Separation of thorium as ascorbato complex by extraction with Aliquat 336S

Thorium was quantitatively extracted with 0.1M Aliquat 336S at pH 4.5 from 0.01M ascorbic acid. It was then stripped with 2M hydrochloric acid. Thorium arsenazo III complex was determined spectrophotometrically at 655 nm. It was separated from binary and tertiary mixtures by exploiting the difference in distribution ratios of various elements from ascorbic acid media. Some separations were accomplished by selective stripping of thorium from nitric and hydrochloric acid. The method was extended for the analysis of thorium in monazite and gas mantles.     

Separation of molybdenum as ascorbate complex by extraction with Aliquat 336S from associated elements

Summary Molybdenum was separated from accompanying elements by extraction with Aliquat 336S in ascorbate medium. The determination was performed spectrophotometrically with Tiron. The standard deviation was found to be ±0.5%.     

Separation of niobium and tantalum by extraction chromatography with bis(2-ethylhexyl)phosphoric acid

A novel method is developed for the reversed-phase extractive chromatographic separation of niobium and tantalum with bis(2-ethylhexyl)phosphoric acid. Niobium is extracted from 1-10M hydrochloric acid and can be stripped with 3M sulphuric acid containing 2% hydrogen peroxide. Tantalum is extracted from 0.1-2M hydrochloric acid and can be stripped with 0.1M hydrochloric acid containing 2M tartaric acid. It is possible to separate niobium and tantalum, in different ratios, from multicomponent mixtures.     

Tracer scale solvent extraction separation of tantalum from niobium using di-(2-ethylhexyl)-phosphoric acid as extractant

A simple solvent extraction procedure for the efficient separation of the radioactive tracers⁹⁵Nb and¹⁸²Ta from each other in a mixture using di-(2-ethylhexyl)phosphoric acid (HDEHP) as extractant is described. Tantalum was found to be quantitatively extracted from an aqueous madium, which is 1.6N in HCl and 10^?2 M in oxalic acid, with a HDEHP solution of 0.1 M concentration. Extractabilities of both niobium and tantalum in mineral acids like HCl, H₂SO₄ and HNO₃ and in some organic acids like oxalic, citric, etc., in HDEHP under the experimental conditions were also studied. The reliability of the separation procedure was verified further by γ-ray spectrometry.     

Separation of niobium and tantalum with cupferron

An attempt to separate niobium and tantalum by cupfcrron was only moderately successful at pH 4.5 to 5.5 in the presence of a magnesia mixture as a coagulating agent. A more satisfactory separation of niobium and tantalum from each other, tried out up to ratios of 30:1 and 1.30, is effected with Sn⁺² or Sn⁺⁴ as a co-precipitating agent under the conditions described niobium can be separated, in the presence of complexone III, from almost all the ions except U, Be, Ti and PO₄^-3. Iron and other tervalent elements, when present in 100 fold excess with respect to niobium, require double precipitation The method gives highly satisfactory results when applied to the analysis of niobium in niobium-molybdenum stainless steel.The use of titanium as a co-precipitant is less successful than that of tin     

Separation of niobium and tantalum with n-benzoyl-n-phenylhydroxylamine

The use of N-benzoyl-N-phenylhydroxylamine for the separation of niobium and tantalum, allows a satisfactory estimation of niobium from a tartrate solution at an acidity of 2.0N. The pH range for complete precipitation can be extended to 6.5. For tantalum precipitation, the pH of the solution should be below 1.5 and the acidity may even be above 2.0N. At pH 3.5–6.5, niobium is completely precipitated and tantalum remains in solution; the latter is precipitated by lowering the pH. Niobium and tantalum in ratios of 1:16 to 100:1 can be separated by a single precipitation, in the case of a ratio of 1:100 precipitation must be carried out twice. Titanium, zirconium, vanadate and molybdate interfere with the determination of niobium though other ions have no effect in the presence of complexone III and tartaric acid. The precipitates are granular and easy to filter and wash. The time taken for a complete analysis is much less than that of other methods     

