Preconcentration and selective determination of traces of tin in natural waters

A combined preconcentration-photometric determination technique has been worked out for trace concentration of tin in fresh and sea waters. After refluxing the sample acidified to 1M HCl for 2 h, tin is preconcentrated by anion-exchange in the presence of thiocyanate and recovered by elution with dilute HNO₃. Tin is then generated as stannane, caught in permanganate solution, and determined spectrpphotometrically with phenylfluorone. The results are quoted on the determination of tin in several fresh and sea waters in the order of submicrogram of tin per litre. The results for tin are in good agreement with those obtained for these samples by manganese dioxide coprecipitation-hydride generation-phenylfluorone spectrophotometric method that is also newly developed.     

Validation of the determination of tin by <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-instrumental neutron activation analysis in foodstuff

Several recent intercomparisons and certification exercises have shown that the determination of tin in e.g. food samples and plastics is not straightforward. k ₀-Instrumental Neutron Activation Analysis (k ₀-INAA) offers some intrinsic quality control opportunities for the determination of the tin content in samples since several monitoring radioisotopes are formed. In this work we will discuss the validation of the determination of tin by k ₀-INAA using different reference materials. The results show that only few of these radioisotopes are reliable in terms of accuracy and that from a survey of the tin content in a range of canned foods detection limits as low as 2 mg/kg can be achieved.     

Determination of tin in ores and concentrates

A method is described for the determination of tin in cassiterite and stannite ores. The method is based on an ammonium iodide fusion of the ore under controlled heating conditions and the subsequent determination of tin by classical iodimetric technique.     

Electrochemical study of the use of tin(II) complexed by sorbitol in volumetric analysis

The possibility of using the sorbitoi complex of divalent tin in volumetric analysis was studied. Potassium dichromate and potassium hexacyanoferrate were used for standardization. The dependences on the pH and ionic strength indicate that the most suitable titration medium is sat. Na₂CO₃. The titrant is stable for 14 days in an inert atmosphere. It was found polarographically and voltammetrically that the Sn(IV)-sorb./Sn(II) sorb, system is irreversible. Standard solutions of Sn(II)-sorb. were used to determine K₂Cr₂O₇, K₃Fe(CN)₆, H₂O₂, and inorganic and organic peroxides, I₂ Hg(II), Ag(I). chloramine T, chlorinated lime. n-bromosuccinimide, and TAR. Potentiometry, bipotentiometry, and biamperometry were used for determination of the equivalence point.     

Effect of surface modification of indium tin oxide by nanoparticles on the electrochemical determination of tryptophan

The effect of surface modification of indium tin oxide (ITO) by multi wall carbon nanotube (MWNT) and gold nanoparticles attached multi wall carbon nanotube (AuNP-MWNT) has been studied to determine tryptophan, an important and essential amino acid for humans and herbivores. A detailed comparison has been made among the voltammetric response of bare ITO, MWNT/ITO and AuNP-MWNT/ITO in respects of several essential analytical parameters viz. sensitivity, detection limit, peak current and peak potential of tryptophan. The AuNP-MWNT/ITO exhibited a well defined anodic peak at pH 7.2 at a potential of ∼669 mV for the oxidation of tryptophan as compared to 760 mV at MWNT/ITO electrode. Under optimum conditions linear calibration curve was obtained over tryptophan concentration range 0.5-90.0 μM in phosphate buffer solution of pH 7.2 with detection limit and sensitivity of 0.025 μM and 0.12 μA μM⁻¹, respectively. The oxidation of tryptophan occurred in a pH dependent, 2e⁻ and 2H⁺ process and the electrode reaction followed adsorption controlled pathway. The method has been found selective and successfully implemented for the determination of tryptophan in human urine and plasma samples using standard addition method. The electrode exhibited an efficient catalytic response with good reproducibility and stability.     

Determination of trace impurities in tin by neutron activation analysis

Two methods are described to determine indium and managenese in high-purity tin. In the first method indium and manganese are separated from the tin and antimony matrix activities on Dowex 1X8 anion exchanger. Tin and antimony are adsorbed in 10M HF while indium and manganese are eluted. In the second method the incident γ-ray intensity due to the tin matrix is reduced by placing a lead absorber between the sample and the detector. The reproducibility and the sensitivity of both methods are of the order of 10 ppb for manganese and of 1 ppb for indium for 1 g samples and a neutron flux of 10¹¹ n·cm⁻²·sec⁻¹. Aspirant of the N. F. W. O.     

