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131.
A novel approach of using a gold disc microelectrode to analyze sweat samples for copper ions by anodic square wave stripping voltammetry (SW stripping voltammetry) is described. Sweat was collected from the lower back of four subjects after physical exercise and the sample volume required for the determinations was 100 μL. Under the optimized conditions, the calibration plot was linear over the range 1-100 μmol L−1 Cu(II) with a limit of detection of 0.25 μmol L−1. The precision was evaluated by carrying out five replicate measurements in a 1 μmol L−1 Cu(II) solution and the standard deviation was found to be 1.5%. Measurements were performed by inserting the microelectrode into sweat drops and Cu(II) concentrations in the analyzed samples ranged from 0.9 to 28 μmol L−1. Values obtained by the proposed voltammetric method agreed well with those found using graphite furnace atomic absorption spectroscopy (GFAAS). 相似文献
132.
Luisa Célia Melo Djenaine De Souza Pedro de Lima‐Neto Adriana Nunes Correia 《Electroanalysis》2010,22(21):2502-2510
The highly boron‐doped diamond electrode (HBDD) combined with square wave voltammetry (SWV) was used in the development of an analytical procedure for diquat determination in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices. Preliminary experiments realised in a medium of 0.05 mol L?1 Na2B4O7 showed the presence of two voltammetric peaks around ?0.6 V and around ?1.0 V vs. Ag/AgCl/Cl? 3.0 mol L?1, where the first peak could be successfully used for analytical proposes due the facility in the electrode surface renovation. After the experimental and voltammetric optimisation, the calculated detection and quantification limits were 1.6×10?10 mol L?1 and 5.3×10?10 mol L?1 (0.057 µg L?1 and 0.192 µg L?1, respectively), which are lower than the maximum residue limit established for fresh food samples by the Brazilian Sanitary Vigilance Agency. The proposed methodology was used to determine diquat residues in potato and sugar cane samples and lemon, orange, tangerine and pineapple juices and the calculated recovery efficiencies indicated that the proposed procedure presents higher robustness, stability and sensitivity, good reproducibility, and is very adequate for diquat determination in complex samples. 相似文献
133.
Manuel A.V. Ribeiro da Silva Luís M.N.B.F. Santos Luís M. Spencer S. Lima 《The Journal of chemical thermodynamics》2010,42(1):134-139
The energetic study of 1,2,3-triphenylbenzene (1,2,3-TPhB) and 1,3,5-triphenylbenzene (1,3,5-TPhB) isomers was carried out by making use of the mini-bomb combustion calorimetry and Knudsen mass-loss effusion techniques. The mini-bomb combustion calorimetry technique was used to derive the standard (p° = 0.1 MPa) molar enthalpies of formation in the crystalline state from the measured standard molar energies of combustion for both isomers. The Knudsen mass-loss effusion technique was used to measure the dependence with the temperature of the vapour pressure of crystalline 1,2,3-TPhB, which allowed the derivation of the standard molar enthalpy of sublimation, by application of the Clausius–Clapeyron equation. The sublimation study of 1,3,5-TPhB had been performed previously. From the combination of data obtained by both techniques, the standard molar enthalpies of formation in the gaseous state, for both isomers, at T = 298.15 K, were calculated. The results indicate a higher stability of the 1,3,5-TPhB isomer relative to 1,2,3-TPhB, similarly to the terphenyls. Nevertheless, the 1,2,3-TPhB isomer is not as energetically destabilized as one might expect, supporting the existence of a π–π displacive stacking interaction between both pairs of outer phenyl rings. The volatility difference between the two isomers is ruled by the enthalpy of sublimation. The volatility of the 1,2,3-TPhB is two orders of magnitude higher than the 1,3,5-TPhB isomer, at T = 298.15 K.
Empty Cell | ||
1,2,3-Triphenylbenzene (1,2,3-TPhB) | ?12248.2 ± 4.1 | 376.7 ± 5.3 |
1,3,5-Triphenylbenzene (1,3,5-TPhB) | ?12224.6 ± 3.6 | 366.8 ± 4.9 |