磷矿粉中二氧化碳含量的简易测定方法

目前,我国国家标准采用气量法测定二氧化碳,其装置是由复杂的成套玻璃器皿组成,对不具备条件的单位无法测定。现将笔者所使用的简易方法介绍如下。1　方法原理将试样用盐酸分解,释放出的二氧化碳用氢氧化钠吸收,在吸收液中加入氯化钡溶液,将生成的碳酸钡沉淀过滤并洗涤,再用0.1mol/LHCl溶解碳酸钡,最后用0.1mol/LNaOH反滴定剩余盐酸。反应式:CaCO3+2HClCaCl2+CO2↑+H2OCO2+2NaOHNa2CO3+H2ONa2CO3+BaCl2BaCO3↓+2NaClBaCO3+2HClBaCl2+CO2↑+H2OHCl+NaOHNaCl+H2O2　杂质离子的干扰与盐酸反应可能释放出气体的反应…     

EDTA滴定法精确测定可溶性氯化物中氯含量

介绍了利用EDTA滴定法精确测定可溶性氯化物中氯含量的原理、条件和方法。试样溶解后,先在强酸性介质中用AgNO3沉淀Cl-离子,沉淀过滤后,加入过量Ni(CN)42-发生置换反应,然后在pH9.5的氨性缓冲溶液中,以紫脲酸铵为指示剂,用EDTA标准溶液滴定置换出的Ni2 离子。结果表明,改进后的本法,准确、干扰小、终点现象明显,是一种准确的测氯方法。测定结果的变异系数仅为0.18%,回收率为98.3%～100.9%。     

对用于活性炭表面含氧官能团分析的Boehm滴定法的几点讨论

不同的研究者在采用Boehm滴定法测定活性炭表面含氧官能团的含量时在操作方法上存在差异.本文探讨了Boehm滴定法中CO2的去除,直接滴定与返滴定,振荡时间,溶液的浓度对滴定过程的影响,提出适宜的操作建议.     

A simple method for determining water-induced gelling times of isocyanate prepolymers

A spectral assay has been developed that permits reliable determination of polymer gelling times. Water-soluble, isocyanate-containing polyether prepolymers initiate chain extension on contact with water and after some period of time form a semisolid hydrogel matrix. Techniques based on visual observations used to determine the end point for this process generally produce erratic results. By following scattered transmittance of visible light by an aqueous solution of prepolymer during the gelation process, it is possible to obtain a more objective determination of the gelation time. It was empirically demonstrated that the minimum of the first derivative of the scattered transmittance versus time spectrum correlated with the observed gel time over a wide time scale. © 1993 John Wiley & Sons, Inc.     

A new rapid titration method for determining the halogen ratio of Wijs solution and of iodine monochloride

The free iodine in Wijs solution is titrated directly, in strong hydrochloric acid solution, with standard potassium iodate solution. From this titration and the usual sodium thiosulfate titration for total halogen, the iodine/chlorine ratio is calculated. Results agree closely with those obtained by the longer chlorine-water method of Lopes. The halogen ratio of reagent grade iodine monochloride, a convenient material from which to prepare Wijs reagent directly, is also determined by the new titration method.     

A CO2 titration electrode Part II: Development of the sensor

The construction and operation of a new titration electrode for measuring C02 are described. Typical results are presented including calibration plots and a comparison of results from the new sensor with those from an infrared analyser. Good agreement is found. Results using the sensor to measure CO₂ levels in a glasshouse and in the ambient atmosphere of the laboratory are presented.     

Standardization of the Boehm titration: Part II. Method of agitation, effect of filtering and dilute titrant

Multiple steps in the Boehm titration are carried out in a variety of manners by different research groups, thereby making results difficult to compare. The methods standardized in this paper include method of agitation, use of dilute titrant, carbon removal from reaction bases and the effect of air on NaOH standardization; uncertainty estimations are also shown. By examining the multiple agitation methods, it was found shaking was the optimal method for use in the Boehm titration as other methods (stirring and sonicating) affect the carbon surface. It was also found that filtering the carbon and reaction base mixture did not affect the titration, nor did the use of dilute titrant. Solutions must be freshly standardized prior to use since storage (even over a one week time period) results in a change in concentration.     

A simple algorithm for the calculation of multiple site titration curves

A simple algorithm for the calculation of multiple site titrationcurves is proposed. It is based on a hybridization of two computationaltechniques: (i) a modified Tanford-Roxby iterative procedure[Tanford and Roxby (1972) Biochemistry, 11, 2193–2198]and (ii) the Boltzmann statistics. The sites characterized bystrong electrostatic coupling were selected for statisticalmechanical treatment, whereas all other sites were treated bymeans of the modified Tanford-Roxby procedure. The selectionof the two sets was made on the basis of a criterion relatedto the interaction energy between the titratable sites in theprotein molecule. The algorithm was tested for bovine pancreatictrypsin inhibitor and the pK values calculated were discussedin the light of experimental data and theoretical results obtainedby other authors. The algorithm can easily be coded and incorporatedinto any program package for the calculation of electrostaticinteractions in proteins.     