Solvent extractions of zirconium and niobium from HCl solutions by Aliquat 336/Alamine 336 and DOSO mixtures

Liquid-liquid extractions of zirconium(IV) from aqueous HCl solutions by mixtures of Aliquat 336 or Alamine 336 and diocytl sulfoxide (DOSO) in the diluent benzene has been found to be always higher than that by any single extractant. While the cationic extractants extract Zr(IV) above 6M HCl, DOSO extracts from 4M onwards. Synergism has been observed in all cases. With any of these extractants extraction becomes almost quantitative at and above 10M HCl, but with mixtures of the cationic and neutral extractants, extraction is quantitative in the range 8–9M HCl. Although the extracted species with DOSO alone seems to be ZrCl₄·DOSO, with the mixture of extractants, however, the extracted species appear to be Q₂ZrCl₆·DOSO where Q is R₃ ⁺NH (for Alamine 336) and R₃ ⁺N(CH₃) (for Aliquat 336). Studies on separation of⁹⁵Zr–⁹⁵Nb pair from aqueous HCl media by Alamine 336 or DOSO and their mixtures in benzene exhibit preferential extraction of⁹⁵Nb leaving behind⁹⁵Zr in the aqueous phase, and extractions have been found to depend both upon the extractant and HCl concentrations.     

Obtimization of separation conditions in reversed phase liquid chromatography using complex solvent mixtures

Summary Four different methods of calculation of retention in ternary mobile phases were compared and it was found that the simple calculation based only on two values of the capacity factors (one for each binary system that composes the ternary mobile phase) provides the accuracy of prediction that is, at least, comparable to the other methods of calculation that require a large number of preliminary experiments. The deviations from ideal behaviour in ternary solvent mixtures are discussed; some sources of errors can be avoided, at least partially, using binary systems of adequate compositions for preparation of ternary mobile phases. Several examples show the comparison of calculated and experimental selectivities in ternary solvent systems. A simple calculation can be used for rapid selection of an adequate ternary (or more complex) mobile phase, if it is necessary to achieve the separation of a given sample mixture.Presented at the 14th International Symposium on Chromatography London, September, 1982     

The quantitative separation and determination of tantalum and niobium using anion exchange chromatographY

A method is described for separating .and determining niobium and tantalum in mixtures of the two. A solution of the two elements in 3M hydrochloric.0.1M hydrofluoric acid is put on a column of Deacidite FF, the niobium is rapidly eluted with 3M hydrochloric.0.1M hydrofluoric acid and the tantalum is recovered by elution with 4M ammonium chloride-M ammonium fluoride. A complete separation is obtained and the two elements are recovered as their oxides after precipitation. The effecth of some other elements have been examined.     

Solid phase extraction of chromium(VI) using Aliquat336 immobilized on a thin film of multiwall carbon nanotubes

We report on a novel and selective method for the preconcentration and determination of Cr(VI) in aqueous samples. Cr(VI) is adsorbed - in a “batch mode” - on multiwalled carbon nanotubes covered with Aliquat 336 and then determined directly, i.e., on the solid, by X-ray fluorescence spectrometry. This reduces the number of reagents and minimizes sample handling. The method combines the advantages of solid-phase extraction with the benefits of the XRF method in that the large areas required by the carbon nanotubes make them a promising solid sorbent for preconcentration. The enrichment factor was calculated after considering that the thin film obtained from the 10?mL solution of 1?mg?L^?1 of Cr(VI) has a real thickness of 0.04?mm and a final diameter of 16.7?mm, so that the volume deposited on the pellet is 0.0088 cm³ and the preconcentration factor is 1000.

Separation of niobium and tantalum with phenylarsonic acid

Phenylarsonic acid permits satisfactory separation of niobium and tantalum and estimation of tantalum from an oxalate solution containing sulphuric acid up to pH 5.8. For complete precipitation of niobium the pH should exceed 4.8. In mixtures, tantalum is precipitated below pH 3.0 and niobium is then precipitated above pH 5.0. When the oxalate concentration is high, recovery of niobium with cupferron is recommended. When the ratio of Nb₂O₅, to Ta₂O₅ exceeds 2:1, reprecipitation of tantalum is necessary. The effect of interfering ions is studied.     

