^II(OH₂)]²⁺ and [(trpy)(bpy)Ru^II(OH₂)]²⁺ (py is pyridine; bpy is 2,2'-bipyridine; trpy is 2,2',2“-terpyridine) with Nation films coated on electrodes demonstrate that the complexes partition amongst three chemically distinct regions or phases. As Ru(II) the complexes reside both in an electroinactive phase and, based on the pH dependence of the Ru(III)/(II) couples, e.g., [(bpy)₂(py)Ru^III(OH)]²⁺/[(bpy)₂(py)Ru^II(OH₂)]²⁺, in two electroactive phases. Partitioning amongst the three phases depends on the pH of the external solution and on the oxidation state and proton content of the complex. Addition of alcohols releases the complex from the electroinactive phase but at the expense of loss of the bound water molecule and binding to the sulfonate sites by anation and, therefore, to a fourth distinct chemical or physical state in which the complex can exist within Nation films.     

The present model of legislation on food irradiation needs to be changed

The present model of legislation needs to be changed as it does not permit to play its essential role as a process that improves public health. It also creates hidden technical barriers to international and even national trade while imparting a bad and negative image to irradiated foods.     

A rapid colorimetric method for the determi nation of aluminium in cu-al alloys

Aluminium is determined colorimetrically using Eriochrome cyanine. 'I'he application in this paper is to copper-aluminium alloys. The red colour obeys the Beer-Lambert law and the maximum absorption is at a wavelength of 550 mm     

Session 4 industrial needs for commercialization

Techno-economic modeling has been a valuable tool in directing and assessing the research and development efforts for biomass-to-ethanol processes. In developing a techno-economic model of a “generic” wood-to-ethanol process, we decided to follow a three-pronged design approach. This initially consisted of a detailed review of the current definition and technical maturity of the process, which concluded that the process remains complex and immature. More recently, we have critically assessed/compared two inherited models, and examined the historical and current trends in modeling design. We confirmed that process complexity and immaturity, in association with the capabilities of the available modeling tools and the ease with which they can be used, influenced the design and implementation of past models. We have discussed these influences with reference to our own model development decisions. For example, on review of two inherited techno-economic models, we decided that our new model would require a greater degree of flexibility in its structure and user interface.