Determination of peroxide value by the colorimetric iodine method with protection of iodide as cadmium complex

Improved procedures of the Swoboda and Lea method for the determination of peroxide values (POV) of fats and lipids are presented. After oxidation of iodide to iodine with the sample for 5 min under an inert atmosphere, an excess of the iodide ion is immediately converted to cadmium complex for protection from atmospheric oxygen. The iodine is measured colorimetrically at 358 or 410 nm, and POV is calculated from the absorbance. This method permits the rapid determination of POV with a small amount of sample at a moderate cost using usual glasswares. For the analysis of lipids in biological materials or food products, the chloroform solution obtained by the Bligh and Dyer method is directly subjected to this procedure without evaporation of the solvent. Conversions between POV obtained by the different methods are discussed.     

Time optimal control of an experimental continuous stirred tank reactor

In this paper the methods for applying Pontryagin's Maximum Principle to determine the time-optimal control policies for both a linearized and non-linear continuous stirred tank reactor system are presented. Both the time optimal control to a desired operating steady-state and to a specified region about this steady-state are considered. The paper also describes the successful simulation and control of the experimental system of the exothermic decomposition of hydrogen peroxide. The reaction is catalyzed by iodide ion which is introduced in a potassium iodide solution. The system is controlled by varying the water flow through an internal cooling coil.     

体声波／生物传感器用于人尿中葡萄糖的酶法分析

在氧存在下,氧化酶催化反应的产物之一为H2O2。酸性条件下,H2O2与KI反应生成单质碘。本文将高选择性的酶技术与灵敏的体声波／生物传感技术有机结合,基于镀银电极对I2的特性吸附,建立了一种简便的酶法分析体系。以葡萄糖氧化酶为模型,完成了人尿中葡萄糖含量的分析。本文还进一步讨论了各种实验条件及某些影响因素。在最佳条件下以3倍信噪比计算得葡萄糖的检测下限为36ng,检测范围为0．2～20μg,相对偏差为2．4％,结果令人满意。     

过氧化苯甲酰的分析

结合面粉品质改良剂过氧化苯甲酰的一些生产企业在产品分析测定时出现的测定结果不稳定,重现性差的情况,通过分析研究,提出一种以柠檬酸为催化剂和掩蔽剂,丙酮为溶剂的间接碘量法。该方法操作简便、迅速,精密度好,准确度高,测定结果令人满意     

Formation and decomposition of peroxides of unsaturated fat esters

Summary 1. A study of reaction time and the effect of oxygen on determination of peroxide by the acetic acidpotassium iodide method shows that a one-hour reaction time in the absence of oxygen is necessary, especially on samples of high peroxide. 2. The peroxide-formation curves at 100°, 75°, 55°, 35°, and 15° show a progressive increase in maximum peroxide value reached as the temperature is lowered to 35°. At 15°, the maximum is the same as at 35°; this value is over 30 percent of what it would be if all the double bonds were converted to peroxide. 3. The agreement between actual peroxide and “theoretical peroxide” calculated from decrease in iodine number extends to higher peroxide values as the temperature is decreased. 4. The rate of decomposition or disappearance of peroxide at 100°, 75°, 55°, and 35° agrees best with that of a bimolecular reaction, but definite exceptions exist. 5. The speed of decomposition of peroxide becomes progressively greater as the degree of oxidation is increased. 6. The changes in unsaturation, OH number, and acid number are small compared to the decrease in peroxide value as the peroxide decomposes. The formation of volatile and inflammable products was qualitatively observed in the decomposition of highly oxidized esters. The Chemical and Engineering Sections of the Soybean Industrial Products Laboratory, Urbana, Illinois, were merged with the Northern Regional Research Laboratory, Peoria, Illinois, July 1, 1942.     

颜色传感器在反应速度常数测定实验中的应用

提出以颜色传感器的输出频率变化监测反应进行的新思路,测定在不同温度下碘化钾与过氧化氢反应的反应速度常数,计算得到碘化钾与过氧化氢反应活化能为56.27 kJ·mo1-1,改进实验装置的实验误差为4.1％.研究成果成功应用于物理化学实验教学,为开发新的基础化学实验提供了一种新思路和有效的手段.     