Application of a fractionary factorial design to the determination of tin in lubricating oils by continuous flow hydride generation-atomic absorption spectrometry

The determination of wear metals and metalloids in used lubricating oils allows the prediction of equipment failure. A number of procedures to determine wear metals in lubricating oils by atomic spectrometry has been published. Industry has lately shown a special interest in the determination of tin, since its appearance at certain levels in used oils indicates severe engine wear. Therefore, a method for the determination of the total tin content in used lubricating oils by hydride generation-atomic absorption spectrometry (HG-AAS) is described. Unused marine lubricating oils spiked with the analyte were digested in closed vessels in a microwave oven and the diluted product was used for continuous stannane generation. There are many factors that influence effective SnH₄ generation; therefore, fractionary factorial design was used to obtain an adequate sensitivity and also to stabilize the signal. Six variables were taken into account and a 2^6–2 _IV design was used with spiked samples containing 30 ng g^–1 Sn. The reproducibility, stability, calibration curve and limit of detection were established. The method was applied to different kinds of used lubricating oils. In all cases, the results were higher than those obtained in the industry by simple dilution.     

Fast determination of the tin content in cassiterite ores by photon activation method

Photon activation analysis has been success-fully applied to the fast and non-destructive analysis of tin in cassiterite ores based on the 159.7 keV gamma line of^123mSn produced in the¹²⁴Sn/γ, n/^123mSn reaction. In order to improve the accuracy of analytical results, corrections for self-absorption and pile-up effects were performed. Under typical conditions /15 μA electron beam current, 15 MeV bremsstrahlung energy, 5 min irradiation time and 10 min measurement/ the sensitivity of the analysis is 10 ppm. The proposed method can be used for routine analysis of tin in geological samples.     

脂肪酸萃取锡精矿中微量稀土元素的方法研究

从锡矿石中测定伴生微量元素,主要采用加碘化铵分离锡.卢国仪等人,在两次氢氧化钠熔矿时加入碘化铵灼烧除锡后,完成微量锆的比色测定.由于锡精矿中含锡量高达50％以上,又极易水解,对于微量稀土元素的偶氮肿Ⅲ比色测定有严重干扰.脂肪酸萃取稀土元素已有报道.但用来萃取锡精矿中微量稀土元素未见报道. 本文指出,脂肪酸用来萃取锡矿石中微量稀土元素有很高的选择性,不因多次分离而损失,只需一次萃取分离后,直接进行比色测定.本文研究了在pH4.0～5.5的饱和硝酸     

The influence of chirality on the difference in flexoelectric coefficients investigated in uniform lying helix,Grandjean and twisted nematic structures

Measurements of the difference in flexoelectric coefficients (e ₁ – e ₃), using the sign convention as originally defined by Meyer, are reported from three experiments employing the flexoelectro-optic effect in different geometries. The uniform lying helix (ULH) structure is used to measure the tilt angle of the liquid crystal director with respect to the helix axis for an applied electric field, in order to infer a value for (e ₁ – e ₃). Alternatively, measurements of the flexoelectric difference can be made by considering the transmission through a device with an in-plane electric field aligned in either the Grandjean structure for highly chiral materials, or a twisted nematic (TN) structure for largely achiral materials. The results from the Grandjean and ULH structures show the equivalence of the measurement techniques with helix axis either perpendicular or parallel to the substrates. Further comparison of these results with the measurement from the achiral TN device shows that the difference in flexoelectric coefficients displays no dependence on chirality, demonstrating that flexoelectricity is purely associated with splay and bend director deformations, as expected from symmetry considerations.     

