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1.
A simple method for the rapid and simultaneous analysis of dichlorvos (DDVP), malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid (2,4-D) in citrus fruit, which uses flow-injection ion spray ionization tandem mass spectrometry, has been developed for the first time. The method involves the combined use of stable isotopically labeled internal standards (DDVP-d6, malathion-d10, carbaryl-d7, and 2,4-D-d5) and a multiple reaction monitoring technique. The average recoveries for the pesticides at the same concentrations as their tolerance levels (DDVP: 0.1-0.2 μg g−1; malathion: 0.5-4.0 μg g−1; carbaryl: 1.0 μg g−1; 2,4-D: 1.0-2.0 μg g−1) ranged from 90 to 119% with the relative standard deviation (R.S.D.) ranging from 1.0 to 13.1% (n = 5). Analysis time, including sample preparation and determination, was only 15 min. The present method is effective for screening DDVP, malathion, carbaryl, and 2,4-D in citrus fruit.  相似文献   

2.
A straight forward room-temperature synthesis of V(III) containing complex fluoride K3VF6, using KF and vanadium(III) acetylacetonate is reported. The pale green colored powder was characterized by chemical analysis, powder X-ray diffraction; diffuse reflectance spectroscopy, infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, scanning electron microscopy, photoluminescence spectroscopy, magnetic susceptibility measurements and photoluminescence spectroscopy. The powder X-ray diffraction pattern was fitted in P21/n space group (monoclinic) with a = 12.106 (1) Å, b = 17.685 (0) Å, c = 11.802 (0) Å, β = 92.23° (1). Differential scanning calorimetry showed phase transitions, occurring at 158 °C and 190 °C. In the FT-IR spectrum, characteristic band for the VF63− group was observed at 508 cm−1. The bands observed in the 335-361 cm−1 region and at 504 cm−1 in the room temperature Raman spectrum of K3VF6 corresponded to the F2g and A1g modes, respectively. The ratio of the frequencies (F2g/A1g) observed in the diffuse reflectance spectrum was fitted on the Tanabe-Sugano diagram to determine the Racah parameter B value of 712 cm−1. Magnetic ordering was not observed down to the lowest measured temperature of 5 K.  相似文献   

3.
A new high temperature, flexible and colorless indium-tin-oxide (ITO) coated plastic substrate has been prepared from a thermally stable, high glass transition temperature (Tg) and colorless polyimide film. The polyimide was synthesized from 3,3′-diaminodiphenylsulfone (3,3′-DDS) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) monomers. Its heat distortion temperature was 278 °C. The ITO was deposited on the polyimide film using the magnetron-sputtering process. After annealing at 250 °C under nitrogen for 1 h, the resistivity of the ITO film was 4.0 × 10−4 Ω cm, and its transmittance was 83.5%. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to observe the surface and morphology of the ITO film. UV-visible spectroscopy and the four-probe method were used to study their optical and electrical properties. The high performance ITO-plastic substrate can be used in the next generation flat panel displays.  相似文献   

4.
3,4-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with terephthaloyl chloride and adipoyl chloride to yield novel Y-type polyesters (4-5) containing 3,4-dioxybenzylidenemalononitrile groups as NLO-chromophores, which constituted parts of the polymer main-chains. The resulting polymers 4-5 are soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed thermal stability up to 300 °C in thermogravimetric analysis with glass-transition temperatures obtained from differential scanning calorimetry in the range 89-91 °C. The second harmonic generation (SHG) coefficients (d33) of poled polymer films at the 1064 nm fundamental wavelength were around 2.47 pm/V. The dipole alignment exhibited high thermal stability even at 10 °C higher than Tg, and there is no SHG decay below 100 °C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.  相似文献   

5.
Novel optically active aromatic poly(amide-imide)s (PAIs) were prepared from newly synthesized N,N′-(4,4′-diphthaloyl)-bis-l-isoleucine diacid (3) via polycondensation with various diamines. The diacid was synthesized by the condensation reaction of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (1) with l-isoleucine (2) in a mixture of acetic acid and pyridine (3:2 v/v). All the polymers were obtained in quantitative yields with inherent viscosities of 0.20-0.43 dL g−1. All the polymers were highly organosoluble in solvents like N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran, γ-butyrolactone, cyclohexanone and chloroform at room temperature or upon heating. These poly(amide-imide)s had glass transition temperatures between 198 and 231 °C, and their 10% weight-loss temperatures were ranging from 368 to 398 °C and 353 to 375 °C under nitrogen and air, respectively. The polyimide films had tensile strengths in the range of 63-88 MPa and tensile moduli in the range of 0.8-1.4 GPa. These poly(amide-imide)s possessed chiral properties and the specific rotations were in the range of −3.10° to −72.92°.  相似文献   

