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91.
Castro K Sarmiento A Maguregui M Martínez-Arkarazo I Etxebarria N Angulo M Barrutia MU González-Cembellín JM Madariaga JM 《Analytical and bioanalytical chemistry》2008,392(4):755-763
A complete study of several English polychromed alabaster sculptures is presented. The support, pigment, and binders were
characterised by combining μEDXRF, μRaman, and FTIR spectroscopies. Among the pigments, minium, vermilion, lead white, carbon
black, red iron oxide, and a degraded green copper pigment were determined, together with gold leaf. The presence of the rare
mineral moolooite (copper oxalate) was also found as a degradation product in the green areas, where weddellite (calcium oxalate
dihydrate) was also determined. These facts, together with degradation of the green copper pigment, suggest microbiological
degradation of the original materials. Remains of glue and a varnish were also determined by FTIR spectroscopy and principal-components
analysis (PCA) of the spectra. Finally, PCA analysis was carried out to confirm whether the pieces came from the same quarry. 相似文献
92.
Prieto A Zuloaga O Usobiaga A Etxebarria N Fernández LA 《Analytical and bioanalytical chemistry》2008,390(2):739-748
A method for the determination of polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs) in water samples
is proposed. The method involving stir bar sorptive extraction (SBSE) and thermal desorption followed by gas chromatography
coupled with mass spectrometry was optimised using statistical design of experiments. In the first place, the influence of
different polydimethylsiloxane stir bars was studied. A Plackett–Burman design was chosen to estimate the influence of five
factors on the efficiency of the SBSE process: desorption time (5–10 min), desorption temperature (250–300 °C), desorption
flow (50–100 mL min−1), cryofocusing temperature (-130 to 40 °C) and vent pressure (0–12.8 psi). Afterwards, two central composite designs were
used to find the optimal process settings that were applied to the optimisation of both desorption and extraction efficiency.
In the case of the desorption parameters, long desorption times (10 min) and desorption flows lower than 70 mL min-1 yielded the best signals for the majority of compounds. However, different behaviour among the analytes was observed for
the vent pressure and we decided to fix it at an intermediate value (7 psi). In the case of extraction parameters, the sample
volume and the addition of NaCl did not have a significant effect, while the addition of methanol yielded better extraction
responses. Remarkable recovery (82–106%) and repeatability (less than 18%) were attained. Furthermore, excellent regression
coefficients (r
2 = 0.991–0.999) and low detection limits (1.1–6.0 ng L−1) were also achieved for the congeners studied. The proposed method was applied to the analyses of PBDEs and PBBs in waters
from the Basque Country, Spain. 相似文献
93.
Martínez-Arkarazo I Sarmiento A Usobiaga A Angulo M Etxebarria N Madariaga JM 《Talanta》2008,75(2):511-516
Thermodynamic and Raman spectroscopic speciation was used to define the operating conditions for an innovative cleaning treatment of the decayed carbonate-based stones using ion exchange technology. The conditioning process of the Lewatit OC1071 anion exchanger with EDTA (Y) was monitored by ionic chromatography. Characterisation of the initial (R-Cl) and the final (R2-H2Y) forms of the ion exchanger was carried out by dispersive Raman microprobe spectroscopy. The subtraction spectrum obtained between the chloride and the EDTA forms of the ion exchanger shows Raman bands at 1403, 1324, 1223, 1122, 932, 908, 591, 431 and 350 cm(-1), which agree with bands showed in the spectrum of the standard solution of the H2Y(2-) species. Therefore, this seems to be the EDTA species which takes part in the cleaning treatment performed by using resin poultices on black crusted limestone samples from an historical building. 相似文献
94.
Pintre IC Serrano JL Ros MB Ortega J Alonso I Martínez-Perdiguero J Folcia CL Etxebarria J Goc F Amabilino DB Puigmartí-Luis J Gomar-Nadal E 《Chemical communications (Cambridge, England)》2008,(22):2523-2525
The synthesis and characterization of bent-core liquid crystals which incorporate TTF groups is reported; different bent-core mesophases are induced depending on the molecular structure and properties derived from their compact packing have been studied. 相似文献
95.
A. Ezcurra M. A. P rez Jubindo M. R. De La Fuente J. Etxebarria A. Rem n M. J. Tello 《Liquid crystals》1989,4(2):125-132
The complex dielectric permittivity of HDOBAMBC has been measured in the vicinity of the chiral smectic C-smectic A transition as a function of temperature and frequency. The Goldstone mode contribution has been clearly identified and its relaxation frequency has been determined over the whole S*C range. High accuracy tilt angle measurements have also been performed by using a new method which allows its determination in a direct and virtually continuous way. These experimental results together with additional measurements of the polarization and helical pitch have been compared with those of DOBAMBC and analized in the framework of the generalized Landau theory. As for DOBAMBC a reentrant behaviour S*C-SC-S*C has been observed under an electric field near the S*C-SA transition. 相似文献
96.
97.
98.
A new and efficient conjugate addition of trialkylphosphites to 3-ω-bromoacetylcoumarin 1 catalysed by p-toluenesulfonic acid (TsOH) has been studied. Under the same conditions, an enolphosphate gave the corresponding esters of 3-acetyl-4-phosphono-2-oxochromans in high yields. The use of TsOH in the reaction of 3-acetyl-, 3-benzoyl-, and 3-ethoxycarbonyl coumarins led mainly to 1,4-addition products—the corresponding 3-acyl-4-dialkylphosphono-2-oxochromans—in very good yields. 相似文献
99.
100.