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971.
Quantitative separation of zinc traces from cadmium matrices by solid-phase extraction with polyurethane foam 总被引:1,自引:0,他引:1
Santiago de Jesus D Souza de Carvalho M Spínola Costa AC Costa Ferreira SL 《Talanta》1998,46(6):1525-1530
A system for separation of zinc traces from large amounts of cadmium is proposed in this paper. It is based on the solid-phase extraction of the zinc in the form of thiocyanate complexes by the polyurethane foam. The following parameters were studied: effect of pH and of the thiocyanate concentration on the zinc extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction, conditions for the separation of zinc from cadmium, influence of other cations and anions on the zinc sorption by PU foam, and required conditions for back extraction of zinc from the PU foam. The results show that zinc traces can be separated from large amounts of cadmium at pH 3.0±0.50, with the range of thiocyanate concentration from 0.15 to 0.20 mol l−1, and the shaking time of 5 min. The back extraction of zinc can be done by shaking it with water for 10 min. Calcium, barium, strontium, magnesium, aluminum, nickel and iron(II) are efficiently separated. Iron(III), copper(II) and cobalt(II) are extracted simultaneously with zinc, but the iron reduction with ascorbic acid and the use of citrate to mask copper(II) and cobalt(II) increase the selectivity of the zinc extraction. The anions nitrate, chloride, sulfate, acetate, thiosulphate, tartarate, oxalate, fluoride, citrate, and carbonate do not affect the zinc extraction. Phosphate and EDTA must be absent. The method proposed was applied to determine zinc in cadmium salts using 4-(2-pyridylazo)-resorcinol (PAR) as a spectrophotometric reagent. The result achieved did not show significant difference in the accuracy and precision (95% confidence level) with those obtained by ICP–AES analysis. 相似文献
972.
Merlin Rosales Janeth Navarro Ligbel Sánchez Angel González Ysaías Alvarado Raúl Rubio Carlos De La Cruz Tamara Rajmankina 《Transition Metal Chemistry》1996,21(1):11-15
Summary The complex [RuH(CO)(NCMe)2(PPh3)2]BF4 (1) is an efficient and regioselective catalyst precursor for the hydrogenation of polyaromatic nitrogen compounds such as quinoline (Q), isoquinoline (iQ), indole (ln), 5,6- and 7,8-benzoquinoline (BQ) and acridine (A) under relatively mild reaction conditions (125 °C, 4 atm H2). The order of individual initial rates was: A > Q > 5,6-BQ > 7,8-BQ > ln > iQ, reflecting both steric and electronic effects. For the regioselective homogeneous hydrogenation of A to 9,10-dihydroacridine (DHA) catalysed by complex (1), a kinetic study was carried out; the experimentally determined rate law was r = k
1 [Ru] [H2]. These findings are consistent with a mechanism involving the hydrogenation of [RuH(CO)(A)(NCMe)(PPh3)2]BF4 to yield DHA and the unsaturated species [RuH(CO)(NCMe)(PPh3)2]BF4 in the rate-determining step. 相似文献
973.
Summary Magnetic susceptibilities of the biacetyldihydrazone (BdH) complexes [M(BdH)3](NO3)2 (M = CoII, NiII, CuII or ZnII), [Fe(BdH)3](NO3)3, [M(BdH)3](Ni(dto)2] (M = CoII, NiII or ZnII; dto = dithiooxalate), [(BdH)2Cu(dto)Ni(dto)] and [Fe(BdH)3]2[Ni(dto)2]3 have been studied in the 4.2–295 K range. ZnII complexes are diamagnetic, and complexes of NiII, CuII and FeIII obey the Curie-Weiss law. The CoII complexes behave anomalously and the results are interpreted in terms of a high spinlow spin equilibrium. 相似文献
974.
Delgado Zamarreño MM Sanchez Perez A Sanchez Rodriguez M Gomez Perez MC Hernandez Mendez J 《Talanta》1996,43(9):1555-1563
A method employing HPLC with electrochemical detection for the rapid and simultaneous determination of vitamins A, D(3) and E is described. The method uses a C-18 reverse phase column and 2.5 mM HAcO-NaAcO in methanol-water (99:1, v/v) solution as the mobile phase. The compounds are quantified using amperometric detection with a glassy carbon electrode at a potential of + 1300 mV (vs. Ag/AgCl) and the results are compared with those obtained using UV detection at a wavelength of 280 nm. The method was successfully applied to the analysis of vitamins A, D(3) and E in yogurt samples. After saponification, fat-soluble vitamins were extracted and the methanolic solution of the extracts was injected directly into the chromatographic system, avoiding the clean-up step which is necessary when no electrochemical detection is used. Good recovery percentages were obtained. 相似文献
975.
A spectrophotometric study of the chlorhexidine/bromocresol green/Triton X-100 system is reported; at pH 5.3, both 2:1 and 1:1 bromocresol green/chlorhexidine complexes are formed. In the manual spectrophotometric method, Beer's law is obeyed for chlorhexidine concentrations of 2.9–32.2 μg ml?1 (r.s.d. 0.4–1.3%); the molar absorptivity is 12 500 l mol?1 cm?1. In the flow-injection method, the calibration graph is linear for the chlorhexidine range 23.0–83.9 μg ml?1 (r.s.d. 0.8%); the injection is ca. 60 h?1. Benzocaine, acetylsalicylic acid, ascorbic acid and sucrose are tolerated at 10?2?10?3 M levels. Hibitane 5% was analyzed successfully. 相似文献
976.