6.
2,4-Di-2-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3-dimethoxy-4,4-biphenylenediisocyanate to yield unprecedented novel Y-type polyurethanes (4-5) containing 2,4-dioxybenzylidenemalononitrile group as a nonlinear optical (NLO) chromophore, which constitutes a part of the polymer backbone. The resulting polyurethanes 4-5 were soluble in common organic solvents such as acetone and DMF. Polymers 4-5 showed a thermal stability up to 260 °C from thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) giving Tg values around 143-156 °C. The approximate lengths of aligned NLO-chromophores estimated from AFM images of poled polymer films were about 10 nm. The SHG coefficients (d33) of poled polymer films were around 7.4 × 10−9 esu. These Poled polymers exhibited a greater thermal stability of dipole alignment even at 10 °C higher than Tg, and no SHG decay was observed below 155 °C due to the partial main chain character of the polymer structure and extensive hydrogen bonds between urethane linkage, which is acceptable for NLO device applications.  相似文献   

7.
In the present study, cadmium and lead in the muscle, lung, liver and kidney of dolphins (Sotalia guianensis and Stenella clymene) of the Bahia coast in the northwest of Brazil were determined by graphite furnace atomic absorption spectrometry. Samples were digested using a diluted oxidant mixture (HNO3 + H2O2) with a microwave heating program performed in five steps. The optimized temperatures and chemical modifier for the pyrolysis and atomization were 700 °C, 1400 °C and Pd plus Mg for Cd, and 900 °C, 1800 °C and NH4H2PO4 for Pb, respectively. Characteristic masses and limits of detections (n = 20, 3σ) for Cd and Pb were 1.6 and 9.0 pg and 0.82 ng g− 1 and 0.50 ng g− 1, respectively. Repeatability ranged from 0.87 to 8.22% for Cd and 4.31 to 8.09% for Pb. The found concentrations presented no statistical differences at the 95% confidence level when compared with the ICP OES methods. Addition and recovery tests were also performed and the results ranged between 87 and 112% for both elements. Samples of cetacean Dolphinidae (S.guianensis and S.clymene) were analyzed, and the higher concentrations ranged from 0.09 to 46.2 µg g− 1 for Cd and 0.04 to 0.47 µg g− 1 for Pb in liver, and from 0.133 to 277 µg g− 1 for Cd in the kidney.  相似文献   

8.
Activation energies for nitrocellulose (NC) degradation have been determined from Arrhenius plots constructed using first-order rate constants measured at 40, 50 and 60 °C. The rate constants were obtained by monitoring the absorbance (A) at a wavelength in the visible region of an anthraquinone dye dispersed in NC thin films. The dye acts as a stabilizer and is slowly depleted as a result of its reaction with NOx from the breakdown of the nitrate ester groups on NC. The data produced two linear regions in the first-order plots of ln(A0/At) vs aging time. The first-region is attributed to the reaction of the dye with NOx desorbed from the NC surface. The activation energy (∼73.5 kJ mol−1) is in line with that found for NOx surface desorption processes. The second linear region is thought to be due to the reaction of NOx from the breakdown of the nitrate ester groups on the NC molecule. The activation energy (∼104.0 kJ mol−1) is consistent with that for nitrate ester hydrolysis. The use of UV-visible spectroscopy has in this way made it possible to monitor the degradation of NC non-destructively without the need for stabilizer extraction and analysis.  相似文献   

9.
3,4-Di-(2′-hydroxyethoxy)-4′-nitrobenzylidene II was prepared by condensation reaction of 3,4-dihydroxy-4′-nitrobenzylidene I with 1-chloro-2-ethanol. Monomer II was reacted with p-phenylene diisocyanate to yield polyurethane containing the non-linear optical chromophore 3,4-di-(2′-hydroxyethoxy)-4′-nitrobenzylidene. Polymer III shows thermal stability up to 300 °C in TGA thermogram. Tg value of the polymer obtained from DSC thermogram was 110 °C. The resulting polyurethane III was soluble in common organic solvents such as acetone, DMF and DMSO. The values of electro optic coefficient d33 and d31 of the poled polymer film were 3.15 × 10 −7 and 1.5 × 10 −7 esu, respectively.  相似文献   

