Solid Phase Extraction and Flame Atomic Absorption Spectrometric Determination of Trace Amounts of Zinc and Cobalt Ions in Water Samples

A simple and rapid method for the preconcentration of Co²⁺ and Zn²⁺ as their 2-guanidino-benzimidazole chelates is proposed using an octadecyl silica cartridge. The retained analytes were recovered with a mixture of 5mL of 0.01M HNO₃ and 5mL of methanol. The metal ions in the effluent were determined by flame atomic absorption spectrometry. The effect of different parameters, such as sample matrix, amount of ligand, type of eluent for elution of ions from cartridge, flow rates of sample solution and eluent, breakthrough volume, and limit of detection, were evaluated. The effects of various cationic and anionic interferences on the percent recovery of Co²⁺ and Zn²⁺ were also studied. Quantitative extraction efficiencies were obtained by elution of the cartridge with a minimal amount of solvent. Hence, with a typical preconcentration factor of 50, the limits of detections of the proposed method are 0.26 and 1.62ngmL^–1 for Zn²⁺ and Co²⁺, respectively. The method was applied to the determination of zinc and cobalt ions in different water samples.     

Separation of peptides and proteins by capillary electrophoresis using acidic buffers containing tetraalkylammonium cations and cyclodextrins

A method for improving separations of peptides and other positively charged species in capillary zone electrophoresis with untreated capillaries using acidic buffers containing tetraalkylammonium cations is described. Tetramethylammonium and tetrabutylammonium cations dynamically modify the capillary surface, leading to a reversal in the direction of the electroosmotic flow. As a result, the adsorption of positively charged peptides and proteins is minimized, and resolution and peak capacity are improved as the migration of cationic analytes is counterbalanced by the electroosmotic flow. The combining effect of reversing electroosmotic flow and cyclodextrin inclusion complexation on separations of closely related peptides and a protein mixture, as well as tryptic digest of hemoglobin is demonstrated.     

Si-tolerance of iron doped Pt/alumina catalyst in the total oxidation of VOC

Summary In the present study the effects of addition of iron on the catalytic activity and Si tolerability of Pt/g-Al₂O₃in the total oxidation of volatile organic compounds were investigated. Preliminary results showed that there is a noticeable improvement effect on Si-tolerance of catalyst, particularly for short term poison exposure. Bulk analysis of deposited silicon on the catalyst surface indicated that both Pt/g-Al₂O₃and iron-doped pellets had roughly the same silicone uptakes. Deactivation of catalyst was reversible and much faster for iron doped sample. The promoting effects of iron were related to its electronegativity and, to blocking of fewer Pt sites when iron is present at the surface of the catalyst.     

Spectrophotometric determination of beryllium in water samples after micelle-mediated extraction preconcentration

A new micelle-mediated phase preconcentration method for preconcentration of ultra-trace quantities of beryllium as a prior step to its determination by spectrophotometry has been developed. Chrome Azurol S (CAS) and cetyltrimethylammonium bromide (CTAB) were used as chelating agent and cationic surfactant, respectively. The method evaluates and eliminates the blank bias error present in such procedures using mean centering of ratio spectra. This procedure gives more accurate results than the traditional approach using absorbance values against reagent blank. The optimal extraction and reaction conditions were studied and the analytical characteristics of the method (e.g., limit of detection, linear range, preconcentration and improvement factors) were obtained. Linearity was obeyed in the range of 0.9-18.0 ng mL⁻¹ (1.00 × 10⁻⁷-2.00 × 10⁻⁶ mol L⁻¹) of beryllium. The detection limit of the method is 0.51 ng mL⁻¹ (5.66 × 10⁻⁸ mol L⁻¹) of beryllium. The interference effect of some anions and cations was also tested. The method was applied to the determination of beryllium in spring water samples.     