Study on peroxide vulcanization thermodynamics of ethylene–vinyl acetate copolymer rubber using 2,2,6,6,‐tetramethylpiperidinyloxyl nitroxide

A step forward in the understanding of rubber vulcanization with organic peroxides is provided by combining a proper arrangement between polymer, vulcanizing agent and cure conditions. For this purpose, an ethylene–vinyl acetate copolymer with a high content of vinyl acetate (70 mol%) was used since a fully saturated polymer backbone allows its vulcanization via peroxide. For the range of conditions analysed here, it is shown that the predominant process taking place is crosslinking via radical recombination, minimizing or even avoiding undesirable secondary reactions such us polymer degradation. Once conditions had been optimized, peroxide vulcanization was analysed in more depth in the presence of 2,2,6,6‐tetramethylpiperidinyloxyl, which is a mediating stable free radical commonly used in controlled radical polymerization. Consequently, it was possible to differentiate the termination reaction from the initiation and propagation steps, allowing the determination of the enthalpy of formed C–C crosslinks as measured using calorimetry. It was possible to isolate and determine the contribution of the crosslinking pathway from the global vulcanization reaction by means of calorimetric methods at optimum conditions. In fact, this simple methodology could be an important tool for understanding in detail the complex peroxide vulcanization of elastomers since reactions involved in this process determine the final network structure, and thus the final elastic properties of these compounds.     

Iodination of arachidonic acid by the iron/H2O2/iodide system

The newly described iron/hydrogen peroxide (H₂O₂)/iodide antimicrobial system iodinates arachidonic acid to form the same products which are generated by peroxidase/H₂O₂/iodide systems. Arachidonic acid is multiply iodinated with the formation ofbis-iodohydrins and monoiodinated products which were identified as iodolactones by their high performance liquid chromatography elution patterns and by gas chromatography-mass spectrometric analysis. Iodination of arachidonic acid by the iron/H₂O₂/iodide system appears to proceed via the formation of hydroxyl radicals as an intermediate species. Iodination of unsaturated lipids may contribute to the cytotoxicity of the iron/H₂O₂/iodide system. Recipient of Allergic Diseases Academic Award AI00487 from the National Institute of Allergy and Infectious Diseases.     

Effect of sodium iodide on growth and chemical composition of lucerne and ryegrass

Growth of lucerne was inhibited by sodium iodide even more than that of ryegrass above a concentration equivalent to 1µg cm^–3 of iodine in an applied solution. In sand-culture the extent to which the iodide depressed yield of dry matter depended on the type of nutrient-solution used to stimulate and maintain vigorous growth. In contrast, where the plants were grown in soil the depression was independent of the nutrient-solution used. This difference between solutions is a reflection of the extent to which growing plants can modify pH in the root-zone of a sandy unbuffered substrate and leads to a conclusion that acidity greatly enhances the toxic effect of the iodine. There are reasons for believing that in sunlight iodine may be lost by volatilization even from living plant-tissue. The implication of these findings is discussed in relation to using either iodized fertilizers or iodized salt-blocks in order to maintain iodine in pastoral systems at levels satisfactory for animal-health.     

Determination of tocopherol in oxidized fats. Interference from heat-formed reducing substances in highly oxidized fats

Summary and Conclusions By application of a heating method to determine tocopherol in oxidized fats it was shown that polymeric reducing substances were produced when fats have a peroxide value exceeding 100. By comparison with a chromatographic method to remove peroxides it was shown that the interference in determining tocopherol from these heat-produced reducing substances was negligible at peroxide levels lower than 100. It is concluded that the heating method is satisfactory within the peroxide range (0–100) most important in oxidative and flavor-stability studies of edible oils. The chromatographic method for removing peroxides can be relied upon for determining tocopherol in more highly oxidized fats as well as in methyl esters of fatty acids which are distillable under conditions of the heating method. The appearance of reducing substances in heated oxidized fats is related to the peroxides present in the fats prior to heating. It is accompanied with an increase in browning, viscosity, acid, and carbonyl values of the fats and with a decrease in iodine values. The polymeric material from heated-oxidized methyl esters of unsaturated fatty acids has been separated by vacuum distillation and chromatography on silicic acid. It is believed to be principally dimeric in nature.     