10.
Biocatalytic reduction of methyl o-chlorobenzoylformate (CBFM) provides a green and direct access to methyl (R)-o-chloromandelate [(R)-CMM], an intermediate for a platelet aggregation inhibitor named clopidogrel. As much as 500 g L−1 of CBFM was stoichiometrically converted into enantiopure (R)-CMM at 20 °C by using a whole-cell catalyst coexpressing an aldo-keto reductase from Bacillus sp. and a glucose dehydrogenase (GDH). In addition to the high productivity of 812 g L−1 d−1, this new whole-cell reduction is attractive by eliminating the need of an added external cofactor.  相似文献   

11.
Phosphorous-bridged bisphenoxy titanium complexes were synthesized and their ethylene polymerization behavior was investigated. Bis[3-tert-butyl-5-methyl-2-phenoxy](phenyl)phosphine tetrahydrofuran titanium dichloride (4a) was obtained by treatment of 3 equiv of n-BuLi with bis[3-tert-butyl-2-hydroxy-5-methylphenyl](phenyl)phosphine hydrochloride salt (3a) followed by TiCl4(THF)2 in THF. THF-free complexes 5a-5d were synthesized more conveniently by the direct reaction of MOM-protected ligands (2a-2d) with TiCl4 in toluene. X-ray analysis of 4a revealed that the ligand is bonded to the octahedral titanium (IV) center in a facial fashion and two chlorine atoms possess cis-geometry. Complexes 4a and 5a-5d were utilized as catalyst precursors for ethylene polymerization. Complex 5c gave high molecular weight polyethylene (Mw = 1,170,000, Mw/Mn = 2.0) upon activation with Al(iBu)3/[Ph3C][B(C6F5)4] (TB). Ethylene polymerization activity of 5d activated with Al(iBu)3/TB reached 49.0 × 106 g mol (cat) −1 h−1.  相似文献   

12.
The heterocyclic amines 2,6-lutidine, pyrazine, piperazine and piperidine were intercalated into layered crystalline hydrated barium phenylphosphonate, Ba(HO3PC6H5)2·H2O, through a batch method in ethanolic solution, to give the maximum amounts 0.39, 0.82, 2.80 and 5.50 mmol g−1, respectively. The original host interlayer distance (d) of 1532 pm increased after intercalation for piperazine (1752 pm) and piperidine (2112 pm) molecules, while for 2,6-lutidine and pyrazine molecules d values were maintained. The enthalpy of intercalation gave −5.60 ± 0.10, −1.00 ± 0.02, −9.55 ± 1.00 and −30.70 ± 0.68 kJ mol−1 for the sequence of heterocyclic amines. The Gibbs free energies are negative and entropies are positive for intercalation.  相似文献   

13.
A synthesis of thieno[2,3-d][1,3,2]dithiazolium salts from commercial tetrahydrothiophene has been developed. The reaction of thieno[2,3-f][1,2,3,4,5]pentathiepin with LiAlH4 in THF at −15 °C, after treatment with acetyl chloride, led to 2,3-(bisacetylthio)thiophene in high yield. Bis(acetylthio)thiophene reacted with sulfuryl chloride and then trimethylsilyl azide was added to afford a 1,3,2-dithiazolium chloride which was converted into a soluble tetrafluoroborate. Electrolytic reduction under controlled potential yielded a thieno[2,3-d][1,3,2]dithiazolyl radical which was characterized by EPR in frozen methylene dichloride.  相似文献   

14.
Enthalpies for the two proton ionizations of glycine, N,N-bis(2-hyroxyethyl)glycine (“bicine”) and N-tris(hydroxymethyl)methylglycine (“tricine”) were obtained in water-methanol mixtures with methanol mole fraction (Xm) from 0 to 0.360. With increasing methanol the ionization enthalpy for the first proton (ΔH1) of glycine increased from 4.4 to 9.4 kJ mol−1 with a minimum of 4.1 kJ mol−1 at Xm = 0.059. The ionization enthalpy of the second proton (ΔH2) for glycine decreased from 46.3 to 38.1 kJ mol−1. ΔH1 of bicine increased from 3.5 to 7.6 kJ mol−1 at Xm = 0.273 before dropping to 4.1 kJ mol−1 at Xm = 0.360. ΔH2 of bicine increased from 24.9 to 29.4 kJ mol−1. For tricine, ΔH1 increased from 6.7 to 9.8 kJ mol−1 at Xm = 0.194 then dropped to 7.4 kJ mol−1 at Xm = 0.360. ΔH2 for tricine first dropped from 30.8 to 28.5 kJ mol−1 at Xm = 0.059 before increasing to 33.3 kJ mol−1 at Xm = 0.273. The solvent composition was selected so as to include the region of maximum structure enhancement of water by methanol. The results were interpreted in terms of solvent-solvent and solvent-solute interactions.  相似文献   