A simple impedance method for determining ethanol and regular gasoline mixtures mass contents

A simple electric impedance sensor embedded in ethanol and regular gasoline blends for determining mass ratios was built and tested in the present work. It was carried out a quantitative evaluation of mixtures for several fuel mass ratios in the temperature range of −10 to 40 °C. A non-linear dimensionless electrical conductivity-fuel mass ratio correlation was obtained for a 0-100% ethanol mass content in gasoline. Tests at different temperatures showed that the temperature had an important influence over the mixture bulk conductivity and sensor signal. This work was carried out following the Brazilian automotive industry trend of using ethanol-gasoline mixtures at any proportion to power passenger automobile engines.     

A simple method for determining protic end-groups of synthetic polymers by H NMR spectroscopy

A simple method for the determination of protic end-groups (-XH) in synthetic polymers involves in situ derivatization with trichloroacetyl isocyanate (TAI) in an NMR tube and observation of the imidic hydrogens of the derivatized products [-X-C(O)-NH-COCCl₃] by ¹H NMR spectroscopy. In this paper, we report that the method is effective for the quantitative determination of hydroxy, primary amino and carboxy end-groups of polymers with . It may also be applied to detect chain ends in higher molecular weight polymers. The signals for the imidic (and, in the case of amines, amidic) hydrogens appear in a region (δ 7.5-11) that is clear of other signals in the case of most aliphatic polymers and many aromatic polymers such as polystyrene and poly(ethylene terephthalate). The method has been applied in the characterization of polymers formed by conventional and living radical polymerization (RAFT, ATRP, NMP), to end functional poly(ethylene oxide) and to polyethylene-block-poly(ethylene oxide). The method appears less effective in the case of sulfanyl end-groups. The chemical shift of the imidic hydrogen shows remarkable sensitivity to the microenvironment of chain end. Thus, the imidic hydrogens of TAI derivatized polyethylene-block-poly(ethylene oxide) [PE-(EO)_mOC(O)NHC(O)CCl₃] are at least partially resolved for m=0, 1, 2, 3 and ≧4 in the 400 MHz ¹H NMR spectrum. It is also sensitive to the chain end tacticity of, for example, amino-end-functional polystyrenes and thus to the relative configuration of groups removed from the chain-end by two or more monomer units. TAI derivatization also facilitates analysis of amine functional polymers by gel permeation chromatography (GPC) which is often rendered difficult by specific interactions between the amine group and the GPC column packing.     

Standardization of the Boehm titration. Part I. CO2 expulsion and endpoint determination

The various steps required in the Boehm titration (CO₂ removal, agitation method, endpoint determination, etc.) are carried out in different ways by different research groups, making a comparison of the results between these groups difficult. Herein, the methods of CO₂ expulsion and endpoint determination for the Boehm titration were standardized. Blank samples of the three Boehm reaction bases, NaHCO₃, Na₂CO₃ and NaOH, were examined for complete CO₂ expulsion through sparging with an inert gas (N₂ or Ar), heating, or utilizing a N₂-filled glove box. Boehm titrations using NaOH as the reaction base were studied through direct titration and back-titration. It was found that to minimize errors both the NaOH titrant and HCl should be standardized prior to titration and that a back-titration is preferable for all three reaction bases. Additionally, the titration should be performed immediately after degassing for 2 h with N₂ or Ar, and degassing should continue during the titration. This is found to be particularly true of the NaOH reaction base, where the effects of dissolved CO₂ are the most noticeable and persistent. With sufficient CO₂ removal, there is no significant difference between pH electrode or colour indication endpoint determination, and either is satisfactory.     

A simple method for determining sol—gel transition temperatures in weak polymer jellies

A simple method for determining sol-gel transition temperatures in mechanically weak thermoreversible gels has been developed. Only 0–3 ml of gel is required and gels with a rigidity modulus as low as 100 dyne cm^?2 can be used.     

Effects of carbon dioxide and acidic carbon compounds on the analysis of Boehm titration curves

In the characterization of the surface functionality of acid-oxidized carbon nanotubes (CNTs) using the Boehm titration method, dissolution of acidic carbon compounds (ACCs) fragmented from the acid-oxidized CNTs and atmospheric carbon dioxide (CO₂) in the reaction base results in a somewhat over-estimation of the surface functionality of the CNTs. We developed a modified Henderson–Hasselbalch equation to show that the influence of the carboxylic and phenolic groups of ACCs and atmospheric CO₂ on the resultant titration curve can be identified and quantitatively measured, which makes it possible to determine the true surface functionality of acid-oxidized CNTs and ACCs.     

A simple method for determining the spontaneous oil absorption capacity of proteins and the kinetics of oil uptake

A simple method was developed for determining the spontaneous oil uptake and the kinetics of oil uptake by several food protein materials. The amount q of oil taken up by a protein powder during time t was described by the equation q=Qt/(B+t), where Q is the total oil uptake at equilibrium and B is the time required to sorb Q/2. The rate of oil uptake was proportional to the square of the amount of oil that must still be absorbed to reach equilibrium. A specific rate constant for the process was calculated as (BQ)⁻¹ and an initial rate of oil uptake as Q/B.     

密闭空间中H2S,CO2在MDEA中的理论溶解度模型

通过估算平衡常数和亨利系数得出密闭空间中H2S-CO2体系在MDE脉溶液中的溶解度,考察了H2S、CO2气体分压,温度以及MDEA胺液浓度对吸收效果的影响,密闭空间条件下的实测数据误差在2%以内,对于整个吸收工艺和工程设计有一定的指导意义.