Villermaux-Dushman protocol for experimental characterization of micromixers

The iodide/iodate chemical test reaction (named Villermaux-Dushman method) initially proposed to characterize micromixing in conventional stirred tank reactors has become an extensive method to characterize continuous micromixers. Several protocols have been proposed and adapted to very efficient devices, but misunderstanding makes the use of this chemical test somewhat difficult which can lead to erroneous results. Furthermore, many papers only present the segregation index which is very dependent of the concentration set when mixing time, a concentration-free feature, should be preferred to compare micromixers. This paper presents the detailed protocol of the iodide/iodate test method, with different concentration sets and a general protocol to determine mixing times in micromixers.     

Eine schnelle Chemilumineszemethode zum Nachweis oxidierter Lipide

Fast Chemiluminescence Method for Detection of Oxidized Lipids Because of the excellent correlation between the peroxide concentration defined by the method of Sully and the integral of the chemiluminescence light curves it is possible to determine the peroxide concentration by the chemiluminescence method. The detection limit of the chemiluminescence method for lipid hydroperoxides is far below that of the method of Sully. In a wide range of peroxide concentrations the chemiluminescence method also shows a good correlation with conventional measuring methods (ferric thiocyanate and iodometric method). The yield of light from the chemiluminescence reaction decreases on addition of different natural and synthetic antioxidants, the effect of BHA or NDGA being much greater than the effect of the tocopherols. Although luminescence efficiency is reduced by diverse ingredients, determination of hydroperoxides in commercial oils is possible. Since in this case there is no linear correlation with the iodometric method anymore, the peroxide concentrations can be determined after calibration only. A possible field of application of the chemiluminescence method is the routine analysis of similar fats and oils. The described method is not timeconsuming and reveals the possibility of automation. Because of its high sensitivity and simplicity it is particularly qualified as a screening-method for an early recognition of deterioration of fats and fatty foods.     

The C-radioisotopic study of methanol conversion on V-MCM-41: The influence of methyl iodide on the transformation

The methanol conversion and a feasible methanol co-reaction with methyl iodide were studied on a vanadium incorporated MCM-41 type (V-MCM-41) mesoporous catalyst, which was prepared by a direct hydrothermal synthesis method. Adsorption/desorption as well as conversion derivates of radioactive methanol were easily followed by radioactivity detectors on V-MCM-41. The transformation and co-reaction products were analyzed by a gas chromatograph equipped with Radio/FID detectors. The radiodetector was applied to distinguish ¹¹C-derivates from the non-radioactive methyl iodide and its derivates. The radio-labeling method proved methanol transformation to methylal and, in the presence of methyl iodide, decided the roles of methyl group and iodide of methyl iodide in newly synthesized methyl iodide formation in the absence of oxygen gas.     

过氧化二异丙苯含量测定方法的研究

过氧化二异丙苯(DCP)是强氧化剂,用其强氧化性质将饱和碘化钾溶液中的碘离子还原为碘,在样品中加入碳酸氢钠和浓盐酸,在低温(65℃)条件下使碳酸氢钠和浓盐酸反应生成二氧化碳形成保护气体,防止碘升华与空气中的氧反应而造成测定误差,在酸性条件下以淀粉作指示剂,用硫代硫酸钠标准溶液滴定反应生成的碘,以此方法测定过氧化二异丙苯(DCP)的含量,在实际工作中可操作性较强、精密度和准确度高、方法操作简单且重现性较好、抗干扰能力强,完全能够满足容量分析方法中规定的2个平行测定结果误差不大于0.2%的要求。     

过氧化氢产品中部分微量元素测定方法

过氧化氢产品中磷、铁、钾的含量,部分终端用户比较关注。提出了一种采用电感耦合等离子体发射光谱仪分析过氧化氢产品中磷、铁、钾含量的方法。首先采用标准加入法检测产品中的磷含量,同时进行了加标回收实验;然后采用标准法测定了产品中的铁和钾的含量,同时验证了铁和钾的标准偏差及方法检测限的符合性;其次提出了实验中存在的影响因素及解决方法。实验结果表明：采用电感耦合等离子体发射光谱仪对过氧化氢产品中的磷、铁、钾等微量元素的含量进行分析,综合优势较为明显。     