15.
2-Thiophenecarboxaldhyde is chemically bonded to silica gel surface immobilized monoamine, ethylenediamine and diethylenetriamine by a simple Schiff’s base reaction to produce three new SP-extractors, phases (I-III). The selectivity properties of these phases toward Hg(II) uptake as well as eight other metal ions: Ca(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) were extensively studied and evaluated as a function of pH of metal ion solution and equilibrium shaking time by the batch equilibrium technique. The data obtained clearly indicate that the new SP-extractors have the highest affinity for retention of Hg(II) ion. Their Hg(II) uptake in mmol g−1 and distribution coefficient as log Kd values are always higher than the uptake of any other metal ion along the range of pH used (pH 1.0-10.0). The uptake of Hg(II) using phase I was 2.0 mmol g−1 (log Kd 6.6) at pH 1.0 and 2.0. 1.8 mmol g−1 (log Kd 4.25), 1.6 mmol g−1 (log Kd 3.90) and 1.08 mmol g−1 (log Kd 3.37) at pH 3.0, 5.0 and 8.0, respectively. Selective separation of Hg(II) from the other eight coexisting metal ions under investigation was achieved successfully using phase I at pH 2.0 either under static or dynamic conditions. Hg(II) was completely retained while Ca(II), Co(II) and Cd(II) ions were not retained. Ni(II), Cu(II), Zn(II), Pb(II) and Fe(III) showed very low percentage retention values to be 0.74, 0.97, 3.5 and 6.3%, respectively. Moreover, the high recovery values (95.5 ± 0.5, 95.8 ± 0.5 and 99.0% ± 1.0) of percolating two liters of doubly distilled water, drinking tap water and Nile river water spiked with 5 ng/l of Hg(II) over 100 mg of phase I packed in a minicolumn and used as a thin layer enrichment bed demonstrate the accuracy and validity of the new SP-extractors for preconcentration of the ultratrace amount of spiked Hg(II) prior to the determination by borohydride generation atomic absorption spectrometry (AAS) with no matrix interference. The detection limit (3σ) for Hg(II) based on enrichment factor 1000 was 4.75 pg/ml. The precision (R.S.D.) obtained for different amounts of mercury was in the range 0.52-1.01% (N = 3) at the 25-100 ng/l level.  相似文献   

16.
The oxidation of a series of substituted pyridines by dimethyldioxirane (1) produced the expected N-oxides in quantitative yields. The second order rate constants (k2) for the oxidation of a series of substituted pyridines (2a-g) by dimethyldioxirane were determined in dried acetone at 23 °C. An excellent correlation with Hammett sigma values was found (ρ = −2.91, r = 0.995). Kinetic studies for the oxidation of 4-trifluoromethylpyridine by 1 were carried out in the following dried solvent systems: acetone (k2 = 0.017 M−1 s−1), carbon tetrachloride/acetone (7:3; k2 = 0.014 M−1 s−1), acetonitrile/acetone (7:3; k2 = 0.047 M−1 s−1), and methanol/acetone (7:3; k2 = 0.68 M−1 s−1). Kinetic studies of the oxidation of pyridine by 1 versus mole fraction of water in acetone [k2 = 0.78 M−1 s−1 (χ = 0) to k2 = 11.1 M−1 s−1 (χ = 0.52)] were carried out. The results showed the reaction to be very sensitive to protic, polar solvents.  相似文献   

