Extraction based on the flow-injection principle: Part 4. Determination of Extraction Constants

A new approach to the determination of extraction constants is described. The aqueous and organic phases, the former containing the counter ion, are pumped continuously as small segments through an extraction coil. The sample ion is introduced into the aqueous phase before it enters the coil, where the ion-pair extraction takes place (during 20 s). After leaving the extraction coil, a certain fraction of the organic phase is pumped through the flow-cell of the spectrophotometer. The extraction constants are calculated by slope analysis from the experimental data (absorbance and counter ion concentration). The constants usually agreed within ±0.1 (log units) with values obtained from batch experiments.     

Extraction based on the flow-injection principle : Part I. Description of the Extraction System

An extraction system has been developed, essentially consisting of a pump, a rotary valve and a spectrophotometer. The sample, 12–25 μl, is introduced via the rotary valve into an aqueous stream (flow injection). The aqueous stream, containing the sample plug, is divided into small segments by an organic phase and led into a Teflon coil so that a regular pattern of the two phases is obtained. No air bubbles should be present. Separation of the two phases is achieved in a specially constructed fitting and the absorbance of the organic phase is measured. The construction and performance of the system are illustrated by analysis of caffeine samples. Up to 100 samples/h can be analysed with a relative precision of better than 1%.     

Extraction based on the flow-injection principle : Part 6. Film formation and dispersion in liquid—liquid segmented flow extraction systems

The dispersion mechanism in flow-injection extraction systems has been investigated. The phase with the highest affinity for the tubing material forms a thin film on the wall (e.g., 0.055 mm in a 0.7-mm i.d. PTFE tube with pentanol/water at a flow velocity of 11 cm s^?1). The film thickness increases linearly with increasing flow velocity and can be related to the viscosity/interfacial tension ratio in such a way that a low ratio indicates a thin film. The analyte is extracted into the film and into the adjacent segments. The film is stationary relative to the moving segments and this results in a backward transport of analyte molecules giving rise to dispersion. The thicker the film, the larger the dispersion. By decreasing the tube diameter and the flow velocity, lower dispersion results. Minimum dispersion is obtained for systems in which the phase carrying the analyte does not form the film.     

Extraction based on the flow-injection principle: Part 3. Fluorimetric Determination of Vitamin B1 (Thiamine) by the Thiochrome Method

The thiochrome method for determination of vitamin B₁ in pharmaceutical preparations has been adapted to a continuous flow system based on the flow-injection principle. The sample volume required for an analysis is about 150 /sml. For routine purposes a concentration range of 3 × 10^-4–6 × 10^-4 mg ml^-1 is used. Results obtained with the system agree well with results obtained manually. The consumption of organic phase is 2–3 ml/sample and the sampling rate is 30/h. A sampling rate of 70/h is easily attained if necessary. The relative standard deviation is about 1%.     

On Acidic Organodiphosphorus Extractants. Part V. Extraction Dependency of Trivalent Europium on the Dielectric Constant of the Organic Phase

Abstract

The extraction of Eu(III) has been carried out from a 1 M (H,Na)Clo₄ solution into different organic solvents at constant total concentration (6.67 × 10^?3 M) of the extractant, di-n-butyl-ethane-(l,2)-diphosphonic acid (H₂B₂-EDP). The distribution coefficient of Eu(III) is influenced quite appreciably by the nature of the organic solvent. We observe that the distribution coefficient can vary by a factor of 10⁶ for two solvents such as chloroform and ieo-octane. The experimental results are compared with those of Dréze¹, who used di-n-butyl-phosphoric acid (HDBP) for the extraction of Eu(lII) into different organic solvents. If we assume that H₂-B₂-EDP remains monomer for a total concentration of 6.67 × 10^?3 M in the solvents used², then we may conclude that the extraction of Eu(III) by the associated HDBP or the monomer H₂B₂EDP is influenced in the same manner in the solvents used.     