Application of a fractionary factorial design to the determination of tin in lubricating oils by continuous flow hydride generation-atomic absorption spectrometry

The determination of wear metals and metalloids in used lubricating oils allows the prediction of equipment failure. A number of procedures to determine wear metals in lubricating oils by atomic spectrometry has been published. Industry has lately shown a special interest in the determination of tin, since its appearance at certain levels in used oils indicates severe engine wear. Therefore, a method for the determination of the total tin content in used lubricating oils by hydride generation-atomic absorption spectrometry (HG-AAS) is described. Unused marine lubricating oils spiked with the analyte were digested in closed vessels in a microwave oven and the diluted product was used for continuous stannane generation. There are many factors that influence effective SnH₄ generation; therefore, fractionary factorial design was used to obtain an adequate sensitivity and also to stabilize the signal. Six variables were taken into account and a 2^6–2 _IV design was used with spiked samples containing 30 ng g^–1 Sn. The reproducibility, stability, calibration curve and limit of detection were established. The method was applied to different kinds of used lubricating oils. In all cases, the results were higher than those obtained in the industry by simple dilution. Received: 30 September 1998 / Revised: 22 January 1999 / Accepted: 27 January 1999     

Interlaboratory comparisons – demonstrating degree of equivalence

 The role of matrix reference materials in the process of demonstrating the degree of equivalence of measurement results obtained from intercomparisons is outlined, reviewing exemplary selected experience gained at BAM regarding the determination of organic contaminants in environmental matrices. The specific characteristics of reference materials employed in the process of demonstrating equivalence between laboratories in the course of proficiency testing as well as the development, comparison and validation of methods are elaborated. The demand is for series of appropriately characterised samples which are fit for the purpose and it is seen from representative examples that the utilisation of such tailor-made RM designed to tackle the specific need of an analytical problem dominates over certified matrix reference materials in this context. Concluding, the role of certified matrix reference materials in quality assurance is briefly looked at both from the user’s and providers’ points of view. Received: 9 September 2002 Accepted: 16 December 2002 Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia Correspondence to R. Becker     

Iron powder and tin/tin chloride as new reducing agents of Meerwein arylation reaction with unexpected recycling to anilines

Abstract

Simple and rapid route for Meerwein arylation reaction using iron powder or a mixture of tin/tin chloride has been developed. In the presence of iron powder, different aryl diazonium salts reacted with methyl vinyl ketone, acrylates, and isopropenyl acetate. Production of oximes was detected as the main product with acrylates or in a mixture with β-aryl methyl ketones in the case of methyl vinyl ketone. The in situ produced HNO₂ from an excess of NaNO₂/HCl was trapped by alkyl aryl radical to form oximes in the E configuration form. The presence of tin/tin chloride mixture in the reaction of the aryl diazonium salts with methyl vinyl ketone produced Michael products along with β-aryl methyl ketones. The predicted α-aryl methyl ketones from the reaction of isopropenyl acetate with the diazotized anilines were obtained using iron or tin/tin chloride mixture.     

Study of interferences in the iodometry of tin its application to ore analysis

The mterference of molybdenum when tin is determined by rodate titration after reduction by aluminium, has been studied. A similar study was made of solutions also containing iron, and it was concluded that the interference in these solutions is almost non-existent. The results are discussed. A modified method for tin determination in ores containing molybdenum was proposed.     

Laws of complex formation in a series of azo-substituted pyrocatechol derivatives and their tin(II) complexes

Physicochemical properties of new reagents, azo-substituted pyrocatechol derivatives and their tin(II) complexes, are studied. The acid-base properties of the hydroxy groups (pK′_i, pK″_i), parameters of complex formation reactions (pH, temperature, time), and instability constants of the complexes formed (pK _i) are determined. Quantitative correlations between the dissociation constants (pK′_a) of the functional analytical group, and the electronic Hammett constant σ for a substituent (pK′_a-pH₅₀ of the complex formation reaction), as well as between pK′_a and instability constants of the complexes (pK _a), are established. The quantitative correlations established allow the prediction of the physicochemical properties of the reagents and tin(II) complexes with new reagents of this class with the same functional analytical group (FAG) but other substituents.     

Pyrochlore‐type tin niobate

A single crystal of Sn_1.59Nb_1.84O_6.35 was grown at 1273 K from a mixture of sodium niobate and tin(II) chloride. The structure is of pyrochlore type A₂B₂O₇. The tin is partially oxidized to tin(IV) and competes with niobium for the occupation of site B. The stereoactivity of the Sn²⁺ lone pair induces displacement of tin towards the O atoms of the tunnel.     

