On-line elimination of spectral interference of iron matrix in the flame atomic absorption determination of zinc by anion-exchange separation

A flow injection analysis (FIA) system has been developed for the flame atomic absorption spectroscopic (FAAS) determination of zinc in iron matrix. The spectral line interference of iron at 213.859 nm was eliminated by on-line separation using a micro-column of strong anion-exchange resin (Dowex 1-X8). The zinc chloro complexes were retained from 2 M HCl solution while most of the iron chloro complexes were passed to waste. For a 2% iron solution, matrix removal efficiency was 98.2% which means that positive spectral line interference of iron at the Zn line was reduced from 0.42 to 0.008 μg ml⁻¹ Zn. The optimized flow injection system can handle up to 48 samples with good precision (less than 3.5% relative standard deviation (R.S.D.)) in the working range of 0.075-2.2 μg ml⁻¹ Zn. Comparative analysis of a certified reference material and synthetic sample solutions containing traces of Zn in 2% Fe by the proposed method and by graphite furnace atomic absorption spectroscopy (GFAAS) showed no evidence of analytical bias at the 95% confidence level.     

ZrCl4 dispersed on dry silica gel provides a useful reagent for S-alkylation of thiols with alcohols under solvent-free conditions

ZrCl₄ which is commercially available and not a costly compound, is a relatively safe chemical [LD₅₀ [ZrCl₄, oral rat] = 1688 mg Kg]. In this report we describe the use of ZrCl₄ dispersed on dry silica gel as an efficient reagent for the efficient preparation of thioethers from thiols with alcohols under solvent-free conditions.     

Investigation of the effects of ionic hydrogen bonds (COH–C and N–HOC) in crystalline dl-proline by ab initio and DFT calculated NQR parameters

In this paper, we have calculated the nuclear quadrupole resonance (NQR) parameters of the quadrupole nuclei involved in the hydrogen bonds (CO⁻H–C and ⁺N–H⁻OC) in the monomer and pentameric cluster of dl-proline by HF and B3LYP methods and basis sets of 6-311+G^* and 6-311++G^**. These computations are performed on the basis of X-ray diffraction structural data of dl-proline. The results indicate that the calculations including hydrogen-bonding (HB) interactions (in pentamer) are in better agreement with the experimental data than those in which these interactions are neglected (in monomer). The quantum chemical calculations show that the intermolecular hydrogen-bonding interactions play an important role in determination of the NQR parameters of ¹⁴N, ²H of group and ¹⁷O.     

Experimental demonstration of diffusocapillary flow in an oil droplet

The phenomenon of diffusocapillary flow is demonstrated utilizing a vegetable oil droplet suspended in a host medium composed of Dow Corning 200 silicone fluids. The host fluid was prepared in such a way that the average polymer length was varied across the surface of the droplet, thus creating an interfacial tension gradient with concomitant Marangoni flow.     

Magnesium triflate [Mg(OTf)2] a highly stable, non-hygroscopic and a recyclable catalyst for the high yielding preparation of diethyl α-trimethylsilyloxyphosphonates from diethyl α-hydroxyphosphonates by HMDS under solventless conditions

A broad, adaptable, high yielding and convenient procedure for the easy conversion of various α-hydroxyphosphonates to α-trimethylsilyloxyphosphonates under mild conditions with HMDS in the presence of a catalytic amount of magnesium triflate as a highly stable and a non-hygroscopic recyclable catalyst in neat conditions is described. In order to show the general applicability of this method, we have also applied this procedure successfully for the silylation of ordinary alcohols and phenols.     

Unprecedented intermolecular transamidation reaction of N-carbamoylmethyl-N'-tosylguanidines

[reaction: see text] N-Carbamoylmethyl-N'-tosyl guanidine 2 reacts easily with primary alkylamines to afford substituted carboxamides 3. The reaction proceeds via a five-membered-ring intermediate 5, which could be isolated, and features a rare example of an intermolecular transamidation reaction under mild conditions.     

Catalytic and chemoselective deprotection of S,S- and S,O-acetals and ketals in the presence of their O,O-analogs with electrophilic halogens under neutral conditions

A novel and catalytic method is described for the selective deprotection of S,S- and S,O-acetals and ketals in the presence of their O,O-analogs to their corresponding carbonyl compounds based on the use of N-bromosuccinimide (NBS), N-chlorosuccinimide (NCS), 2,4,4,6-tetrabromo-2,5-cyclohexadiene-1-one (TABCO), trichlorocyanuric acid (TCCA) or molecular bromine as sources of electrophilic halogens in the presence of DMSO as the source of oxygen in CHCl₃.     

Silicaphosphine (Silphos): a filterable reagent for the conversion of alcohols and thiols to alkyl bromides and iodides

Silicaphosphine (Silphos), [P(Cl)_3−n(SiO₂)_n], as a new heterogeneous reagent is introduced. This reagent converts alcohols and thiols to their corresponding bromides and iodides in the presence of X₂ (X=Br, I) in refluxing CH₃CN in high to quantitative yields. Use of Silphos provides a highly practical method for the easy separation of the Silphos oxide byproduct by a simple filtration.     

Sorption of trace metals on human hair and application for cadmium and lead pre-concentration with flame atomic absorption determination

Human hair shavings were characterized as a sorbent for trace metals. At pH 7.0 metal sorption follows the order Pb(II)>Cd(II)>Cr(VI)>Fe(III)>Cu(II)>Ni(II)>Mn(VI). Metal recovery is quantitative for Pb and Cd after 30 min of equilibration. Recovery of other metals is less quantitative and varies with pH. For example, while Cu is best recovered at pH 5, Ni and Mn are sorbed optimally in the basic pH region. Sorbed metals can be washed off the sorbent with 0.5 mol L(-1) strong mineral acids or more completely with 0.1 mol L(-1) ethylenediaminetetraacetic acid (EDTA). Typical sorption isotherms were obtained for Cd and Pb with sorption capacities of 39 and 26 micromol g(-1), respectively.Hair sorbent was used for 40-fold pre-concentration of Cd and Pb from treated wastewater samples followed by flame atomic absorption spectroscopic (FAAS) determination. Comparison of the data obtained for lead and cadmium by the proposed pre-concentration method with that by graphite furnace atomic absorption spectroscopy (GFAAS) showed 79 to 86% recovery and comparable analytical precision. Common cations and anions at the levels normally present in natural water do not interfere in the proposed pre-concentration-FAAS method.