Novel coated-graphite membrane sensor based on N,N′-dimethylcyanodiaza-18-crown-6 for the determination of ultra-trace amounts of lead

A novel selective membrane electrode for determination of ultra-trace amount of lead was prepared. The PVC membrane containing N,N′-dimethylcyanodiaza-18-cown-6 (DMCDA18C6) directly coated on a graphite electrode, exhibits a Nernstian response for Pb²⁺ ions over a very wide concentration range (from 1.0×10⁻² to 1.0×10⁻⁷ M) with a limit of detection of 7.0×10⁻⁸ M (∼14.5 ppb). It has a fast response time of ∼10 s and can be used for at least 2 months without any major deviation in potential. The electrode revealed very good selectivity with respect to all common alkali, alkaline earth, transition and heavy metal ions. The proposed sensor was used as an indicator electrode in potentiometric titration of lead ions and in determination of lead in edible oil, human hair and water samples. The proposed sensor was found to be superior to the best Pb²⁺-selective electrodes reported in terms of detection limit and selectivity coefficient.     

Neue Derivate der 2-Acylamino-thiophen-(und-benzo[b]thiophen-)-3-carbonsäure sowie des ([1]Benzo-)Thieno[2,3-d]-pyrimidin-4(3H)-ons

The title substances1 and2 were prepared by acylation of the corresponding ethyl 2-amino-thiophene- (or:-4,5,6,7-tetrahydro-benzo[b]thiophene)-3-carboxylates, in some cases followed by reactions introducing a basic substituent.Additionally a group of 2-aroylamino-thiophene-(or:-4,5,6,7-tetrahydro-benzo[b]thiophene)-3-carboxamides was subjected to ring closure reactions, yielding the corresponding 2-aryl-thieno[2,3-d]pyrimidin-4(3H)-ones and 2-aryl-[1]benzothieno[2,3-d]pyrimidin-4(3H)-ones (both:3).

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Zum Teil unter Mitarbeit vonFerdinand Fuhrmann     

Development of a new fluorimetric bulk optode membrane based on 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) for nickel(II) ions

A highly sensitive and selective fluorimetric optode membrane for the determination of ultra trace amounts of Ni²⁺ ions was prepared. The plasticized PVC-membrane incorporating potassium tetrakis(p-chlorophenyl)borate (KTpClPB) and 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) (TTBB), as a highly fluorescent chromoionophore, displays a calibration response for Ni²⁺ ions over a wide concentration range of 1.0×10⁻³ to 1.0×10⁻⁸ M. It has a relatively fast response of <40 s. In addition to high stability and reproducibility, and relatively long working lifetime, the sensor possesses good selectivity for nickel ions over several common diverse ions. The fluorescence signal of the optode membrane can be easily recovered by immersion in EDTA solution. The optode was applied successfully to the determination of traces of Ni²⁺ ion in edible oil and a wastewater sample from nickel electroplating industries.     

A Review on Effects of Lubricant Formulations on Tribological Performance and Boundary Lubrication Mechanisms of Non-Doped DLC/DLC Contacts

Tribological efficiency of industrial applications involving boundary lubrication regime can be improved to an appreciable extent by the deposition of hard coatings on interacting surfaces. Among such coatings, diamond-like carbon (DLC) coatings are considered to be one of the most suitable ones for the said role. DLC coatings possess a unique combination of physical, chemical, and material properties due to which they can help in minimizing friction-induced energy and material losses even under starved lubrication conditions. Since commercial lubricants are optimized for steel surfaces, therefore, a lot of experimental investigations were carried out to analyze the tribological compatibility of these lubricants with various DLC coatings. However, there is still a lack of understanding about how DLC coatings interact with conventional lubricant additives. Some researchers reported tribologically beneficial interactions between DLC coatings and formulated lubricants while others observed no such behavior. To address these inconsistencies, there is a need to rearrange the published data in a more apprehensible and organized manner with a special emphasis on the mechanisms responsible for a particular tribological behavior. In this way, it can be determined whether synergistic or antagonistic correlation exists between a particular DLC-lubricant combination and research on DLC coatings can be continued in a logical way. In this article, most widely investigated non-doped DLC coatings (ta-C, a-C:H, a-C, and ta-C:H) are tribologically analyzed. Average values of friction and wear coefficients are calculated for various DLC-lubricant combinations using already published data and compared to quantify the effectiveness of a particular lubricant additive in enhancing tribological characteristics of symmetrical non-doped DLC contacts. Moreover, tribological performance parameters of non-doped DLC coatings are compared with those of doped-DLC coatings to understand differences in their tribological behavior in combination with additives.