23种挥发性有机化合物在3种吸附剂上漏出容量的测定评价

采用吸附热解吸－气相色谱－质谱法对23种挥发性有机化合物Chromosorb 106、Tenax TA、Tenax TG等3种吸附剂上漏出容量进行了测定。根据实验结果确定了不同的化合物应选择不同的吸附剂及相应的采样体积。结果表明,Chromosorb 106可较好地吸附低沸点的挥发性有机化合物,Tenax TA、Tenax TG均可用于沸点较高的挥发笥有机化合物吸附,这对测定大气中的有机化合物含量采样有一定的参考价值。     

Extraction of Sodium and Potassium Perchlorates with Dibenzo-18-crown-6 into Various Organic Solvents. Quantitative Elucidation of Anion Effects on the Extraction-Ability and -Selectivity

The constants for overall extraction into various diluents of low dielectric constants (K_ex) and aqueous ion-pair formation (K_MLA) of dibenzo-18-crown-6 (DB18C6)–sodium and potassium perchlorate 1:1:1 complexes (MLA) were determined at 25°C. The K_ex value was analyzed by the four underlying equilibrium constants. The K_MLA values were determined by applying our established method to this DB18C6/alkali metal perchlorate extraction system. The K_M(DB18C6)A value of the perchlorate is much greater for K⁺ than for Na⁺, and is much smaller than that of the picrate. The K_MLA value makes a negative contribution to the extractability of DB18C6 for MClO₄, whereas the value of the MLA distribution-constant does a major one. The partition behavior of M(DB18C6)ClO₄ obeys the regular solution theory. However, the M(DB18C6)ClO₄ complexes in the diluent of high dipole moment somewhat undergo the dipole–dipole interaction. DB18C6 always shows high extraction selectivity for KClO₄ over NaClO₄, which is governed largely by the much greater K_MLA value for K⁺ than for Na⁺. The K⁺ extraction-selectivity of DB18C6 over Na⁺ for perchlorate ions is comparable to that for picrate ions. By comparing this perchlorate system with the picrate one, the anion effects on the extraction-efficiency and -selectivity of DB18C6 for Na⁺ and K⁺ was discussed in terms of the fundamental equilibrium constants.     

Extraction of Alkali Metal (Li, Na, K) Picrates with Benzo-15-crown-5 into Various Organic Solvents. Elucidation of Fundamental Equilibria Determining the Extraction-ability and -selectivity

To quantitatively elucidate the effects of the benzo group on the extraction-selectively and -ability of benzo-15-crown-5 (B15C5)for alkali metal ions, the constants of the overall extraction (K_ex), thedistribution for various diluents having low dielectric constants (K_D,MLA), and the aqueousion-pair formation (K_MLA) of B15C5-alkali metal (Li, Na, K) picrate 1:1:1 complexes (MLA) weredetermined at 25 °C. The partition constants of B15C5were also measured at 25 °C. The log K_MLA values for Li⁺, Na⁺, and K⁺ are -0.32 ± 0.22, 2.66 ± 0.19, and 0.71 ± 0.47, respectively. In going from 15-crown-5 (15C5) to B15C5, the benzo group considerably decreasesthe K_MLA value for the same alkali metal ion. The distributionbehavior of B15C5 and its 1:1:1 complexes with the alkali metal picrates closely obeys regularsolution theory, omitting chloroform. Molar volumes and solubility parameters of B15C5and the 1:1:1 complexes were determined. For every diluent, the K_ex valuefor B15C5 increases in the order Li⁺ < K⁺ < Na⁺. K_D,MLA makes anunfavorable contribution to the Na⁺ extraction-selectivity of B15C5 because of the smallest molar volume of the Na(B15C5)A complex. The Na⁺ extraction-selectivity of B15C5 is determined completely by much the highest K_Na(B15C5)A value.The extraction-ability and -selectivity of B15C5 for the alkali metal picrates are compared with those of 15C5on the basis of the underlying equilibrium constants.     

利用溶解度参数选择有机溶剂提取土壤中多种有机氯农药

采用基团贡献法计算了提取溶剂（正己烷、二氯甲烷、正己烷—甲醇（体积比4：1)、正己烷—丙酮（体积比1：1)、正己烷—二氯甲烷(体积比1：1))和有机氯农药（o,p′—DDT,o．p′—DDE,o,p′—DDD,α—endosubn,endrin,HCB)的色散溶解度参数(δd)、极性溶解度参数(δp)和氢键溶解度参数(δh),运用溶解度参数的理论筛选有机溶剂提取江西红壤中多种有机氯农药：研究表明正己烷—甲醇（体积比4：1)和正己烷—丙酮（体积比1：1)是提取江西红壤中o,p′—DDT,o,p′—DDE,o,p′—DDD多种有机氯农药的最佳提取溶剂（回收率大于82％),对α—endosulfan,endrin,HCB的提取也能满足检测需要（回收率大于75％)。超声波提取的结果验证了溶解度参数预测的合理性。     