M. García-Leòn 《Journal of Radioanalytical and Nuclear Chemistry》1990,138(1):171-179
In this paper, the physical and chemical methods used in our laboratory for the measurement of99Tc in natural samples are reviewed. Levels of99Tc in rainwater, algae, and freshwater samples are given. In addition, and estimation of the radiological impact of99Tc to the population, derived from our earliear atmospheric99Tc measurements, is presented. For rainwater, levels of137Cs are also given for comparison.Work partially supported by the contract PB86-0207 of the Spanish CICYT. 相似文献
977.
The reaction between arachno-4-CB(8)H(14) and PCl(3) in the presence of PS (PS = proton sponge = 1,8-dimethylamino naphthalene) (dichloromethane, rt, 24 h) produced the neutral phosphacarborane closo-2,1-PCB(8)H(9) (35% yield), while a similar reaction of nido-1-CB(8)H(12) gave the isomeric compound closo-6,1-PCB(8)H(9) (27% yield). The structures of both compounds were derived on the basis of the combined ab initio/GIAO/NMR ((1)H, (11)B, (13)C) approach. The optimized structures at a correlated level of theory (MP2) with 6-31G* basis set were used as a basis for calculations of the (11)B and (13)C chemical shifts at GIAO-SCF/II and GIAO-MP2/II, the latter showing excellent agreement with experimental data. 相似文献
978.
A new flow injection (FI) system for the determination of Pb(II) at trace level with a preconcentration step and spectrophotometric detection is proposed. It is based on preconcentration of lead ions on chitosan and dithizone-lead complex formation in aqueous medium (pH 9). The chemicals and FIA variables influencing the performance of the system were optimized and applied to the determination of lead in natural, well, and drinking water samples. It is a simple, highly sensitive, and low cost alternative methodology. The method provided a linear rage between 25 and 250 μg l−1, a detection limit of 5.0 ng ml−1 and a sample throughput of 15 h−1. The obtained results of spiked samples are in good agreement between the proposed method and ICP-AES. 相似文献
979.
Darío Gmez Marina Dos Santos Fabin Fujiwara Griselda Polla Julieta Marrero Laura Dawidowski Patricia Smichowski 《Microchemical Journal》2007,85(2):276-284
A study was undertaken to evaluate the distribution of Al, As, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn in fly ashes collected in the electrostatic precipitator of a thermal power plant in San Nicolás (Argentina). Five samples were collected during one week of operation. For the fractionation, the scheme applied consisted in extracting the elements in four fractions namely (i) soluble and exchangeable elements; (ii) carbonates, oxides and reducible elements; (iii) bound to sulfidic metals; and (iv) residual elements. Metals and metalloids at μg g− 1 level were determined in each fraction by inductively coupled plasma optical emission spectrometry (ICP OES). For validation, a standard reference material (SRM 1633 coal fly ash) from NIST was subjected to the same chemical sequential extraction procedure that the samples. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the major minerals present in the matrix. Total analyte concentration (in μg g− 1) varied from 10.6 for Pb to 17,622 for Al. Minimum and maximum concentrations (in μg g− 1) found in individual samples in the four fractions were: Al, 92.7–9668; As, < 0.3–143; Cr, 2.0–10.4; Cu, < 0.2–35.6; Fe, < 0.3–4992; Mn, < 0.1–128; Ni, < 0.3–139; Pb, < 0.5–9.1; Ti, < 0.3–2243; V, 17.0–112.9; and Zn, < 0.1–68.2. The leachability of the 11 elements under study proved to be different. Low percentages of Al (1%), V (7%) and Cr (8%) were detected in the most bioavailable fraction. Arsenic was found to be most abundant in the non-silicate phase, represented by the second and third fractions, while Cr, Fe, Ni, Pb and Zn were mostly associated to the residual fraction. 相似文献
980.
Transformation
of dynamic DSC results into isothermal data for the curing kinetics study
of the resol resins 总被引:1,自引:0,他引:1
M. V. Alonso M. Oliet J. García F. Rodríguez J. Echeverría 《Journal of Thermal Analysis and Calorimetry》2006,86(3):797-802
Kinetics of thermosetting polymers curing is difficult to study by isothermal
methods based on the differential scanning calorimetry (DSC) technique. The
difficulty is due to the low sensitivity of the equipment for total reaction
heat measurements during high temperature process. The aim of this paper is
to display the equivalence between a dynamic model, the Ozawa method, and
an isothermal isoconversional fit, which allows predicting the isothermal
behavior of the resol resins cure through dynamic runs by DSC. In this work,
lignin–phenol–formaldehyde and commercial phenol–formaldehyde
resol resins were employed. In addition, the isothermal kinetic parameters
for both resins were performed by means of transformation of the data obtained
from the dynamic Ozawa method. 相似文献