Graft copolymerization to cellulose in the presence of hydrogen peroxide with ultraviolet irradiation

The decomposition of hydrogen peroxide in the presence of cellulose with ultraviolet irradiation and graft copolymerization occurring upon addition of methyl methacrylate to this system was investigated. Graft copolymerization barely began in the hydrogen peroxide system without ultraviolet irradiation, but was markedly accelerated by ultraviolet irradiation. Ultraviolet light is capable of initiating the graft copolymerization even without addition of hydrogen peroxide, and this capability is enhanced further with the use of hydrogen peroxide. However, an increase in the hydrogen peroxide concentration was observed to exercise a zero or negative effect on the number of grafts. Such a phenomenon is absent in the ceric ion initiator system and, in the present study, is believed to be brought about by a characteristic enhancement of the stabilization of grafting sites effected by hydroxyl radicals. The number of grafts of copolymers obtained in the present initiator system is only approximately 0.085 mmole/100 g of cellulose at its maximum and is within the range of results obtained for the hydrogen peroxide initiator system in general.     

电位滴定法测定过氧化氢溶液中的过氧化氢含量

利用自动电位滴定仪测定过氧化氢溶液中的过氧化氢含量,研究了仪器的最佳操作条件及方法的准确度和精密度。结果表明:采用电位滴定法,在自动电位滴定仪自动找终点、等量滴定及搅拌速率为8 r/s的条件下测定过氧化氢溶液中的过氧化氢含量,其相对误差为0.10%,相对标准偏差为0.39%,测定1个试样耗时为683 s左右;在电位滴定法的基础上,在等量滴定前预加入高锰酸钾标准滴定溶液12 mL,改进后的电位滴定法测定过氧化氢溶液中的过氧化氢含量,与用GB/T 1616—2014《工业过氧化氢》的测定方法测定试样的结果没有显著差异,同时耗时更短,测定1个试样耗时为213 s左右,而GB/T 1616—2014《工业过氧化氢》的测定方法耗时为900 s左右。     

Iodination of docosahexaenoic acid by lactoperoxidase and thyroid gland in vitro: Formation of an lodolactone

In the presence of iodide, hydrogen peroxide and lactoperoxidase, docosahexaenoic acid (22∶6ω3) was converted into iodinated compounds. The major product was identified as 5-iodo-4-hydroxy-7, 10,13,16,19-docosapentaenoic acid, γ-lactone, on the basis of¹²⁵I incorporation, mass spectrometry, chemical modifications and proton nuclear magnetic resonance spectroscopy. Iodolactonization of docosahexaenoic acid occurred in the rat thyroid in vitro and was inhibited by the peroxidase inhibitor methimazole. These data indicate that formation of an idolactone constitutes one pathway of docosahexaenoic acid metabolism which could be expressed in tissues containing an iodide peroxidase.     

巯基棉富集分离5-Br-PADAP分光光度法测定锡锭中微量锑

采用盐酸-过氧化氢溶解试样巯基棉富集锑使其与基体分离,5-B r-PADAP分光光度法测定锡锭中微量锑。对仪器条件、试剂影响、共存离子干扰进行了试验,方法的相对标准偏差为6.26%,加标回收率在98.0%~101.0%之间,与孔雀绿法结果的相对误差在4.17%~6.56%之间,满足锡锭中0.001%~0.030%锑量的测定。     

聚四氟乙烯膜的表面改性研究

利用氩等离子体对聚四氟乙烯膜进行预处理，经与空气接触后接枝丙烯酸。用碘化钠法测定了膜表面过氧基团的浓度，探讨了等离子体处理时间、放电功率对膜表面过氧基团浓度的影响；过氧基团的浓度对接枝率的影响。利用红外光谱和X射线光电子能谱图鉴定了接枝产物，对改性后薄膜的表面亲水性进行了测试。