Membrane Extraction Combined with Thermodesorption/Gas Chromatography and Mass Selective Detection for the Analysis of Volatile Organic Compounds in Water

The range of application of a commercial thermodesorption-cryofocussing unit connected to a gas chromatograph/mass selective detector was extended to water analysis by using it in conjunction with membrane extraction. A flow of nitrogen passes through a silicone hollow fiber immersed in the water sample and extracted volatile organic compounds are enriched in a sorption tube mounted on top of the extraction cell. The sorption tube is then placed in the thermodesorption unit and analyzed by GC/MS. The optimal extraction parameters of this combined method were found to be 30 min extraction at 20°C with a stirring speed of 1,250 rpm and a flow rate of 100 mL/min nitrogen using a silicone hollow fiber of 0.3 m length. Under these conditions the reproducibility of the method was 5.2–10.5% RSD. The linear dynamic range of the optimized method spans three orders of magnitude and detection limits were found to be 0.02–0.1 μg/L for cis/trans-1,2-dichloroethene, benzene, trichloroethene, chlorobenzene, bromobenzene, ethylbenzene, 1,1,2,2-tetrachloroethane, and 1,2/1,4-dichlorobenzene. The method was found to be suitable for compounds with boiling points up to 220°C as memory effects increased considerably from dichloro- to hexachlorobenzene. Highly contaminated groundwater samples were analyzed. Quantitative results corresponded well with those achieved with conventional headspace-GC/FID.     

Cyanide ion-selective electrodes based on thin electroplated membranes of silver chalcogenides: Part I. Membrane preparation and characterization

Cyanide-responsive ion-selective electrodes have been developed based on thin tellurium-doped silver selenide membranes electrodeposited on platinum substrates. The chemical composition of the electroplated film membranes could be expressed by the general formula Ag_2+δSe_1?xTe_x (where 0.2 < δ < 0.8 and 0.2 ? × ? 0.1). These electrodes exhibit a linear response in cyanide solutions with concentrations ranging from 10^?2 to 10^?6 M, with a slope of the electrode function of about 90 mV (pCN)^?1 (i.e., lower than the theoretically predicted double-Nernstian slope). These electrodes showed very stable behaviour during long-term investigation (several months). The conditions for the electrochemical preparation of cyanide-responsive silver chalcogenide membranes are discussed both from theoretical and practical points of view. X-ray diffraction, energy-dispersive x-ray fluorescence microanalysis (EDAX) and scanning electron microscopy (SEM) were used to examine the membrane composition, structure and surface morphology.     

Selective flow-injection determination of methanol in the presence of ethanol based on a multi-enzyme system with chemiluminescence detection

A highly selective flow-injection system was developed for the determination of methanol. The system consisted of three immobilized enzymes with luminol chemiluminescence detection. First, methanol was oxidized in the presence of alcohol oxidase to yield formaldehyde and hydrogen peroxide. The hydrogen peroxide produced was then destroyed by catalase. The formaldehyde formed in the first stage was further oxidized by NAD⁺-formaldehyde dehydrogenase. The NADH formed was oxidized by 1-methoxy-5-methylphenazinium methylsulphate (1-MPMS), and finally the reduced 1-MPMS was spontaneously oxidized and hydrogen peroxide was produced. The concentration of the hydrogen peroxide produced, which was proportional to the initial concentration of methanol, was determined by luminol chemiluminescence. The determination range was from 0.1 to 100 mg l⁻¹ and the response time was less than 2 min per sample with a relative standard deviation of less than 3%. The system showed good selectivity for methanol; the response was ca. 50 times higher than for ethanol.     

一种在线液-液萃取微型多用分相器的设计和应用 Ⅳ.流动注射液-液萃取电感耦合等离子体原子发射光谱法测定矿石中稀土元素

设计了在线液－液萃取多用重力分相器及相应流动注射流路系统与ＩＣＰ－ＡＥＳ法联用，具有良好的分析性能．通过对矿石中某些重稀土元素在硝酸介质中被ＴＢＰ萃取的应用研究表明钇、镱、铒的检出限（３σ）分别为：６．８ｎｇ／ｍＬ、０．２ｎｇ／ｍＬ和１．５ｎｇ／ｍＬ．精密度（ＲＳＤ％）分别为０．２４、０．４７和１．８．进样频率为２５～３０个／ｈ．     

Studies in Cyclocopolymerization. IX. A Systematic Kinetic Study on the Cyclocopolymerization of Vinyl Ethers with Maleic Anhydride in Different Solvents