Comparison of theoretical and experimental models for characterizing solvent properties using reversed phase liquid chromatography

Theoretical and experimental quantitative structure–retention relationships (QSRR) models are useful for characterizing solvent properties and column selectivity in reversed phase liquid chromatography (RPLC). The chromatographic behavior of a model analyte, the herbicide atrazine, in a system derived from nine organic solvents and three chromatographic columns was used for developing QSRR models. Multiple linear regression (MLR) and partial least squares regression (PLSR) were used as statistical approaches. The similarities and differences between linear solvation energy relationships (LSER), and semi-empirical and theoretical molecular models were demonstrated. QSRR models show high predictive power, and can successfully predict retention factor (log k) for new solvents. The models are useful for solvent optimization and reducing time for method development in RPLC. The herbicide atrazine can be readily analyzed at a low level, and all three columns provided good resolution, high-performance and symmetrical peaks. The method is suitable for analysis of atrazine in water samples.     

Use of cyclohexanedimethanol as a nonflammable organic solvent for industrial scale reversed phase chromatography

This work demonstrates that cyclohexanedimethanol is an effective nonflammable organic solvent for the pilot scale reversed phase chromatography of recombinant apolipoprotein A-I(Milano). Cyclohexanedimethanol has low viscosity in water, enabling the use of conventional low pressure process scale chromatography columns and hardware. Results from pilot scale manufacturing using a 30 cm diameter CG71M packed column indicate that a 5.7 log reduction in E. coli host cell protein with >80% yield can be obtained for the purification of apolipoprotein A-I(Milano).     

Separation of structurally similar nocathiacin analogues by reversed phase chromatography

The complete separation of structurally similar compounds has been a challenge due mainly to their similarity on physical and chemical properties. In the present study, a simple and effective chromatographic method to separate and purify nocathiacin acid from its structural analogue nocathiacin I was developed. After evaluating mobile phase compositions on the retention characteristics by reversed phase high-performance liquid chromatography (HPLC), the elution order of nocathiacin I and nocathiacin acid was completely reversed, and the resolution value between the two analogues was improved, by varying pH value and ionic strength, to greater than 10 from merged peaks under initial conditions. In addition, a preparative isolation of nocathiacin acid was performed by reversed phase column chromatography under the guidance of the HPLC study. This chromatographic method resulted in an efficient process to obtain pure nocathiacin acid with a recovery rate of 83%. The present approach offers a new methodology for the separation of structurally closely related secondary metabolites.     

一种混合模式反相/阴离子交换色谱固定相的制备与评价

通过在硅胶表面同时化学键合十八烷基和环氧基团,再用小分子叔胺进行环氧开环,制备得到表面带正电荷的反相模式固定相.该方法避免了反相模式固定相必要的封尾步骤,可在碱性样品分离中起到电荷屏蔽作用,消除因静电吸附而导致的峰拖尾现象,同时有利于提高固定相的耐水能力.该固定相表现出反相和亲水作用的双重保留机理,具有良好的运行稳定性...     

Separation of tantalum from niobium in rock phosphates and its determination through neutron activation analysis

A simple solvent extraction procedure for an effective separation of traces of tantalum from rock phosphate samples has been developed and used in its determination through neutron activation analysis. The tantalum contents in the samples were found to be about 3.10⁻⁷%.     

Separation of niobium and tantalum with benzo- and phenylacetylhydroxamic acids

Benzohydroxamic acid (I) or phenylacetylhydroxamic acid (II) is suggested for the quantitative separation of tantalum from niobium in an oxalate solution. The tantalum precipitate must be ignited for weighing; niobium is determined in the filtrate with another reagent. The pH range for complete separation is 4.0–6.4 for I and 4.5–6.2 for II. Single precipitation is satistactory for Nb: Ta ratios of 18 : 1 to 1 : 20 for I, and 8 : 1 to 1 : 23 for II. Titanium, zirconium, tartrate, citrate and a large excess of oxalate interfere.