17.
The kinetics of pyrolysis of a micro-crystalline cellulose in nitrogen were studied from TGA and DTG data, obtained with two different modes of heating: a dynamic mode at constant heating rates between 1 and 11 °C/min and an isothermal mode at various temperatures, kept constant between 280 and 320 °C. In isothermal mode, it appeared very clearly that the mass depletion shows a sigmoid profile characteristic of an auto-accelerated reaction process. This behaviour is consistent with kinetics of nuclei-growth, well represented by the models of Avrami-Erofeev (A-E) and of Prout-Tompkins (P-T) type. All the other kinetic models commonly applied to the thermal decomposition of solids revealed unsatisfactory. The TGA and DTG data were, thus, found ideally simulated from a reaction scheme consisting in two parallel reactions, termed 1 and 2, each one described by the kinetic law: dx/dt=−AE/RTxn(1−0.99x)m. Reaction 1 is related to the bulk decomposition of cellulose and is characterised by the set of parameters: E1=202 kJ/mol; n1=1; m1=0.48. Reaction 2 is related to the slower residual decomposition, which takes place over approximately 350 °C and affects only 16% by weight of the raw cellulose. With m2 constrained to 1, the optimised parameters of this reaction were: E2=255 kJ/mol; n2=22. Finally, the proposed model allowed to correctly fit not less than to 10 sets of ATG-DTG data, isothermal and dynamic.  相似文献   

18.
2,3-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-4′-nitrostilbene dianhydride (4) was prepared and reacted with 1,4-phenylenediamine, 4,4′-oxydianiline, 4,4′-diaminobenzanilide and 4,4′-(hexafluoroisopropylidene)dianiline to yield novel polyimides 5-8 containing 2,3-dioxynitrostilbenyl groups as NLO-chromophores, which constituted parts of the polymer backbones. The resulting polyimides 5-8 were soluble in polar solvents such as acetone and DMF. Polymers 5-8 showed a thermal stability up to 300 °C in TGA thermograms with Tg values obtained from DSC thermograms in the range of 135-160 °C. The SHG coefficients (d33) of poled polymer films at the 1064 cm−1 fundamental wavelength were around 5.26 × 10−9 esu. The dipole alignment exhibited exceptionally high thermal stability even at 30 °C higher than Tg and there was no SHG decay below 170-190 °C due to the partial main chain character of polymer structure, which was acceptable for NLO device applications.  相似文献   

19.
A fluorinated tetracarboxylic dianhydride (amide-type TA-TFMB) was prepared from trimellitic anhydride chloride and 2,2′-bis(trifluoromethyl)benzidine (TFMB). A chemically imidized polyimide (PI) derived from TA-TFMB and TFMB was rather soluble in various solvents. Solution casting of this PI (TA-TFMB/TFMB) led to a flexible, non-turbid, and seemingly almost colorless PI film with a high Tg of 328 °C and a considerably low coefficient of thermal expansion (CTE) of 9.9 ppm K−1 which results from significant in-plane chain orientation induced during solution casting. The self-orientation mechanism is discussed. The properties of TA-TFMB/TFMB were compared with those of some relevant systems. The results suggest that an electron-withdrawing effect of the 2,2′-CF3 substituents of TA-TFMB and a twisted conformation of the central biphenyl moiety greatly contribute to the suppressed coloration of the TA-TFMB/TFMB film. The use of a TA-TFMB counterpart (ester-type TA-TFBP) was effective for further enhancing the transparency owing to reduced charge-transfer interaction. However, the thermal properties of TA-TFBP/TFMB were not always satisfactory. Copolymerization using 2,3,6,7-naphthalenetetracarboxylic dianhydride led to a PI film with an increased Tg of 277 °C and a very low CTE of 12.6 ppm K−1 without significant decreases in the transparency and the solubility. Thus, this work proposes promising candidates as novel heat-resistant plastic substrate materials in display devices.  相似文献   

20.
The suitability of coacervates for the preservation of organic pollutants after their extraction from water samples was investigated for the first time. Acid-induced sodium dodecanesulfonic acid (SDSA) micelle-based coacervates were selected for this purpose. Their capacity to preserve benzalkonium homologue (C12, C14 and C16) surfactants (BASs) and different polycyclic aromatic hydrocarbons (PAHs) [benzo(a)pyrene (BaP), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(ghi)perylene (BghiP), benzo(a)anthracene (BaA) and indene(1,2,3-c-d)pyrene (IP)] was investigated. BASs and PAHs were efficiently extracted by the coacervate by formation of mixed aggregates and hydrophobic interactions, respectively. Their stability into the coacervate was investigated under three temperature conditions (room temperature, 4 °C and −20 °C) and two hydrochloric acid concentrations (3.75 M and 4.2 M), which was used to induce coacervation. No losses were observed during at least 3 months at the different experimental conditions tested. The increase of the temperature up to 35 °C for a month did not affect the stability of the target compounds. No influence of the water matrix (distilled, river or wastewater) on the stabilization of BASs and PAHs was observed. The high-stabilizing capacity of the coacervate for the target compounds and its low volume make easy the transport and storage of analytes.  相似文献   

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