Abstract

The kinetics of the AIBN-initiated copolymerization of divinyl ether (DVE) and ethyl vinyl ether (EVE) with maleic anhydride (MA) was extensively studied in seven different solvents. The yield at 100% conversion as a function of the feed composition when the total monomer concentration is kept constant gave a confirmation of the composition of these copolymers: DVE/MA=½ and EVE/MA=1/1. The study of the initial rate as a function of the feed composition made it possible to determine the relative values of the different propagation rate constants consistent with a mechanism by successive and selective additions: in the EVE-MA system, the addition of EVE is slower than the addition of MA; in the DVE-MA system, the addition of DVE is slower than the addition of the first MA molecule, while the addition of the second MA molecule is slower than the first one. The study of the dependence of the monomer concentration, of the AIBN concentration, and of the efficiency of the initiator, on the rate of polymerization, shows finally that the true order of the monomer concentration is close to 1 while its apparent order varies from 1 to 2. From all the kinetic data it was observed that the mechanism of these co polymerizations can be explained without reliving upon the concept of participation of the charge-transfer complex formed between the monomers. However, participation of the complex in a competing mechanism with the above cannot be completely excluded.     

The surface morphology of ion-selective membrane electrodes: Part 3. Studies on the Lead Ion-selective Membrane

Studies of the changes in the surface state of the ion-selective membrane and in the performance of the silver sulphide-lead sulphide (2:1) precipitate-based electrode are described. A scanning electron microscope was used to examine the surface of the electrode membrane. The results indicate that passivation of the lead-selective electrode caused by chemical and electrochemical oxidation is due to transformation of the lead sulphide at the membrane surface. The electrode surface becomes depleted in lead sulphide; lead sulphate crystals are formed during chemical oxidation with hydrogen peroxide, and lead oxide crystals during anodic oxidation.     

Influence of the main parameters of single-line flow-injection systems without chemical reaction on the output signal : Part 2. Simulation of the Mathematical Models

Simulations based on the mathematical models outlined in Part 1 are used to study the dependence of peak broadening on design and performance parameters as well as on the diffusion coefficient of the analyte particles (e.g., ions, molecules), the viscosity of the carrier solution and the temperature of the flow. The Peclet numbers of the various sections of the flow system are calculated by the equations discussed in Part 1. The predictions from the simulations agree fairly well with earlier experimental data. On the basis of the results obtained, various possibilities for increasing the sample frequency of single-line flow-injection systems are outlined.     

Interaction of acetone with ammonia and alcohols over a HZSM-5 zeolite: Part 1. Methanol

Temperature-programmed desorption accompanied by conversion (TPDC) of preadsorbed acetone was studied on a HZSM-5 zeolite with Si/Al=13.5. The reactivity of surface species created from acetone with methanol, ammonia and mixtures of these was investigated by analysing the composition of the products released (using a mass spectrometer) and the composition of the surface species (using a ¹³C MAS NMR spectrometer). It was found that ammonia reacts with the carbonyl group of acetone surface species to imino carbocations in both the absence and presence of methanol, and methanol alkylates the acetone surface species whether ammonia is present or absent. The decomposition of the species created from acetone, methanol and ammonia leads to different products than the decomposition of the species formed on the zeolite either from acetone (or methanol) alone or from acetone (or methanol) and ammonia. The strong dehydrogenation function of HZSM-5 resulted in the release of acetonitrile and HCN from acetone and methanol, respectively (in the presence of ammonia), while pyridinium bases (in the presence of all 3 reactants) appeared only in trace amounts.     

Representation of Electrical Conductances for Polyvalent Electrolytes by the Quint-Viallard Conductivity Equation. Part 4. Symmetrical 2:2, 3:3 and Unsymmetrical 2:1, 3:1 and 1:3 Type Electrolytes in Pure Organic Solvents

Conductivities of symmetrical and unsymmetrical electrolytes of 2:2, 3:3, 2:1, 3:1 and 1:3 charge types in pure organic solvents (methanol, ethanol, 1-propanol, dimethyl sulfoxide, acetonitrile, formamide, N-methylformamide, N,N-dimethylformamide, N-methylacetamide and N,N-dimethylacetamide) were analyzed using the Quint-Viallard conductivity equation and taking into account the ion association effect. The molar limiting conductances and the ion association constants were determined for various multivalent electrolytes in these solvents using the literature conductivities. In many cases, for the first time, it was possible to obtain consistent values of the limiting ionic conductances in organic solvents.