Determination of metals, metalloids and non-volatile ions in airborne particulate matter by a new two-step sequential leaching procedure Part B: Validation on equivalent real samples

Due to the lack of proper standard materials for airborne particulate matter collected on filters, a validation scheme was developed, which is here described, to the aim of testing the application of leaching procedures performing both ions and elemental determinations on real samples of airborne particulate matter collected on filters. The scheme has been developed on a two-step leaching method (extraction in acetate buffer and acid dissolution of residue) previously developed by authors and consists of two series of tests to be run on n pairs of equivalent parallel samples filter-collected. The first series of tests aims to assess on real samples the equivalence between results obtained by the tested procedure with those obtained by the EMEP ions extraction and the EN 12341 standard methods, whereas the second aims to evaluate the reproducibility of analytical results of elemental determination in the leached and dissolved fractions; in the latter case data reliability is also evaluated as a function of the environment-intrinsic variability of real samples.To avoid errors due to sampling differences data from filter pairs were standardized both by gravimetric determination of loaded filters, according to the EN 12341 standard and by the rate [SO₄²⁻]_A/[SO₄²⁻]_B, where [SO₄²⁻] indicate the soluble sulphate concentration in the extract; in the latter case values improved for all elements and in both fractions. Results of equivalence with standard methods and reproducibility tests are evaluated as mean relative percentage differences (Δ%) and percentage elements recoveries (R%). The application of the validation scheme to the two-step leaching method is here discussed for non-volatile ions and for 17 elements detected on 22 pairs of low-volume collected PM₁₀ samples on Teflon filters.     

Modified solid electrodes for stripping voltammetric determination of tin

The paper describes the determination of tin by ASV using modified thick film electrodes. Three different types of electrodes were developed: One modified with a mixture of Nafion and mercury(II)acetate, one modified with diethyldithiocarbamate (DDC) or pyrrolidinedithiocarbamate (PDC) and mercury(II)acetate, and one modified with calomel. The analyte was accumulated on the electrode surface after special electrochemical pretreatment of the modified electrode. After recording the voltammogram the electrodes were electrochemically regenerated. By virtue of their lifetime and their measurement reproducibility, we preferred the DDC and PDC modified electrodes. They can be used for months without changing their chemical characteristics. The linear range for tin determination with these electrodes is between 1 and 100 μg/L; the detection limit was calculated as 0.9 μg/L. The electrodes were applied to the direct determination of tin in different canned fruit juices without special sample pretreatment. Received: 20 December 1996 / Revised: 11 March 1997 / Accepted: 13 March 1997     

Modified solid electrodes for stripping voltammetric determination of tin

The paper describes the determination of tin by ASV using modified thick film electrodes. Three different types of electrodes were developed: One modified with a mixture of Nafion and mercury(II)acetate, one modified with diethyldithiocarbamate (DDC) or pyrrolidinedithiocarbamate (PDC) and mercury(II)acetate, and one modified with calomel. The analyte was accumulated on the electrode surface after special electrochemical pretreatment of the modified electrode. After recording the voltammogram the electrodes were electrochemically regenerated. By virtue of their lifetime and their measurement reproducibility, we preferred the DDC and PDC modified electrodes. They can be used for months without changing their chemical characteristics. The linear range for tin determination with these electrodes is between 1 and 100 μg/L; the detection limit was calculated as 0.9 μg/L. The electrodes were applied to the direct determination of tin in different canned fruit juices without special sample pretreatment. Received: 20 December 1996 / Revised: 11 March 1997 / Accepted: 13 March 1997     

The determination of tin in tin ores and concentrates by atomic absorption spectrophotometry in the nitrous oxide-acetylene flame

Tin in tin ores and concentrates can be determined by atomic absorption measurement in the nitrous oxide-acetylene flame. Solutions are prepared by heating the samples with ammonium iodide and dissolving the resulting tin iodide in dilute hydrochloric acid. Calibrating solutions contain ammonium iodide and hydrochloric acid at approximately the concentrations present in the sample solutions. The method has a limit of detection of 0.02% tin in the sample and is suitable for application to geochemical prospecting samples. The results are similar to those obtained by standard chemical methods.